Functional traits and elemental uptake in urban coastal wetland plants under variable hydrology and edaphic conditions

Coastal wetland plants are adapted to fluctuating and often harsh environmental conditions. In urban wetlands, plant functional groups display a range of physiological and morphological strategies in response to abiotic stress. However, differences amongst functional groups and the coordination between leaf traits, nutrient status, and environmental variation remain poorly understood in these systems. This study evaluates trait-environment relationships in three dominant species-<i>Acrostichum danaeifolium</i> (fern), <i>Dalbergia ecastaphyllum</i> (nitrogen-fixer shrub), and <i>Laguncularia racemosa</i> (halophytic tree)-across contrasting wetland soils and seasonal periods in a tropical urban reserve. We measured leaf gas exchange, specific leaf area (SLA), nutrient content, and photosynthetic nitrogen use efficiency (PNUE) across wet and dry periods on two soils in the Ciénaga Las Cucharillas Natural Reserve, Puerto Rico. Soil bulk density, salinity, and bioavailable nutrients were also quantified. Multivariate analyses (principal component analysis) were used to assess trait covariation. Species differed significantly in morphological and physiological traits. <i>L. racemosa</i> exhibited the highest assimilation rates, PNUE, and succulence, consistent with an acquisitive resource-use strategy. In contrast, <i>A. danaeifolium</i> showed high SLA and water content but conservative stomatal behaviour and lower PNUE, indicative of a shade-tolerant strategy. <i>Dalbergia ecastaphyllum</i> maintained high water-use efficiency during the dry period and exhibited adaptive responses to slightly and moderate saline soils, indicative of a nutrient acquisitive strategy. Soil type influenced elemental availability but had limited effects on photosynthetic rates. Trait differentiation amongst coexisting wetland species reflects contrasting resource-use strategies shaped by both seasonality and soil environment. These findings underscore the functional diversity and adaptive capacity of tropical wetland vegetation under urban and hydrological pressures.