Elevational trends in leaf size of Campylotropis polyantha in the arid Minjiang River valley, SW China

• We examined changes in leaf size and structure of a leguminous shrub with elevation.
• Leaf size increased with increasing elevation in the arid Minjiang River valley.
• Spongy mesophyll and epidermis cell expansion accounted for the increased leaf size.
• Water related factors controlled variations in leaf size across elevations.

Leaf traits are determinants of plant performance in ecosystems. The arid Minjiang River valley offer optimal opportunity to reveal climate-leaf function relationship because steep climatic gradients (e.g., dryness and high temperature decreased with elevation). We investigated the leaf size and structure of Campylotropis polyantha occurring in five 80–100 m elevational bands from 1650 m to 2200 m in this arid valley. Plants growing at higher elevations had larger leaves, epidermal cell and leaf thickness with thicker spongy mesophyll and epidermis, but had lower epidermal cell density and cutin thickness. These variations in leaf size and spongy mesophyll as well as cutin and total leaf thickness were mainly associated with annual precipitation and soil water content, while epidermal cell dimensions were associated with temperature. We conclude that water-related factors are the main mechanisms underlying leaf variations across elevations. High air temperature during the growing season imposes multiple stresses on plants at low elevations. The larger leaf size of high elevation plants is related more to their larger spongy mesophyll and epidermal cell sizes than to their larger palisade cell. These results provide a new understanding of functional ecology and the anatomical plasticity of plants in varying environments with different elevations.