Response Of Soil Labile Organic Carbon Fractions And Carbon Mineralization To Land-use Changes In Mid-subtropical Hilly Region Of China

Land use activities in tropical-subtropical make a major contribution to anthropogenic CO2emission which is just the second source to the emission from fossil fuel combustion. In this study, four typical land-use patterns adjacented to each other were selected in eastern Hunan Province, including natural forest (NF), Chinese fir plantation (CF), orchard (OR) and sloping tillage (ST). The soil profiles were selected and digged, and the soil sample was collected vertically at each plot. The soil labile organic carbon fractions was analysed and the carbon mineralization was studied by incubation experiment under laboratory in order to examine the effect of land use changes on soil labile organic carbon and carbon mineralization. The main results were as follows:(1) The storage of SOC decreased significantly by13%～25%after the NF converted to other land uses. However, the storage of liable organic carbon fractions extracted by physical biochemical techniques responded to the land use changes with different degree. The light fraction organic carbon (LFOC) and microbial biomass carbon (MBC) storages declined separately by24%～61%and48%～66%, while the particulate organic carbon (POC), rasily oxidized organic carbon (ROC) and dissolved organic carbon (DOC) storages decrease slightly. It seems that LFOC and MBC could be used as sensitive indicator to evaluate the effect of land use changes on soil carbon pool.(2) Land use changes significantly affected on the profile distribution of SOC and its labile carbon fractions, particularly affected the DOC profile distribution. The distribution of DOC content was changed after the land use changes, while the profile distribution of LFOC, POC, ROC, MBC storage consistented with SOC which decreased with the increasing soil depth.(3) Land use changes also affected the quality of soil carbon, four land use were selected, The NF had the highest proportion of liable organic carbon to SOC and best SOC quality, while after the NF was converted to other land use, the proportion was decreased(4) Land use also affected soil carbon mineralization. The CO2-C cumulative mineralization for42d in the laboratory, following the order of NF>CF>ST>OR, which consistented with the change of liable carbon storage, indicating liable soil organic carbon pool could be used as predictive indicator for soil mineralization. The proportion of estimated mineralizable organic carbon (16d) to SOC ranged from1.6%to1.8%, following the order of ST>OR>CF>NF. The SOC mineralization was mainly affected by the amount of input of organic matter and quality. Additive release of CO2under different land use were well related with add the number of carbon and nitrogen.