东北黑土区坡耕地表层土壤颗粒有机碳和团聚体结合碳的空间分布

Spatial distribution of particulate organic carbon and aggregate associated carbon in topsoil of a sloping farmland in the Black Soil region,Northeast China

以东北黑土区典型漫岗坡耕地为研究对象,测定不同侵蚀程度地形部位表层土壤不同粒级有机碳、水稳性团聚体及其结合碳含量,探讨土壤侵蚀和沉积作用对表层土壤有机碳(SOC)损失、迁移和累积的影响。研究结果表明:与侵蚀微弱的坡顶相比,严重侵蚀的坡肩部位表层土壤水稳性大团聚体、矿质结合碳(IOC)和团聚体结合碳含量分别减少23%、17.5%和8.7%,而土壤颗粒有机碳(POC)含量无明显差异。长期处于沉积状态的坡脚部位,表层土壤大团聚体、POC和大团聚体结合碳含量分别较坡顶低56.1%、47.9%和67%;而IOC和微团聚体结合碳分别较坡顶高10%和18.7%。研究结果反映了土壤侵蚀以及耕作倾向于破坏水稳性大团聚体,其内部包裹的轻质、细颗粒物质易被地表水流迁移流失,加上下层土壤的稀释作用,导致侵蚀部位SOC减少。轻质活性碳组分在迁移和累积过程中易被微生物利用分解,沉积区土壤以IOC和微团聚体碳为主,形成一个惰性碳汇。

A typical rolling farmland in the Black Soil region of Northeast China was selected in a case study to analyze impact of soil erosion and deposition on the loss, transportation and accumulation of soil organic carbon （SOC） in topsoil by measuring particulate organic carbon （POC）, composition of water stable aggregates of different sizes and contents of associated carbon in different slope positions. Results showed that the contents of macro-aggregates, incorporated organic carbon （IOC） and microaggregate associated carbon at the shoulder-slope with serious erosion were 23% , 17.5% and 8.7% lower than those of summit with weak erosion, respectively, while there was no significant difference in POC among three erosion sites. At foot-slope, a longterm soil deposition recipient, the contents of POC, macro-aggregates and macro-aggregate associated carbon were 56.1%, 47.9% and 67% lower than those of summit, while IOC and micro-aggregate associated carbon were 10% and 18.7% higher than those of summit, respectively. The findings suggest that soil erosion and cultivation tend to break down macro-aggregates, whose content light in weight and fine in particle size are hence easily lost and transported with surface water flow, which in addition to the dilution function of subsurface soil leads to decrease in SOC content at erosion sites. Moreover, the fraction of light labile organic carbon is apt to be exploited and decomposed by soil microbes in the process of transportation and accumulation. As a result, SOC in the depositional sites was dominated by IOC and micro-aggregate associated carbon, forming a big passive carbon pool in the topsoil.