Effects Of Changing Carbon Input On Soil Carbon Composition Of Three Forests In Subtrophic-Warm Temperate Climate Transitional Region

Aboveground litter inputs have been greatly altered by human disturbances and climate change,which have important effects on soil carbon(C)pools.A small change in soil C pools can profoundly impact global C cycle and consequent feedbacks to climate change.Aboveground litterfall regulates energy flow and nutrient cycling in forest ecosystems.Changes in aboveground litter inputs can affect decomposition of litterfall and indirect effects on biological processes in soil.Litter removal may reduce decomposition of soil organic C due to decreasing the easily decomposable substrate for microbes.Root decomposition and exudates are the main contributors to ecosystem C cycle.Forest is the largest C pool in terrestrial ecosystem,and most of C in forest is stored in the soil.How do aboveground litters and roots affect C pool and its different components? As part of a field experiment,this study was conducted to assess the effects of changes in plant roots and litters on C composition.The above-and below-ground litterfall manipulation experiment was conducted in three forests in Central China,which is located in northern subtropical and warm temperate climate transition zone,to examine the C composition responses to different litter and roots input since October 2015.These forest types included a coniferous forest(dominanted by Pinus massoniana Lamb.),a broad-leaved forest(dominanted by Quercus acutissima Carruth.),and a coniferous-broad-leaved mixed forest(P.massoniana-Q.acutissima mixed forest).This experiment included six treatments: control,litter addition,litter removal,root exclusion,root exclusion plus litter addition,and root exclusion plus litter removal.Total organic carbon(TOC),dissolved organic carbon(DOC),microbial biomass carbon(MBC),light fraction organic carbon(LFOC),heavy fraction organic carbon(HFOC),labile organic carbon(Lab-C),and recalcitrant organic carbon(Rec-C)were measured.Based on the two-year data,1)TOC did not change under litter addition treatment,litter removal and root exclusion treatments across all three forests.Litter removal decreased TOC by 20% both in coniferous forest and broad-leaved forest.2)DOCwas decreased(-16%)by the litter removal,but increased(13%)by litter addition across all three forests.Root exclusion decreased DOC by 8%.Litter addition had no effect on DOC in the coniferous forest.Litter removal did not affect DOC in coniferous-broad-leaved mixed forest.3)MBC was reduced 14% both in litter removal and root exclusion across all three forests.4)Litter and roots manipulation did not significantly influence the LFOC across all three forests,but root exclusion treatment increased LFOC by 9%.5)Both litter removal and root exclusion treatments reduced the content of HFOC by 14% and 4%,respectively.Heavy fraction organic carbon was increased by 14% in the litter addition treatments in broad-leaved forest.6)Lab-C was decreased by 15% and 7% respectively in the litter exclusion and root exclusion treatments.Litter removal reduced lab-C by 20% in coniferous forest and 19% in broadleaved forest.The lab-C was decreased by 14% in root exclusion treatments in broad-leaved forest.7)Heavy fraction organic carbon does not respond to litter and root treatmentLitter directly affects soil C composition through mechanical crushing,leaching and other decomposition processes.Litter addition and removal can change soil microenvironment,and affect soil C composition indirectly through temperature and moisture.The quantities of litter and the microenvironment of the soil are different,depending on the type of forest.The response of soil C components to litter treatment is different in three forest types.After root exclusion,there were no root decomposition and root exudates,which reduces the input of organic matter in the soil C pool and changed the structure of the microbial community,thus reducing soil C components such as DOC,MBC,HFOC,and lab-C.This experiment revealed the effects of litter and root on the C composition of forest soil in northern subtropical and warm temperate climate transition zone.The response degree and mechanism of soil carbon composition to soil carbon input in the context of global change were studied.The finding can provide basic data for predicting soil C pool change and feedback of global change.