土壤易氧化有机碳与溶解性有机碳对荒漠草地沙漠化过程中土壤碳库变异的表征

Characterization of readily oxidizable carbon and dissolved organic carbon within the soil carbon pool during desertification of grassland in central China

以干旱、半干旱地区荒漠草地不同沙漠化阶段土壤为研究对象,研究不同沙漠化阶段土壤易氧化有机碳与溶解性有机碳含量和分配比例变异规律,分析不同沙漠化阶段土壤碳库指数变化,探讨荒漠草地沙漠化过程中土壤易氧化有机碳与溶解性有机碳对土壤碳库的表征作用。结果表明,随着荒漠草地沙漠化程度的加剧,易氧化有机碳含量表现出一定的波动性,但整体呈下降趋势,溶解性有机碳含量呈线性下降。易氧化有机碳和溶解性有机碳分配比例均在荒漠草地达到最大值,在半固定沙地达到最小值。利用易氧化有机碳含量计算的土壤碳库管理指数随荒漠草地沙漠化程度增加表现出先下降后上升趋势,利用溶解性有机碳含量计算的土壤碳库管理指数呈线性下降趋势。易氧化有机碳、溶解性有机碳含量与土壤有机碳均显著正相关,但溶解性有机碳的相关系数略高于易氧化有机碳。通过比较活度敏感指数和碳库管理指数敏感指数发现,荒漠草地逆向演替至固定沙地过程中,易氧化有机碳的各项敏感指数均高于溶解性有机碳。固定沙地演替至流动沙地过程中,溶解性有机碳的各项敏感指数均高于易氧化有机碳,表明易氧化有机碳能够较好地表征荒漠草地沙漠化前期土壤碳库变化,而荒漠草地沙漠化中期和后期利用溶解性有机碳表征效果更好。

The readily oxidizable carbon(ROC)and dissolved organic carbon(DOC)are important indicators of transformation status of soil organic carbon in areas undergoing land use change.However,there is no consensus as to which indicator is best suited for assessing change in soil organic carbon status during desertification of grassland in arid and semiarid regions.The content and proportion of ROC and DOC,an index called here the carbon management indicator(CMI)and sensitivity indices based either on DOC or ROC data were compared.ROC and DOC decreased gradually during the grassland desertification process.Grasslands had the highest values for ROC and DOC,while semi-fixed dunes had the lowest values.With increasing desertification of the arid grassland under study,CMI values calculated from ROC data initially decreased and then increased,while the CMI calculated from DOC data steady decreased.There was a significant positive correlation between ROC,DOC and soil organic carbon,and the correlation coefficient between DOC and soil organic carbon was higher than that between ROC and soil organic carbon.In the transition from grasslands to fixed dunes,sensitivity indices of carbon activity and of the carbon pool calculated using ROC data were more sensitive than those using DOC data.However,in the transition from fixed dunes to mobile dunes,the two sensitivity indices were more sensitive when derived from DOC data,than when derived from ROC.Hence,ROC data is more suitable for evaluation of grassland status during the early stage of desertification in arid grassland,while DOC is a better indicator of change in soil organic carbon status in the middle and later stages of desertification in the grassland studied.