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Université du Henan (2018)

Effects of Global Change Driving Factors on Ecosystem Carbon Stable Isotope Composition and Soil Carbon Pool in A Semi-arid Grassland of Northern China

井水水;

Titre : Effects of Global Change Driving Factors on Ecosystem Carbon Stable Isotope Composition and Soil Carbon Pool in A Semi-arid Grassland of Northern China

Auteur : 井水水;

Grade : Master’s Theses 2018

Université : Université du Henan

Résumé
Since the Industry Revolution,resulted from intensified anthropogenic activities,atmosphericgreenhouse gas concentration has been increasing rapidly,which leads to climate warming.Global precipitation regimes have been changing with intensifying global hydrological cycles as a result of climate warming.In addition,increasing artificial fertilization and fossil fuel combustion has been exacerbating atmospheric nitrogen(N)deposition.Global change(e.g.,rising CO2,climate warming,changing precipitation regimes,and atmospheric N deposition)has exerted profound influences on terrestrial ecosystem carbon(C)cycle.As an important component of ecosystem C cycle,soil organic carbon(SOC)dynamics under global change are crucial for evaluating C budgets and cycle at regional or global scales.As part of a field manipulative experiment,this study was conducted to examine the effects of four global change driving factors(elevated CO2,climate warming,increased precipitation,and N addition)on SOC in a semi-arid grassland in Duolun County,Inner Mongolia,China.Theδ13C of plant-soil system,fraction of new carbon(FNC),mean residence time(MRT),and C fractions(i.e.labile pool(LP),recalcitrant pool(RP),light fraction(LF),and heavy fraction C(HF))in SOC were evaluated.Across the 2 years from 2014 to 2015,elevated CO2 decreased shootδ13C by 1.8‰and 1.4‰(absolute change)at community and C3 functional group levels,respectively.At the species level,elevated CO2 declined shootδ13C of Agropyron cristatum,Astragalus scaberrimus,Potentilla tanacetifolia,Leymus chinensis,Stipa krylovii,and Cleistogenes squarrosa by 1.1‰,1.4‰,1.3‰,0.8‰,0.9‰,and 1.3‰,respectively.Night warming had no effects on shootδ13C at community,functional groups,and species levels.Increased precipitation significantly suppressed shootδ13C of C3 functional group by 0.8‰,whereas had no effects on that at community or C4 functional group level.However,increased precipitation enhanced shootδ13C of Cleistogenes squarrosa by 1.2‰.Nitrogen addition stimulated shootδ13C by 1.2‰and 1.3‰at community and C4 functional group levels,respectively.However,N addition did not influence shootδ13C of C3 functional group and any species.No interactive effects of elevated CO2,night warming,increased precipitation,and N addition on communityδ13C were found across the 2 years(2014-2015).Elevated CO2,increased precipitation,and N addition had interactive effects on shootδ13C of C3 functional group.Elevated CO2 reduced rootδ13C at 0-10 cm depth by 0.9‰in 2015.Increased precipitation suppressed rootδ13C at 10-20 cm depth by 0.75‰.However,neither night warming nor N addition influenced rootδ13C.Elevated CO2,night warming,and increased precipitation interactively affected rootδ13C at the depth of 10-20 cm.Across the 3 years(2015-2017),soilδ13C was not influenced by all the 4 treatments.However,N addition increased soilδ13C by 0.2‰at the deapth of 0-10 cm in 2016.Across the 3 years from 2015 to 2017,soil FNCshoot(fraction of new C from shoot)did notrespond to night warming,increased precipitation,or N addition.However,night warming elevated soil FNCshoothoot by 7.3%(absolute change)in 2015.Night warming stimulated soil FNCroot(fraction of new C from root)by 5.4%across the 3 years(2015-2017).In addition,increased precipitation enhanced soil FNCrootoot by15.0%in 2017.Nitrogen addition suppressed soil FNCrootoot by 7.7%in 2015.Across the 3 years(2015-2017),night warming lengthened soil MRTroot(mean residence time of soil calculated based on rootδ13C)by 36.8yr.Increased precipitation shortened soil MRTshoot(mean residence time of soil calculated based on shootδ13C)by 109 yr,but extended soil MRTrootoot by 26.4 yr.Nitrogen addition reduced soil MRTshoothoot by 108 yr.In 2016,elevated CO2 had no effect on LF at the depth of 0-10 cm,but decreased HF by 0.1 mgg-1,and thus led to 16.0%(absolute change)reduction of LF:HF.In addition,elevated CO2 increased LF at the depth of 10-20 cm by 0.8 mg g-1.Increased precipitation declined HF by 0.1 mg g-1,and decreased LF:HF by 12.3%.Increased precipitation did not affect LP,whereas suppressed LP1 by 0.5 mg g-1.Neither night warming nor N addition had effects on soil C fractions.Increased LF under the elevated CO2 treatment can enhance soil C sequestration,whereas thedecreased HF indicate that increasing CO2 may stimulate the decomposition and turnover of SOC,and consequently offset the accumulated C induced by elevated CO2.In addition,although increased precipitation stimulated soil FNC,the declined HF and LP1 may have adverse effects on soil C sequestration.The decreased FNC due to reduced species richness,and the suppressed MRT under the N addition treatment may also have negative effects on soil C sequestration.

Mots clés : Carbon fraction; Carbon residence time; New carbon input; Plant; Temperate steppe;

Présentation (CNKI)

Page publiée le 30 avril 2019