The scaling relationship between leaf nitrogen and phosphorus concentrations in vascular epiphytes

Tao Hu¹T. T. Zhang²D. D. Tang³S. Liu⁴Su Li⁵X. W. Hu⁶Yu-Xuan Mo⁵WENYAO LIU^5*

• ¹Jiangxi Provincial Key Laboratory of Carbon Neutrality and Ecosystem Carbon Sink, Lushan Botanical Garden, Jiangxi Province and Chinese Academy of Sciences, Jiujiang, China
• ²Henan University of Urban Construction, Pingdingshan, China
• ³Qianxinan State Nanpanjiang Forest Farm, Xingyi, China
• ⁴Anhui Normal University School of Ecology and Environment, Wuhu, China
• ⁵Yunnan Key Laboratory of Forest Ecosystem Stability and Global Change, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, China
• ⁶National Field Scientific Observation and Research Station of Subtropical Forest Ecosystem in Ailao Mountain, Jingdong, China

The scaling relationship between leaf nitrogen (N) and phosphorus (P) concentrations provides key insights into plant adaptation strategies and evolutionary dynamics. Although this relationship has been widely examined in terrestrial plants, vascular epiphytes—an important yet understudied component of global plant diversity—remain poorly understood. Exploring their nutrient stoichiometry is crucial for understanding how epiphytes adapt to nutrient-limited canopy environments. We complied new measurements on leaf N and P concentrations from 38 vascular epiphyte species distributed across tropical seasonal rainforests and subtropical montane moist forests in southwest China. These data further complemented by a global literature synthesis to examined patterns of leaf N-P scaling relationships across forest types, functional groups, and habitats. Our analyses revealed that epiphytes exhibit a distinct leaf N-P scaling exponent (β=0.78), significantly higher than that of global terrestrial plants. While β values showed marginal differences among tree species across forest types, no significant variation was observed among epiphyte species. Notably, facultative epiphytes in subtropical montane moist forests displayed contrasting scaling relationship patterns, with lower β values in epiphytic habitats (0.69) than in terrestrial habitats (0.91). However, β remained relatively consistent across functional groups, forest types, and microhabitats, suggesting conserved nutrient allocation strategies among epiphytes. Our findings highlight the overlooked but critical role of epiphytic habitats in shaping leaf N-P stoichiometry. The distinct scaling relationships of epiphytes provides new perspectives into their adaptive nutrient-use strategies and ecological specialization in canopy environments. This study expands the global understanding of plant nutrient scaling relationships by incorporating the unique functional niche of epiphytes into the broader framework of plant stoichiometric theory.