Microbial, enzymatic, and soil nutrient dynamics associated with debris dam
revegetation efforts of low degraded tobosa grasslands in the Chihuahuan Desert at
Big Bend National Park
By Apolinar Ortiz Jr, B.S.
A Thesis
in
Microbiology
Submitted to the Graduate Faculty
of Texas Tech University in
the Requirements for
the Degree of
MASTER OF SCIENCE
Approved
Dr. John C. Zak
Chair of Committee
Dr. Veronica Acosta-Martinez
Dr. Randall Jeter
Dr. Peggy Miller,
Interim Dean of the Graduate School
August, 2011
Copyright, 2011
Apolinar Ortiz Jr
Texas Tech University, Apolinar Ortiz Jr, August 2011
ii
Acknowledgments
I would like to thank Dr. John Zak without whom, I would not have been able to
experience research and pursue my degree. I have been very fortunate to have such a
knowledgeable person guide me through my Masters. I would also like to thank Dr.
Acosta-Martinez and Dr. Jeter for all their time, patience and guidance in my pursuits for
a higher education. I would like to give a big thanks to all the lab helpers at the USDA,
and John Cotton for aiding me in my experiments. I would like to thank the
undergraduates and graduates in Dr. Zak lab for all their knowledge, patience and time
they have given me during my research, without which I would have never experienced
what real lab work was. Finally I would like to thank my friends and family for their
support. My wife Michelle for always being there when I needed her, my mother Maria
for teaching me so many important values growing up, my Sister Lorena for making fun
of me for enjoying science, my Aunt Jacinta for showing me to appreciate what I have
and work hard. My Uncle Camilo and cousins for helping me enjoy life, and my
grandmother Emilia for teaching me to be tough. My son Dacien Ortiz for reminding me
to be a good example for him and show him that learning can be fun.
Texas Tech University, Apolinar Ortiz Jr, August 2011
iii
Table of Contents
Acknowledgments……………………………………………………………………..….ii
Abstract…………………………………………………………………………………...iv
List of Figures………………………………………………………………………….....vi
I. Introduction …………………………………………………………………………….1
Desert Systems………………………………………………………………...…1
Restoration ……………………………………………………………………...3
References ……………………………………………………………………....5
II. Relating re-vegetation efforts in a degraded low-elevation grassland at Big Bend
National Park, Chihuahuan Desert to microbial community structure and
nutrient dynamics …………………………………………………………………8
Introduction…………………………………………………………….….…..…..8
Methods…………………………………………………………………..……....10
Results…………………………………………………………………………....14
Discussion………………………………………………………………………..24
References………………………………………………………………………..37
III. Restoring microbial functionality as a prerequisite to successful restoration effort
of low-elevation grassland in the Chihuahuan Desert in Big Bend
National Park……………………………………………………………….……40
Introduction……………………………………………….……………………..40
Methods………………………………………………….……………………....43
Results…………………………………………………………………………...45
Discussion……………………………………………………………………….49
References……………………………………………………………………….57
Texas Tech University, Apolinar Ortiz Jr, August 2011
iv
Abstract
With the increase of temperature and the amount of land lost to desertification,
scientists must learn to monitor, control, and reestablish the land for future generations.
This study, conducted in the northern part of Big Bend National Park, Chihuahuan Desert
examined the ability of the debris dam approach to reestablish critical soil microbial
activity and community structure and activity in conjunction with revegetation efforts of
low-elevation arid grasslands. Debris dams previously established by resource managers
at Big Bend National Park in 2006 were sampled in January, May, August and October
2010 and January 2011 along with bare soil and an adjacent intact tabosa grassland. For
all locations, a 7-cm diameter by 15-cm long bucket auger was used to take soil samples
at 15-cm increments to a depth of 45 cm total (3 increments per core). At each sample
date microbial biomass carbon and fatty acid methyl ester (FAME) analyses were
conducted to ascertain microbial community structure. Functional characteristics of the
soil bacteria and fungi were evaluated using BIOLOG and FUNGILOG procedures and
key microbial enzyme activities of soil nutrient cycling (phosphodiesterase, β-
glucosidase, and phenol oxidase). Soil nutrient and edaphic properties were also obtained
for each sample date. The debris dam approach did reestablish important microbial
activity in these degraded low desert grasslands. Microbial biomass carbon had increased
substantially as compared with the bare soils and were even higher than the natural
grassland. Microbial community structure was similar between the natural vegetation and
the debris dams after 4 years. Although fungi dominated all three locations, Gram-
negative bacteria and Actinomycetes dominated the bare soil while Gram-positive
Texas Tech University, Apolinar Ortiz Jr, August 2011
v
Bacteria dominated the natural vegetation and debris dam soils. Soil nutrient dynamics
were similar between the debris dams and natural vegetation areas as important microbial
and plant linkages were reestablished. Importantly, the high levels of extractable NO3-
that characterize the bare soils in this region of Big Bend National Park with the loss of
vegetation were reduced under the debris dams as nitrogen becomes immobilized in the
vegetation and with greater microbial biomass. All microbial enzyme activities were
higher under the natural vegetation with the debris dams intermediate in activity levels
between the natural vegetation and the bare soil. Microbial carbon use was also similar in
that microbial functional capabilities were intermediate between the natural vegetation
and the bare soil. The microbial and nutrient data indicates that debris dams can be
effective in restoring plant cover to formally bare regions in the Chihuahuan Desert
without the need for supplemental water. Once plants are reestablished, regardless of
species, important microbial dynamics and associated ecosystem processes are increased
above levels that had been occurring in the bare or disturbed soils. Moreover the
trajectory of the microbial and soil nutrients suggests that these vegetated bands are
sustainable as critical aspects of nutrient mineralization coupled with increased microbial
activity have been promoted. In addition from a practical standpoint, the debris dams will
be more effective than the intensive investment of planting drought-tolerant plants that
can become invasive and threatening to the naturally occurring plants within Big Bend
National Park.
Texas Tech University, Apolinar Ortiz Jr, August 2011
vi
List of Figures
2.1 Seasonal patterns of microbial biomass carbon by depth associated with a
restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park…………………………………..29
2.2 Seasonal patterns of Fatty acid methyl esters (FAME) by depth associated with a
restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park…………………………………..30
2.3 Seasonal patterns of nitrate (NO3-) by depth associated with a
restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park…………………………………..31
2.4 Seasonal patterns of ammonium (NH4+) by depth associated with a
restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park…………………………………..32
2.5 Seasonal patterns of pH by depth associated with a
restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park…………………………………33
2.6 Seasonal patterns of available phosphorus by depth associated with a
restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park………………………………….34
2.7 Seasonal patterns of potassium by depth associated with a
restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park…………………………………..35
2.8 Seasonal patterns of Soil Organic Matter (SOM) by depth associated with a
restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park…………………………………..36
3.1 Seasonal patterns of Biolog GN-2 microtiter plate activity by depth associated
with a restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park…………………………………..52
3.2 Seasonal patterns of Fungilog SFN-2 microtiter plate activity by depth
associated with a restoration effort at a low-elevation degraded tabosa grassland
in the Chihuahuan Desert at Big Bend National Park……………………………53
Texas Tech University, Apolinar Ortiz Jr, August 2011
vii
3.3 Seasonal patterns of phosphodiesterase activities by depth associated with a
restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park…………………………………..54
3.4 Seasonal patterns of β-glucosidase activities by depth associated with a
restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park…………………………………..55
3.5 Seasonal patterns of phenol oxidase values by depth associated with a
restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park…………………………………56
Texas Tech University, Apolinar Ortiz Jr, August 2011
1
Chapter I
Introduction
Desert System
“With the desert fathers you have the characteristic of a clean break with a
conventional, accepted social context in order to swim for one’s life into an apparently
irrational void.”
Thomas Merton
Desertification occurs in arid and semi-arid environments, as these areas are
primarily limited by the amount of rainfall available for soil microbial activity and plant
growth (Weltzin et al. 2003). A secondary factor limiting ecosystem processes in arid
ecosystems is the high temperatures that occur during the day and the drastic drop in
temperatures at night. These two factors restrict ecosystem function over much of the
year leading to reduced soil microbial activity and primary production. If arid systems are
secondarily impacted by human activity, ecosystem process can further decline leading to
desertification. Lovich and Bainbridge (1999) have noted that many areas around the
world are becoming converted to dry lands and deserts due to overgrazing, firewood
harvesting, poor farming, and off-road recreation along with business operations,
introduction of exotic animals and plants, and more recently due to climate change. Once
arid landscapes are damaged they are very difficult but not impossible to repair (Lovich
and Bainbridge 1999). Tolba (1984) compared desertification to a skin disease and
Texas Tech University, Apolinar Ortiz Jr, August 2011
2
suggested as with any disease, treating the symptoms is secondary to tackling the cause.
If we look at desertification at a landscape level disease we must look at the abiotic and
biotic constraints as they influence system dynamics to help restore health with proper
management and treatments.
Deserts have limited biological potential and activity due to adverse abiotic
factors that limit diversity and activity except during intermittent ephemeral periods of
time (Goodall 1976; Whitford, 2002). Across seasons, water availability is the major
abiotic constraint to all biotic structure and activity (e.g., Weltzin et al. 2003). For most
arid ecosystems precipitation events occur primarily as small scattered rain events that
are usually less than two millimeters (Collins et al. 2008; Robertson et al 2009). Whitford
(2002) also reported for desert ecosystems moisture lost from evaporation and
transpiration in desert systems was greater than the moisture gained during that period for
when plant productivity is the highest. With limited water availability, the desert growing
season can be short with plants showing the stress of water deficit. Patrick et al. (2007)
showed that in mid-elevation grassland in the Chihuahuan Desert at Big Bend National
Park, during the winter months, the levels of evaporation and transpiration are much
lower than the summer months due to lower levels of solar radiation, lower precipitation
and decreased plant activity. This evaporation and transpiration combined with limited
precipitation can account for the pulse patterns in biological activity that has been
documented for soil processes as well as with plant activity. Gallo et al. (2006) and
Collins et al. (2008) showed how these stress periods cause the accumulation of nutrients
due to suppressed microbial activity and lack of degradation of organic materials. As
Texas Tech University, Apolinar Ortiz Jr, August 2011
3
ecosystem processes in arid ecosystems are tightly linked to moisture availability and
subsequent microbial activity, any perturbation that disrupts these plant-soil linkages
either through direct or indirect results of human activity will likely lead to desertification
and system degradation.
With the stress from high temperature, microbial activity slows down and even
causes microbes to die off, leaving pockets of nutrients that become available when
moisture is present (Belnap et al. 2005). With large precipitation events and low plant
uptake, nutrients can be lost due to leaching or runoff further decreasing ecosystem
productivity. With limited vegetation, movement of nutrients in desert systems to deeper
soil or to adjacent areas can be attributed to the soil topography and soil texture (Collins
et al. 2008). Some plant roots can access these pockets of nutrients and with available
moisture, primary productivity can continue even when the soil moisture levels do not
remain at optimum levels (Robertson et al. 2009). However, loss of nutrients and the
aggregation of nutrients into patches is a hallmark of desertification (Whitford 2002).
Restoration
Natural recovery of desertified ecosystems in arid regions is limited due to
extreme temperatures, high winds, low levels of moisture, and loss of fertility within the
soil even if the disturbance has halted (Bainbridge 2007). Favorable conditions for plant
establishment occur infrequently in desert systems and could take hundreds of years to
recover without human involvement. Bainbridge (2007) showed that arid systems that
have had human activity beyond a simply hunter-gatherer level of existence are in need
Texas Tech University, Apolinar Ortiz Jr, August 2011
4
of restoration. Restoration efforts globally have been noted to start in the early 1900s for
many dry lands (Griffiths 1901; Cox et al. 1982). Progress was limited due to lack of
scientific testing, controlled experiments, and a way to distribute findings. Hall (2001)
said that another limiting factor was the lack of understanding of arid and semi-arid
ecosystems because most of the research was collected from areas that had humid
environments and had natural recovery of vegetation. Natural vegetation restoration can
be minimal or large scale; some projects are short term or long term, each project is
designed for the affected area, and with positive results it can be established in other
similar areas such as soil type, cover type or location.
Texas Tech University, Apolinar Ortiz Jr, August 2011
5
References
1. Belnap, J., Welter, J.R., Grimm, N.B., Barger, N., and Ludwig, J.A., 2005.
Linkages between Microbial and Hydrologic Processes in Arid and Semiarid
watersheds. Ecology 86, 298-307.
2. Bainbridge, D.A., 2007. A Guide to Desert and Dryland Restoration. Island Press.
Washington, DC.
3. Collins, S.L., Sinsabaugh, R.L., Cresnshaw, C., Green, L., Porras-Alfaro, A.,
Stursova, M., and Zeglin L.H., 2008. Pulse dynamics and microbial processes in
arid lands ecosystems, Journal of Ecology 96, 413-420.
4. Cox, J.R., H.L., Morton, T.N., Johnson, G.L., Jordan, S.C., Martin, and L.C.,
Fierro. 1982. Vegetation Restoration in the Chihuahuan and Sonoran Deserts of
North America. Agriculture Reviews and Manuals #28. USDA Agricultural
Research Service, Tucson, AZ.
5. Gallo, M.E., Sinsabaugh, R.L., and Cabaniss, S.E., 2006. The role of ultraviolet
radiation in litter decomposition in arid ecosystems. Applied Soil Ecoogy 34, 8-
91.
6. Goodall, D.W., 1976. Evolution of desert biota. University of Texas Press,
Austin, TX.
7. Griffiths, D., 1901. Range improvements in Arizona. USDA Bureau of Plant
Industry Bulletin #4. Washington, DC.
Texas Tech University, Apolinar Ortiz Jr, August 2011
6
8. Hall, M., 2001. Repairing mountains: Restoration ecology and wilderness in 20th
century. Utah. Environmental history 6,574-601.
9. Lovich, J.E., D. Bainbridge. 1999. Anthropgenic degradation of the Southern
California desert ecosystem and prospects for natural recovery and restoration.
Environmental Management 24,309-326.
10. Mostafa K. Tolba 1984. A Harvest of Dust? Envrironmental Conservation 11,1-2.
11. Patrick, L., Cable, J., Potts, D., Ignace, D., Barron-Grafford, G., Griffith, A.,
Alpert, H., van Gestel, N., Robertson, T., Huxman, T.E., Zak, J., Loik, M.E., and
Tissue, D., 2007. Effects of a decrease in summer precipitation on leaf, soil an
ecosystem fluxes of CO2 and H2O in a sotol grassland in Big Bend National Park,
Texas. Oecologia 151,704-718.
12. Robertson, T.R., Bell, C.W., Zak, J.C., and Tissue, D.T., 2009. Precipitation
timing and magnitude differentially affect aboveground annual net primary
productivity in three perennial species in Chihuahuan Desert grassland. New
Phytologist 181, 230-242.
13. Whitford, W.G., 2002. Ecology of Desert Systems, Academic Press, London, UK
Texas Tech University, Apolinar Ortiz Jr, August 2011
7
14. Weltzin, J.F., Loik, M.E., Schwinnings, S., Williams, D.G., Fay, P.A., Haddad,
B.M., Harte, J., Huxman, T.E., Knapp, A.K., Lin, G., Pockman, W.T., Shaw,
M.R., Small, E.E., Smith, M.D., Smith, S.D., Tissue, D.T., and Zak, J.C., 2003.
Assessing the response of terrestrial ecosystems to potential changes in
precipitation. BioScience 53,941-952.
Texas Tech University, Apolinar Ortiz Jr, August 2011
8
Chapter II
Relating re-vegetation efforts in a degrade low-elevation grassland at Big Bend
National Park, Chihuahuan Desert to microbial community structure and nutrient
dynamics
Introduction
The low-elevation grasslands in the Chihuahuan Desert in Big Bend National
Park (BBNP) are a patchwork of bunchgrasses, shrubs, and succulents (Alex 2006,
Fenstermacher et al. 2006). These grasslands are important for maintaining the
hydrologic and ecological processes, nutrient cycling, and preserving biodiversity across
large areas of the Chihuahuan Desert. Unfortunately, these low elevation grasslands in
BBNP have changed since the park was established in the early 1940s due to overgrazing
in the early 19th
century combined with periods of drought. As a consequence, these low-
elevation grasslands have experienced the greatest change in vegetation cover and
structure within the National Park and have been modified to bare areas, shrubs lands or
banded grasslands (Rinas 2007).
Restoration of arid region grasslands is hindered by the amount of precipitation
they receive (e.g., Weltzin et al. 2003), the high evaporation rates from bare soil surfaces
and the changes in soil temperatures on a daily basis that occur within these soils
throughout the year. Hadley (1970) reported that soil surface temperatures in a
creosotebush in the Sonoran Desert exhibited daily fluctuations of 45 C during the
summer. Once vegetation is removed from a site that experiences these high soil
Texas Tech University, Apolinar Ortiz Jr, August 2011
9
temperatures, the links between plant productivity and microbial dynamics decline,
increasing plant loss and subsequent soil erosion. Consequently, areas that have
experienced a reduction in vegetation cover lose moisture faster than they gain resulting
in exaggerated periods of dry days that occur between critical moisture pulses (Huxman
et al. 2002, 2004).
Under typical conditions in desert systems, nutrient dynamics, microbial activity
and plant growth are tightly linked with moisture pulses and the amount and timing of
these pulses (Whitford 2002). However, due to increased moisture stress in bare areas
combined with high soil temperature, many soil microbes die from desiccation thus
decreasing subsequent microbial activity when moisture does become available (Orchard
& Cook 2002) In addition, a negative feedback loop can be established, whereby the
amount of microbial death that has occurred results in the occurrence of moderate to
high soil nutrient levels that can subsequently be transported off-site following a large
rain event furthering the decline of the ecosystem (e.g. Belnap et al. 2005).
One approach that has shown promise in reducing erosion and promoting plant
establishment in arid ecosystems is establishing buffer strips using coarse woody debris
on highly erodible low-elevation grassland soils at BBNP (Rinas 2007). The approach
involves the building of debris dams that are perpendicular to the flow of water across the
landscape. These structures can help in the reallocation of nutrients and water to provide
sufficient moisture for the reestablishment of grasses. Debris dams have been shown to
collect nutrients from bare areas in grasslands (Marino 2004) and redistribute these
resources to vegetated areas. The goal is to restore these degraded areas back to their
Texas Tech University, Apolinar Ortiz Jr, August 2011
10
previous state, having the same microbial diversity and dynamics to help sustain
ecosystem processes critical for that system (Allen 1988). Restoration or rehabilitation is
designed to reestablish critical paths of energy flow, nutrient water filtration and linkages
between the plant and microbial subsystem throughout the ecosystem (Allen 1988, 1989).
Our goals for this investigation are to evaluate the success of the “debris dam” approach
to ameliorate the adverse effects of bare soil on soil microbial and nutrient dynamics as a
precursor to effective low-elevation grasslands restorations in Big Bend National Park.
Methods
The restoration efforts for this project were initiated at North Rosillos site on the
former Harte ranch beginning in May 2006. As restoration managers at Big Bend
National Park were aware that soil temperatures and water infiltration issues were a
major concern in establishing vegetation on former low-elevation tobosa (Pleuraphis
mutica) grasslands, a new approach using a combination of erosion control blankets,
hydro-seeding and coarse woody debris obtained from management efforts within the
National Park was attempted (Rinas 2007). Revegetation strips for this site are 1-1.2
meters wide (three to four feet) and about 9 meters (thirty feet) long and placed along
contours to decrease water runoff and increase infiltration. Strips were also formed to
mimic the natural patterns of the shrubs and grasses in this low-elevation grassland
(Rinas 2007). A disk plow was used to break-up the soil to a depth of 15 cm to increase
infiltration. After plowing, a seed mixture consisting of native and range grass and forb,
mulch and a glue substance that had been used in road revegetation was sprayed on the
soil of each debris dam strip. Following seeding, erosion control blankets were placed on
Texas Tech University, Apolinar Ortiz Jr, August 2011
11
top of the hydro mulch and the strips were covered with brush obtained from trail
management to a depth of 1 m. Plant growth was initiated with the onset of the summer
rains for the area. The debris dams established at the North Rosillos location are part of a
larger restoration project on the Hart Ranch where 77.3 hectares (191 acres) of low-
elevation grasslands are considered for restoration.
Soil at the North Rosillos Site is a deep silty loam originally classified as Tornillo
(fine-silty, mixed, superactive, thermic Fluventic Haplocambids) and recently reclassified
as Chalkdraw. Mean elevation at the North Rosillos site is 835 masl with site aspect of
0.6%. Total annual precipitation for the region has averaged approximately 268 mm since
1982 with mean monthly rainfall ranging between 8.8 mm (March) and 41.1 mm
(September). Mean daily high temperatures range from 17.59 °C (December) to 36.20 °C
(June), while daily lows range from 1.10 °C (January) to 22.32 °C (July). Of note, surface
temperatures recorded in situ at the North Rosillos location rank among the highest
recorded in BBNP.
Three debris dames, three bare areas and three locations in an intact tobosa
grassland adjacent to the reclaimed areas were sampled during each designated period.
Two samples were taken at each location, the bare and debris dams were sampled relative
to each other with the bare areas above and below the debris dam sampled, while the
vegetated areas were sampled west of the debris dams. For all locations a 7-cm diameter
by 15-cm long bucket auger was used to take soil samples at 15-cm increments to a depth
of 45 cm total (3 increments per core). Approximately 250 g of soil were obtained per
depth increment per sample. Soils were transported in a cooler and stored at 4ºC at Texas
Texas Tech University, Apolinar Ortiz Jr, August 2011
12
Tech University for no longer than one week after collection. Soil moisture and nutrient
analyses were conducted immediately after returning from the field.
Soil microbial biomass carbon was evaluated using the chloroform fumigation
procedure described by Vance et al. (1987). Two 10-g dry weight equivalent subsamples
from each sample were fumigated with chloroform for 48 hours under vacuum. A second
set of 10-g subsamples was processed without chloroform fumigation as controls. After
the fumigation, samples were extracted using a 5M K2SO4 solution and filtered through
Whatman 43 filter paper. Filtered samples were transferred to a cuvette and absorbance
measured for biomass estimates at 280 nm on a spectrophotometer (Nunan et al. 1997).
The amount of microbial biomass carbon obtained in the controls was subtracted from the
amount of carbon obtained in the fumigated samples to obtain the amount of carbon
present as microbial biomass carbon using the correction factors provided in Nunan et al.
(1997).
Fatty Acid Methyl Ester amounts and compositions from soil samples collected in
the natural vegetation, bare soil, and debris dams at each sample period were obtained
using procedures for the MIDI system as established by Acosta-Martinez et al. (2003).
The microbial fatty acid subsamples obtained from each sample period were compared
and identified with the fatty acid recognition software 6890 GC series II. This program
will use a Microbial Identification system to profile microbial community structure based
Texas Tech University, Apolinar Ortiz Jr, August 2011
13
upon FAME signatures were classified as:
1. saprophytic fungi: 18:1ω9c, 18:2ω6.9, 18:3ω3c, 18:3ω6c, and 20:5ω3;
2. arbuscular-mycorrhizal fungi: 16:1ω5c, 20:1ω9c, 20:2ω6c and 22:1ω9c;
3. Gram-positive bacteria: 14:0 iso, 15:0 iso. 15:0 anteiso, 16: iso, 17:0 iso and
17:0 anteiso markers;
4. Gram-negative bacteria: 16:1ω9c, 16:1ω7c, 16:1ω7t, cyclo17:0, 18:1ω7c,
18:1ω7t, 18:1ω5c and cyclo19:0;
5. Actinomycetes: 10 methyl 16:0, 10 methyl 17:0 and 10 methyl 18:0 fungi
(Madan et al., 2001; Olsson et al. 1999).
A 100-g subsample of soil from each sample was sent within 24 hours to Waters
Agriculture Laboratories Inc. (city, state) to obtain levels of extractable NH4+, and NO3
-,
soil pH, percentage soil organic matter and a suite of minor nutrients including levels of
extractable phosphorus.
Statistical Analyses
Data Analysis was conducted using SPSS 19 at three levels of analysis. A
Levene’s test was used on all parameters to ensure the variance of each group are
homogenous. Tukey Post hoc tests were run when ANOVAs were significant to
determine the source of the significance. For the level one assessment, ANOVAs of
depth by location with seasons combined and location by season with depths combined
Texas Tech University, Apolinar Ortiz Jr, August 2011
14
were conducted for all data. For the level two assessments a repeated measures ANOVA
using time as the repeated measure was run for depth by location with seasons combined.
The level three analyses also employed a one-way ANOVA for each depth if the location
and season interaction was significant in the previous level two assessments.
Results
Microbial Community Structure
Microbial Biomass Carbon
Across all sample dates and depths combined, Microbial Biomass Carbon (MBC)
values were significantly highest under the debris dams (p<0.001) than in either the
natural grassland or bare soils for a full year of sampling (Figure 2.1A, B, C). MBC
values from the natural grasslands were significantly higher than values obtained from
the bare soil (p<0.001) across all depths and seasons. Across all sample times there was
no effect of depth on levels of microbial biomass for all locations combined. However,
within sample times there were significant effects of depth on MBC. For 0-15-cm depth
the highest MBC levels occurred in October, this event happened in both 15-30 and 30-
45 depths as well Figure (2.1). These values were significantly (p<0.001) different than
for any other sample month. However there were no significant (p=0.167) differences
among any location for MBC values for the other three sample dates for 0-15-cm depth.
In the analysis of location by sample date there were significant differences by
season (between subject effects) with the highest values of MBC in all locations
Texas Tech University, Apolinar Ortiz Jr, August 2011
15
occurring in October (Figure 2.1). The repeated measures analysis showed that the
highest MBC values were associated with the debris dams (wilks lambda p=.001) and
there was no significant interaction of sample date and location (wilks lambda p=0.327).
The lowest values of MBC were observed in January 2010 for all locations. Though
MBC differed among depths by location the seasonal effects were consistent within each
of the three depths.
FAME
Actinomycetes
Across all sample times, location is significant (p<0.001) with the highest
percentage FAME values for actinomycetes occurring under the bare soil and the lowest
values under the natural vegetation (Figure 2.2). Values for the debris dam restoration
approach were intermediate and similar to the natural vegetation. Across all sample times
there was a significant (p=0.031) effect on actinomycetes percentages by depth (15-30
cm) in all locations (Figure 2.2B). For 15-30-cm depth the highest actinomycetes
percentages occurred in August 2010. These values were significantly (p<0.001) different
than January 2010 and 2011; however there were no significant (0.658) difference among
any location for actinomycetes percentage for the other three sample dates.
In the analysis of location by sample date there were significant differences by
season (between subject effects) with the highest values of actinomycetes in all locations
occurring in August 2010 (Figure 2.2). The repeated measures analysis showed that the
highest actinomycetes percentages were associated with the bare soils (wilks lambda
Texas Tech University, Apolinar Ortiz Jr, August 2011
16
p<0.001) and there was no significant interaction of sample date and location (wilks
lambda p=0.826). The lowest values of actinomycetes percentages were observed in
January 2011. Although actinomycetes percentages differed among depth by location, the
seasonal effect was consistent at each of the three depths.
Fungi
Across all sample times, location was significant (p< 0.001) with the highest
values of fungi percentage FAME levels occurring under the natural vegetation and the
lowest value under the bare soil, and the values associated with the debris dams were
intermediate and similar to the natural vegetation (Figure 2.2). Across all sample times
there was not a significant (p= 0.343) effect on fungal FAME levels by depth for all
locations combined (Figure 2.2). Also within sample times there was not a significant
effect on depths. For the 15-30-cm depth the highest fungal FAME levels occurred in
October 2010. The fungal FAME values were not significantly (p= 0.401) different
among any location for the other three sample months. In the analysis of location by
sample date there was not a significant difference by season effect (between subject
effects) as the percentages of fungal FAME levels were very similar across sample dates
(Figure 2.2). The repeated measures analysis showed that the highest fungal FAME
percentages were associated with the natural vegetation (wilks lambda p<0.001). There
was no significant interaction of sample date and location (wilks lambda p=0.616). The
lowest values of fungal FAME levels were observed in January 2010. Although Fungal
FAME levels differed among depth by location, the seasonal effect was also not
consistent at each of the three depths.
Texas Tech University, Apolinar Ortiz Jr, August 2011
17
Gram-Negative Bacteria
Across all sample times, location was significant (p< 0.001) with the highest
levels of Gram-negative FAME occurring under the bare soil and the lowest values under
the debris dams (Figure 2.2). Gram-negative FAME levels in natural vegetation were
intermediate and similar to the debris dams. Across all sample times there was a
significant (p< 0.001) effect on Gramnegative FAME percentages by depth (0-15 cm) in
all locations (Figures2.2). For 0-15cm depth the highest Gram-negative percentage
occurred October 2010 these values were significantly (p<0.001) different than January
2010; however there were no significant (p= 0.700) differences among any location for
Gram-negative percentages for the other three sample dates.
In the analysis of location by sample date, there were significant differences by
season (between subject effects) with the highest values occurring in October 2010. The
repeated measures analysis showed that the highest Gram-negative percentages were
associated with bare soils (wilks lambda p<0.001) and there was no significant
interaction of sample date and location (wilks lambda p= 0.373). The lowest levels of
Gram-negative FAME were observed in January 2010. Although Gram-negative
percentages differed among depth by location, the seasonal effects were consistent at
each of the three depths (Figure 2.2).
Gram-Positive Bacteria
Across all sample times location was significant (p< 0.001) with the highest
values for Gram-positive percentages occurring under the bare soil and the lowest values
Texas Tech University, Apolinar Ortiz Jr, August 2011
18
under the natural vegetation (Figure 2.2), and the levels associated with the debris dams
were intermediate and similar to levels from the bare soil. Across all sample times there
was not a significant (p= 0.081) effect of depth on Gram-positive FAME levels by depth
for all locations combined. For 15-30-cm depth (Figure 2.2) the highest Gram-positive
percentages occurred in August 2010 (p<0.001). Gram-positive FAME levels were not
significantly (p= 0.261) different among any location for the other three sampled months.
In the analysis of location by sample date there were not significant differences by
season (between subject effects) Figure 2.2 for Gram-positive FAME levels for any
location. The repeated measures analysis also showed that the highest Gram-positive
percentages were associated with the bare soil (wilks lambda < 0.001) and that there was
no significant interaction of sample date and location (wilks lambda p=0.453). The lowest
values of Gram-positive FAME levels were observed in January 2011. Though Gram-
positive percentages differed among depth by location the seasonal effect was also not
consistent for 0-15 cm and 30-45 cm (Figure 2.2 A, C).
Soil Nutrient Dynamics
Extractable NO3-
Across all sample times, location was significant (p<0.001) with the highest
values of extractable nitrate under bare soils reaching levels of 250 parts per million
(Figure 2.3) and the lowest values under the natural vegetation, and values associated
with the debris dams were intermediate and similar to the levels under the natural
vegetation. Across all sample times there was a significant (p<0.001) effect of depth for
Texas Tech University, Apolinar Ortiz Jr, August 2011
19
all locations combined (Figure 2.3). Within sample times there were also significant
effects of depth on levels of extractable NO3-. For the 0-15-cm depth the highest nitrate
levels occurred in October 2010. These values were significantly (p=0.024) higher than
August 2010; however there was a significant (p=0.024) difference among location for
nitrate values where January 2010 differed from August 2010 and January 2011.
In the analysis of location by sample date there were significant differences by
season (between subject effects) with the highest values of nitrate in all locations
occurring in January 2010. The repeated measures analysis showed that the highest
nitrate values were associated with the bare soil (wilks lambda p<0.001). There was no
significant interaction of sample date and location (wilks lambda p=0.166). The lowest
values of nitrate were observed August 2010. Though nitrate levels were similar among
depth by location the seasonal effects were consistent at each of the three depths as well.
Ammonium NH4+
Across all sample times, location was significant (p<0.001) with the highest
values of extractable ammonium under natural vegetation and the lowest values under
bare soil, and the levels associated with the debris dams were intermediate and similar to
the natural vegetation. Across all sample times there was no effect of depth on levels of
ammonium for all locations combined. Within sample times there was also no significant
effect on depths across all locations. For 0-15-cm depth the highest extractable
ammonium levels occurred in August 2010 as these values were significantly (p<0.001)
Texas Tech University, Apolinar Ortiz Jr, August 2011
20
different than any other sampled month. However there were no significant (p=0.144)
differences among any locations for ammonium values for the other three sample dates.
In the analysis of location by sample date there were significant differences by
season (between subject effects) with the highest values of ammonium occurring in
August 2010. The repeated measures analysis showed that the highest ammonium values
were associated with natural vegetation (wilks lambda p<0.001). There was no significant
interaction of sample date and location (wilks lambda p=0.065). The lowest values of
ammonium were observed in January 2011. Though extractable ammonium values
differed among depth by location the seasonal effects were consistent at each of the three
depths.
pH
Across all sample times, location was significant (p<0.001) with the highest
values of pH occurring under the natural vegetation and the lowest values under the bare
soil. Soil pH values under the debris dams were intermediate and similar to the natural
vegetation. Across all sample times there was not a significant (p=0.665) effect on pH
values by depth for all locations combined. However, within sample times there was a
significant effect of depth. For 0-15-cm depth the highest pH values occurred in August
2010. These values were significantly (p<0.001) different than any other sampled month;
however there were no significant (p=0.291) differences among any locations for pH
values for the other three sampled dates.
Texas Tech University, Apolinar Ortiz Jr, August 2011
21
In the analysis of location by sample date there were significant differences by
season (between subject effects) with the highest values of pH in all locations occurring
in August 2010. The repeated measures analysis showed that the highest pH values were
associated with the natural vegetation (wilks lambda p<0.001) and that there was no
significant interaction of sample date and location (wilks lambda p=0.479). The lowest
pH values were observed in January 2011.
Phosphorus
Across all sample times, location was significant (p<0.001) with the highest
values of available phosphorus occurring under the bare soil and the lowest values under
the natural vegetation, and the levels associated with the debris dams were intermediate
and similar to the bare soil. Across all sample times there was a significant (p<0.001)
effect on phosphorus levels by depth for all locations combined. Within sample times
there was also a significant effect of depth on levels of available soil phosphorus. For 0-
15-cm depth the highest phosphorus values occurred in January 2011. These values were
significantly (p<0.001) different than October 2010; however there were no significant
(p=0.754) differences among any locations for phosphorus for the other three sample
dates.
In the analysis of location by sample date there were significant differences by
season (between subject effects) with the highest values of phosphorus in all locations
occurring in January 2011. The repeated measures analysis showed that the highest
values of available phosphorus were associated with the bare soils (wilks lambda
Texas Tech University, Apolinar Ortiz Jr, August 2011
22
p<0.001) and there was significant interaction of sample date and location (wilks lambda
p=0.022). The lowest values of phosphorus were observed in October 2010. Though
phosphorus levels were similar among depth by location the seasonal effects were
consistent at each of the three depths as well.
Potassium
Across all sample times location was significant (p<0.001) with the highest values
of potassium occurring under bare soil and the lowest values under natural vegetation,
and the values associated with the debris dams were intermediate and similar to the bare
soil. Across all sample times there was a significant (p<0.001) effect on potassium by
depth (0-15 cm) for all locations combined. Within sample times there were significant
effects on depths. For 0-15-cm depth the highest potassium values occurred in January
2010. These values were significantly different than any other sampled month; however,
there was no significant (p=0.795) difference among any location for potassium values
for the other three sample dates.
In the analysis of location by sample date there were significant differences by
season (between subject effects) with the highest values of potassium in all locations
occurring in January 2010. The repeated measures analysis showed that the highest
potassium values were associated with the bare soil (wilks lambda p<0.001) and there
was no significant interaction of sample date and location (wilks lambda p=0.227). The
lowest values of potassium were observed in October 2010. Although potassium values
Texas Tech University, Apolinar Ortiz Jr, August 2011
23
were similar among depth by location, the seasonal effects were consistent at each of the
three depths as well.
Soil Organic Matter (SOM)
Across all sample times, location was significant (p<0.001) with the highest
values of SOM occurring under the natural vegetation and the lowest values under the
bare soil. SOM levels for the debris dams were intermediate and similar to the bare soil.
Across all sample times there was a significant (p=0.006) effect on SOM values with
depth (0-15 cm) in all locations. Within sample times there were also significant effects
on depths. For 0-15-cm depth the highest SOM values occurred in October 2010. These
values were significantly different than any other sampled month; however there were no
significant (p=0.593) differences among any locations for SOM values for the other three
sample dates.
In the analysis of location by sample date there were significant differences by
season (between subject effects) with the highest values of SOM in all locations
occurring in October 2010. The repeated measures analysis showed that the highest SOM
values were associated with the natural vegetation (wilks lambda p<0.001) and there was
no significant interaction of sample date and location (wilks lamda p=0.242). The lowest
values of SOM were observed in January 2011. Though SOM values were similar among
depth by location the seasonal effects were consistent at each of the three depths as well.
Texas Tech University, Apolinar Ortiz Jr, August 2011
24
Discussion
Results from this one-year study indicate that a debris dam approach does
reestablish important microbial activity on degraded low desert grasslands. After debris
dams were in place for four years, microbial biomass carbon levels had increased
substantially as compared with the bare soils and were even higher than the natural
grassland possibly due to initial inputs of carbon from the hydroseeding and different
vegetation composition. Soil nutrient dynamics were also becoming similar between the
debris dams and natural vegetation areas as important microbial and plant linkages are
reestablished. Importantly, the high levels of extractable NO3
- that characterize the bare
soils in this region of Big Bend National Park with the loss of vegetation (Haralson 2010)
are reduced under the debris dams as nitrogen becomes immobilized in the vegetation
and greater microbial biomass. For arid grasslands, increases in soil nitrogen levels have
been implicated in the conversion of grasslands to shrub lands as nitrogen becomes
concentrated at high levels (Whitford 2002).
The debris dam approach was found to be more effective than other procedures
that have been used at Big Bend to reestablish vegetation, such as developing water
reservoir holes and planting of drought tolerant plants at the North Rosillos location
(Rinas 2007). While the water reservoirs holes could allow for water to get deeper into
the soil, this restoration approach was unable to distribute the water over a large enough
area and did not reduce evaporation of the collected water nor reduce the high soil
temperatures that prevent seedling establishment. The debris dams capture and reduce
soil evaporation as soil moisture levels were higher under the debris dams as compared
Texas Tech University, Apolinar Ortiz Jr, August 2011
25
with the bare soil. The debris dams were designed to capture run-off from adjacent bare
areas, and to increase infiltration. Moreover, shading from the coarse woody debris that is
piled up to a meter high on top of the erosion control blankets reduces soil temperatures,
aiding in moisture retention while reducing temperatures stress on soil microbes (Rinas
2007).
Seasonal patterns of microbial activity under the debris dam after 4 years did
approach levels and follow the trends from the tabosa grasslands that are characteristic of
this low desert in the Chihuahuan Desert. However, for some aspects of microbial
community structure and soil nutrient dynamics the debris dams had higher activity or
levels than found under the natural tabosa grasslands. The high levels of microbial
biomass under the debris dams can reflect the lower soil temperatures and greater
moisture retention provided by the hydroseeding and debris (Rinas 2007). The similarity
in microbial activity with depth under the debris dams and the natural vegetation
underscores the importance of plant cover in regulating soil microbial and nutrient
dynamics and edaphic constraints. Holden and Fierer (2005) showed that MBC is
influenced with depth by plant uptake dynamics and seasonal patterns in soil moisture
and temperature. Belnap et al. (2005) discussed the effect of plant cover type on MBC in
arid systems with the highest values occurring in the vegetated areas.
The debris dam treatment has substantially altered microbial community structure
in this highly disturbed former low-elevation grassland site. Moreover the length of time
for recovery of microbial community structure was quick as these former bare and eroded
sites now mimic that of the natural grasses. In all depths the pattern of high levels of
Texas Tech University, Apolinar Ortiz Jr, August 2011
26
fungi, followed by Gram-negative bacteria, actinomycetes, and finally low levels of
Gram-positive bacteria is seen in both dams and natural grasses. The high levels of fungi
under the vegetated locations are supported by Ibekwe and Kenndy (1999). While
saprophytic fungi were detected in all locations the lowest levels occurred in the bare
soil. For Gram-negative bacteria the highest levels were seen in the bare soil and almost
nonexistent in the other two treatments. This could be a result of the high levels of soil
nitrate as the genus Pseudomonas is an important denitrifier.
Halving et al. (2005) stated that nitrate is one of the most readily available forms
of nitrogen for plants. This can be attributed to its ability to move in the soil solution and
is readily used by plants and soil microbes, which can contribute to the varying levels of
nitrate across season and moisture patterns (Havlin et al. 2005). The high levels of nitrate
in the bare soil can be attributed to the lack of vegetation cover at the levels that occur at
the site (Marrett et al. 1990). The debris dams, which started off as a bare soil, did show
slightly higher levels of extractable nitrate than the natural vegetation at all three depths
but these levels were significantly lower than the levels under bare soil. The higher levels
of extractable ammonium under the natural vegetation followed by levels associated with
the debris dams suggest that critical aspects of organic matter decomposition and
mineralization are occurring that is not associated with the bare soils. The increase of
organic matter and mineralization under the debris dams could account for the levels
occurring in the areas with plant availability compared to bare soils (McLain and Martens
2005). As ammonium levels under the debris dams did not reach levels seen in the natural
vegetation during any portion of the year, the rates of mineralization can be inferred to be
Texas Tech University, Apolinar Ortiz Jr, August 2011
27
lower than for functional low-elevation grasslands. Moreover, this study did not evaluate
the rate of dentrification that could be occurring under the debris dams or the level of
nitrogen fixation that occurs in desert grasslands from cyanobacterial crusts (Whitford
2002).
Soil pH showed how the debris dams are still similar to the bare soil but were
developing characteristics of the soil under the natural vegetation. Moreover nutrient
availability can be influenced by pH, in particular higher pH (Havlin et al. 2005). The
higher pH under the debris dams did not diminish phosphorus availability. The higher
level of phosphorus under the debris dams as compared to natural vegetation suggests
that this nutrient is highly immobilized in the plant and microbial biomass. The higher
levels of SOM at all depths in the natural vegetated sites could account for differences in
phosphorus levels between the natural vegetation and the debris dams (Thompson et al.
2006). As phosphorus is not fixed from the atmosphere, the lower levels in the natural
vegetation suggest that previous erosion could have reduced phosphorus levels and that
arbuscular mycorrhizae will be needed to compensate for the loss of phosphorus.
Patterns of phosphorus and potassium with depth are similar to previous reports (e.g.,
Jobbagy and Jackson 2001).
The microbial and nutrient data indicate that debris dams can be effective in
restoring plant cover to formerly bare regions in the Chihuahuan Desert without the need
for supplemental water. Once plants are reestablished, regardless of species, important
microbial dynamics and associated ecosystem processes are increased above levels that
had been occurring in the bare or disturbed soils. Moreover the trajectory of the microbial
Texas Tech University, Apolinar Ortiz Jr, August 2011
28
and soil nutrients suggests that these vegetated bands are sustainable as critical aspects of
nutrient mineralization coupled with increased microbial activity have been promoted. In
addition, from a practical standpoint the debris dams will be more effective than the
intensive investment of planting drought-tolerant plants that can become invasive and
threaten the naturally occurring plants within Big Bend National Park.
Texas Tech University, Apolinar Ortiz Jr, August 2011
29
References
1. Acosta-Martinez, V., Zobeck, T.M., et al. 2003. Enzyme activities and microbial
community structure in semi-arid agricultural soils. Biol Fertil Soils 38, 216-227
2. Acosta-Martinez, V., Upchurch D.R., et al. 2004. Early impacts of cotton and
peanut cropping systems on selected soil chemical, physical, microbiological and
biochemical properties. Bio Fertil Soils 40, 44-54
3. Alex, B.L., Leavitt, A., Timmer, J., and Sirotnak, J., 2006. Final report on the
sensitive plant project, Big Bend National Park, Texas, Field Seasons: June 2003–
April 2006. Science & Resource Management, Big Bend National Park, Texas.
Unpublished report to the National Biological Infrastructure Inventory, U.S.
Geological Survey, Washington, D.C.
4. Allen, E. B., 1988. The reconstruction of disturbed arid lands. Westview Press,:
9, 267
5. Allen, M. F. 1989. Mycorrhizae and rehabilitation of disturbed arid soils:
processes and practices. Arid soil Research and Rehabilitation 3, 229-241.
6. Belnap, J., Welter, J.R., Grimm, N.B., Barger, N., and Ludwig, J.A., 2005.
Linkages Between Microbial and Hydrologic Processes in Arid and Semiarid
Watersheds. Ecology 86, 298-307
Texas Tech University, Apolinar Ortiz Jr, August 2011
30
7. Fenstermacher, J., Sirotnak, J., Michael P.A., Terry, M., 2006. Annotated vascular
flora of the DEAD HORSE MOUTAINS, Big Bend National Park, Texas, with
notes on local vegetation communities and regional floristic relationships.
National Park Service Big Bend National Park
8. Hadley, N., 1970. Water relations of the desert. Ecology 53, 547-548.
9. Huxman, T.E., Cable, J.M., Ignace, D.D, Eilts, J.A., English, N.B., Weltzin, J,
Williams, D.G., 2002. Response of net ecosystem gas exchange to a simulated
precipitation pulse in a semi-arid grassland: the role of native versus non-naïve
grasses and soil texture, Oecologia 141, 295-30
10. Huxman, T.E., Snyder, K.A., Tissue, D., Leffler, A.J., Ogle, K., Pockman, W.T.,
Sandquist, D.R., Potts, D.L., and Schwinning, S., 2004. Precipitation pulses and
carbon fluxes in semi-arid and arid ecosystems. Oecologia 141, 254-268
11. Huxman, T.E., Smith, M.D., Fay, P.A., Knapp, A.K., Shaw, M.R., Loik, M.E.,
Smith, S.D., Tissue, D.T., Zak, J.C., Weltzin, J.F., Pockman, W.T., Sala, O.E.,
Haddad B.M., Harte, J., Koch, G.W., Schwinning, S., Small, E.E., and Williams,
D.G., 2004. Convergence across biomes to a common rain-use efficiency. Nature
429, 651-654
12. Marino, A. P., 2004. Stream community structure and the role of allochthonous
inputs in quebrada moquina at Montverde
13. Nunan, N., M. A. Morgan, et al. 1998. Ultraviolet absorbance (280 nm) of
compounds released from soil during chloroform fumigation as an estimate of the
microbial biomass. Soil Biol. and Biochem. 30, 1599-1603.
Texas Tech University, Apolinar Ortiz Jr, August 2011
31
14. Orchard, V. A., and Cook, F.J., 2002. Relationship between soil respiration and
soil moisture. Soil Biology and Biochemistry 15, 447-453.
15. Rinas, C., 2007. Grasslands not badlands: Arid grassland restoration in Big Bend
National Park. Nature science 1-10.
16. Vance, E.D., et al., 1987. An extraction method for measuring soil microbial
biomass C. Soil Biol. and Biochem. 19, 703-707
17. Whitford, W.G., 2002. Ecology of Desert Systems. Academic Press, London, UK
18. Weltzin, J.F., Loik, M.E., Schwinnings, S., Williams, D.G., Fay, P.A., Haddad
B.M, Harte. J., Huxman, T.E., Knapp, A.K., Lin, G., Pockman, W.T., Shaw, M.R.
Small, E.E., Smith, M.D., Smith, S.D., Tissue, D.T., and Zak, J.C, 2003.
Assessing the response of terrestrial ecosystems to potential changes in
precipitation. BioScience 53, 941-952
Texas Tech University, Apolinar Ortiz Jr, August 2011
32
Figure 2.1 Seasonal patterns of microbial biomass carbon by depth 0-15(A), 15-30 (B),
and 30-45 cm (C) associated with a restoration effort at a low-elevation degraded tabosa
grassland in the Chihuahuan Desert at Big Bend National Park. Values are means ± SE.
n= 6. Dam = vegetation associated with debris dams, veg = natural tobosa grassland, and
bare = areas with no vegetation cover.
0
1000
2000
3000
4000
5000
Jan-10 Aug Oct Jan-11
µg/
g d
ry w
t o
f so
il
A.
0
1000
2000
3000
4000
5000
Jan-10 Aug Oct Jan-11
µg/
g d
ry w
t o
f so
il
B.
0
1000
2000
3000
4000
5000
Jan-10 Aug Oct Jan-11
µg/
g d
ry w
t o
f so
il
Sample Date
Dam
Veg
Bare
C.
Texas Tech University, Apolinar Ortiz Jr, August 2011
33
Figure 2.2 Seasonal patterns of Fatty acid methyl esters (FAME) by depth 0-15(A), 15-30
(B), and 30-45 cm (C) associated with a restoration effort at a low-elevation degraded
tabosa grassland in the Chihuahuan Desert at Big Bend National Park. Values are means
± SE. n= 6. Dam = vegetation associated with debris dams, veg = natural tobosa
grassland, and bare = areas with no vegetation cover.
0%
20%
40%
60%
80%
100%
Jan
-10
Au
g
Oct
Jan
-11
Jan
-10
Au
g
Oct
Jan
-11
Jan
-10
Au
g
Oct
Jan
-11
Dam Dam Dam Dam Veg Veg Veg Veg Bare Bare Bare Bare
Pe
rce
nta
ge
0%
20%
40%
60%
80%
100%
Jan
-10
Au
g
Oct
Jan
-11
Jan
-10
Au
g
Oct
Jan
-11
Jan
-10
Au
g
Oct
Jan
-11
Dam Dam Dam Dam Veg Veg Veg Veg Bare Bare Bare Bare
Pe
rce
nta
ge
0%20%40%60%80%
100%
Jan
-10
Au
g
Oct
Jan
-11
Jan
-10
Au
g
Oct
Jan
-11
Jan
-10
Au
g
Oct
Jan
-11
Dam Dam Dam Dam Veg Veg Veg Veg Bare Bare Bare Bare
Pe
rce
nta
ge
Treatment by Date
Actinomycetes
Fungi
Gram -
Gram +
C.
A.
B.
Texas Tech University, Apolinar Ortiz Jr, August 2011
34
Figure 2.3 Seasonal patterns of nitrate (NO3-) by depth 0-15(A), 15-30 (B), and 30-45 cm
(C) associated with a restoration effort at a low-elevation degraded tabosa grassland in
the Chihuahuan Desert at Big Bend National Park. Values are means ± SE. n= 6. Dam
= vegetation associated with debris dams, veg = natural tobosa grassland, and bare =
areas with no vegetation cover.
0
10
20
30
40
50
60
Jan-10 Aug Oct Jan-11
mg/
kg d
ry s
oil
A.
0
50
100
150
200
250
300
Jan-10 Aug Oct Jan-11
mg/
kg d
ry s
oil
B.
0
20
40
60
80
100
120
Jan-10 Aug Oct Jan-11
mg/
kg d
ry s
oil
Sample Date
Dam
Veg
Bare
C.
Texas Tech University, Apolinar Ortiz Jr, August 2011
35
Figure 2.4 Seasonal patterns of ammonium (NH4+) by depth 0-15(A), 15-30 (B), and 30-
45 cm (C) associated with a restoration effort at a low-elevation degraded tabosa
grassland in the Chihuahuan Desert at Big Bend National Park. Values are means ± SE.
n= 6. Dam = vegetation associated with debris dams, veg = natural tobosa grassland, and
bare = areas with no vegetation cover.
0
0.5
1
1.5
2
2.5
3
3.5
Jan-10 Aug Oct Jan-11
mg/
kg d
ry s
oil
A.
0
0.5
1
1.5
2
2.5
3
3.5
Jan-10 Aug Oct Jan-11
mg/
kg d
ry s
oil
B.
0
0.5
1
1.5
2
2.5
3
3.5
Jan-10 Aug Oct Jan-11
mg/
kg d
ry s
oil
Sample Date
Dam
Veg
Bare
C.
Texas Tech University, Apolinar Ortiz Jr, August 2011
36
Figure 2.5 Seasonal patterns of pH by depth 0-15(A), 15-30 (B), and 30-45 cm (C)
associated with a restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park. Values are means ± SE. n= 6. Dam =
vegetation associated with debris dams, veg = natural tobosa grassland, and bare = areas
with no vegetation cover.
7
7.2
7.4
7.6
7.8
8
8.2
8.4
8.6
8.8
Jan-10 Aug Oct Jan-11
pH
A.
7
7.2
7.4
7.6
7.8
8
8.2
8.4
8.6
8.8
Jan-10 Aug Oct Jan-11
pH
B.
77.27.47.67.8
88.28.48.68.8
Jan-10 Aug Oct Jan-11
pH
Sample Date
Dam
Veg
Bare
C.
Texas Tech University, Apolinar Ortiz Jr, August 2011
37
Figure 2.6 Seasonal patterns of available phosphorus by depth 0-15(A), 15-30 (B), and
30-45 cm (C) associated with a restoration effort at a low-elevation degraded tabosa
grassland in the Chihuahuan Desert at Big Bend National Park. Values are means ± SE.
n= 6. Dam = vegetation associated with debris dams, veg = natural tobosa grassland, and
bare = areas with no vegetation cover.
0
20
40
60
80
100
Jan-10 Aug Oct Jan-11
mg/
kg d
ry s
oil
A.
0
20
40
60
80
100
Jan-10 Aug Oct Jan-11
mg/
kg d
ry s
oil
B.
0
20
40
60
80
100
Jan-10 Aug Oct Jan-11
mg/
kg d
ry s
oil
Sample Date
Dam
Veg
Bare
C.
Texas Tech University, Apolinar Ortiz Jr, August 2011
38
Figure 2.7 Seasonal patterns of potassium by depth 0-15(A), 15-30 (B), and 30-45 cm (C)
associated with a restoration effort at a low-elevation degraded tabosa grassland in the
Chihuahuan Desert at Big Bend National Park. Values are means ± SE. n= 6. Dam =
vegetation associated with debris dams, veg = natural tobosa grassland, and bare = areas
with no vegetation cover.
0
5
10
15
20
Jan-10 Aug Oct Jan-11
mg/
kg d
ry s
oil
A.
0
5
10
15
20
Jan-10 Aug Oct Jan-11
mg/
kg d
ry s
oil
B.
0
5
10
15
20
Jan-10 Aug Oct Jan-11
mg/
kg d
ry s
oil
Sample Date
Dam
Veg
Bare
C.
Texas Tech University, Apolinar Ortiz Jr, August 2011
39
Figure 2.8 Seasonal patterns of Soil Organic Matter (SOM) by depth 0-15(A), 15-30 (B),
and 30-45 cm (C) associated with a restoration effort at a low-elevation degraded tabosa
grassland in the Chihuahuan Desert at Big Bend National Park. Values are means ± SE.
n= 6. Dam = vegetation associated with debris dams, veg = natural tobosa grassland, and
bare = areas with no vegetation cover.
0
0.5
1
1.5
2
2.5
Jan-10 Aug Oct Jan-11
Soil
Org
anic
Mat
ter
(%)
A.
0
0.5
1
1.5
2
2.5
Jan-10 Aug Oct Jan-11
Soil
Org
anic
Mat
ter
(%)
B.
0
0.5
1
1.5
2
2.5
Jan-10 Aug Oct Jan-11
Soil
Org
anic
Mat
ter
(%)
Sample Date
Dam
Veg
Bare
C.
Texas Tech University, Apolinar Ortiz Jr, August 2011
40
Chapter 3
Restoring microbial functionality as a prerequisite to successful restoration efforts
of low elevation grassland in the Chihuahuan Desert in Big Bend National Park
Introduction
Cattle grazing and sequent drought during the early 1900’s, prior to the creation
of Big Bend National Park, caused subsequent degradation of once extensive grasslands
across much of the Park (Maxwell 1985). While rangeland improvement was evident at
higher elevations during the 1930’s with an increase in rainfall (Maxwell 1985), much of
the former lowland grasslands did not recover. Once the Park was established in 1945 the
National Park Service in cooperation with the Soil Conservation Service began a
reseeding project (Maxwell 1985) involving pitting of the soil surface, shallow pit
development and the construction of low, net-wire spreader dams across washes and
sheet-wash overflow areas to trap moisture and debris. All of these efforts had limited or
no long-term success (Rinas 2007). Once disturbances occurred within these lowland
grassland sites, changes in soil microbial dynamics quickly follow leading to declines in
soil nutrient cycling and critical plant-microbe interactions. These negative biotic
changes are in addition to the higher soil temperatures and decreased infiltration of
rainfall that follow with the loss of vegetation in desert areas (Whitford 2002).
Recent discussions concerning the need to reduce sediment loading within the Rio
Grande (Rinas 2007) has refocused attention on degraded low-elevation grasslands within
the national park and across the region as a critical component in this problem. Analysis
Texas Tech University, Apolinar Ortiz Jr, August 2011
41
of the landscape by park managers has shown that efforts have to be taken to reestablish
low-elevation grasslands as one countermeasure to decrease sediment loading along the
Rio Grande in the Big Bend region. Initial attempts in early 2000 to reestablish
vegetation on bare sites that contribute to sediment deposition into the Rio Grande
included micro-pits to stop overland flow and to retain and increase rain fall infiltration.
These efforts were unsuccessful as they could not overcome the harsh abiotic conditions
of these sites with little vegetation (Rinas 2007). Current attempts at reestablishing
vegetation cover on bare locations has focused on building debris dams to help “jump
start” plant growth in bare soil sites by providing seedling shade within the debris dams,
to help capture water moving across the site as sheet flow and to provide lower soil
temperatures thereby increasing microbial activity. The debris dams are placed in a
staggered pattern mimicking the natural vegetation structure and contour lines (Rinas
2007). Debris dams have been shown to collect nutrients from bare areas in grasslands
(Marino 2004) and redistribute these resources to vegetated areas. Shading from the
coarse woody debris should also reduce soil temperature and increase soil moisture for
longer periods following rainfall events as these structures will increase water infiltration
rates by decreasing surface flow across the debris dams. With increased soil moisture,
decreased temperature and increased carbon input from established vegetation, microbial
activity and functionality should also aid in the reestablishment of critical ecosystem
process of decomposition and nutrient recycling.
The goal of this investigation is to determine the degree to which the “debris dams”
approach can ameliorate the harsh abiotic conditions associated with bare areas in these
Texas Tech University, Apolinar Ortiz Jr, August 2011
42
low-elevation grassland and restore necessary microbial functions comparable with
microbial functional activity associated with undisturbed low-elevation grasslands in this
region of the Chihuahuan Desert.
Site Description
The current restoration efforts for this project were initiated at North Rosillos site
on the former Harte ranch beginning in May 2006. As restoration managers at Big Bend
National Park were aware that soil temperatures and infiltration issues were a major
concern in establishing vegetation on former low-elevation tobosa grasslands, a new
approach using a combination of erosion control blankets, hydro-seeding and coarse
woody debris obtained from management efforts to modify soil temperatures was
employed (Rinas 2007). Mean elevation at the North Rosillos site is 835 masl with site
aspect of 0.6%. Total annual precipitation for the region has averaged approximately 268
mm since 1982 with mean bimonthly rainfall ranging between 8.8 mm (March) and 41.1
mm (September). Mean daily high temperatures range from 17.59 °C (December) to
36.20 °C (June), while daily lows range from 1.10 °C (January) to 22.32 °C (July). Of
note, surface temperatures recorded at the North Rosillos location rank among the highest
recorded in BBNP. The debris dams established at the North Rosillos location are part of
a larger restoration project on the Harte Ranch where 77.3 hectares (191 acres) are to be
restored to low-elevation grasslands. Additional information on the site can be found in
Chapter 2. Soil at the North Rosillos site is deep silty loam originally classified as
Texas Tech University, Apolinar Ortiz Jr, August 2011
43
Tornillo (fine-silty, mixed, superactive, thermic Fluventic Haplocambids) and now
reclassified as Chalkdraw.
Methods
Microbial Enzyme Analysis
Microbial enzymatic activity was evaluated to determine the degree to which the
“debris dam” approach to grassland restoration in an arid environment could reestablish
important soil microbial processes that are critical for decomposition and nutrient cycling
(Acosta-Martinez et al. 2004) after being in place for four years. The activity of a suite of
microbial exoenzymes was assessed over a year (January 2010 through January 2011)
within the debris dams, in undisturbed tobosa grassland and in association with highly
disturbed non-vegetated soil. Soil samples from each location were collected in January,
August, October 2010 and January 2011. Sampling details are provided in Chapter 2.
Phenol oxidase was used to determine how the microbial community can utilize lignin
using the protocol described by Sinsabaugh et al. (2003). Briefly, 0.5 grams of soil from
each site was mixed with 62.5 ml of acetate buffer and homogenized for 1 minute,
filtered using Whatman 43 filter paper, dispensed in 100-µl aliquots into Costar
microtiter plates and read after 18 hrs at 650 nm. The substrate L-3,4-
dihydroxyphenylalanine (DOPA) produces the color change needed to observe the
reaction. DOPA alone was loaded into the blank wells, and a DOPA and sample soil
solution was placed in the complete-assay wells for analysis.
Texas Tech University, Apolinar Ortiz Jr, August 2011
44
The overall activity of the microbial community within the three different habitats
was evaluated by assaying for β-glucosidase activity. The assay is a good indicator of
cellular degradation and soil quality. Three replicates of 0.5 grams from each sample soil
were used for this enzyme assay (Eivazi and Tabatabai 1988). p-Nitrophenyl-b-D-
glucopyranoside will give an absorbance reading of the reaction at 560nm.
To evaluate soil microbial contributions to phosphorus availability in response to
seasons and debris dam influences, phosphodiesterase activity was measured.
Phosphodiesterase activity determines the degree to which nucleic acids in the soil are
being degraded and were used to monitor the P dynamics in the soil as influenced by
grassland restoration efforts. The phosphodiesterase assays were conducted as described
by Browman and Tabatabai (1978) and (Acosta-Martinez et al. 2003).
Microbial Carbon Use
The BIOLOG procedure (Zak et al. 1994) was used to determine the effects of
debris dams on reestablishment of bacterial functional diversity across season and with
depth compared with bacterial functional diversity from the intact tabosa grassland.
Biolog plates were read at 590 nm after incubation for 72 hrs and 120 hrs using a 10-4
dilution. The evaluation of fungal functional ability on carbon substrates from each of the
three locations was conducted using the FungiLog procedure as described by Sobek and
Zak (2003) at a 120-hr incubation time. Microplates were placed into Ziploc storage bags
to conserve moisture, incubated at 25° C and read at 590 nm at 72 hrs and 120 hrs (Sobek
and Zak 2003). From each microtiter plate from the 120-hr incubation time, substrate
Texas Tech University, Apolinar Ortiz Jr, August 2011
45
activity and substrate richness were obtained. Substrate activity is the sum of the
absorbance values for each plate, and substrate richness is the number of carbon
substrates that are utilized at each sample period and depth (Sobek and Zak 2003).
Nutrient Analysis
Soil nutrient data are presented in Chapter 2.
Data Analysis
Data analysis was conducted as described in Chapter 2 using the microbial carbon
use and enzyme data.
Results
Bacterial Functional Activity
Across all sample times location is significant (p<0.004) with the highest values
of Biolog activity occurring under the natural vegetation and the lowest values under the
bare soil, and the values associated with the debris dams were intermediate and similar to
the natural vegetation. Across all sample times there was not a significant (p=0.065)
effect on Biolog activity with depth for all locations combined. Within sample times there
was a significant effect of depth. For 0-15-cm depth the highest Biolog activity occurred
in October 2010. These values were significantly different than any other sampled month;
however there were no significant difference among any location for Biolog activity for
the other three sampled dates.
Texas Tech University, Apolinar Ortiz Jr, August 2011
46
In the analysis of location by sample date there were significant differences by
season (between subject effects) with the highest values of Biolog activity in all locations
occurring in October 2010. The repeated measures analysis showed that the highest
Biolog activity was found associated with the natural vegetation (wilks lambda p<0.001)
and there was a significant interaction of sample date and location (wilks lambda
p=0.004). The lowest values of Biolog Activity were observed in January 2010. Although
Biolog activity differed among depth by location, the seasonal effects were consistent at
each of the three depths.
Fungal Functional Activity
Across all sample times location is significant (p<0.001) with the highest values
of Fungilog Activity occurring under the debris dams and the lowest values under the
bare soil, and the values associated with natural vegetation were intermediate and similar
to the debris dams. Across all sample times there was not a significant (p=0.859) effect
on Fungilog activity by depth for all locations combined. For 0-15-cm depth the highest
Fungilog activity occurred in August 2010. These values were significantly different than
October 2010; however there were no significant differences among any location for
Fungilog activity for the other three sampled dates.
In the analysis of location by sample date there were significant differences by
season (between subject effects) with the highest values of Fungilog activity in all
locations occurring in August 2010. The repeated measures analysis showed that the
highest Fungilog activity was associated with the debris dams (wilks lambda p<0.001)
Texas Tech University, Apolinar Ortiz Jr, August 2011
47
and there was a significant interaction of sample date and location (wilks lambda
p<0.001). The lowest values of Fungilog Activity were observed in October 2010.
Although Fungilog activity differed among depth by location, the seasonal effects were
consistent at each of the three depths.
Phosphodiesterase
Across all sample times location was significant (p<0.001) with the highest values
of phosphodiesterase activity occurring under the natural vegetation and the lowest
values under the bare soil, and the value associated with the debris dams were
intermediate and similar to the bare soil. Across all sample times there was a significant
(p=0.001) effect on phosphodiesterase activity by depth for all locations combined. Also,
within sample times there were significant effects of depths. For the 0-15cm depth, the
highest phosphodiesterase activity occurred in January 2010. These values were
significantly different than any other sampled month; however there were no significant
differences among any location for Fungilog activity for the other three sampled dates.
In the analysis of location by sample date there were significant differences by
season (between subject effects) with the highest values of phosphodiesterase activity in
all locations occurring in August 2010. The repeated measures analysis showed that the
highest Fungilog activity was associated with the natural vegetation (wilks lambda p-
0.012) and there was a significant interaction of sample date and location (wilks lambda
p<0.001). The lowest values of phosphodiesterase activity were observed in January
Texas Tech University, Apolinar Ortiz Jr, August 2011
48
2011. Although phosphodiesterase activity differed among depth by location, the
seasonal effects were consistent at each of the three depths.
β-Glucosidase Activity
Across all sample times location is significant (p<0.001) with the highest values
of β-glucosidase activity occurring under the natural vegetation and the lowest values
under the bare soil, and values associated with the debris dams were intermediate and
similar to the natural vegetation. Across all sample times there was not a significant
(p=0.253) effect on β-glucosidase activity by depth for all locations combined. For 0-15-
cm depth the highest β-glucosidase activity occurred in January 2010. These values were
significantly different than any other sampled month; however there were no significant
differences among any location for β-glucosidase activity for the other three sampled
dates.
In the analysis of location by sample date there were significant differences by
season (between subject effects) with the highest values of β-glucosidase activity in all
locations occurring in August 2010. The repeated measures analysis showed that the
highest β-glucosidase activity was associated with the natural vegetation (wilks lambda
p<0.001) and there was a significant interaction of sample date and location (wilks
lambda p<0.001). The lowest values of β-glucosidase Activity were observed in October
2010. Although β-glucosidase activity differed among depth by location the seasonal
effects were consistent at each of the three depths.
Texas Tech University, Apolinar Ortiz Jr, August 2011
49
Phenol Oxidase Activity
Across all sample times, location was significant (p<0.001) with the highest
values of phenol oxidase activity occurring under the natural vegetation and the lowest
values under the bare soil, and values associated with the debris dams were intermediate
and similar to the natural vegetation. Across all sample times there was not a significant
(p=0.176) affect on phenol oxidase activity by depth for locations combined. For the 0-
15-cm depth the highest phenol oxidase activity occurred in January 2010. These values
were significantly different than any other sampled month; however there were no
significant differences among any location for phenol oxidase activity for the other three
sampled dates.
In the analysis of location by sample date there were significant differences by season
(between subject effects) with the highest values of phenol oxidase activity in all
locations occurring in January 2010. The repeated measures analysis showed that the
highest phenol oxidase activity was found associated with the natural vegetation (wilks
lambda p<0.001) and there was a significant interaction of sample date and location
(wilks lambda p<0.001). The lowest values of phenol oxidase activity were observed in
October 2010.
Discussion
The low levels of bacterial substrate activity associated with the debris dams
suggest that bacterial carbon dynamics have not reestablished to the level expressed
under the natural vegetation. The idea of restoring what took centuries to achieve in a few
Texas Tech University, Apolinar Ortiz Jr, August 2011
50
years is possible as there has been the reestablishment of vegetation in areas that had
none four years ago. As with all restoration efforts recovery will take time (Rinas 2007).
As bacterial substrate activity was not significantly different under the debris dams in
comparison with the bare soils except for October 2010, when the site received
substantial rainfall, the length of time needed to establish the full extent of soil microbial
activity is certainly longer than the five years since initial establishment of the debris
dams. Although FAME levels (Chapter 2) were similar for Gram-positive bacteria under
the debris dams and the natural vegetation, differences in carbon substrate use could
reflect major taxonomic differences or physiological differences.
The debris dams did have an increase in fungal substrate diversity as compared
with the bare soils suggesting that the increase in microbial biomass reflects changes in
fungal abundances. The increase in Soil Organic Matter (SOM) from primary production
over the four years coupled with the carbon input from the coarse woody debris can be a
reason why the debris dams had similar fungal substrate activity levels compared to the
natural vegetation. The pattern in fungal substrate activity by depth under the natural
vegetation and debris dams also reflects the impact of the vegetation on reducing the
nitrate levels that build up under bare soil.
The influences of a few factors such as temperature, increased microbial activity,
and pH, all of which can have an impact on the rate of breaking down carbon sources,
can account for the high levels of bacterial and fungal activity under the natural
vegetation and debris dams (Eivazi and Tabatabai 1990). The debris dams aid in retaining
moisture and increase infiltration helping to prevent further soil erosion and reestablish
Texas Tech University, Apolinar Ortiz Jr, August 2011
51
microbial activity by supplying material for decomposition (Rinas 2007). Fontaine et al.
(2003) showed how the addition of SOM to areas with plant cover and a similar
environment, temperature, pH and microbial activity can have a major impact on soil
enzymes.
The increase in SOM under the debris dams, coupled with lower soil temperatures
and increased soil moisture, could account for changes in soil enzyme activity (Rinas
2007). Importantly, as the vegetation continues to establish and provide carbon input to
the system, critical linkages through decomposition and mineralization are established.
The high levels of phenol oxidase in soils with vegetation emphasizes that the debris dam
approach can reestablish critically important soil microbial activity levels. Excess
nitrogen can have a negative effect on the activity of phenol oxidase and other lignin-
degrading enzymes (Carreiro 2000 and DeForest 2004). The lower levels of phenol
oxidase under the bare soil could be attributed to high soil nitrate levels in addition to
lower levels of SOM.
The addition of nitrogen should have no influence on β-glucosidase activity and
its role in hydrolysis of glycosidic molecules that release glucose for energy for the
microbial flora (Dick 1997). While β-glucosidase levels under the debris dams have not
reached those seen in the natural vegetation, they have increased under the debris dams.
With β-glucosidase not being affected by high nitrogen, it is one of the few soil enzymes
that is not affected by the changes in C:N ratios within the soil (Sinsabaugh et al. 2005).
As β-glucosidase does contribute to the carbon dynamics, it does have influence on other
soil enzymes.
Texas Tech University, Apolinar Ortiz Jr, August 2011
52
References
1. Acosta-Martinez, V., T.M. Zobeck, et al. 2003, Enzyme activities and microbial
community structure in semi-arid agricultural soils. Biol Fertil. Soils 38, 216-227
2. Acosta-Martinez, V., D.R. Upchurch, et al. 2004, Early impacts of cotton and
peanut cropping systems on selected soil chemical, physical, microbiological and
biochemical properties. Bio Fertil. Soils 40, 44-54
3. Browman, M.G., Tabatabai, M.A., 1978. Phophodiesterase activity of soils. Soil
Sci. Am. J. 42, 284-290
4. Eivazi and Tabatabai, 1977 F., Phosphatases in soils, Soil Biol. Biochem. 9, 167–
172
5. Ekenler, M. and Tabatabai, M.A., 2002. β-Glucosaminidase activity of soils:
effect of cropping systems and its relationship to nitrogen mineralization. Biol
Fertil. Soils. 36, 367-376.
6. Maxwell, R.A., 1985. Big Bend History: A History of Big Bend National Park.
Big Bend National History Association, Big Bend National Park, Texas. 88
7. Rinas, C., 2007, Grasslands not badlands: Arid grassland restoration in Big Bend
National Park. Nature science 1-10.
8. Shaw. J.L., and Burns. G. R., 2006, Enzyme activity profiles and soil quality,
Microbiological methods for assessing soil quality 158-170
Texas Tech University, Apolinar Ortiz Jr, August 2011
53
9. Sinsabaugh, R.L., Saiya-Cork, K, Long, T, Osgood, M.P, Neher, D.A., Zak, D.R.,
and Norby, R.J. 2003, Soil microbial activity in a Liquidambar plantation
unresponsive to CO2-driven increases in primary production. Appl. Soil Ecol. 24,
263-271.
10. Sobek, E., and J. Zak. 2003. A microtiter plate method for evaluating soil
fungal functional diversity. Mycologia 95, 590-602.
11. Whitford, W.G., 2002. Ecology of Desert Systems. Academic Press, London, UK
12. Zak, J. C., Willig, M.R., Moorhead, D.L., Wildman, H.G., 1994. Functional
diversity of bacterial communities: a quantitative approach. Soil Biol. Biochem.
26, 1101-1108.
Texas Tech University, Apolinar Ortiz Jr, August 2011
54
Figure 3.1 Seasonal patterns of Biolog GN-2 microtiter plate activity by depth 0-15(A),
15-30 (B), and 30-45 cm (C) associated with a restoration effort at a low-elevation
degraded tabosa grassland in the Chihuahuan Desert at Big Bend National Park. Values
are means ± SE. n= 6. Dam = vegetation associated with debris dams, veg = natural
tobosa grassland, and bare = areas with no vegetation cover.
0
2
4
6
8
10
Jan-10 Aug Oct Jan-11
Ave
rage
SA
0
1
2
3
4
5
6
7
8
9
Jan-10 Aug Oct Jan-11
Ave
rage
SA
0123456789
Bio Bio Bio Bio
Jan-10 Aug Oct Jan-11
Ave
rage
SA
Sample Date
Dam
Veg
Bare
C.
Texas Tech University, Apolinar Ortiz Jr, August 2011
55
Figure 3.2 Seasonal patterns of Fungilog SFN-2 microtiter plate activity by depth 0-
15(A), 15-30 (B), and 30-45 cm (C) associated with a restoration effort at a low-elevation
degraded tabosa grassland in the Chihuahuan Desert at Big Bend National Park. Values
are means ± SE. n= 6. Dam = vegetation associated with debris dams, veg = natural
tobosa grassland, and bare = areas with no vegetation cover.
0
10
20
30
40
50
60
70
80
Jan-10 Aug Oct Jan-11
Ave
rage
SA
0
10
20
30
40
50
60
70
80
Jan-10 Aug Oct Jan-11
Ave
rage
SA
0
20
40
60
80
100
Jan-10 Aug Oct Jan-11
Ave
rage
SA
Sample Date
Dam
Veg
Bare
Texas Tech University, Apolinar Ortiz Jr, August 2011
56
Figure 3.3 Seasonal patterns of phosphodiesterase values by depth 0-15(A), 15-30 (B),
and 30-45 cm (C) associated with a restoration effort at a low-elevation degraded tabosa
grassland in the Chihuahuan Desert at Big Bend National Park. Values are means ± SE.
n= 6. Dam = vegetation associated with debris dams, veg = natural tobosa grassland, and
bare = areas with no vegetation cover.
0
100
200
300
400
500
600
Jan-10 Aug Oct Jan-11
Ph
osp
ho
sdie
ste
ras
Act
ivit
ym
gPn
Kg-1
soil
h-1
0
100
200
300
400
500
Jan-10 Aug Oct Jan-11
Ph
osp
ho
sdie
ste
ras
Act
ivit
ym
gPn
Kg-1
soil
h-1
0
100
200
300
400
500
Jan-10 Aug Oct Jan-11Ph
osp
ho
sdie
ste
ras
Act
ivit
ym
gPn
Kg-1
soil
h-1
Sample Date
Dam
Veg
Bare
Texas Tech University, Apolinar Ortiz Jr, August 2011
57
Figure 3.4 Seasonal patterns of β-glucosidase values by depth 0-15(A), 15-30 (B), and
30-45 cm (C) associated with a restoration effort at a low-elevation degraded tabosa
grassland in the Chihuahuan Desert at Big Bend National Park. Values are means ± SE.
n= 6. Dam = vegetation associated with debris dams, veg = natural tobosa grassland, and
bare = areas with no vegetation cover.
0
100
200
300
400
500
600
Jan-10 Aug Oct Jan-11
β-G
luco
sid
ase
mg
pn
kg-1
soil-1
0
100
200
300
400
500
600
700
Jan-10 Aug Oct Jan-11
β-G
luco
sid
ase
mg
pn
kg-1
soil-1
0
100
200
300
400
500
600
Jan-10 Aug Oct Jan-11
β-G
luco
sid
ase
mg
pn
kg-1
soil-1
Sample Date
Dam
Veg
Bare
Texas Tech University, Apolinar Ortiz Jr, August 2011
58
Figure 3.5 Seasonal patterns of phenol oxidase values by depth 0-15(A), 15-30 (B), and
30-45 cm (C) associated with a restoration effort at a low-elevation degraded tabosa
grassland in the Chihuahuan Desert at Big Bend National Park. Values are means ± SE.
n= 6. Dam = vegetation associated with debris dams, veg = natural tobosa grassland, and
bare = areas with no vegetation cover.
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Jan-10 Aug Oct Jan-11
Ph
en
ol O
xid
ase
Act
ivit
yµ
mo
l h-1
g-1
0
0.1
0.2
0.3
0.4
0.5
0.6
Jan-10 Aug Oct Jan-11
Ph
en
ol O
xid
ase
Act
ivit
yµ
mo
l h-1
g-1
0
0.1
0.2
0.3
0.4
0.5
0.6
Jan-10 Aug Oct Jan-11
Ph
en
ol O
xid
ase
Act
ivit
yµ
mo
l h-1
g-1
Sample Date
Dam
Veg
Bare