Effects Of Organic Matter Input On Soil Organic Carbon Fractions Under Different Land Use Patterns

In this research,the study objects were natural forest(Altingia gracilipes),secondary forests(Castanopsis carlesii),plantation(Cunninghamia lanceolata)and orchard(citrus orchard),all of which had the same background conditions in the subtropical region.Soil samples were collected from the soils under vegetations of Altingia gracilipes forest(A),Castanopsis carlesii forest(M),Cunninghamia lanceolata forest(S),and citrus orchard(J),respectively.Based on a soil incubate experiment which joined the 13C labeled fir sample,the SIC values and 51lC values of soil can be estimated,those values then were used to study the renewal and turnover of SOC,and the turnover of SOC with different particle sizes.Eventually,the effects of organic matter input on soil organic carbon fractions under different land use patterns were revealed.The results showed that:1.With the increase of the residual quantity(CK,L0(0.2%leaf),L1(1.2%leaf)),soil components present inconsistent performance which could be observed based on the percentage of each component accounting for soil quality.After incubating 90 days,the results showed that:(1)free LF(free light fraction organic matter),L1>LO>CK;(2)cPOM(coarse particulate organic matter),L1>L0>CK;except L0>CK>L1 in Castanopsis carlesii soil;(3)fPOM(fine particulate organic matter),L1>L0>CK in Altingia gracilipes and Cunninghamia lanceolata soils,L0>CK>L1 in Castanopsis carlesii soil,CK>L0>L1 in citrus orchard soil;(4)mSOM(mineral-associated soil organic matter),CK>L0>L1 in Altingia gracilipes and Cunninghamia lanceolata soils,CK>L1>L0 in Castanopsis carlesii soil,L0>CK>L1 in citrus orchard soil.After incubating 180 days,the results in terms of the percentage of each component accounting for soil quality showed that:(1)free LF,L1>L0>CK;(2)cPOM,L0>L1>CK in Altingia gracilipes soil,L1>L0>CK in Castanopsis carlesii soil,L1>CK>L0 in other soils,(3)fPOM,L0>L1>CK in Altingia gracilipes and Castanopsis carlesii soils,L1>CK>L0 in Cunninghamia lanceolata and citrus orchard soils;(4)mSOM,CK>L0>L1 in Altingia gracilipes and Castanopsis carlesii soils,L0>CK>L1 in Cunninghamia lanceolata and citrus orchard soils.Based on the incubation time,it could be seen that longer incubation time resulted in the increased percentage of free LF in soil,while the results of cPOM,fPOM and mSOM showed the reverse.2.With the increase of the residual quantity,the content of organic carbon was increasing.Overall,along with the residual increase,the carbon content of free LF,cPOM and fPOM fractions increased,while the results of the mSOC(mineral-associated soil organic carbon)showed that:After incubating 90 days,CK>L1>L0 in Altingia gracilipes soil,L0>L1>CK in Castanopsis carlesii soil,CK>L0>L1 in Cunninghamia lanceolata soil,L1>L0>CK in citrus orchard soil;however,after incubating 180 days,CK>L1>L0,except L1>L0>CK in citrus orchard soil.According to incubation time,expect ALo?JLo?AL1,the SOC of all treatments had a downward trend with longer incubation period.As for the fractions,the longer incubation time resulted in:increased free LF fraction and decreased cPOM,fPOM and mSOM fractions.3.After incubating 90 days,the carbon derived from the residue under different incubation was that:(1)L0,cPOM>fPOM>free LF in Altingia gracilipes and citrus orchard soils,fPOM>cPOM>free LF in other soils;(2)L1,free LF>fPOM>cPOM in Castanopsis carlesii soil,cPOM>fPOM>free LF in other soils;(3)G1(1.2%root),cPOM>fPOM>free LF,except cPOM>free LF>fPOM in Castanopsis carlesii soil.After incubating 180 days,the carbon derived from the residue under different incubation was that:(1)L0,fPOM>cPOM>free LF;(2)L1,free LF>cPOM>fPOM in Altingia gracilipes and Castanopsis carlesii soils,fPOM>cPOM>free LF in Cunninghamia lanceolata soil,cPOM>fPOM>free LF in citrus orchard soil;(3)G1,free LF>cPOM>fPOM in Altingia gracilipes and Castanopsis carlesii soil,fPOM>cPOM>free LF in other soils.With longer incubation time,both the SOC derived from the residues and the soil had a downward trend,expect the free LF fraction.It explained that inputting residues mostly could slow down the decomposition rate of soil organic carbon and with incubation time prolonging,the effect was weakened.