Impacts Of Litter Input Manipulation On Soil Organic Carbon Dynamics And Stability In Coniferous Plantation Ecosystem

Global change greatly alters the quality and quantity of plant litter inputs to soils and further impacts the dynamic of soil organic carbon(SOC).However,how soil respiration may change with future shifts in litter input is not fully understood.The Detritus Input and Removal Treatment(DIRT)experiment provides a unique opportunity for better understanding the influence of different quality and quantity of plant litter inputs on soil organic C dynamics.In this study,we conducted a DIRT experiment in an around 20 years" old coniferous plantation(Platycladus orientalis(Linn.)Franco)ecosystem(i.e control,CK;no litter;NL;no root;NR;no litter and no root;NRNL;Double litter,DL)of central China,to identify the effects of litter input manipulation on the dynamics of SOC,and the microbial and enzyme activity being associated with SOC.The main conclusions are as follows:(1)Impacts of litter input manipulation on SOC.Litter input manipulation strongly affected the distribution of soil aggregates class size and the organic C content of each aggregate size,as well as soil C content.Compared to CK treatment,the abundance of macro-aggregates(>2000 pm)was 23.4%and 27.7%lower under NR and NRNL treatment,respectively,and the mean weight dimeter(MWD)was lower in NR and NRNL treatment,likely weakening the stability and structure of soil aggregates and accelerating soil erosion.Meanwhile,the C concentration of macro-aggregates under NR and NRNL treatment decreased compared to the CK treatment.Whereas the distribution of soil aggregates class size and the SOC content of each aggregate did not significantly change under DL treatment compared to the CK.The significant linearly relationships between the abundance of macro-aggregates and SOC content further confirmed the importance of macro-aggregates to the maintainance of SOC.Litter input manipulation changed the relative abundance of liable and recalcitrant C,the liable C significantly decreased,while the recalcitrant C did not change under NL and NR treatment,resulting in higher relative abundance of recalcitrant C in these treatments,particularly in NRNL treatment.Two years after litter input manipulation,the recalcitrance index of carbon(RIC)increased by 9.7%,10.6%and 12.2%under NL,NR and NRNL treatment,respectively,compared to CK treatment.But the influence of litter addition on relative abuncance of liable and recalcitrant C was not as significant as the other treatments.(2)Impacts of litter input manipulation on microbial community structure and enzyme activity.Litter input manipulation significantly affected the soil microbial biomass and community structure.The microbial biomass significantly decreased under litter exclusion treatment,especially under NRNL treatment,meanwhile,the relative abundance of fungi increased under NRNL treatment compared to the control.The microbial biomass increased and the relative abundance of fungi decreased after two years' litter addition,however,the microbial biomass and community structure were not affected by litter addition after half a year or one year litter addition.Overall,the response of microbial biomass and community structure to litter exclusion was much stronger than to litter addition.Litter input manipulation also significantly affected the soil enzyme activity,however,the hydrolases and oxidases responsed differently to litter input manipulation.Compared to control,higher enzyme activity was detected for four of the five hydrolases in DL treatment,while the activity of hydrolases did not significantly change under litter exclusion treatment.The activity phenol oxidase and peroxidase significantly increased under litter exclusion treatment,but these cases were not happened under litter addition treatment.(3)Impacts of litter input manipulation on soil respiration and its carbon isotope signature.Litter input manipulation affected soil respiration and the carbon-isotopic signature due to changes in substrate availability and soil C input.Two years after litter input manipulation,based on annual flux values,soil respiration decreased by 34.4%,25.5%and 35.3%under NL,NR and NRNL treatment,respectively,compared to the control CK treatment.However,our results demonstrated that soil respiration was susceptible to decrease in litter inputs but was relatively resistant to increased litter,suggesting the priming effect was negligible.The underlying mechanisms were partly because substrate availability was more influential under NL or NR treatment compared with DL treatment.Meanwhile,NL or NR treatment increased the relative abundance of fungi but lowered respiration quotients(qCO2),resulting in lower soil respiration.Conversely,this was not the case under the DL treatment.The carbon-isotope signature of soil-respired CO2 was enriched in the NL and NRNL and slightly depleted under the DL treatment,primarily resulting from the alterations in component of soil respiration and soil microclimate under litter input manipulation conditions.Overall,this study highlights our process-based understanding of how soil respiration may change with future shifts in plant litter in response to either global changes or human activities in Northern subtropical coniferous forests.