Leaf anatomical traits determine the 18O enrichment of leaf water in coastal halophytes.

Anatomical adaptations to high‐salinity environments in mangrove leaves may be recorded in leaf water isotopes. Recent studies observed lower 18O enrichment (ΔL) of leaf water with respect to source water in three mangrove species relative to adjacent freshwater trees, but the factors that govern this phenomenon remain unclear. To resolve this issue, we investigated leaf traits and ΔL in 15 species of true mangrove plants, 14 species of adjacent freshwater trees, and 4 species of semi‐mangrove plants at five study sites along south‐eastern coast of China. Our results confirm that ΔL was generally 3–4‰ lower for mangrove species than for adjacent freshwater or semi‐mangrove species. We hypothesized that higher leaf water content (LWC) and lower leaf stomatal density (LS) both played important roles in reducing ΔL in mangroves relative to nearby freshwater plants. Both differences acted to elongate effective leaf mixing length (L) in mangroves by about 200% and lower stomatal conductance by about 30%. Péclet models based on both LWC and LS could accurately predict ΔL. Our findings highlight the potential species‐specific anatomical determinants of ΔL (or L), which has important implications for the interpretation of environmental information from metabolites produced by leaf water isotopes in palaeoclimate research. Mangrove forests evolve typical leaf structures to adapt to high‐salinity environments, and many of these adaptations may leave imprints in leaf water isotopes. Our comprehensive field study confirmed that the isotope enrichment of leaf water (ΔL) in mangroves were generally lower than those of the adjacent nonmangrove at multiple‐site and multiple‐species scales and that leaf anatomies play key roles in determining these differences in ΔL. The potential species‐specific anatomical determinants of ΔL based on a large pool of species can be incorporated into the leaf water model, which will have considerable potential applications not only for palaeoclimate reconstruction but also in distinguishing what kinds of plants with strong Péclet effect. [ABSTRACT FROM AUTHOR]