# Different Leaf Strategies Between Lithophytic and Terrestrial Orchids in a Subtropical Karst Forest

## TL;DR

Lithophytic orchids in subtropical karst forests adapt to harsh conditions by investing more in leaf structure and stress tolerance rather than photosynthesis.

## Contribution

This study reveals how lithophytic orchids prioritize structural traits and nitrogen allocation for survival in drought-prone karst environments.

## Key findings

- Lithophytic orchids have higher leaf mass per area and biomechanical resistance but lower photosynthetic efficiency than terrestrial orchids.
- Nitrogen allocation to photosynthesis correlates with maximum photosynthetic rate and inversely with biomechanical resistance.
- Saturated water content is a key driver of leaf trait variation in orchids within karst ecosystems.

## Abstract

The leaf economic spectrum framework explains how plants optimize leaf traits for productivity, distribution, and stress tolerance. Orchids in Southwestern China’s karst forests, especially lithophytic species, are challenged by prolonged drought and limited light availability. This study investigated different leaf strategies between lithophytic and terrestrial orchids under the harsh karst environment. We measured key leaf traits, including photosynthesis, structure, biomechanics, nitrogen allocation, and water relations, in twenty-two lithophytic and six terrestrial orchids in a subtropical karst forest. After accounting for phylogenetic influences, we found that lithophytic orchids had a higher leaf mass per area, cuticle thickness, and biomechanical resistance (Fp) but a lower maximum photosynthetic rate (Amax-mass), nitrogen allocation to photosynthesis (NT), and saturated water content (SWC) than terrestrial orchids. These results suggest that lithophytic orchids prioritize structural investment and stress tolerance over photosynthetic efficiency. Across species, NT correlated positively with Amax-mass and negatively with Fp, highlighting nitrogen allocation as a key mechanism in leaf cost–benefit strategies. Additionally, SWC emerged as a critical driver of variation in multiple traits, supporting its integration into the leaf economic spectrum for orchids in karst ecosystems. This study offers new insights into orchid adaptation in subtropical karst environments, with implications for plant resilience under changing climates.