Nutrient Effects on Stand Structure, Resorption Efficiency, and Secondary Compounds in Everglades Sawgrass

Abstract

Long‐term studies along a 30‐yr nutrient‐enrichment gradient in the northern part of the subtropical Everglades fen allowed us to assess the effects of nitrogen (N) and phosphorus (P) additions on plant community structure and chemical qualities of wetland plants. Areas in the highest P‐enriched zones (>1000 mgP/kg), once dominated by open‐water sloughs and surrounding monocultures of sawgrass (Cladium jamaicense, a stress‐tolerant low‐nutrient‐status species), are now dominated by cattail (Typha domingensis, a competitive, high‐nutrient‐status species). Areas of moderate (750–500 mg/kg) and low (<500 mg/kg) P soil concentrations have maintained their original plant composition. Analysis of nutrient‐use efficiency indicates that sawgrass is highly efficient in nutrient resorption and nutrient proficiency, but this efficiency decreases at high soil P concentrations. Both indices indicate that suboptimal concentrations of P, which limit growth and optimize retention of P within the plant, exist in the Everglades. This information, when coupled with the low levels of P found in the plants, soil, and pore water of the unenriched portions of the Everglades, indicates that this ecosystem is extremely P limited. High molar N:P leaf ratios suggested P limitations for sawgrass at unenriched sites, but not in highly enriched areas. Intermediate P loadings resulted in either N or P limitations. Increased leaf P concentrations correspond to decreased phenolic content of sawgrass leaves, suggesting that this species’ metabolic growth response follows the carbon–nutrient balance hypothesis of decreased production of phenolics with increased nutrient supply. Concomitant with decreased foliar phenolic content at high P enrichment was an increase in herbivory and fungal infections.

Phenolic content and growth of wetland macrophytes: Is the allocation to secondary compounds driven by nutrient availability?

“…Apparently, even the low P addition was enough to prevent P limitation at low and medium N. The prediction of a negative relationship between phenolic concentration and growth was confirmed for both species from both environments (greenhouse and marshes). Similar findings were reported for Cladium jamaicense in the Florida Everglades (Richardson et al 1999). Plants growing in the P-enriched areas had much higher biomass while containing only half of the concentration of phenolics found in the plants from Plimited sites.…”

“…According to my predictions, both species, TD and EC, grew larger and denser in marshes with a higher concentration of P in the sediments, which is not surprising in a system that is generally P-limited (Rejmánková and Komárková 2000). In a similar wetland system, the Florida Everglades, a sedge, Cladium jamaicense, was reported to grow significantly better in P-enriched areas than in P-limited sites (Richardson et al 1999). The lack of a response to N found in the Belize dataset can be explained by the fact that P limitation overrides any potential effect of higher N content in sediments (Rejmánková and Snyder 2008).…”

“…EC is a species well adapted to growth in nutrient-(particularly P-) limited marshes. On the contrary, TD prefers more nutrient-rich sites and can grow very fast when notlimited by nutrients (Rejmánková et al 1996;Richardson et al 1999). The results did not confirm my prediction.…”

“…Their growth and response to nutrient increase have been well described (Craft et al 1995;Rejmánková et al 1996;Richardson et al 1999;Rejmánková 2001;. My main question was: How do growth and phenolic compounds of these two species respond to different levels of nitrogen and phosphorus?…”

Recent Changes in Soil Total Phosphorus in the Everglades: Water Conservation Area 3

“…Unlike the nutrient concentrations in the water column that are highly variable in time (Reddy, White, Wright, & Chua, 1999), nutrient concentrations in Everglades soils are integrators of long-term environmental conditions Craft & Richardson, 1997;Richardson, Ferrell, & Vaithiyanathan, 1999;King, Richardson, Urban, & Romanowicz, 2004). Furthermore, nutrient inputs to Everglades wetlands are primarily stored in the peat, as the vegetation represents only a shortterm nutrient sink (Craft & Richardson, 1993a;Newman et al, 1997).…”