Abstract: Mangrove forests often display distinct community succession and zonation patterns in the intertidal zone, whereas differences in growth strategies among different mangrove species remain incompletely understood. To address this gap, the present study was conducted in the Gaoqiao Mangrove National Nature Reserve, aiming to examine variations in functional traits and resource trade-offs of mangrove plants distributed at different intertidal positions along the elevation gradient. The results demonstrated that with increasing elevation, along the succession sequence from the pioneer Avicennia marina community, the transitional Aegiceras corniculatum community, to the late-successional Bruguiera gymnorrhiza community, stomatal density (SD), the effective quantum yield of photosystem II [Y(II)] and the maximum quantum yield of photosystem II (Fv/Fm) gradually decreased, whereas non-photochemical quenching (NPQ) showed a continuous increasing trend. These changes implied that the photosynthetic strategy of mangrove plants shifted toward conservatism. In terms of morphological structure and construction cost, late-successional species adopted a more conservative resource-investment strategy compared with pioneer species, as reflected by the declined specific leaf area (SLA), and elevated leaf thickness (LT) and leaf tissue density (LTD). Meanwhile, leaf structural carbon (SC) content and the C:N ratio both increased, indicating a conservative shift in carbon allocation strategy as well. Additionally, there was a significant coordination between leaf and root functional traits. Late-successional species developed a relatively conservative root system, featured by greater root diameter (RD), higher root tissue density (RTD) and lower specific root length (SRL). Collectively, within the framework of the leaf-root economics spectrum, this study revealed that mangrove functional traits exhibit a transition from resource-acquisitive to resource-conservative strategies with increasing elevation. These findings not only deepen the understanding of the adaptation mechanisms of mangrove plants to the intertidal zone, but also provide theoretical support for the conservation and restoration of mangrove ecosystems.

Key words: Mangrove forests, Succession, Functional traits, Resource trade-offs, Gaoqiao Nature Reserve