Contribution Of Biotic And Abiotic Decomposition Soil Organic Carbon And Its Sensitivity To Temperature And Moisture In Subtropical Forests

The effect of climate changes on soil organic carbon(SOC)decomposition is one of the hot spots.However,large uncertainties remain in the influence and mechanism of temperature and moisture changes on forest SOC.In this study,we separate the SOC decomposition components by sterilization incubation,to investigate the contribution of abiotic and biotic processes and the response to temperature and moisture changes.Dinghushan experiences a typical subtropical humid monsoon climate,and there is a typical South Asian tropical forest succession series.This region has high temperature and high humidity climate characteristics and is experiencing the seasonal distribution changes of temperature and precipitation,which has a deep impact on SOC decomposition.Therefore,we conducted a laboratory incubation experiment using the surface layer(0-10 cm)and deep layer soil(30-40 cm)of subtropical forest in different succession stages of Dinghushan.The biotic decomposition was eliminated by sterilization treatment and the control treatment without sterilization was set up,conducted a laboratory incubation experiment in two temperature levels(20?and 30?)and three moisture levels(30%,60%,90%water holding capacity,WHC).Under each treatments,the soil CO₂emission rate was observed continuously,to detect the contributions of abiotic and biotic decomposition in different forest depths and its sensitivity to temperature and moisture.The main conclusions are as follows:(1)The average contribution rate of abiotic decomposition was 53.95±19.21%under different treatments,indicating that abiotic decomposition was also very important in highly active subtropical forest.With the succession,the accumulation of abiotic decomposition and biotic decomposition increased continuously,the contribution rate of biotic decomposition increased,but the contribution rate of abiotic decomposition decreased.These indicate that both abiotic and biotic decomposition had a promoting effect on the SOC total decomposition and the increase rate of biotic decomposition was higher than that of abiotic decomposition,the biotic decomposition was the dominant factor in the later stage of forest.(2)Among the soil layers,the abiotic and biotic decomposition all decreased with the soil depth increase,and the contribution rate of abiotic decomposition in deep soil layer was significantly greater than that of the surface soil layer,the contribution of biotic decomposition was opposite.These indicate that with the soil depth increase,the SOC decomposition decreases and the biotic process was more sensitive to the change of soil layer.With the temperature increase,the accumulation of biotic decomposition increased,and the abiotic decomposition increased at 30%and 60%WHC.The contribution rate of biotic decomposition increased significantly,but the contribution rate of abiotic decomposition decreased or tends to decreased with the temperature increase.Moreover,the Q₁₀of biotic decomposition was higher than abiotic decomposition and total decomposition.These results imply that the biotic process was more sensitive to climate warming than abiotic in the surface layer.With the soil moisture increase,the accumulation of abiotic decomposition and biotic decomposition increased.The contribution rate of biotic decomposition was significantly higher under high soil moisture,while that of abiotic decomposition was opposite.These show that biotic decomposition was more sensitive than abiotic decomposition when soil moisture changes.(3)Under low temperature and low moisture conditions in this study,the abiotic process has the greatest contribution to soil CO₂emission,and the contribution of biotic decomposition was low.These indicate that in tropical forest with high soil biological activity,abiotic process may account for a large proportion of total CO₂emission in low temperature and low water conditions.In conclusion,the research shows that the potential importance of abiotic decomposition,even in the forest with strong biotic decomposition,may affect the global greenhouse gases budget and future climate change.In the future,climate change may affect the decomposition process of succession forest SOC in Southern China through abiotic decomposition and biotic decomposition,and then affect the carbon cycle of terrestrial ecosystem.