Abstract: The understory vegetation is a key component of subtropical forests closely linked to the structure and functional services of forest ecosystems. Long-term soil warming may alter leaf functional traits, affecting species diversity and community structure in the understory. Aim To investigate the effects of long-term soil warming on leaf structure of dominant shrubs of subtropical natural forest. Methods This study based on an eight-year in-situ soil warming(+4 ℃)experiment, examined the effects of long-term soil warming on the leaf structure of three dominant shrubs (Ardisia lindleyana, Mussaenda pubescens and Ilex dasyphylla) under warming and control treatments in a natural forest. Important findings The results indicated that long-term soil warming affected the stomatal and anatomical structure of leaves, leading to a decrease in stomatal density and leaf thickness, along with an increase in specific leaf area. Specifically, the thickness of the palisade and spongy tissue in large shrubs significantly decreased, while the thickness of the lower epidermis increased, likely due to the proliferation of dense epidermis trichomes on leaves induced by soil warming. In subshrub, both epidermis and palisade tissue thickness decreased, while the spongy tissue thickness increased, reflecting an adaptive strategy to enhance water retention capacity and buffer water pressure of the leaves. In ground-lying shrubs, the thickness of the upper epidermis and spongy tissue decreased, while palisade tissue thickness increased, likely enhancing water transport efficiency and drought tolerance of the leaves.The above results suggest that long-term soil warming has significantly impacted the water use efficiency of understory shrubs in subtropical forest. These findings provide scientific insights into the response mechanisms of understory shrub structure to global warming, contributing to biodiversity conservation.

Key words: warming, leaf structure, understory shrubs