碳库管理指数对退耕还林土壤有机碳库变化的指示作用

Carbon management index as an indicator for changes in soil organic carbon pool under conversion from cropland to forestland

探讨了黄土丘陵区退耕种植10～40a柠条、沙棘、刺槐林地土壤有机碳库和相关指标的变化特征.结果表明,随退耕期延长,100cm深土层总有机碳及活性有机碳均呈显著增加趋势,但退耕10a 0～40cm浅层土有机碳库既有显著增加,40～100cm深层有机碳库到退耕20～40a才显著提高.3种还林地碳库活度和活性有机碳占总有机碳比例并未随土壤有机碳库增加而持续增长,而是在各土层间分别维持在0.35～0.75和0.25～0.42;碳库管理指数不仅随退耕期延长与土壤有机碳库变化一致,即在浅层土呈直线快速增加,在深层土以指数函数相对缓慢增长,而且与有机碳库变化呈极显著正相关关系.此外,对比其他碳库指标,到退耕40a时仅碳库管理指数与土壤总有机碳及活性有机碳在不同林地差异变化一致,均为刺槐>沙棘>柠条,说明碳库管理指数能够良好的指示退耕还林土壤有机碳库的变化.

Soil organic carbon pool and its indicative indices including carbon management index （CMI）, ratio of labile organic carbon （LOC） to total organic carbon （TOC）, and non-labile organic carbon （A） were investigated for three typical kinds of forestlands： Caragana, Buckthorn, and Robinia, which have been converted from cropland for 10 to 40 years in Loess Hilly Area. Our objective was to determine the indicative capacity of CMI for changes in soil organic carbon. In general, the contents of TOC and LOC at 0-100 cm soil depth increased significantly. At 0--40 cm soil depth, soil organic carbon increased 10 years after conversion from cropland to forestland, while at 40-100 cm soil depth it began to show increases 20 years after conversion. Among the carbon indices, LOC/TOC （0.35-0.75） and A （0.25-0.42） did not increase with the increasing carbon pool during long-term conversion in the three kinds of foresflands indicating that they only reflected the active extent of soil carbon pool. In contrast, CMI showed increasing trends with soil carbon pool and its labile fraction, with greater increases for shallower soil （0--40 cm） and lower increases for deeper soil （40-100 cm）, as confirmed by a positive linear correlation between CMI and content of carbon pool. Moreover, atter 40 years of farmlands being converted to forestiands, CMI was significantly different among forestlands with an order： Robinia 〉 Buckthorn 〉 Caragana, which was the same sequences of TOC and LOC in the three forestland soils. Thus, CMI could be a better quantitative and qualitative indicator for the changes in soil organic carbon pool under conversion from cropland to forestland.