Abstract: The relationship between leaf anatomical characteristics and environmental adaptability in the endangered mangrove Lumnitzera littorea, a first-class nationally protected plant in China, remains poorly understood. In this study, we collected L. littorea leaf samples from three restoration sites: Dongzhaigang National Nature Reserve in Haikou, Xincun Port in Lingshui County, and Chitian Village in Lingshui County, Hainan Province. We measured nine plant functional traits at the cellular and tissue levels, including leaf thickness (LT), cuticle thickness of upper epidermis (CTUE), cuticle thickness of lower epidermis (CTLE), and thickness of upper epidermis (TUE). By analyzing functional traits correlations with soil factors, we elucidated the mechanisms underlying the species’ adaptation to saline environments. The results showed that leaf structure of L. littorea from the three sites was similar. Specifically, the upper and lower epidermal cells were closely arranged, with the cuticles distributed outside the epidermal cells and the palisade and spongy tissues distributed inside the epidermal cells. However, there were differences in the quantitative characteristics of leaf structure among the three sites. The leaf thickness (1472.78 μm), upper and lower cuticle thickness (3.83-8.12 μm), palisade tissue thickness (228.79 μm), and spongy tissue thickness (1271.63 μm) in Xincun Port were significantly higher than those of other two sites, while the ratio of palisade tissue to spongy tissue was significantly lower than that of Dongzhaigang and Chitian Village. The compactness of leaf structure was the highest in Chitian Village (0.28), and the porosity of leaf structure was the highest in Xincun Port (0.84). Results of the principal component analysis (PCA) revealed that soil total phosphorus was the primary factor influencing leaf structure in Dongzhaigang, soil microbial biomass carbon and nitrogen were the dominant factors in Xincun Port, while soil organic carbon and total potassium constituted the major influencing factors in Chitian Village. These results demonstrate habitat-specific trade-offs in leaf structural characteristics of L. littorea for adapting to environmental variations.

Key words: Lumnitzera littorea, leaf structure, anatomical structure, ecological adaptation, ex-situ restoration