Abstract: 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.

Key words: readily oxidizable carbon, dissolved organic carbon, carbon management indicator, desertification, desert grassland