Non-additive effects on biodegradability of litter-derived dissolved organic carbon (DOC) at species level are critical to carbon cycle in forests, yet such effects at organ level remain elusive. Both leaf- and twig-litter-derived DOC, dissolved total nitrogen, and dissolved total phosphorus (DTP) were extracted from one dominant broadleaf tree species and one dominant coniferous tree species in a subtropical plantation in southern China. A 42-day incubation study was conducted to investigate DOC biodegradability of monospecific treatment and the relative mixing effects on DOC biodegradability of mixed treatment at both species and organ levels. Irrespective of tree species, the DOC biodegradability of leaf was lower than that of twig in litter leachates. At both species and organ levels, mixed litter leachates generated non-additive effects on DOC biodegradability and decay index. Specifically, antagonistic effects were detected at species level, and synergistic effects occurred at organ level. Non-additive effects on DOC biodegradability positively correlated with variations in the DOC:DTP ratio and DOC aromaticity between the component litter leachates. These findings extend our knowledge of the non-additive effects on litter-derived DOC biodegradability from interspecific level to intraspecific level and highlight the crucial role of senescent twigs in regulating soil DOC dynamics in subtropical plantations.
Xu et al. (Thu,) studied this question.