扬黄灌区开垦时间对土壤剖面有机碳含量和组分变化的影响

基于开垦时间长短和跨度大小，研究了近40 a来宁夏中部扬黄灌区土壤有机碳含量、组分及其化学稳定性的变化规律。结果表明:代尺度上（15~35 a，10 a为最小单位），随开发年限的延长，依次以0—40 cm土壤活性有机碳垂直分布格局（15 a）、10—20 cm土壤活性有机碳含量（25 a）、10—40 cm土壤总有机碳含量（35 a）的显著变化为标志，灌区土壤有机碳表现出一种渐进式演变格局。在此过程中，表层0—10 cm土壤有机碳含量与组成、0—40 cm分层土壤有机碳化学稳定性维持不变。年尺度上（0~12 a，3 a为最小单位），耕作层土壤总有机碳、活性有机碳含量在0~12 a间表现出先增加后下降的波动变化格局，而有机碳化学稳定性除第3年大幅下降外，基本保持稳定。就扬黄灌区土壤有机碳的变化格局而言，其相对快速而不稳定的变化主要体现在较小的年尺度上；代尺度上土壤总有机碳和活性有机碳含量则以一种相对平缓、渐进的方式不断推进其演变进程，直到35 a左右才开始出现显著增长。而有机碳化学稳定性则表现出与时间尺度无关的不变性。

Soil Organic Carbon and Its Component Dynamics Following the Development Years of the Pumping-Yellow River Irrigation Area in Ningxia

We investigated the dynamics on two time scales of soil organic carbon content, components and chemical stability in middle Ningxia Yellow River irrigation area over the past 40 years. The results showed that soil organic carbon in this area showed a progressive evolution with the years of development on the decade scale(15~35 years,10 years as an interval), marked by a significant change of the distribution of soil labile organic carbon in 0—40 cm layer(15 years), soil labile organic carbon content in 10—20 cm layer (25 years), and soil organic carbon content in 10—40 cm layer(35 years). During this process, surface soil organic carbon content and composition in 0—10 cm layer, chemical stability of soil organic carbon in 0—40 cm layer remained unchanged. On the year scale (0~12 years, 3 years as an invertal), total organic carbon and soil labile organic carbon contents of the plow layer (0—40 cm) increased firstly and then decreased. While the chemical stability of organic carbon kept stable in addition to the first three years of sharp decline. For the changes at the multi-scale of soil organic carbon in middle Ningxia Yellow River irrigation area, the quick and unstable changes occurred on the smaller time scale. But on the larger time scales, the contents of total soil organic carbon and labile soil organic carbon kept the gentle and gradual change, and increased significantly at last until 35 years. while organic carbon stability exhibited the stability across all the scales.