Isotopic Composition of Organic and Inorganic Carbon in Desert Biological Soil Crust SystemsKathryn Alexander1, Hilairy Hartnett1,2, Ariel Anbar1,2, Hugo Beraldi3, Ferran Garcia-Pichel3

Location Field Sites and Samples

Dark, Lichen dominated BSC

Light, Cyanobacteria dominated BSC

Sunday Churt Site

Green Butte Site

Dark Crusted-Sunday Churt (09B)

Dark Crusted-Green Butte (10J)

Light Crusted-Green Butte (10H)

Light Crusted-Green Butte(10G)

Dark Uncrusted-Sunday Churt (09C)

Ave

rage

Dep

th (

cm)

g (C,N)/mg soil 13C vs VPDB (‰)

Total Carbon Total Nitrogen Inorganic Carbon Organic Carbon

Global distribution of BSCs

Cyanobacteria dominated

Green algal dominated

Lichen dominated

Moss/Liverwort dominated

(Büdel, 2001)

1. School of Earth & Space Exploration, Arizona State University; 2. Department of Chemistry & Biochemistry, Arizona State University; 3. School of Life Sciences, Arizona State University

B13C-1116

Carbon (C) Cycle

(Adapted from Rost et al., 1998)

Nitrogen (N) Cycle

N2

NH4+

NO2-

NO3-NO2

-Denitrification

NitrificationNitrogen Fixation

Organic N CompoundsAssimilation

Mineralization

Nitrate Reduction

(Adapted from Schink, 1999)

How do Biological Soil Crusts manipulate

geochemical systems to obtain required nutrients

and metals in a chemically and physically stressful

environment?

Biological Soil Crusts (BSCs)

• Crucial components of arid ecosystems• Cyanobacteria, algae, lichen, micro-fungi, mosses, and others• Involved in C and N cycling

N fixation Photosynthesis Decomposition

• Tolerate extremes UV radiation Temperature Desiccation

(Belnap et al., 2001)

Methods

1) Soil cores collected in March, 20062) Samples dried, ground, sieved, and homogenized3) Analyzed on an elemental analyzer connected to a Finnigan Deltaplus isotope

ratio mass spectrometer4) Organic carbon measured after fuming bulk samples with concentrated HCl5) Inorganic carbon calculated as the difference between bulk and organic (with full

error propagation)6) 20% of samples were analyzed in duplicate7) Isotope measurements made relative to three laboratory working standards

previously calibrated to the VPDB scale by measurement against IAEA standards.

Dep

th

Light Heavy

Isotopic Composition

Organic C

Total C

Inorganic C

Carbon Content

Less More

Dep

th

Organic C Inorganic C

Conceptual Model – Idealized Soil ProfilePredictions:1) Organic C will reflect photosynthetically derived C, -20 to

-30 ‰

2) Inorganic C will be isotopically heavy relative to organic C (i.e., -10 to 0 ‰)

Results: 1) In some cores, data support predictions

2) Green Butte cores have heavier C than expected

Current Research Directions

1) Higher resolution sampling with depth

2) Direct measurement of inorganic carbon content and isotopic composition

3) Concurrent analysis of clay mineralogy

DenitrificationNitrification

CO2

Arid regions of North America(Rosentreter and Belnap, 2001)

Cold deserts

Hot deserts

1

2

~ 3 km

Map of field sites near Moab, Utah1) Sunday Chert2) Green Butte3) Colorado River (no crust here!)

ConsumersProducers

Organic C

Sedimentary Rock

Photo-, Chemosynthesis

Respiration

Preservation

Burial

Decomposition

Gap in sequence Gap in sequence

Qua

rtz

Ort

hocl

ase

Cal

cite

Ca-

smec

tite

Illite

Wei

ght

%

Minerals Present in Core 10G1

14% Clays

87.7% Non-clays

% Clays in Core 10G1

Acknowledgements: A. Michaud, L. Williams, M. Kelly, S. Klonowski, M.Kraft

References:Belnap, J., Budel, B, and Lange, O.L. (2001) In Biological Soil Crusts: Structure, Function, and Management (ed. J. Belnap and O.L. Lange), pp. 3-30. Springer.Büdel, B. (2001) In Biological Soil Crusts: Structure, Function, and Management (ed. J. Belnap and O.L. Lange), pp. 141-152. Springer.Eberl, D.D. (2003) U.S.G.S. Open-File Report 03-78, Boulder, Colorado, 46 p.Schink, B. (1999) In Biology of the Prokaryotes (ed. J.W. Lengeler, G. Drews, and H.G. Schlegel), pp. 804-814. Blackwell Science.Rosentreter, R. and Belnap, J. (2001) In Biological Soil Crusts: Structure, Function, and Management (ed. J. Belnap and O.L. Lange), pp. 31-50. Springer.Rost, T.L., Barbour, M.G., Stocking, C.R., and Murphy, T.M. (199) Plant Biology. Wasdsworth.

(Eberl, 2003)

4) Soil solution organic content, composition and presence of metallophores

- Metal acquisition- Metal isotopic fractionation

5) The BIG picture: - Impact of BSCs on biogeochemical cycles - Isotopic or mineralogical biosignatures

For questions or further information contact Katie Alexander at katiealex@asu.edu

3

Pea

k In

tens

ity (

x103

)

2-Theta (deg)20 6050403010

Quartz

Calcite

Zincite*

Illite

*Zincite added as a standard

Raw Spectrum of Bulk Mineralogy for Core 10G1

16

14

12

10

8

6

4

2

0

Thanks to the National Science Foundation for funding (0525569)!

Results

Schematic diagram describing a range of geomicrobiological interactions and their components present in Biological Soil Crusts.

Atmosphere

Aqueous phase

Biological Components

Solid Phases

Net exports

Emergent properties, lasting signatures

L I GHT

* Soil crust cutter is 23cm x 28cm

Soil crust community extends about 0.5 cm below the soil surface

ObjectiveTo evaluate influence of BSC on underlying soil mineralogy and geochemistry

Sites chosen based on previous work and geomicrobiological data