Effects of Repeated Adding Exogenous Carbon on Soil Organic Carbon Fractions
[Objective]Exogenous carbon(C),such as root exudates and residues,is continuously input into soils under the farmland ecosystem.Research on the formation and fixation characteristics of soil organic C(SOC)after the repeated input of exogenous C into soil would provide a basis for soil C sequestration in farmland.[Method]In this study,the topsoil(0-20 cm)samples were collected from the plots of no fertilization at the long-term experimental station of Shenyang Agricultural University.The 13C-labeled glucose was added to the soil samples as a single or repeated(once every 15 days)way,and then they were incubated in the laboratory.The sub-samples were collected at the 14th,29th,57th,100th and 365th days of incubation.The contents of particulate organic C(POC)derived from glucose C and that of mineral-associated organic C(MAOC)derived from glucose C were determined and their contribution percentages in these fractions were calculated,in order to differentiate the distribution of exogenous C in SOC fractions between single and repeated additions.[Result]The content of MAOC derived from glucose C reached the maximum value at the 57th day and the 100th day under the single and repeated ways,respectively,and then it decreased with incubation time.At the 365th day,the contents of glucose C derived-POC and glucose C derived-MAOC under the single addition way were 1.50 times those under the repeated addition way;The contribution percentage of glucose C derived-POC in POC and that of glucose C derived-MAOC in MAOC under the repeated addition way were 0.10%and 0.57%,respectively.And they were decreased by 36.20%and 31.75%(P＜0.05)compared with single addition way,respectively.About 14.69%and 9.78%of glucose C was allocated to MAOC under the single and repeated ways(P＜0.05),respectively.[Conclusion]Repeated addition reduces the formation of exogenous C in SOC fractions,while single addition may overestimates the SOC sequestration potential.
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