岩溶山区不同土地利用方式对土壤活性有机碳动态的影响

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

对贵州茂兰自然保护区内三种典型土地利用方式(林地、草地和耕地)下土壤活性有机碳组分(土壤溶解有机碳和土壤微生物量碳)的月变化及其对环境因子的响应进行了研究,结果表明在不同的土地利用方式下上覆植被类型不同,其凋落物数量、质量及分解行为不同,有机质的输入量及质量也不相同,从而形成不同的土壤溶解有机碳含量差异,土壤有机碳的大小也存在较大差别。研究结果显示:从全年平均值来看,林地土壤溶解有机碳分别比草地和耕地高25%、48%;从3月到8月,三者均随气温的上升呈增加的趋势,林地和耕地在8月均达到最大值,而草地则在10月达到最大值;林地和草地土壤微生物量碳分别高于耕地81%和45%,林地和草地在10月达到最大值。不同的土地利用方式导致土壤活性有机碳的差异较大,这说明岩溶生态系统中土地利用方式对土壤碳库的大小有较大影响。不同土地利用方式下土壤活性有机碳对环境因子的响应也各不相同,这表明土壤活性碳受众多因素的制约而呈现出一种动态平衡关系,进一步的机理仍需要进行深入研究。

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 biomass 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 temperature. 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.