Plant size is closely linked to its leaf trait characteristics, which are essential for determining its form and function. These relationships constitute a fundamental component of the global spectrum of plant diversity. Despite this, the size-trait relationships in coastal mangroves have often been overlooked, with a common assumption that they would mirror those found in terrestrial tropical trees. However, recent studies have begun to challenge this assumption, revealing unique adaptations and trait variations in mangroves that are influenced by their specific environmental conditions, such as salinity and nutrient availability.

In this research, we investigated the leaf structural traits, plant height, and diameter at breast height or basal height (DBH) of 10 shrub and tree species. This study was carried out along an intertidal gradient within a mangrove forest located in Southeast China.

We found that leaf traits differed significantly between shrubs and trees in their response to intertidal gradients, indicating that different species have evolved specific adaptations to thrive in their respective intertidal zones. This insight can help us decipher the selective pressures that have shaped trait evolution. Among all species, leaf carbon (C) economics (leaf dry mass content, leaf mass per area, and leaf density) decreased significantly with increasing plant height and DBH. For each growth form and intertidal zone, the relationships between plant size (height or DBH) and leaf C economics traits were consistent with those in the pooled dataset.

Our study reveals that mangrove plants exhibit size-related adjustments in leaf C economic strategies, indicating that plant size potentially acts as a proxy for the “slow-fast” continuum of plant performance. This discovery is pivotal for advancing our understanding of plant functional ecology and for enhancing the precision of global C cycle models, which are highly responsive to perturbations in atmospheric CO₂ and climate change.