Where wetlands receive urban runoff, Typha spp. and other invasive plants often displace the native vegetation. We tested the ability of nutrients (N and P) to increase vegetative growth of T. × glauca (a hybrid of T. latifolia and T. angustifolia). In the greenhouse, 17 treatments revealed that T. × glauca required both N and P for growth, and total leaf length was most stimulated where a higher proportion of P was added (7N:1P vs. 14N:1P, with N constant and P changed), regardless of concentration (the High treatment was 4× the Low treatment). In Gardner Marsh (Madison, Wisconsin, USA), we set up 28 plots (1 × 6 m) that bisected the boundary between sedge meadow (graminoids) and T. × glauca, and we added a common lawn fertilizer (9N:1P:4K) at high (62.5 g/m2), medium (31.3 g/m2), low (15.6 g/m2), and control (0 g/m2) rates on five dates, with n=7 plots/treatment. After one growing season, fertilizer addition increased T. × glauca ramet density, height, and biomass, especially where the sedge meadow graminoids were initially dominant. Aboveground biomass of T. × glauca in the high nutrient addition treatment (1029 ± 256.1 g/m2) was more than double that for control plots (431 ± 80.52 g/m2) overall, with the greatest percent increase in sedge meadow subplots. In contrast, native graminoids (mostly Carex spp.) did not respond to treatment, either in biomass or percent cover. Typha × glauca allocated nutrients to both growth and storage, as indicated by higher N and P concentrations in leaves, shoot bases, and rhizomes in plots with high nutrient addition. Because fertilizing the marsh enhanced the shoot growth of T. × glauca but not native graminoids, and because the 7N:1P treatment stimulated growth in the greenhouse, we suggest that wetland managers focus on reducing P inflows to urban wetlands. Fertilizer additions below those recommended by the manufacturer for new lawns (5× that of our highest treatment) should be more economical and have fewer impacts on receiving wetlands.
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Vol. 22 • No. 3