Red mangrove (Rhizophora mangle) advancing through a saltwater-freshwater ecotone demonstrates a coordinated leaf trait response to environmental resource and stress

<title>Abstract</title> <p> The mangrove <italic>Rhizophora mangle</italic> L. has encroached into subtropical freshwater wetlands in the last few decades while negotiating variable landscapes. We characterized variation in <italic>R. mangle</italic> leaf traits related to leaf economics, water use, and plant defense across a gradient of encroachment in the Florida Everglades to assess whether <italic>R. mangle</italic> demonstrates a coordinated response to multiple resource and stress factors as it expands its range. Through this approach we determined the strongest environmental drivers of <italic>R. mangle</italic> trait variation among phosphorus availability, water salinity, flooding depth, and hydroperiod. We then interpreted what this variation means for plant productivity and ecosystem services provided. Analysis of leaf area, specific leaf area (SLA), stomatal density, stomatal size, leaf total nitrogen (TN), leaf total phosphorus (TP), leaf carbon isotope ratio (δ ¹³ C), and leaf total phenolic concentration showed that <italic>R. mangle</italic> trait response was aligned with differences in water depth, hydroperiod, and soil TP, but not with pore water salinity, a classic stress agent. <italic>R. mangle</italic> showed increased SLA and TP, typical of more productive plants, with increased soil phosphorus – the limiting nutrient in Everglades ecosystems. A limited coordination between water use and leaf economics traits was suggested by the negative correlation of δ ¹³ C, which can serve as a metric of stomatal control, with both SLA and leaf TP. Our findings suggest that local variation in soil phosphorus, water depth, and hydroperiod will drive the characteristics of and ecosystem services provided by <italic>R. mangle</italic> as it encroaches into freshwater wetlands. </p>