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United States Department of Agriculture

Agricultural Research Service

Title: Root Size and Depth Distributions for Three Species of Submersed Aquatic Plants Grown Alone Or in Mixtures: Evidence for Nutrient Competition.

Authors
item SPENCER, DAVID
item Ksander, Gregory

Submitted to: Journal of Freshwater Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 31, 2004
Publication Date: March 1, 2005
Citation: Spencer, D.F., Ksander, G.G. 2005. Root size and depth distributions for three species of submersed aquatic plants grown alone or in mixtures: evidence for nutrient competition. Journal of Freshwater Ecology. 20(1):109-116.

Interpretive Summary: Aquatic plant roots are involved in nutrient uptake. Thus, root growth and distribution in the sediment have important consequences for a plant's competitive ability. We hypothesized that if plants were competing for nutrients then the spatial distribution and sizes of roots should change when competitors were present. We grew three species of aquatic plants in mixtures or alone in containers that were 39 inches tall by 18 inches in diameter. Four 2 inch diameter clear plastic tubes were mounted horizontally across the containers so that they were 1, 5, 10, or 20 inches below the surface of the sediment. We inserted a specialized video camera into each tube and recorded images at 21 locations along the top of each tube. Root length density and root diameters were determined. In two of three cases adding plants of another species changed the root depth distribution and increased the volume of soil occupied by roots. Smaller diameter roots were more abundant when plants were grown in mixtures. This implies that the plants adjusted to the presence of competitors by producing more roots capable of nutrient uptake. These results imply that competition for sediment-based nutrients occurred in these systems, and suggest that additional study may lead to increased understanding of aquatic plant competitive relationships.

Technical Abstract: Aquatic plant roots are involved in nutrient uptake. Thus, root growth and distribution in the sediment have important consequences for a plant's competitive ability. We hypothesized that if plants were competing for nutrients then the spatial distribution and sizes of roots should change when competitors were present. Stukenia pectinatus, Potamogeton nodosus, and Hydrilla verticillata (monoecious type) were grown in either monocultures or mixtures in PVC containers that were 1 m tall by 0.45 m diameter. The containers were filled (0.58 m) with modified UC Mix. Overlying this was 0.42 m of water. Four 5 cm diameter minirhizotrons were mounted horizontally across the containers so that they were 2.5, 12.5, 22.5, or 32.5 cm below the surface of the sediment. We inserted a specialized video camera into each minirhizotron tube and recorded images at 21 locations in each tube. Root length density and root diameters were determined. For two of three cases adding plants of another species changed the root depth distribution and increased the volume of soil occupied by roots compared to monocultures. The size distributions of root diameters were also influenced by the presence of competitors. Smaller diameter roots were more abundant when competitors were present. This implies that the plants adjusted to the presence of competitors by producing more roots capable of nutrient uptake. These results imply that competition for sediment-based nutrients occurred in these systems, and suggest that additional study may lead to increased understanding of aquatic plant competitive relationships.

Last Modified: 9/29/2014
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