The Effect Of Warming And Precipitation On Process Of Carbon Budget In Stipa Breviflora Desert Steppe

The Stipa breviflora desert grassland is an important part of the ecological carbon（C）pool,and its carbon budget process is not only an important part of affecting the global climate,but also an important part of responding to global climate change.Studying the impact of different climate change scenarios on the key processes of desert grassland carbon budget and the regulation mechanism can improve people’s understanding of the process of ecosystem carbon balance under the background of climate change.At the same time,it has important scientific significance for understanding the soil carbon cycle process of fragile habitats.Thus,an experiment was conducted to investigate the photosynthetic capacity of dominant plants in the Stipa breviflora desert steppe,the characteristics of the stable carbon isotope of leaf-litter-root-soil continuum,soil respiration and oxidation and reduction of soil methane under three levels of warming（T0:ambient temperature;T1:T0+2℃;T2:T0+4℃）,three levels of increased precipitation（W0:ambient precipitation;W1:W0+25%;W2:W0+50%）treatments and their interaction（T*W）in Inner Mongolia,China.Temperature enhancement was achieved by open-top growth chamber（OTC）,and precipitation enhancement was achieved by self-made rain interception device.The results as follows:（1）Physiological parameters of plant photosynthesisWarming（T）,increased precipitation（W）and their interactions treatment significantly improved the gas exchange parameters of the leaves of Stipa breviflora,Cleistogenes songorica and Kochia prostrata.The C₃ plants was significantly restricted by stomatal factors,while the C₄ plants was not restricted by it.The instantaneous water use efficiency（WUE）and intrinsic WUE of the five plants have a very significant negative correlation with intercellular carbon dioxide（CO₂）concentration（Ci）.The parameters fitting the photosynthetic/CO₂ response curve showed that Stipa breviflora had a wider growth range of photosynthetically active radiation（PAR）,was more adaptable to low PAR,had the ability to preferentially accumulate photosynthetic products and higher assimilation adaptability.However,the activity of Rusbico and electron transfer rate in Cleistogenes songorica were higher,and it has a higher ability to utilize PAR.It indicates that C₃ and C₄ plants have their own advantages in the desert steppe.Some of the photosynthetic dominance indexes of Stipa breviflora and Cleistogenes songorica increased significantly,and some inhibition indexes decreased under the T1 and W1 treatment.It illustrates that moderate warming and increased precipitation can significantly improve the photosynthesis mechanism of plants,make plants better cope with the physiological limitations caused by changes in environmental factors,which is conducive to the input of soil C in the desert steppe.The parameters of the OJIP polyphasic chlorophyll（Chl）a fluorescence rise kinetics curve of Stipa breviflora are sensitive to the individual effects of T and W,but not to the T*W treatment.The potential activity and maximum quantum yield of PSII were significantly affected by T,W and their interactions.Furthermore,T treatment significantly increased the performance index values of Stipa breviflora and Cleistogenes songorica.Therefore,warming can increase the dry matter accumulation of dominant plants in desert steppe.（2）Stable carbon isotopic composition of plant leaves,litter,roots and soilThe stable carbon isotope values(δ¹³C_leaf)of C₃ plant leaves measured under different treatments ranged from-31.99‰to-26.21‰,and C₄ plants ranged from-15.53‰to-13.81‰.Among C₃ dominant plants,Stipa breviflora has the highestδ¹³C_leaf value（meaning the long-term water use efficiency is the highest）.Theδ¹³C value(δ¹³C_root)of roots is more enriched than theδ¹³C_leaf value,and the fractionation difference is between 1-3‰units.And the overall performance is that theδ¹³C in the underground part is more enriched than the above-ground part.δ¹³C_leaf,δ¹³C_root andδ¹³C of soil(δ¹³C_soil)were significantly correlated with the corresponding C/N values.The T,W and T*W treatments have significant effects on theδ¹³Cleaf,δ¹³Croot andδ¹³Csoil.The T treatment has the highest model interpretation,indicating that theδ¹³Cleaf,δ¹³Croot andδ¹³Csoil values of the desert steppe are more sensitive to temperature.（3）Soil CO₂ and CH₄ fluxes and their stable carbon isotope valuesDesert steppe soil is the source of CO₂ and the sink of CH₄.The single effect of T and W significantly increased soil respiration CO₂ flux.The influx of CH₄ increased significantly by 25.92%and 20.36%under T1 and T2 treatments,respectively.Warming by 2℃is more conducive to the enrichment of soil ¹³C signal.Theδ¹³CO_2evalue enrichen with warming treatments and depleted with the precipitation.Warming treatment significantly increased theδ¹³CH_4e value,but precipitation increased treatment had no significant effect on theδ¹³CH_4e value.