EFFECTS OF HYDROLOGY AND NUTRIENTS ON SEEDLING EMERGENCE AND BIOMASS OF AQUATIC MACROPHYTES FROM NATURAL AND ARTIFICIAL SEED BANKS

In greenhouse experiments we examined the effects of water depth and nutrient addition on seedling emergence from natural and artificial seed banks and biomass of emergent aquatic macrophytes. A natural seed bank in which seed densities varied (variable seed density experiment) and an artificial seed bank in which seed densities were fixed (fixed seed density experiment with Polygonum lapathifolium and Asclepias incarnata) were investigated. Seedling emergence and aboveground dry weight were measured in moist and submerged soils with four nutrient treatments: no addition (control), nitrogen addition, phosphorus addition, and nitrogen-phosphorus addition. In the variable and fixed seed density experiments, emergence was higher in moist soil but did not increase with any nutrient addition. In the variable seed density experiment, biomass increased with nitrogen addition in both moist and submerged soils. In the fixed seed density experiment, biomass increased primarily with nitrogen addition in submerged soil. Thus, our findings suggest that hydrology influences seedling emergence and that nutrient availability controls biomass in aquatic macrophytes.