Leaf Nutrient Resorption of Vascular Epiphytes Is Regulated by Stoichiometry and Nutrient Limitation Control Strategies

Nitrogen (N) and phosphorus (P) resorption are assumed to be crucial for epiphyte growth in nutrient-poor canopies, yet remain poorly understood due to unique habitats and limited access. We examined the N, P and ¹⁵N natural abundance in mature and senesced leaves of 10 vascular epiphyte species in southwest subtropical China, integrating data from a previous study in tropical lowland forest. We found that subtropical epiphytes experienced N-limitation, likely because of the high P availability, making N relatively scarce. The mean N and P resorption efficiencies per leaf unit were 63.1% and 67.7%, with 14.7% and 12% higher than those on leaf mass, and 3.9% and 3.8% higher than those on leaf area. The combination of strategy analysis, generalized linear models and variance decomposition revealed that the N and P resorption in tropical epiphytes were combinedly regulated by stoichiometry and nutrient limitation control strategies, while subtropical epiphytes employed either the combined strategies or stoichiometry strategy alone. Notably, functional group type strongly influenced N resorption. Leaf δ¹⁵N reflected nutrient resorption with species-specific variation, driven by functional traits. Epiphytes and terrestrial plants exhibit similar nutrient resorption patterns, which help alleviate the N and P deficiencies and support high biodiversity in forest canopies.