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

ABSTRACT We hypothesized that if aquatic 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 polyvinylchloride containers. 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, and we inserted a specialized video camera in each minirhizotron tube and recorded root images at 21 locations in each tube. 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. Additionally, 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 impl...