[Characteristics of Easily Oxidized Soil Carbon Content and Carbon Pool Management Index in Typical Climate Zones in...

Climate and land use are important factors affecting the soil carbon pool and organic carbon influx. To explore the characteristics of active organic carbon content and carbon pool management index in farmland soils in typical climate zones, two types of farm land （dry land and paddy fields） and adjacent forest soils in four climate zones （temperate, warm temperate, subtropical, and tropical） in eastern China spanning north to south were selected for study. The permanganate oxidizable carbon （POXC） content in each climate zone was analyzed, and the soil lability of carbon （L）, soil lability index （LI）, carbon pool index （CPI）, and carbon pool management index （CMI） under each land use type were calculated. The following trends were observed across the three land use types： Soil POXC content was generally slightly higher in the north than in the south and consistently higher in paddy fields than in dry lands. L was significantly higher in warm-temperate regions than in the other three climatic regions. This suggests that soils in warm temperate regions （primarily fluvio-aquic soils） and paddy field soils have high organic carbon activity and soil carbon pool quality. However, measures to avoid soil organic carbon （SOC） loss during agricultural use must be crucially implemented. Paddy field soils exhibited higher CPI values than dry land soils across all four climatic regions. Specifically, the CPI of paddy fields was >1 in all regions, whereas dry lands had carbon pool indices of <1, except in the warm temperate region. This indicates that long-term paddy field cultivation enhanced organic carbon soil stocks, whereas long-term dry land farming reduced them compared with those in adjacent forested areas. Except for the subtropical dry lands, the average CMI for both types of farmland soil in all four climatic regions was >100. Furthermore, the index was higher in paddy fields than in adjacent dry lands and higher in the north than in the south, suggesting that long-term agricultural use can improve SOC quality, thereby promoting the conversion and supply of soil organic nutrients. Correlation analysis revealed significant positive correlations between POXC and SOC, total nitrogen, pH, and sand and significant negative correlations with clay, silt, mean annual temperature （MAT）, and mean annual precipitation （MAP）. CMI correlated positively with pH and sand and negatively with MAT and MAP. These findings provide a scientific basis for understanding the impacts of long-term agricultural use on soil carbon pool activity and soil quality in the typical climatic regions of eastern China. This can guide appropriate agronomic management practices aimed at enhancing carbon pool management.