Influences of water column nutrient loading on growth characteristics of the invasive aquatic macrophyte Myriophyllum aquaticum (Vell.) Verdc.
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Nuisance growth of Myriophyllum aquaticum has often been attributed to high amounts of nutrients. The uptake of nitrogen and phosphorus from sediments and their allocation have been documented in both natural and laboratory populations. However, nutrient loading to surface water is increasingly becoming an important issue for water quality standards. Aquatic macrophytes that develop adventitious roots may be able to survive through the uptake of water column nutrients. Our objectives for this study were to assess M. aquaticum growth when combinations of nitrogen and phosphorus were added to the water column. Mesocosm experiments were conducted where nitrogen (1.8, 0.8, and 0.4 mg l−1; high, medium, and low) and phosphorus (0.09, 0.03, 0.01 mg l−1; high, medium, and low) concentrations were paired and added to the water column. After 12 weeks, the combination of 1.80:0.01 N:P resulted in greater (P < 0.01) total biomass and greater biomass for all plant tissues. Total biomass at the 1.80:0.01 N:P combination was 53% greater than biomass at all other combinations. The yield response of M. aquaticum was a quadratic function of tissue nutrient content. Yield was positively (r 2 = 0.82) related to increasing nitrogen content, whereas a negative (r 2 = 0.89) relationship was determined for increasing phosphorus content. We propose the negative relationship is due to increased nutrient competition and shading by algae resulting in reduced M. aquaticum growth. Tissue nutrient content indicated that critical concentrations (1.8% nitrogen and 0.2% phosphorus) for growth were not attained except for nitrogen in plants grown in the 1.80:0.01 N:P combination. These data provide further evidence that M. aquaticum requires high levels of nitrogen to achieve nuisance growth. Survival through uptake of water column nutrients may be a mechanism for survival during adverse conditions, a means of long distance dispersal of fragments, or may offer a competitive advantage over species that rely on sediment nutrients.
KeywordsNitrogen Phosphorus Aquatic plant Parrotfeather Non-native Exotic
Funding for this research was provided by the Aquatic Plant Management Society and Aquatic Ecosystem Restoration Foundation through a graduate research grant, the United States Geological Survey Invasive Species Program under Award Number 08HQAG013908121105, and additional support through graduate student scholarships from the MidSouth Aquatic Plant Management Society and the Midwest Aquatic Plant Management Society. The authors would like to thank Dr. Patrick Gerard for assistance with statistical analyses. We thank Jimmy Peeples, Matt Gower, Alan Pryor, Thomas Hendrix, and other student employees for assistance setting up and harvesting the study. We also thank Dr. David Shaw, Dr. Eric Dibble, Dr. John Byrd, and Dr. Linda Nelson for providing comments on earlier versions of this manuscript. This manuscript has been approved for publication as Journal Article No. J-11922 of the Mississippi Agricultural and Forestry Experiment Station, Mississippi State University.
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