Effects of substrate nutrients on growth of threesubmersed aquatic plants

摘要

Nutrient studies with submersed plants were conducted on select invasive species in the 1970s and 1980s, but little research has been reported in this area in recent years. Additionally, there is a dearth of substrate and nutrient experiments that focuson native submersed plants, but these studies are needed to identify locations where these species may successfully be introduced as a component of aquatic restoration projects. These experiments were designed to obtain a better understanding of the effects of substrate nutrients on growth of submersed plants. There was no difference in growth of Illinois pondweed (Potamo-geton illinoensis Morong) and hydrilla [Hydrilla verticillata (L.f.) Royle] during an 11-wk study that evaluated the effects of controlled-release fertilizer with and without micronutri-ents. Other experiments compared the growth of Illinois pondweed, hydrilla, and southern naiad [Najas guadalupensis (Spreng.) Magnus] when plants were cultured with water-soluble fertilizers mixed in sand to simulate controlled-release fertilizers. Those studies revealed that optimum growth was achieved by Illinois pondweed at 25 to 150 mg nitrogen per kilogram of sand, by southern naiad at 75 mg nitrogen per kilogram of sand, and by hydrilla at 150 mg nitrogen per kilogram of sand. Growth of all three species decreased at substrate nitrogen concentrations of 450 to 500 mg nitrogen per kilogram of sand. Substrate phosphorus concentrations that produced optimum growth of southern naiad and Illinois pondweed were > 150 mg phosphorus per kilogram of sand, while maximum hydrilla growth was attained at 200 to 350 mg phosphorus per kilogram of sand. Illinois pondweed was not affected by the addition of potassium to the substrates until > 500 mg potassiumper kilogram of sand. At low nitrogen concentrations, Illinois pondweed growth was greatest with urea as the nitrogen source, followed by ammonium and nitrate. Highest biomass was produced when plants were fertilized with ammonium at total nitrogen concentrations of 100 and 400 mg nitrogen per kilogram of sand, compared to the other nitrogen sources.