不同开垦年限坡地黑土耕层土壤有机碳库分配特征

因耕作和侵蚀的共同作用,农田坡地景观多为坡上侵蚀、坡下沉积的空间格局,同时伴随侵蚀区和沉积区土壤有机碳(SOC)含量及稳定机制的差异.为探明长期耕作的农田黑土有机碳库积累-损耗特征,采用Stewart物理-化学联合分组方法,以典型黑土区不同开垦年限坡耕地为研究对象,探讨基于侵蚀-沉积作用的不同稳定机制碳库(游离未保护碳、物理保护碳、化学保护碳、生物化学保护碳)的分配特征.结果表明: 长期耕作与侵蚀导致坡下沉积区显著富积SOC,4种碳库含量整体表现为沉积区显著大于侵蚀区;黑土区坡耕地SOC以化学保护碳库和生物化学保护碳库为主(>90%),侵蚀区主要积累化学保护有机碳(84.6%),沉积区主要积累生物化学保护有机碳(51.4%);随着开垦年限的延长,4种碳库积累速率随着碳稳定程度的增加而增加,为生物化学保护碳库(48%)>化学保护碳库(42.2%)>物理保护碳库(6.4%)>游离未保护碳库(3.4%);游离未保护有机碳库占比和积累速率最小,但其对外界干扰最敏感,在黑土管理过程中应引起足够重视.

Distribution characteristic of soil organic carbon pool in the plow layer of sloping farmland with different cultivation years in black soil region

Tillage and erosion simultaneously cause soil movement from the top-slope position to the foot-slope position in a sloping farmland, with consequences on variation of soil organic carbon (SOC) content as well as its stability mechanism. To identify the accumulation-loss characteristics of organic carbon pool (OCP) of black soil under long-term cultivation, the distribution characteristics of different OCPs (free unprotected, physical protection, chemical protection, biochemical protection) of sloping farmland with different years of cultivation were quantified by Stewart physical-chemical fractionation method. The results showed that long-term cultivation and associated erosion resulted in significant accumulation of SOC in the foot-slope deposition area. The contents of four OCPs in the foot deposition area were significantly higher than those in top-slope eroded areas. SOC of sloping farmland was dominated by chemically protected carbon and biochemically protected carbon (>90%). Furthermore, the top-slope erosion areas and foot-slope deposition areas mainly accumulated chemically protected organic carbon (84.6%) and biochemically protected organic carbon (51.4%), respectively. With the increases of cultivation years, the accumulation rate of four OCPs increased with the stability degree of SOC, that is, biochemical protection carbon pool (48%) > chemical protection carbon pool (42.2%) > physical protection carbon pool (6.4%) > free unprotected carbon pool (3.4%). The proportion and accumulation rate of the free unprotected organic carbon pool were the smallest, but they were most sensitive to external interference. Thus, more attention should be paid to free unprotected organic carbon during the management of black soil.