The Effect Of Warming On The Change Of Soil Organic Carbon And Its Components In Subtropical Forests

Soil is the largest active carbon pool in the Earth's system.Soil organic carbon(SOC)is a key player in the global carbon cycle,and a chief component of soil organic matter.Global warming is now an indisput able fact,to which the subtropical regions have given more sensitive responses.Forest SOC pool interacts with global warming—any small change of the forest SOC pool might promote the negative feedback between soil carbon and climate;the rising temperature could in turn cause changes in SOC.However,changes in SOC under the effect of warming remained a subject of debate.To study the effect of warming on SOC and its components in subtropical forests,in 2015at Sanming Forest Ecosystem and Global Change Observation and Research Station of Fujian Province,our research group laid cables in the seedling forest of Chinese fir(GSF),the mature forest of Chinese fir(GMF)and the natural forest(GNF)respectively for temperature increase,and set the control treatment(CT,no warming)and the warming treatment(W,+4?)in each forest,each kind of treatment with 5 repeats.In 2018,we collected soil samples from the depth of 0-10cm,10-20cm,20-40cm and 40-60cm in each quadrat,and analyzed the characteristics of changes in SOC and its components after warming.Main results achieved are as follows:(1)Compared with CT,after warming,the labile C pool?(LP I-C)in GSF reduced by 12%and 16%respectively in the 0-10cm and 10-20cm depth ranges;the labile C pool?(LPII-C)reduced significantly by 13%in 20-40cm.However,LP I-C and LP II-C content in each depth range remained unchanged after warming.SOC in GSF,GMF and GNF showed no significant change after warming.(2)Compared with CT,after warming,soil microb ial biomass carbon(MBC)in the 0-10cm and 10-20cm depth ranges in GSF reduced by 29%and21%respectively;MBC in 0-10 cm in GMF reduced by 31%.After warming,MBC in the 20-40cm depth range in GNF increased by 30%.(3)After warming,the cold water-extracted dissolved organic carbon(C_DOC)in 0-10cm and the hot water-extracted dissolved organic carbon(H_DOC)in 0-10cm and 10-20cm in GSF reduced significantly(by 45%,26%,26%respectively).C_DOCin the 10-20cm and 40-60cm depth ranges in GMF also dropped significantly after warming(by 22%and 23%respectively).C_DOC,H_DOC and the salt solution-extracted dissolved organic carbon(S_DOC)concentrations in GNF,on the other hand,showed no significant change after warming.(4)After warming,hexose re duced by 56%and 52%in the 0-10cm and10-20cm depth ranges respectively in GSF,the content of pentose not detected.In GMF,hexose and pentose in 0-10cm reduced by 15%and 73%respectivel y after warming,with no significant change in other soil layers;hexose/pentose increased by 181%in 0-10cm,the ratio greater than 2.In GNF,pentose content in 0-10cm increased by 38%after warming;hexose increased by 19%in 20-40cm.Hexose/pentose in each depth range in GNF remained unchanged,the ratio greater than 2.And for the ratio being greater than 2 in the soil.(5)Compared with CT,easily extractable Glomalin-related soil protein(EE-GRSP)in GSF showed no change after warming while total Glomalin-related soil protein(T-GRSP)in the depth range of 10-20cm reduced by 29%.No significant change was found in other depth ranges.Compared with CT,T-GRSP and EE-GRSP in different depth ranges in GMF and GNF remained unchanged after warming.Compared with CT,the aromaticity index(AI)in 10-20cm and 20-40cm in GSF reduced by 48%and increased by 37%respectively after warming,no change in other soil layers.AI of soil in GMF and GNF showed no significant change after warming.(6)According to the research results,warming had a different effect on SOC of GSF,GMF and GNF,the effect on active organic carbon of GSF the greatest.After warming,GSF presented significant changes in most active organic carbon experimental parameters,followed by GMF and then GNF.