Effects Of Alpine Grassland Degradation On Soil CO₂ Release Rate And Temperature Sensitivityand Its Regulatory Factors

There are large amount of organic carbon store in the soil of the alpine grassland,due to the limitation of low temperature.Since the 1940s,about 40%of the alpine grassland has been degrade due to the joint influence of global climate change,unreasonable human use and other factors.Grassland degradation has caused to a series of negative effects,such as reduction of plant biomass,deterioration of soil structure,and decline in soil nutrients,which will significantly change the decomposition process of SOC and its response to climate warming.However,at present,most studies on the temperature sensitivity(Q₁₀)of soil CO₂release in alpine grassland have been conducted in healthy grassland,and the impact of grassland degradation on Q₁₀ is not clear.Therefore,this study took the alpine grassland of Qinghai-Tibet Plateau as the research object,through field multi-point sampling and indoor culture experiments,compared the difference of CO₂ release rate and temperature sensitivity between degraded and non-degraded grassland soil,and analyzed its regulatory factors from soil environment,substrate and microorganism.The main results are as follows:（1）At the same temperature,the cumulative CO₂ release of heavily degraded grassland was significantly lower than that of non-degraded grassland in different sites.Under the same degradation level,the cumulative CO₂ release at 15℃was significantly higher than that at 5℃.After degradation,although the CO₂ release rate significantly decreased,its temperature sensitivity increased significantly.（2）After grassland degradation,soil p H increased significantly,soil water content（SM）and inorganic nitrogen（SIN）content decreased significantly,but soil total phosphorus（TP）and available phosphorus（AP）content did not change significantly.In terms of substrates,such as soil organic carbon（SOC）,total nitrogen（TN）,dissolved organic carbon（DOC）and total dissolved nitrogen（TDN）,the contents decreased significantly.The SOC:TN showed a downward tendency while DOC:TDN had no regular trend.In terms of the molecular composition of organic matter,the recalcitrant carbon component（relative peak area of aromatic C-O bonds）increased significantly,the labile carbon component（relative peak area of aliphatic C-H bonds）decreased significantly,and the ratio of the two increased significantly.In terms of soil microbial factors,the contents of microbial biomass carbon（MBC）and microbial biomass nitrogen（MBN）decreased significantly after grassland degradation.（3）Soil CO₂ release rate was significantly negatively correlated with p H,and significantly positively correlated with soil sand content,soil water content,DOC,TDN content,SOC:TN,MBC and R_SOC:TN/B_C:N.These factors jointly explained 31.2%of variation in soil CO₂ release rate.There was a quadratic relationship between Q₁₀ and soil p H,the Q₁₀ increased with recalcitrant carbon components and the ratio of recalcitrant carbon to labile carbon,but decreased with labile carbon components.Soil p H and substrate qualitiy jointly explained 29.8%of Q₁₀ variation.In conclusion,this study showed that grassland degradation affects the process of soil organic carbon decomposition by change soil environment,substrate and microorganisms,resulting in degraded alpine grassland showing greater sensitivity to warming.This finding helps to predict the feedback relationship between soil carbon release and climate warming in the alpine grasslands of the Qinghai-Tibet Plateau more accurately,and provides scientific inspiration for my country’s national strategy of"carbon peaking and carbon neutralization".