Biomass and nutrient allocation of sawgrass and cattail along a nutrient gradient in the Florida Everglades

Biomass and nutrient allocation in sawgrass (Cladium jamaicense Crantz) and cattail (Typha domingensis Pers.) were examined along a nutrient gradietn in the Florida Everglades in 1994. This north to south nutrient gradient, created by discharging nutrient-rich agricultural runoff into the northern region of Water Conservation Area 2A, was represented by three areas (impacted, transitional and reference). Contrasting changes of plant density and size along the gradient were found for communities of both species. For the sawgrass community, more small plants were found in reference areas, whereas few large plants were found in impacted areas. In contrast, for the cattail community, bigger plants were found in reference areas, and smaller plants were found in impacted areas. Both species allocated approximately 60% of their total biomass to leaves and 40% to belowground tissues. However, sawgrass biomass allocation to leaves, roots, shoot bases and rhizomes (65%, 19%, 11%, and 5%, respectively) was similar among the three areas. In contrast, cattail plants growing in reference areas showed higher root allocation (27.3%), but lower leaf allocation (51.5%) than those growing in impacted areas (14.6% and 65.8% for root and leaf allocation, respectively). Cattail had higher phosphorus concentrations than sawgrass in tissues associated with growth functions (leaves, roots and rhizomes). In contrast, sawgrass had higher phoshorus and nitrogen concentrations than cattail in tissues primarily associated with resource storage (shoot bases). From impacted to reference areas, for sawgrass, there was a decrease of leaf TP from 605 to 248 (mg/kg), root TP from 698 to 181 (mg/kg), rhizome TP from 1,139 to 143 (mg/kg), and shoot base TP from 5,412 to 400 to (mg/kg). For cattail, leaf TP decreased from 1,175 to 556 (mg/kg), root TP decreased from 1,100 to 798 (mg/kg), rhizome TP decreased from 1390 to 380 (mg/kg), and shoot base TP decreased from 2,990 to 433 (mg/kg). N/P ratios of sawgrass in reference areas were 27, 63, 38, and 50 for leaves, roots, rhizomes, and shoot bases, respectively, whereas in impacted areas they were 11, 21, 6, and 2, respectively. The greatest TP storage was found in impacted areas. Differences in seed output, seed number, and mean seed weight were found for both species as well. Each cattail flower stalk produced approximately 105 tiny seeds (0.048 ± 0.001 ,g) while each sawgrass flower stalk produced about 103 large seeds (3.13 ± 0.005 mg). These results suggest that phosphorus is a limiting resource in the Everglades and that the two species have different life history strategies. These data provide an ecological basis for making informed managament and planning decisions to protect and restore the Everglades.