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|Title:||Effects of sediment nitrogen availability and plant density on interactions between the growth of Hydrilla verticillata and Potamogeton americanus|
|Authors:||Aquatic Plant Control Research Program (U.S.)|
McCreary, Nancy J.
McFarland, Dwilette G.
Barko, John W.
|Publisher:||Environmental Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: This study examines the growth of Hydrilla verticillata (L.f.) Royle and Potamogeton americanus C. & S. on both nitrogen-poor and nitrogen-rich sediments and assesses the nature and degree of interspecific interactions between the two species. Extensive greenhouse experiments conducted from May through July 1989 employed sediments differing initially only in sediment nitrogen (fertilized containers: 0.21 ± 0.01 mg exchangeable N per gram dry sediment; unfertilized containers: 0.01 ± 0.00 mg exchangeable N per gram dry sediment). Species were grown monotypically, as well as in 50:50 mixtures, on each sediment type. Although shoot production did not differ between species in monoculture, shoot production in Hydrilla was diminished by 60 to 76 percent in the presence of Potamogeton. Likewise, canopy development for Hydrilla was reduced in mixtures compared to monocultures, but Potamogeton did not show a similar reduction in canopy. High sediment nitrogen increased canopy development by 50 percent in both species. Aboveground biomass for monotypically grown species was similarly low on unfertilized sediment (6 to 8 g per container). However, on fertilized sediment, aboveground biomass in Potamogeton (approaching 25 g per container) was significantly greater than in Hydrilla (approximately 15 g per container). Under both conditions of sediment fertility, Potamogeton, in the presence of Hydrilla, achieved at least 75 percent of its monotypic aboveground biomass, while Hydrilla in mixtures achieved less than 25 percent of the aboveground biomass it exhibited alone. Belowground biomass was twofold greater for both species on unfertilized sediment than on fertilized sediment, yet Potamogeton consistently allocated threefold greater biomass to belowground structures than did Hydrilla. In fertilized sediment treatments, exchangeable sediment nitrogen fractions were depleted by 94 to 96 percent in containers supporting Potamogeton or mixtures, but only 65 percent of exchangeable nitrogen pools was depleted in containers supporting Hydrilla. Patterns of interstitial-water nitrogen were similar to those of exchangeable nitrogen. Sediment fractions of both potassium and phosphorus remained relatively high, regardless of sediment nitrogen fertility or macrophyte species grown. Total plant tissue nitrogen content was an order of magnitude higher in plants grown on fertilized sediment, with Potamogeton consistently having a higher tissue nitrogen content than Hydrilla. As a measure of competitive ability, suppression coefficients calculated from biomass data for Potamogeton on unfertilized sediment exceeded those for Hydrilla by a factor of 4.64. Although Potamogeton still outcompeted Hydrilla, higher sediment nitrogen reduced Potamogeton's advantage to a factor of 2.86. Based on results of this study, it is postulated that Potamogeton should displace Hydrilla when sediment nitrogen is in short supply.
|Appears in Collections:||Technical Report|