Abstract:
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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