Effects of burning and nitrogen addition on foliar stoichiometry and nutrient resorption in a subtropical–temperate ecotonal forest

Fire disturbances and atmospheric nitrogen (N) deposition can significantly soil nutrient dynamics and plant nutrient uptake, thereby influencing on biogeochemical cycles within forest ecosystems. Despite these known effects, the combined impact of burning and N addition on leaf nutrient characteristics and the underlying mechanisms remains largely unexplored, particularly within forest ecosystems. This study presents a three-year field experiment designed to assess the responses of leaf N and phosphorus (P) concentrations, N:P ratios, and nutrient resorption in six dominant species (comprising two tree species and four understory species) to burning and N addition in a coniferous-broadleaved mixed forest located within a subtropical-warm temperate transition zone in Central China. The findings revealed that burning did not affect N concentrations in either green or senesced leaves, nor did it influence N or P resorption across any of the tree or shrub species. However, it did increase P concentrations in green leaves and reduce N:P ratios in shrub species. N addition elevated the N concentrations and N:P ratio in green and/or senesced leaves (with the exception of Quercus acutissima Carruth.), without affecting N or P resorption. These results suggest that shrubs enhanced P uptake due to increased soil P availability but maintain consistent internal P cycling (i.e., nutrient resorption) following low-severity fires. Additionally, most shrub species exhibited lower N:P ratios compared to tree species post-burning, indicating distinct nutrient requirements and fire responses based on life form. This study provides essential insights, demonstrating that burning mitigates P limitation on plant growth in subtropical–warm temperate ecotonal forests. Furthermore, the differential responses of leaf nutrient traits and associated stoichiometry across diverse life forms to environmental disturbances may influence plant diversity and community composition within these forests.