Responses Of Ecosystem Respiration And Its Components To Simulated Gradient Warming During The Growing Seasons In Paddy Field In Northeast China

Global warming has become an indisputable fact.As one of the most important types of cropland ecosystems,paddy field plays a nonnegligible role in maintaining the carbon balance of global and regional ecosystems.Ecosystem respiration（ER）,as an important link of carbon exchange in terrestrial ecosystems,is extremely sensitive to climate change.However,there are few studies on the effects of warming on ER in paddy field,especially under different warming magnitudes conditions,the response and mechanism of ER are still unclear.Therefore,under the background of future climate change,clarifying the response patterns and mechanisms of ER and its components to different warming levels in paddy field is crucial for predicting the carbon budget of cropland ecosystems.In the study,the paddy field in Northeast China was taken as the research object.During the growing seasons of rice in2018 and 2019,five warming treatments were set using the free air temperature increase system with control（CK）,500 W warming（T1）,1000 W warming（T2）,1500 W warming（T3）and 3000 W warming（T4）treatments,respectively.ER and its two components,autotrophic respiration（AR）and heterotrophic respiration（HR）,were measured by using the static chamber-infrared gas analyzer method,and relevant biotic and abiotic factors were measured,exploring the response of ER and its components to simulated gradient warming and influencing factors,so as to reveal the process mechanism of gradient warming affecting ER in paddy field in Northeast China.The main conclusions are as follows:（1）Gradient warming significantly increased the soil temperature at 5 cm in paddy field.During the 2-year growing seasons,the average increases in soil temperature were 0.34°C（T1）,0.60°C（T2）,1.00°C（T3）and 2.32°C（T4）.（2）Gradient warming significantly increased rice total biomass（TB）and soil microbial biomass carbon（MBC）.The promoting effects of different warming treatments on TB and MBC were T3>T2>T1>T4.Besides,gradient warming did not significantly change soil organic carbon（SOC）and total nitrogen（TN）.（3）Gradient warming significantly increased ER,AR and HR,and the increase was greater in AR than HR.The change trend of ER,AR and HR under different treatments showed that T3>T2>T1>T4>CK,that is,T3 treatments had the greatest promoting effects on ER,AR and HR,followed by T2 and T1 treatments,while T4 treatments had the least promoting effects.Thus,ER,AR,and HR showed significant nonlinear responses to simulated gradient warming.ER,AR,and HR would reach the peaks when soil temperature increased by between 1.0 and 1.5°C.Besides,there were significant interannual differences in ER and AR,but no significant interannual differences in HR.（4）Gradient warming significantly increased the proportion of AR in ER（AR/ER）,and decreased the proportion of HR in ER（HR/ER）.The effect degree of different warming treatments on AR/ER and HR/ER was T3>T2>T1>T4.Therefore,AR/ER and HR/ER exhibited nonlinear responses to simulated gradient warming.Meanwhile,AR/ER under different treatments were much greater than HR/ER.（5）There were significant correlations in ER and its components with biotic and abiotic factors under gradient warming conditions.ER,AR and HR all increased exponentially with soil temperature at 5 cm（P<0.001）.The temperature sensitivity(Q₁₀)of AR was higher than that of ER and HR,and warming decreased the Q₁₀ values.Furthermore,warming-induced increases in ER,AR,and HR were significantly and positively correlated with warming-induced increases in TB and MBC,but not with increases in SOC and TN.By comparing R²,warming-induced increase in AR was closely related to warming-induced increase in TB,while warming-induced increase in HR was mainly related to warming-induced increase in MBC.（6）There were significant linear positive correlations between ER and AR,ER and HR under gradient warming conditions.Compared with HR,the correlation between AR and ER was stronger,indicating that the effect of AR on ER was dominant.In conclusion,gradient warming significantly affected biotic and abiotic factors in paddy field,and further altered ER and its components.The nonlinear responses of ER to simulated gradient warming were dominated by AR,and the nonlinear responses of AR were mainly related to warming-induced changes in TB.Therefore,future warming may increase the carbon emissions mainly by promoting AR in paddy field ecosystems in Northeast China.