Objective  The paper aimed to investigate the effects of tree species traits and nutrient addition on the nutrient contents and stoichiometric ratios of coarse woody debris decomposition in subtropical forests, and to provide a theoretical basis for forest nutrient management and carbon (C) cycling.

  Methods  Six typical tree species were selected from the forest of Tiantong Field Observation and Research Station in Zhejiang Province. The field experiment of nitrogen (N) and phosphorus (P) addition included four treatments: control (CK, distilled water), N addition (N, 100 kg hm⁻² a⁻¹), P addition (P, 15 kg hm⁻² a⁻¹) and N + P addition (N + P, 100 kg hm⁻² a⁻¹ + 15 kg hm⁻² a⁻¹). The nutrient contents and stoichiometric ratios of coarse woody debris were determined to analyze the effects of tree species traits and exogenous nutrient addition on endogenous nutrient contents and stoichiometric ratios at the initial stage of decomposition (3 years).

  Results  Compared with the initial nutrient content, after three years of decomposition, the treatment of CK significantly increased N, P concentrations and decreased C/N under angiosperms, while P content was significantly decreased under gymnosperms (P < 0.05). Compared with CK, P and N + P addition significantly increased the P content of gymnosperms by 57.29% and 53.79%, respectively. N + P addition significantly decreased the C content, C/N and C/P of gymnosperms by 24.0%, 30.58% and 44.91% (P < 0.05), respectively. N and P addition had no significant effects on the nutrient content and stoichiometric ratio of angiosperms. Principal component analysis showed that the effects of N and P addition on the contents of C, N and P and their stoichiometric ratios of gymnosperms were greater than those of angiosperms, and P element was the main factor affecting the nutrient and stoichiometric characteristics of coarse woody debris. After three years of decomposition, the nutrient content of coarse woody debris was positively correlated with the initial density, but negatively correlated with the initial C content.

  Conclusion  In general, due to the differences in the nutrient contents and physical properties of coarse woody debris, there were significant differences in the responses of the nutrient contents and stoichiometric ratio of coarse woody debris to N and P addition between the angiosperms and gymnosperms. The nutrient contents and stoichiometric ratio of coarse woody debris to gymnosperms with lower initial nutrient contents were significantly affected by the addition of N and P. Therefore, future studies on the effects of climate change (such as N and P deposition) on forest nutrient pools and organic C decomposition should consider the differences in the tree species traits of coarse woody debris.