Biodegradability of dissolved organic carbon (DOC) represents a critical component of the riverine C cycle. Current knowledge of DOC biodegradation in rivers is limited, especially in the subtropical regions. Here, we collected 66 water samples from 63 tributaries of the Yangtze River in the Three Gorges Reservoir Region, China, and subsequently examined the biodegradability of DOC and its controlling factors. We found that DOC biodegradation was quite spatially variable within the river networks and ranged from 15.8% to 35.2%, with a mean of 24.5 +/- 8.0%. The biodegradability of DOC was positively correlated with the initial dissolved total phosphorus (P) concentration, but was not significantly correlated with the initial DOC and dissolved total nitrogen (N) concentrations. In addition, DOC biodegradation was negatively correlated with the initial C:P and N:P ratios, and exhibited no significant relationship with the initial C:N ratio in these rivers. Our findings suggest that DOC biodegradation is limited by P availability in the subtropical rivers, and also imply that P enrichment induced by anthropogenic activities would enhance the biodegradability of DOC and decrease the spatial heterogeneity of DOC biodegradation in the subtropical river networks. (C) 2016 Elsevier B.V. All rights reserved.