六盘山林区几种土地利用方式对土壤有机碳矿化影响的比较

THE MINERALIZATION OF SOIL ORGANIC CARBON UNDER DIFFERENT LAND USES IN THE LIUPAN MOUNTAIN FOREST ZONE

应用土壤培养法 ,比较分析了六盘山林区天然次生林 (杂灌林、山杨 (Populusdavidanda)和辽东栎 (Quercusliaotungensis)林 )、农田、草地和人工林 (13a、18a和 2 5a华北落叶松 (Larixprincipis_rupprechtii) )土壤在 30℃和 6 0 %田间饱和含水量条件下培养 180d有机碳矿化速率的差异 (以 180d累计释放的CO2 _C计 )。结果显示 :农田和草地土壤碳矿化释放的CO2 _C含量 (180d释放的gCO2 _C·kg-1干土 )分别比天然次生林低 6 5 %和 2 3% ,差异主要在 0～ 4 0土层 ;人工林比农田和草地分别高 15 5 %和 17% ,差异主要在 0～ 70cm土层。农田土壤碳矿化释放的CO2 _C分配比例 (即 180d释放CO2 _C/土壤C)比天然次生林平均低 12 % ,草地比天然次生林平均高 18% ,差异主要在 0～ 4 0cm土层 ;人工林比农田平均高 2 9% ,草地比人工林平均高 9% ,差异主要在 0～ 5 0cm土层。不同土地利用方式土壤碳矿化释放的CO2 _C含量的差异比其分配比例的差异大。土壤碳矿化释放的CO2 _C含量和分配比例总体上都随土层加深而递减。分配比例随土层加深而递减的幅度方面 ,不同土地利用方式间的差异不大 ;含量随土层加深而递减的幅度方面 ,天然次生林和人工林比农田和草地中大 ;随土层递减的幅度方面 ,土壤碳矿化释放的CO2 _C含量比其分?

Soil organic carbon (SOC) is a large component of the global carbon cycle and the influence of land-use changes on SOC pools can significantly affect atmospheric CO 2 concentrations. The response of soil carbon mineralization rates to changes in land-use type is the crux for understanding the influence of land-use changes on SOC. Over the last several centuries, extensive areas of the native vegetation of the Liupan Mountain forest zone has been converted to cropland or rangeland and, over the last several decades, some of these former croplands and rangelands have returned to forests. However, the impacts of these land-use changes on the SOC are unclear. In order to assess the impacts of land-use change on LSC, we compared the LSC concentrations in adjacent plots of natural secondary forest (i.e. dominated by Querces liaotungensis, Populus davidiana, or brushwood), cropland, rangeland, and 13, 18 and 25-year old larch (Larix principis-rupprechtii) plantations that were planted on former croplands and rangelands. To determine the rate of SOC mineralization, soils were collected from each of these land use types, incubated in the laboratory at 30 ℃ with a constant moisture of 60% field water capacity over 180 days and the amount of cumulative CO 2-C released over 180 days was compared among the different land use types. It was found that the mean concentration (g CO 2-C·kg -1 soil·180 d -1) of SOC mineralization in the 0-110 cm soil layer was 155% and 17% higher under the plantation than under cropland and rangeland, respectively, and was 65% lower under cropland and 23% lower under rangeland as compared to the natural secondary forest. The change in the concentration of cumulative CO 2-C released by SOC mineralization with soil depth under the natural secondary forest and plantation was greater than under the cropland or rangeland. The difference in the cumulative CO 2-C released by SOC mineralization between natural secondary forest and cropland or rangeland was greater in 0-40 cm depth than the 50-110 cm soil layer, but the difference between the plantation and cropland or rangeland was greater in 0-70 cm than 70-110 cm soil layer. The fraction of cumulative CO 2-C mineralized as a percent of total SOC in the 0-110 cm soil layer was 12% lower under cropland than under the natural secondary forest, 29% higher under plantation than cropland, 18% and 9% higher under rangeland than natural secondary forest and plantation, respectively. There were no significant differences in the change of the fraction of cumulative CO 2-C released by SOC mineralization with soil depth among the different land uses. The difference between the fraction of cumulative CO 2-C released by SOC mineralization from the natural secondary forest and cropland or rangeland was greatest in the 0-40 cm soil layer, whereas this difference between plantation and cropland or rangeland was greatest in the 0-50 cm soil layer. In general, the concentration of cumulative CO 2-C released by SOC mineralization was greater than the fraction among different land uses as well with changes with soil depth. These differences were attributed to differences in the inputs of SOC, stabilization, and quality of soil organic matter among different land uses. Overall, our results suggest that the rate of SOC mineralization will decline with conversion from natural forests to cropland or rangeland and will increase following afforestion of former croplands or rangelands. In addition, the distribution of cumulative CO 2-C released by SOC mineralization in different soil layers will also change with the magnitude of change greater in concentration than the fraction following changes in land use.