坡耕地黑土不同密度的土壤有机碳组分的空间分布特征

以东北黑土区一典型漫岗坡耕地为研究对象,通过测定不同侵蚀程度地形部位的轻组、重组有机碳含量,分析土壤侵蚀和沉积过程对土壤不同密度组分有机碳的影响。研究结果表明:在各地形部位,表层土壤(0～20cm)轻组有机碳(LF-C)含量显著高于亚表层土壤,介于45.3～65.8mgkg-1之间,占土壤总有机碳(TOC)的2.91%～5.87%。侵蚀严重的坡肩部位LF-C、重组有机碳(HF-C)和TOC分别比侵蚀微弱的坡顶部位减少了27.4%、17.2%和18.1%,表明LF-C对土壤侵蚀和沉积过程的响应比土壤总有机碳更为强烈,土壤TOC的减少是土壤LF-C和HF-C减少共同作用的结果。LF-C/TOC的变化和LF-C的变化相似,说明土壤侵蚀优先导致LF-C的损失。各地形部位表层土壤LF-C和微生物量碳显著正相关,在沉积部位富集的LF-C的最终归宿问题还有待于进一步研究,沉积部位仍以惰性的HF-C为主。

Spatial Distribution of Density Fractions of Soil Organic Carbon at a Sloping Farmland of a Black Soil

A typical undulating farmland in Black Soils region of Northeast China was taken as a case study to analyze the impact of soil erosion and deposition process on density fractions of soil organic carbon based on measurement of light and heavy organic carbon in different geomorphic positions, which were under various levels of erosion. The results showed that the carbon concentration in light fraction decreased with increasing in soil depth. In the surface 20 cm soil, light fraction carbon (LF-C) ranged from 45.3 mg kg-1 to 65.8 mg kg-1, which account for 2.91-5.87% of total soil organic carbon (TOC). The amount of LF-C, HF-C and TOC at the shoulder-slope where is subject to serious erosion was 27.4, 17.2 and 18.1% lower than those of summit where erosion is weak. Relevant to total soil organic carbon, the LF-C is more sensitive to soil erosion and deposition process, but the decrease of TOC is the combination of the decrease of LF-C and HF-C. The change of LF-C/TOC is similar as LF-C, indicating that soil erosion can preferentially cause the loss of LF-C. Accordingly, LF-C can be a good indicator of the early change of soil equality as affected by soil erosion. At foot-slope and toe-slope positions, C re-deposition has lead to significantly higher of LF-C compared than that at shoulder-slope. LF-C and microbial biomass carbon (MBC) showed the similar pattern along the slope, indirectly indicating that the dependence of soil microbes on the light-fraction of organic matter. The fate of the LF-C deposited in the foot-slope and toe-slope positions should be studied further, and HF-C is still the dominating fraction in deposited area.