Understanding stoichiometric mechanisms of nutrient retention in wetland macrophytes: stoichiometric homeostasis along a nutrient gradient in a subtropical wetland.

Nutrient homeostasis relates ambient stoichiometric conditions in an environment to the stoichiometry of living entities of that ecosystem. Plant nutrient sequestration in wetland ecosystems is a key process for downstream water quality. However, few studies have examined stoichiometric homeostasis of aquatic vegetation despite the importance of stoichiometry to plant nutrient uptake efficiency. This study investigated stoichiometric homeostasis of dominant emergent and submerged aquatic vegetation (EAV and SAV, respectively) within two treatment flow-ways of Everglades Stormwater Treatment Area 2 (STA-2). These flow-ways encompass a large gradient in plant nutrient availability. This study hypothesizes that wetland vegetation is homeostatic relative to ambient nutrients and consequently nutrient resorption does not vary along the nutrient gradient. We developed a framework to investigate how vegetation uptake and resorption of nutrients contribute separately to homeostasis. Overall, we determined that the wetland vegetation in this study was non-homeostatic with respect to differential uptake of nitrogen (N) versus phosphorus (P). In EAV, P resorption was relatively high and N resorption was moderate, and resorption efficiency did not vary significantly along the gradient. In separating the proportional contribution of resorption and uptake to the degree of homeostasis, resorption did not affect overall homeostatic status in EAV.