不同农业土地利用年限干旱区土壤剖面碳存储动态变化

摘要

干旱区农业土地开发利用对土壤碳库的源汇效应一直存有争议,为研究该过程对土壤剖面碳存储作用,该文以新疆三工河流域阜北农场不同土地开发利用时段的农田为研究对象,对比分析近50 a 0~200 cm土壤剖面有机碳和无机碳分布格局及其变化.结果表明:土壤碳含量随利用年限增加而增大,但有机碳与无机碳变化趋势相反;长期的农业土地利用显著影响0~80 cm土壤碳的分布,其变异性在80~100 cm有明显的突变现象,即变异系数均减小40%以上;无机碳与有机碳的比例随土层深度和利用年限增加,变化率从荒地的0.028到50 a的0.088(P<0.01),增幅达2.14倍;随土地利用年限,有机碳和无机碳的碳储效应在土层间与时间尺度上不同,但剖面土壤碳密度为典型的碳汇进程.研究可为干旱区农业土地开发提供依据.%The impact of agricultural land use on soil carbon storage is one of the international scientific focuses in climate-change mitigation. Aimed to understand the effect of agricultural land development and utilization on soil carbon storage, a study was conducted in different period of farmland at the Fubei Farm of Sangong River Basin in Xinjiang, northwest of China (87°49′-88°16′E, 43°50′-44°22′N). The agricultural lands were selected within different land use years such as 1, 5, 15, 30 and 50 a in the studied area, and the wasteland with little disturbance was selected as a reference land in the same soil type and near position of cropland. Soil samples from these sites were obtained by handy soil auger at 20 cm intervals in a depth of 200 cm and analyzed in the laboratory. Samples were air-dried and crushed to pass through a 2-mm mesh. The patterns of soil carbon storage and its dynamic change were analyzed and compared with the depth of 0-200 cm in recent 50 years, including soil organic carbon, soil inorganic carbon and soil salinity. The results revealed the following: 1) Soil carbon content generally increased with land use years. Soil inorganic carbon content changed by soil depth, with a maximum value of 20.96 g/kg at 180-200 cm. Soil organic carbon presented an opposite trend with the maximum value of 9.51 g/kg at 0-20 cm; 2) In the soil profile, The coefficients of variation of soil carbon content (including organic carbon and inorganic carbon) was gradually increased to moderate intensity variation in 0-80 cm, and then rapidly reduced by more than 40%underneath 80 cm, indicating that the long-term agricultural land development and utilization in arid area had a significant impact on the distribution of soil carbon at 0-80 cm. The variability of soil inorganic carbon and soil total carbon tended to be enhanced with the land use years, while the organic carbon tended to weaken in recent 50 years; 3) The ratio of SIC to SOC increased with the depths of soil layer, and it changed from 0.028 in wasteland to 0.08 in 50 years of cropland (P<0.01). It suggested that the proportion of soil inorganic carbon increased with soil depth and land use years, indicating the role of soil inorganic carbon was enhanced in the long-term agricultural land use process in arid area; 4) During the development and utilization of agricultural land in the past 50 years, the soil carbon storage increased significantly at 0-200 cm depth of soil profile, which was a typical process of carbon sequestration in the studied area. The increased soil inorganic carbon storage and organic carbon storage were mainly showed in 100-200 cm and 0-100 cm respectively. But the amounts of carbon source/sink were different in the soil layer and land use years; 5) Soil salinity showed a decreasing trend along with land use years. Compared to value in wasteland, soil salinity decreased by 655% in land use of 50 a (P<0.001). The linear fitting of salinity and carbon content showed that there was a significant negative correlation between salinity and soil inorganic carbon and total carbon (P<0.10), while no significant correlation with the soil organic carbon (P>0.05). The results showed that the agricultural use leads to an obvious C sink in the soil only in the long term.