research article environmental factors and soil co

Research ArticleEnvironmental Factors and Soil CO

2Emissions in

an Alpine Swamp Meadow Ecosystem on the TibetanPlateau in Response to Experimental Warming

Bin Wang12 Ben Niu3 Xiaojie Yang2 and Song Gu3

1Key Laboratory of Marine Ecosystem and Biogeochemistry Second Institute of Oceanography State Oceanic Administration36 North Baoshu Road Hangzhou 310012 China2College of Life Science and Agriculture and Forestry Qiqihar University 42 Wenhua Road Qiqihar 161006 China3College of Life Science Nankai University 94 Weijin Road Tianjin 300071 China

Correspondence should be addressed to Bin Wang wbin03sinacom

Received 27 October 2015 Accepted 28 February 2016

Academic Editor Yuangen Yang

Copyright copy 2016 Bin Wang et alThis is an open access article distributed under theCreativeCommonsAttribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

We examined the response of soil CO2emissions to warming and environmental control mechanisms in an alpine swampmeadow

ecosystem on the Tibetan Plateau Experimental warming treatments were performed in an alpine swamp meadow ecosystemusing two open-top chambers (OTCs) 40 cm (OA) and 80 cm (OB) tall The results indicate that temperatures were increased by279∘C in OA and 496∘C in OB that ecosystem CO

2efflux showed remarkable seasonal variations in the control (CK) and the two

warming treatments and that all three systems yielded peak values in August of 1236 1423 and 1662 g Cmminus2monthminus1 AnnualCO2efflux also showed a gradual upward trend with increased warming OB (6841 g Cmminus2 yearminus1) gt OA (5807 g Cmminus2 yearminus1) gt

CK (4733 g Cmminus2 yearminus1) Path analysis revealed that the 5 cm depth soil temperature was themost important environmental factoraffecting soil CO

2emissions in the three systems

1 Introduction

Sharp increase in the concentrations of atmospheric carbondioxide (CO

2) and other greenhouse gases has led to a global

average temperature increase of 076∘C [1] This scenario ismore significant at high elevations and latitudes [2] Areaswith temperature increases of more than 1-2∘C over the 30-year period of 1965ndash1995 were located primarily at latitudesgreater than 50∘ north [1] At high elevations and latitudes cli-matewarmingwill cause degradation of permafrost and affectplant phenology and precipitation patterns [3ndash5] Warmingcan facilitate the decomposition of a large amount of organiccarbon previously sequestered in the permafrost therebyallowing gaseous carbon to enter the atmosphere and accel-erating the process of global warming [6]Therefore accuratepredictions of the impact of future climate change on thecarbon cycle depend on accurate assessments of ecosystem

respiration in response to warming at high elevations and lat-itudes [7] Ecologists havemade the effect of warming on highaltitude and high latitude ecosystems the topic of much cur-rent research [8ndash10] Mertens et al (2001) [11] monitored netecosystemCO

2exchange in tundra underwarmed conditions

in Greenland a temperature increase of 25∘C caused thetundra ecosystem to act as a carbon source and caused a 39increase in belowground respirationMertens et al [11] inves-tigated trends in CO

2exchange at the end of the growing sea-

son due to a temperature increase of 25∘C at a tundra site theelevated temperature significantly increased the rate of soilrespiration whereas gross photosynthesis by vegetation wasless affected by the simulated warmingWelker et al [12] usedopen-top chambers (OTCs) to raise the temperature 1ndash3∘Cabove ambient temperatures andmonitored the net exchangein a Canadian alpine ecosystem over a 9-year periodThe ele-vated temperature increased the near-surface volume fraction

Hindawi Publishing CorporationJournal of ChemistryVolume 2016 Article ID 2573185 7 pageshttpdxdoiorg10115520162573185

2 Journal of Chemistry

and significantly enhanced gross ecosystem photosynthesisthereby causing the ecosystem to gradually change from acarbon source to a carbon sink Biasi et al [13] conducted a 2-year study of experimental warming using OTCs and foundthat warming promoted tundra ecosystem respiration lead-ing to a decrease in soil carbon and an increase in nitrogencontent Despite a marked decrease in the carbonnitrogenratio there were no significant changes in the number andcomposition of soil microbes The findings suggested thatthe tundra ecosystem will change from a carbon sink to acarbon source with future warming Wu et al [14] summa-rized 85 studies of experimental warming performed world-wide which involved various terrestrial ecosystems such asforests tundra temperate grasslandmountainmeadows andshrubland The relationship between net CO

2exchange and

warming in the various ecosystems was evaluated via a meta-analysis It was concluded that warming promotes photosyn-thesis and respiration however it has no significant effect onnet carbon absorption by the entire ecosystem

Heating methods for ecosystem warming include field-style greenhouses tents and open-top chambers (OTCs)of various shapes and sizes soil heating pipes and cablesinfrared reflector and infrared radiator [15] in which theOTC is an experimental warming first used by the Interna-tional Tundra Experiment to study the influence of globalwarming to high altitude and latitude region ecosystems [16]The advantages of OTC warming equipment are low costconvenient operation easy repeatability fitting to long-termfield experiments and minimal disturbance of the soil at theexperiment site

The Tibetan Plateau is located in southwestern China andspans an area of sim250 times 104 km2 that is sim25 of the territoryofChinaThe average elevation of theTibetanPlateau exceeds4000m making it the worldrsquos highest plateau [17] In thisregion swamp meadow spans an area of 49 times 104 km2 andaccounts for 196 of the plateau making it one of themost extensive grassland ecosystems on the Tibetan Plateau[18] These alpine ecosystems have developed in the extremeenvironments of the plateau and mountains Due to theirinherent vulnerability and instability alpine ecosystems areextremely sensitive to human disturbance and global warm-ing Investigating the response of alpine ecosystems to risingtemperatures is therefore highly valuable [18] There havebeen studies of greenhouse gas fluxes in grassland ecosystemsof the Tibetan Plateau However these studies have focusedprimarily on monitoring and investigating flux dynamics ofgreenhouse gases (particularlyCO

2) in various types of alpine

grassland ecosystems [19ndash21] Little research has involved theeffects of global climate change (particularly warming) oncarbon fluxes in alpine swamp ecosystems Studies elsewherein theworld have shown that key processes in the carbon cycledisplay significant responses to global warming in variousecosystems [22ndash24] In the present study we used an OTCsystem to perform experimental warming treatments to ana-lyze soil CO

2emissions dynamics and their relationshipswith

environmental factors in an alpine swamp ecosystem on theTibetan Plateau This study has implications for understand-ing the carbon cycle in grassland ecosystems and in terrestrialecosystems in general in China

2 Material and Methods

21 Study Site Thestudy site was located in a swampmeadowof Koeleria tibetica in Dawu Town of Maqin County GologTibetan Autonomous Prefecture Qinghai Province ChinaThe swamp meadow is in the Sanjiangyuan region in thehinterlands of the Tibetan Plateau The site coordinates are34∘275691015840N and 100∘130651015840E The meadow is at an elevationof 3700ndash4020m with a relief of 200ndash300m and measures25 km north to south The region has a continental plateauclimateTheweather is cold and dry and air pressures are lowThe spring and autumn are short and the freezing period lastsfrom October to the next April The permafrost is generally50ndash120 cm thick and its upper limit is at a depth of 08ndash25mThe growing season spans fromMay to SeptemberTheannual average temperature is minus56ndash38∘C with an extrememaximum of 28∘C and an extreme minimum of minus48∘CThe multiyear average precipitation is 15535ndash69793mm andmore than 75 of the rainfall falls from June to SeptemberThe annual average evaporation is 730ndash1700mm and theaverage relative humidity is 55 The maximum wind speedis 31msdotsminus1 and the prevailing wind is westerly The averagenumber of days with thunderstorms is 478 per year [25]

In the study site the plants are predominantly perennialmesophytic herbs The dominant species of the grass com-munity include Kobresia littledalei Carex moorcroftii Fes-tuca ovina Kobresia pygmaea Kobresia capillifolia Kobresiabellardii and Kobresia graminifolia The vegetation cover isgreater than 90 The predominant soil type is swampy soilwith a maximum depth of 23mThe soil pH ranges from 53to 85 The soil contains 60ndash359 g kgminus1 organic matter 02ndash149 g kgminus1 total nitrogen 022ndash10 g kgminus1 total phosphorusand 80ndash352 g kgminus1 total potassium [18]

22 Determination of Soil CO2 Efflux an MicrometeorologicalFactors The experiment was conducted from January 1 toDecember 31 2012 Three plots with similar vegetation andaboveground biomass were selected at the study site Attwo of the plots two types of OTCs with a hexagonal conestructure were installed The hexagonal surfaces were madeof plexiglass with light transmittance of 95The OTCs were40 cm (OA) and 80 cm (OB) tall There was a 60 cm openingon the cone and all sides of the cone were positioned at anangle of 60∘ fromhorizontalTheopening design ensured thatthe systems received the same amount of precipitation duringrainfall The third plot was left untreated and served as anatural control (CK) Each treatment was providedwith threereplicates Air temperatures within the plots were monitoredusing an air hygrothermograph (HMP45AC Vaisala Fin-land) mounted 20 cm above the ground Data were collectedautomatically every 30min using data loggers (CR5000Campbell Scientific Inc Logan UT USA)

During the experiment CO2efflux from the plots was

measured using an open-type soil carbon flux measurementsystem (LI-8100 LI-COR Inc USA) For the first measure-ment the soil collar was embedded into the soil 1 day inadvance to avoid short-term fluctuations in system respira-tion due to the OTC installation The soil collar was a PVCcylinder 20 cm in base diameter and 10 cm tall embedded

Journal of Chemistry 3

7 cm into the soil The frequency of observation wasas follows during the vegetation growing season (MayndashSeptember) diurnal variations were measured once every 7days During the nongrowing season (JanuaryndashApril andOctoberndashDecember) diurnal variations were measured onceevery 15 days These measurements were taken from 800to 800 the next day at 2-h intervals The cumulative valuesmeasured on all days during amonth were averaged and thenmultiplied by the number of days in the month to obtain thecumulative value for the month

The soil temperature at a depth of 5 cm was measuredusing a soil thermocouple (105T Campbell Scientific Inc)The soil water content was measured using frequency-domain reflectometers (CS616 Campbell Scientific Inc) withan accuracy of plusmn2The reflectometers were buried at depthsof 5 20 40 and 60 cmThe resulting soil water content is thevolumetric water content of unfrozen water in the soil Thesesensors were installed directly below the top openings of theOTCs in the geometric center of the plots to minimize theblocking of rainfall by the OTCs and thus reduce systematicerrors in the results All soil temperature soil water contentand air temperature data were automatically collected every30min by the data loggers

23 Determination of Biomass From April to October 2012the aboveground biomass belowground biomass and soilorganicmatter in each plot weremeasured on the 15th of eachmonth The aboveground biomass was measured using theharvest method In OA and OB and at plot CK we delineated15 cm times 15 cm quadrats The vegetation in each quadrat wascut evenly from the roots placed in bags and numberedBelowground live roots were collected fromdepth intervals of0ndash10 cm 10ndash20 cm and 20ndash40 cm using a 5 cm diameter soilaugerThe soil waswashed through a l-mmmesh sieveAll theaboveground and belowground samples were transported tothe laboratory The samples were dried at 65∘C in an oven toconstant weight and thenweighed (gm2) three times for eachtreatment

24 Statistical Analysis The data were statistically analyzedusing SAS 94 software (SAS Institute Inc Cary NC USA)Significant differences between the treatments were testedusing one-way ANOVA The relationships between CO

2

efflux and environmental factors were evaluated using pathanalysis Path analysis is the continuation of the simplecorrelation coefficient and decomposes the correlation coef-ficient on the basis of multiple regression It uses direct andindirect paths to indicate the direct effect of a variable on adependent variable and the indirect effects of other variableson a dependent variable [26 27] In path analysis the decisioncoefficient 1198772

(119895)is often used to quantify the integrated deter-

mination effect of environmental factors (119909119895) on soil CO

2

emissions (119910)1198772(119895)

contains not only the direct determinationeffect 1198772

119895of 119909119895on 119910 but also the indirect determination

coefficient related to 119909119895

1198772

(119895)= 1198772

119895+sum

119895 =119894

119877119895119894 (1)

minus25minus20minus15minus10minus5

05

1015

1-Ja

n

1-Fe

b

1-M

ar

1-Ap

r

1-M

ay

1-Ju

n

1-Ju

l

1-Au

g

1-Se

p

1-O

ct

1-N

ov

1-D

ec

DateCKOAOB

Ta(∘

C)

Figure 1 Seasonal variations in the air temperature of the alpineswamp ecosystem corresponding to the warming treatments

3 Results and Discussion

31 Changes in Environmental Factors Inside the OTCswind velocities air turbulence and heat dissipation werereduced These reductions and the penetration of solarinfrared radiation through the glass walls caused warmingin the OTCs [28] Temperature measurements in the threesystems indicated that the daily average air temperatures (119879

119886)

in OA and OB increased significantly (119865 = 4652 119875 lt 0001)compared with those at the control plot (CK) The 119879

119886values

were 279∘C and 496∘C higher in OA and OB than that atplot CK respectively (Figure 1) According to Yu [29] theannual average air temperature on the Tibetan Plateau rose07∘C every 10 years from 1981 to 2010 The warming systemsused in the current study are therefore representative of thesignificant warming expected over the next 40ndash70 years

Due to the high air temperature and weak air circulationwithin the OTCs the 5 cm soil temperature (119879soil) waselevated As shown in Figure 2 119879soil was 101

∘C and 304∘Chigher in OA and OB than that at plot CK respectively andthese differences were statistically significant (119865 = 16938119875 lt 0001)

Meanwhile the elevated air temperature and soil tem-perature accelerated the evaporation of soil water and thetranspiration of plants resulting in a lower water content inthe surface soil in the OTCs As shown in Figure 3 the dailyaverage 5 cm soil water content (SWC) was less in OB than inOA (22) and CK (49) these differences were statisticallysignificant (119865 = 58936 119875 lt 0001)

32 Changes in Biological Factors In this study the experi-mental treatments with different magnitudes of warming hadsignificant effects on biomass production in the alpine swampmeadow ecosystem (Figures 4 and 5) Continued warmingresulted in significant increases in the aboveground andbelowground biomass inOA andOB relative to plot CKDur-ing the growing season the aboveground biomass increasedby 211ndash764 and 449ndash1682 in OA and OB respectivelyand the belowground biomass increased by 473ndash602 and


minus15

minus10

minus5

0

5

10

15

201-

Jan

1-Fe

b

1-M

ar

1-Ap

r

1-M

ay

1-Ju

n

1-Ju

l

1-Au

g

1-Se

p

1-O

ct

1-N

ov

1-D

ec

DateCKOAOB

Tso

il(∘

C)

Figure 2 Seasonal variations in 5 cm depth soil temperaturecorresponding to the warming treatments

0

10

20

30

40

50

60

1-Ja

n

1-Fe

b

1-M

ar

1-Ap

r

1-M

ay

1-Ju

n

1-Ju

l

1-Au

g

1-Se

p

1-O

ct

1-N

ov

1-D

ec

SWC

()

DateCKOAOB

Figure 3 Seasonal variations in 5 cm depth soil water contentcorresponding to the warming treatments

0

200

400

600

800

1000

1200

1400

May Jun Jul Aug SepMonth

CKOAOB

Abov

egro

und

biom

ass(

gmminus2)

Figure 4 Growing season variations in aboveground plant biomasscorresponding to the warming treatments

0

500

1000

1500

2000

2500

3000

3500

4000

May Jun JulMonth

Aug Sep

CKOAOB

Belo

wgr

ound

bio

mas

s(gm

minus2)

Figure 5 Growing season variations in belowground plant biomasscorresponding to the warming treatments

020406080

100120140160180

1 2 3 4 5 6 7 8 9 10 11 12Month

CO2

flux(g

Cm

minus2)

CKOAOB

Figure 6 Seasonal variations in CO2efflux corresponding to the

warming treatments

590ndash1013 in these two OTCs respectively compared tothat in plot CK Thus the short-term warming had a pos-itive effect on the vegetation biomass in this alpine swampmeadow This trend is attributed to changes in the microcli-mate of the plant community produced by the OTCs To acertain extent these changes satisfied the demand for heat forplant growth and benefitted the growth and development ofthe plants [30] The current result is consistent with previousfindings by Jonasson et al [31] who reported a significantcorrelation between warming and plant growth at least in theshort term

33 Effect of Warming on CO2 Efflux The carbon emissionsin the alpine swampmeadow ecosystem exhibited significantseasonal variations (Figure 6) The carbon emissions duringthe distinct stages of plant development in all three systems


(CK OA and OB) ranked as follows vigorously growingstage (July-August) gt rapidly growing stage (June) gt yellow-ing stage (September)gt reviving stage (April-May)Thehigh-est ecosystem carbon emissions in the three systems occurredinAugust 1236 1423 and 1662 g Cmminus2monthminus1 in CKOAand OB respectively During the nongrowing season ecosys-tem carbon emissions remained relatively low in all three sys-tems Because respiration by grassland ecosystems is closelyassociated with air temperatures respiration by their plantroots and soil microbes is sensitive to soil temperature varia-tions [32] In the current study site rainfall and air tempera-tures were at maximums during the vigorously growing stage(July-August) These synchronous hydration and thermalconditions contributed to the high levels of plant respirationand soil microbial activity

The warming also had a significant effect on CO2efflux

from the swamp meadow ecosystem (Figure 6) CO2efflux

was ranked as follows OB (6841 g Cmminus2 yearminus1) gt OA(5807 g Cmminus2 yearminus1) gt CK (4733 g Cmminus2 yearminus1) Greaterwarming led to greater ecosystem respiration This resultis consistent with the conclusion developed by Hobbie andChaimn III [33] who performed an experimental warmingstudy under greenhouse conditions in a permafrost tundrasite in Alaska Hobbie and Chaimn III [33] suggested thatwarming enhances plant respiration and increases the pop-ulation and activity of microbes these mechanisms accel-erate the decomposition of soil carbonaceous materials andthereby increase CO

2efflux

34 Effects of Environmental Factors on CO2 Efflux Pathanalysis is the analysis of relationships between the inde-pendent variables and between independent and dependentvariables It indicates direct and indirect effects of indepen-dent variables on a dependent variable [26 27] Path analysissolves the one-sidedness of multiple correlation analysisby including the effects of additional variables in a linearcorrelation of any two variables It also addresses the defectof multiple regression analysis that cannot directly comparethe effect of a cause on a result due to the inclusion of a unit forpartial regression coefficients Path analysis thus allows one toquantify the contributions of several environmental factors toecosystem CO

2[34]

In the present study path analysis was conducted to eval-uate the relationship between various environmental factorsand soil CO

2emissions in the CK OA and OB systems

during the growing season In the three systems 119879soil was themost important environmental factor controlling soil CO

2

emissions in the alpine swampmeadow ecosystemThe directpath coefficients of119879soil for soil CO2 emissionswere 053 059and 063 and the total path coefficients were 052 072 and089 (Figure 7) These values all represented contributionsgreater than those of other environmental factors to soil CO

2

emissions in this ecosystem This conclusion agrees with theconclusions of Zhao et al [20] and Bai et al [25] Temperatureis an important factor regulating several ecological processesand properties associated with ecosystem respiration Theseprocesses and properties include root development evapo-transpiration and soil water content [35 36] Mielnick and

Dugas [37] concluded that if only temperature factors aretaken into consideration 46 of the variation in soil respi-ration is due to variations in soil temperature

The effect of SWC on ecosystem respiration is complexVery different findings have been obtained in differentecosystem In the current study the total path coefficients ofSWC for soil CO

2emissions were minus035 (CK) minus022 (OA)

andminus014 (OB) (Figure 7)These values indicate that the SWCis a major factor limiting soil CO

2emissions in these three

systems consistent with findings by Kato et al [19] from analpine meadow ecosystem in Haibei station Kato et al [19]concluded that a 30 SWCproducesmaximum carbon emis-sions in alpine meadow ecosystems on the Tibetan PlateauA SWC exceeding this value can hinder O

2diffusion in the

soil thereby inhibiting organic matter decomposition andmicrobial respiration [38] In the current study the experi-mental plots were located in a humid natural environmentand the SWC was constantly at supersaturation throughoutthe growing season and thus unfavorable for soil microbialrespiration Thus the SWC is an important environmentalfactor inhibiting soil CO

2emissions in this ecosystem We

also noted that the total path coefficients of SWC for CO2

successively increased in the CK OA and OB systemsTheseresults indicate that the inhibition of soil CO

2emissions by

soil water decreases with warming This relationship existsbecause warming promotes evapotranspiration and reducesthe SWC With future climate warming an SWC decreasewill also be an important contributor to soil CO

2emissions

in alpine swamp ecosystemsIn the CK OA and OB systems 119879

119886was not the most

important environmental factor affecting ecosystem CO2

emissions However the changes in other factors due to the119879119886increase had a more profound impact on ecosystem respi-

rationThis study spanned only one year andmore-extensivework has not yet been performed regarding the effects ofwarming on carbon emissions in alpine swamp meadowecosystems Additional studies of this type should be con-ducted

4 Conclusions

Warming had a significant effect on carbon emissions fromthe swamp meadow ecosystem of the Sanjiangyuan regionAnnual soil CO

2emissions in OA and OB were respectively

227 and 445 greater than those in plot CKThe warmingeffect was more evident in OB resulting in higher air andsoil temperatures and a lower soil water content whichwere conducive to the decomposition of soil organic matterand the production of CO

2 Ecosystem carbon emissions

were jointly affected by multiple environmental factors Pathanalysis indicated that temperature and soil water were thetwo most important factors affecting soil CO

2emissions at

the study site With global climate change temperature andprecipitation patternswill change in this region Such changeswill in turn act on the local carbon cycle and have additionaldeleterious effects on the local climateTherefore theChinesegovernment should devote attention to and support themonitoring of carbon cycle processes in various ecosystemson the Tibetan Plateau


CK Tsoil

Biomass CO2 flux SWC

Ta

009

009

026 minus017

053minus013

minus008006

003

011

(a)

OA Tsoil


Ta

009

003

015059

030 minus014

minus011

minus013010

014

(b)

OB Tsoil


Ta

018063

minus009

037 minus010

012

minus016

002

014

015

(c)

Figure 7 Path diagrams showing the effects of air temperature (119879119886) 5 cm depth soil temperature (119879soil) 5 cm depth soil water content (SWC)

andplant biomass (biomass) on ecosystemCO2efflux (CO

2flux) during the growing season in plotCK (a)OA (b) andOB (c)The thicknesses

of the arrows and the adjacent values represent the path coefficients The analysis was based on the daily average values of all variables

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This study was supported by the Scientific Research Fund ofSecond Institute of Oceanography SOA under Contract noSZ1515 and State Key Laboratory of Grassland Agroecosys-tems Open Projects Fund (SKLGAE201506) The authorsthankDr Haiyan Jin for his valuable comments and help withEnglish writing

References

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[2] C D Thomas A Cameron R E Green et al ldquoExtinction riskfrom climate changerdquo Nature vol 427 no 6970 pp 145ndash1482004

[3] K Klanderud ldquoClimate change effects on species interactions inan alpine plant communityrdquo Journal of Ecology vol 93 no 1 pp127ndash137 2005

[4] H Yin T Lai X Cheng X Jiang and Q Liu ldquoWarming effecton growth and physiology of seedlings of Betula albo-sinensisand Abies faxoniana under two contrasting light conditionsin subalpine coniferous forests of western Sichuan ChinardquoFrontiers of Forestry in China vol 4 no 4 pp 432ndash442 2009

[5] J AMorgan D R LeCain E Pendall et al ldquoC4 grasses prosperas carbon dioxide eliminates desiccation in warmed semi-aridgrasslandrdquo Nature vol 476 no 3 pp 202ndash205 2011

[6] F E Nelson O A Anisimov and N I Shiklomanov ldquoClimatechange and hazard zonation in the circum-arctic permafrostregionsrdquo Natural Hazards vol 26 no 3 pp 203ndash225 2002

[7] X Lin Z Zhang SWang et al ldquoResponse of ecosystem respira-tion to warming and grazing during the growing seasons in thealpine meadow on the Tibetan plateaurdquo Agricultural and ForestMeteorology vol 151 no 7 pp 792ndash802 2011

[8] Intergovernmental Panel on Climate Change (IPCC) TheScientific Basis Contribution of Working Group I to the Third


Assessment Report of the Intergovernmental Panel on ClimateChange Cambridge University Press Cambridge UK 2001

[9] M T Jorgenson C H Racine J C Walters and T EOsterkamp ldquoPermafrost degradation and ecological changesassociated with a warming climate in central Alaskardquo ClimaticChange vol 48 no 4 pp 551ndash579 2001

[10] D B Lobell G L Hammer G McLean C Messina M JRoberts andW Schlenker ldquoThe critical role of extreme heat formaize production in the United StatesrdquoNature Climate Changevol 3 no 5 pp 497ndash501 2013

[11] S Mertens I Nijs M Heuer et al ldquoInfluence of high temper-ature on end-of-season tundra CO

2exchangerdquo Ecosystems vol

4 no 3 pp 226ndash236 2001[12] J MWelker J T Fahnestock G H R Henry KW OrsquoDea and

R A Chimner ldquoCO2exchange in three Canadian high arctic

ecosystems response to long-term experimental warmingrdquoGlobal Change Biology vol 10 no 12 pp 1981ndash1995 2004

[13] C Biasi H Meyer O Rusalimova et al ldquoInitial effects of exper-imental warming on carbon exchange rates plant growth andmicrobial dynamics of a lichen-rich dwarf shrub tundra inSiberiardquo Plant and Soil vol 307 no 1-2 pp 191ndash205 2008

[14] Z Wu P Dijkstra G W Koch J Penuelas and B A HungateldquoResponses of terrestrial ecosystems to temperature and precip-itation change a meta-analysis of experimental manipulationrdquoGlobal Change Biology vol 17 no 2 pp 927ndash942 2011

[15] E L Aronson and S G McNulty ldquoAppropriate experimentalecosystem warming methods by ecosystem objective andpracticalityrdquoAgricultural and ForestMeteorology vol 149 no 11pp 1791ndash1799 2009

[16] J A Klein J Harte and X-Q Zhao ldquoDynamic and complexmicroclimate responses to warming and grazing manipula-tionsrdquoGlobal Change Biology vol 11 no 9 pp 1440ndash1451 2005

[17] S Zhang D Hua X Meng and Y Zhang ldquoClimate change andits driving effect on the runoff in the ldquoThree-River Headwatersrdquoregionrdquo Acta Geographica Sinica vol 66 no 1 pp 13ndash24 2011

[18] J F Wang G X Wang and Q B Wu ldquoEnvironmental factorsand near-surface air CO

2concentration of swamp-meadow

ecosystem on Qinghai-Tibetan Plateau in response to long-term experimental ecosystem warmingrdquo Journal of LanzhouUniversity (Natural Sciences) vol 45 no 3 pp 27ndash33 2009

[19] T Kato Y H Tang S Gu et al ldquoCarbon dioxide exchangebetween the atmosphere and an alpine meadow ecosystem onthe Qinghai-Tibetan Plateau Chinardquo Agricultural and ForestMeteorology vol 124 no 1-2 pp 121ndash134 2004

[20] L Zhao Y N Li S X Xu et al ldquoDiurnal seasonal and annualvariation in net ecosystemCO

2exchange of an alpine shrubland

on Qinghai-Tibetan plateaurdquoGlobal Change Biology vol 12 no10 pp 1940ndash1953 2006

[21] B Wang J Li W-W Jiang L Zhao and S Gu ldquoImpacts ofthe rangeland degradation on CO

2flux and the underlying

mechanisms in theThree-River Source Region on the Qinghai-Tibetan Plateaurdquo China Environmental Science vol 32 no 10pp 1764ndash1771 2012

[22] Y Luo S Wan D Hui and L L Wallace ldquoAcclimatization ofsoil respiration to warming in a tall grass prairierdquo Nature vol413 no 6856 pp 622ndash625 2001

[23] L Rustad J Campbell G Marion et al ldquoA meta-analysis of theresponse of soil respiration net nitrogen mineralization andaboveground plant growth to experimental ecosystem warm-ingrdquo Oecologia vol 126 no 4 pp 543ndash562 2001

[24] M J I Briones J Poskitt and N Ostle ldquoInfluence of warmingand enchytraeid activities on soil CO2 and CH4 fluxesrdquo SoilBiology and Biochemistry vol 36 no 11 pp 1851ndash1859 2004

[25] W Bai G X Wang and G S Liu ldquoEffects of elevatedtemperature on CO

2flux during growth season in an alpine

meadow ecosystem of Qinghai-Tibet Plateaurdquo Chinese Journalof Ecology vol 30 no 6 pp 1045ndash1051 2011

[26] T E Huxman A A Turnipseed J P Sparks P C Harley andR K Monson ldquoTemperature as a control over ecosystem CO

2

fluxes in a high-elevation subalpine forestrdquo Oecologia vol 134no 4 pp 537ndash546 2003

[27] M Saito T Kato and Y H Tang ldquoTemperature controls ecosys-tem CO

2exchange of an alpine meadow on the northeastern

Tibetan Plateaurdquo Global Change Biology vol 15 no 1 pp 221ndash228 2009

[28] E M Debevec and S F MacLean ldquoDesign of greenhouses forthe manipulation of temperature in tundra plant communitiesrdquoArctic and Alpine Research vol 25 no 1 p 56 1993

[29] H Yu Dynamics of grassland growth and its response to climatechange onTibetan Plateau [PhD dissertation] LanzhouUniver-sity Lanzhou China 2011

[30] X M Zhou H K Zhou and X Q Zhao ldquoA preliminarystudy on the effect of simulated warming on short high grassmeadowrdquo Chinese Journal of Ecology vol 24 no 5 pp 547ndash5532000

[31] S Jonasson A Michelsen I K Schmidt and E V NielsenldquoResponses in microbes and plants to changed temperaturenutrient and light regimes in the arcticrdquo Ecology vol 80 no6 pp 1828ndash1843 1999

[32] G M Cao Y H Tang W H Mo Y Wang Y Li and X ZhaoldquoGrazing intensity alters soil respiration in an alpine meadowon the Tibetan plateaurdquo Soil Biology amp Biochemistry vol 36 no2 pp 237ndash243 2004

[33] S E Hobbie and F S Chaimn III ldquoThe response of tundra plantbiomass aboveground production nitrogen and CO

2flux to

experimental warmingrdquo Ecology vol 79 no 5 pp 1526ndash15441998

[34] Y F Wang X Y Cui Y B Hao et al ldquoThe fluxes of CO2

from grazed and fenced temperate steppe during two droughtyears on the InnerMongolia Plateau Chinardquo Science of the TotalEnvironment vol 410-411 no 1 pp 182ndash190 2011

[35] S QWan J Y XiaW X Liu and S Niu ldquoPhotosynthetic over-compensation under nocturnal warming enhances grasslandcarbon sequestrationrdquo Ecology vol 90 no 10 pp 2700ndash27102009

[36] HW Polley P C MielnickW A Dugas et al ldquoIncreasing CO2

fromsubambient to elevated concentrations increases grasslandrespiration per unit of net carbon fixationrdquo Global ChangeBiology vol 12 no 8 pp 1390ndash1399 2006

[37] P C Mielnick and W A Dugas ldquoSoil CO2flux in a tallgrass

Prairierdquo Soil Biology and Biochemistry vol 32 no 2 pp 221ndash228 2000

[38] W C Oechel G L Vourlitis S J Hastings R P Ault Jr and PBryant ldquoThe effects of water table manipulation and elevatedtemperature on the net CO

2flux of wet sedge tundra ecosys-

temsrdquo Global Change Biology vol 4 no 1 pp 77ndash90 1998

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


and significantly enhanced gross ecosystem photosynthesisthereby causing the ecosystem to gradually change from acarbon source to a carbon sink Biasi et al [13] conducted a 2-year study of experimental warming using OTCs and foundthat warming promoted tundra ecosystem respiration lead-ing to a decrease in soil carbon and an increase in nitrogencontent Despite a marked decrease in the carbonnitrogenratio there were no significant changes in the number andcomposition of soil microbes The findings suggested thatthe tundra ecosystem will change from a carbon sink to acarbon source with future warming Wu et al [14] summa-rized 85 studies of experimental warming performed world-wide which involved various terrestrial ecosystems such asforests tundra temperate grasslandmountainmeadows andshrubland The relationship between net CO

2exchange and

warming in the various ecosystems was evaluated via a meta-analysis It was concluded that warming promotes photosyn-thesis and respiration however it has no significant effect onnet carbon absorption by the entire ecosystem

Heating methods for ecosystem warming include field-style greenhouses tents and open-top chambers (OTCs)of various shapes and sizes soil heating pipes and cablesinfrared reflector and infrared radiator [15] in which theOTC is an experimental warming first used by the Interna-tional Tundra Experiment to study the influence of globalwarming to high altitude and latitude region ecosystems [16]The advantages of OTC warming equipment are low costconvenient operation easy repeatability fitting to long-termfield experiments and minimal disturbance of the soil at theexperiment site

The Tibetan Plateau is located in southwestern China andspans an area of sim250 times 104 km2 that is sim25 of the territoryofChinaThe average elevation of theTibetanPlateau exceeds4000m making it the worldrsquos highest plateau [17] In thisregion swamp meadow spans an area of 49 times 104 km2 andaccounts for 196 of the plateau making it one of themost extensive grassland ecosystems on the Tibetan Plateau[18] These alpine ecosystems have developed in the extremeenvironments of the plateau and mountains Due to theirinherent vulnerability and instability alpine ecosystems areextremely sensitive to human disturbance and global warm-ing Investigating the response of alpine ecosystems to risingtemperatures is therefore highly valuable [18] There havebeen studies of greenhouse gas fluxes in grassland ecosystemsof the Tibetan Plateau However these studies have focusedprimarily on monitoring and investigating flux dynamics ofgreenhouse gases (particularlyCO

2) in various types of alpine

grassland ecosystems [19ndash21] Little research has involved theeffects of global climate change (particularly warming) oncarbon fluxes in alpine swamp ecosystems Studies elsewherein theworld have shown that key processes in the carbon cycledisplay significant responses to global warming in variousecosystems [22ndash24] In the present study we used an OTCsystem to perform experimental warming treatments to ana-lyze soil CO

2emissions dynamics and their relationshipswith

environmental factors in an alpine swamp ecosystem on theTibetan Plateau This study has implications for understand-ing the carbon cycle in grassland ecosystems and in terrestrialecosystems in general in China

2 Material and Methods

21 Study Site Thestudy site was located in a swampmeadowof Koeleria tibetica in Dawu Town of Maqin County GologTibetan Autonomous Prefecture Qinghai Province ChinaThe swamp meadow is in the Sanjiangyuan region in thehinterlands of the Tibetan Plateau The site coordinates are34∘275691015840N and 100∘130651015840E The meadow is at an elevationof 3700ndash4020m with a relief of 200ndash300m and measures25 km north to south The region has a continental plateauclimateTheweather is cold and dry and air pressures are lowThe spring and autumn are short and the freezing period lastsfrom October to the next April The permafrost is generally50ndash120 cm thick and its upper limit is at a depth of 08ndash25mThe growing season spans fromMay to SeptemberTheannual average temperature is minus56ndash38∘C with an extrememaximum of 28∘C and an extreme minimum of minus48∘CThe multiyear average precipitation is 15535ndash69793mm andmore than 75 of the rainfall falls from June to SeptemberThe annual average evaporation is 730ndash1700mm and theaverage relative humidity is 55 The maximum wind speedis 31msdotsminus1 and the prevailing wind is westerly The averagenumber of days with thunderstorms is 478 per year [25]

In the study site the plants are predominantly perennialmesophytic herbs The dominant species of the grass com-munity include Kobresia littledalei Carex moorcroftii Fes-tuca ovina Kobresia pygmaea Kobresia capillifolia Kobresiabellardii and Kobresia graminifolia The vegetation cover isgreater than 90 The predominant soil type is swampy soilwith a maximum depth of 23mThe soil pH ranges from 53to 85 The soil contains 60ndash359 g kgminus1 organic matter 02ndash149 g kgminus1 total nitrogen 022ndash10 g kgminus1 total phosphorusand 80ndash352 g kgminus1 total potassium [18]

22 Determination of Soil CO2 Efflux an MicrometeorologicalFactors The experiment was conducted from January 1 toDecember 31 2012 Three plots with similar vegetation andaboveground biomass were selected at the study site Attwo of the plots two types of OTCs with a hexagonal conestructure were installed The hexagonal surfaces were madeof plexiglass with light transmittance of 95The OTCs were40 cm (OA) and 80 cm (OB) tall There was a 60 cm openingon the cone and all sides of the cone were positioned at anangle of 60∘ fromhorizontalTheopening design ensured thatthe systems received the same amount of precipitation duringrainfall The third plot was left untreated and served as anatural control (CK) Each treatment was providedwith threereplicates Air temperatures within the plots were monitoredusing an air hygrothermograph (HMP45AC Vaisala Fin-land) mounted 20 cm above the ground Data were collectedautomatically every 30min using data loggers (CR5000Campbell Scientific Inc Logan UT USA)

During the experiment CO2efflux from the plots was

measured using an open-type soil carbon flux measurementsystem (LI-8100 LI-COR Inc USA) For the first measure-ment the soil collar was embedded into the soil 1 day inadvance to avoid short-term fluctuations in system respira-tion due to the OTC installation The soil collar was a PVCcylinder 20 cm in base diameter and 10 cm tall embedded






2




2

emissions (119910)1198772(119895)




1198772

(119895)= 1198772

119895+sum

119895 =119894

119877119895119894 (1)


05

1015

1-Ja

n

1-Fe

b

1-M

ar

1-Ap

r

1-M

ay

1-Ju

n

1-Ju

l

1-Au

g

1-Se

p

1-O

ct

1-N

ov

1-D

ec

DateCKOAOB

Ta(∘

C)




119886)


119886values







minus15

minus10

minus5

0

5

10

15

201-

Jan

1-Fe

b

1-M

ar

1-Ap

r

1-M

ay

1-Ju

n

1-Ju

l

1-Au

g

1-Se

p

1-O

ct

1-N

ov

1-D

ec

DateCKOAOB

Tso

il(∘

C)


0

10

20

30

40

50

60

1-Ja

n

1-Fe

b

1-M

ar

1-Ap

r

1-M

ay

1-Ju

n

1-Ju

l

1-Au

g

1-Se

p

1-O

ct

1-N

ov

1-D

ec

SWC

()

DateCKOAOB


0

200

400

600

800

1000

1200

1400


CKOAOB

Abov

egro

und

biom

ass(

gmminus2)


0

500

1000

1500

2000

2500

3000

3500

4000

May Jun JulMonth

Aug Sep

CKOAOB

Belo

wgr

ound

bio

mas

s(gm

minus2)


020406080

100120140160180

1 2 3 4 5 6 7 8 9 10 11 12Month

CO2

flux(g

Cm

minus2)

CKOAOB


warming treatments








2efflux


2[34]




2


2








2diffusion in the





2emissions by


2emissions






4 Conclusions






2emissions at



CK Tsoil


Ta

009

009

026 minus017

053minus013

minus008006

003

011

(a)

OA Tsoil


Ta

009

003

015059

030 minus014

minus011

minus013010

014

(b)

OB Tsoil


Ta

018063

minus009

037 minus010

012

minus016

002

014

015

(c)





Competing Interests


Acknowledgments


References








































2











2flux to





















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






2




2

emissions (119910)1198772(119895)




1198772

(119895)= 1198772

119895+sum

119895 =119894

119877119895119894 (1)


05

1015

1-Ja

n

1-Fe

b

1-M

ar

1-Ap

r

1-M

ay

1-Ju

n

1-Ju

l

1-Au

g

1-Se

p

1-O

ct

1-N

ov

1-D

ec

DateCKOAOB

Ta(∘

C)




119886)


119886values







minus15

minus10

minus5

0

5

10

15

201-

Jan

1-Fe

b

1-M

ar

1-Ap

r

1-M

ay

1-Ju

n

1-Ju

l

1-Au

g

1-Se

p

1-O

ct

1-N

ov

1-D

ec

DateCKOAOB

Tso

il(∘

C)


0

10

20

30

40

50

60

1-Ja

n

1-Fe

b

1-M

ar

1-Ap

r

1-M

ay

1-Ju

n

1-Ju

l

1-Au

g

1-Se

p

1-O

ct

1-N

ov

1-D

ec

SWC

()

DateCKOAOB


0

200

400

600

800

1000

1200

1400


CKOAOB

Abov

egro

und

biom

ass(

gmminus2)


0

500

1000

1500

2000

2500

3000

3500

4000

May Jun JulMonth

Aug Sep

CKOAOB

Belo

wgr

ound

bio

mas

s(gm

minus2)


020406080

100120140160180

1 2 3 4 5 6 7 8 9 10 11 12Month

CO2

flux(g

Cm

minus2)

CKOAOB


warming treatments








2efflux


2[34]




2


2








2diffusion in the





2emissions by


2emissions






4 Conclusions






2emissions at



CK Tsoil


Ta

009

009

026 minus017

053minus013

minus008006

003

011

(a)

OA Tsoil


Ta

009

003

015059

030 minus014

minus011

minus013010

014

(b)

OB Tsoil


Ta

018063

minus009

037 minus010

012

minus016

002

014

015

(c)





Competing Interests


Acknowledgments


References








































2











2flux to





















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


minus15

minus10

minus5

0

5

10

15

201-

Jan

1-Fe

b

1-M

ar

1-Ap

r

1-M

ay

1-Ju

n

1-Ju

l

1-Au

g

1-Se

p

1-O

ct

1-N

ov

1-D

ec

DateCKOAOB

Tso

il(∘

C)


0

10

20

30

40

50

60

1-Ja

n

1-Fe

b

1-M

ar

1-Ap

r

1-M

ay

1-Ju

n

1-Ju

l

1-Au

g

1-Se

p

1-O

ct

1-N

ov

1-D

ec

SWC

()

DateCKOAOB


0

200

400

600

800

1000

1200

1400


CKOAOB

Abov

egro

und

biom

ass(

gmminus2)


0

500

1000

1500

2000

2500

3000

3500

4000

May Jun JulMonth

Aug Sep

CKOAOB

Belo

wgr

ound

bio

mas

s(gm

minus2)


020406080

100120140160180

1 2 3 4 5 6 7 8 9 10 11 12Month

CO2

flux(g

Cm

minus2)

CKOAOB


warming treatments








2efflux


2[34]




2


2








2diffusion in the





2emissions by


2emissions






4 Conclusions






2emissions at



CK Tsoil


Ta

009

009

026 minus017

053minus013

minus008006

003

011

(a)

OA Tsoil


Ta

009

003

015059

030 minus014

minus011

minus013010

014

(b)

OB Tsoil


Ta

018063

minus009

037 minus010

012

minus016

002

014

015

(c)





Competing Interests


Acknowledgments


References








































2











2flux to





















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






2efflux


2[34]




2


2








2diffusion in the





2emissions by


2emissions






4 Conclusions






2emissions at



CK Tsoil


Ta

009

009

026 minus017

053minus013

minus008006

003

011

(a)

OA Tsoil


Ta

009

003

015059

030 minus014

minus011

minus013010

014

(b)

OB Tsoil


Ta

018063

minus009

037 minus010

012

minus016

002

014

015

(c)





Competing Interests


Acknowledgments


References








































2











2flux to





















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


CK Tsoil


Ta

009

009

026 minus017

053minus013

minus008006

003

011

(a)

OA Tsoil


Ta

009

003

015059

030 minus014

minus011

minus013010

014

(b)

OB Tsoil


Ta

018063

minus009

037 minus010

012

minus016

002

014

015

(c)





Competing Interests


Acknowledgments


References








































2











2flux to





















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of
































2











2flux to





















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

research article environmental factors and soil co

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