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Changes of soil active organic carbon under different land use types in karst area

MO Bin1, 2, CAO Jianhua1, XU Xiangming1, 2, SHEN Honggang1, YANG Hui1, LI Xiaofang1, 3 1. Institute of Karst Geology, Chinese Academy of Geological Science//Key Laboratory of Karst Dynamics, Ministry of Land and Resources, Guilin 541004, China; 2. College of Life Sciences, Guangxi Normal University, Guilin 541004, China; 3. College of Chemistry and Chemical Engineering, Guangxi Normal University, Guilin 541004, China  
Soil active organic carbon (SAC) refers to the fractions of organic carbons that are easy to move and to be oxidized and mineralized, and they are quite available to plants and soil microorganisms. Soil dissolved organic carbon (DOC) and microbial bio- mass carbon (MBC) are considered to be the useful indicators of SAC. Soil active organic carbon is involved in all biological and biochemical processes in soil, the minor change of SAC can be detected before the content of total organic carbon (TOC) in soil has changed, although it accounts for small fraction of TOC. The types of vegetation influence the size and quality of soil organic matter. Over the last several centuries, extensive areas of native vegetation of karst areas in Maolan, Guizhou Province have been converted to croplands and grasslands. The impacts of these land use changes on soil organic carbon (SOC) are unclear. In order to assess the impacts of land use changes on active soil organic carbon, we compared the DOC, MBC concentrations in adjacent plots of native forest, cropland, grassland with the same elevation, exposure and soil type. The results showed that the mean forest DOC were higher than that of grassland and cropland 25% and 48% respectively. From May to August, they all increased with the increase of tempera- ture. The forest and cropland DOC reached the highest value in August while the grassland reached the peak value in October. The forest MBC was higher than that of grassland and cropland 81% and 45% respectively. Land use changes play an important role in the changes of DOC and MBC in soils. The relationship between active soil organic carbon and environmental factors is complicated which still needs to be further studied.
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