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Ecological Characteristics of the Rhizosphere Microflora of Myriophyllum heterophyllum¹

ABSTRACT

Bacterial populations associated with the rhizosphere and rhizoplane of Myriophyllum heterophyllum were studied in the littoral zone of a soft water, mesotrophic lake during the period of active growth of the plants. The composition of the rhizoplane community was found to differ distinctly from that of the adjacent sediments, while the population density of heterotrophic bacteria in each environment did not differ significantly. Higher populations of bacteria capable of nitrate reduction and ammonification did occur in the rhizoplane. Nitrogen-fixing (acetylene-reducing) activity was significantly higher on the root surface than in the sediment. The intensity of the rhizosphere effect was apparently related to the bimodal productivity cycle of Myriophyllum communities. Higher populations of bacteria involved in nutrient transformations in the rhizoplane suggest that these have a greater potential for supplying aquatic plants with readily available nutrients than do the nonrhizosphere populations.

Key Words: water milfoil • rhizoplane • microbial populations • transformation

¹ Contribution from the Dep. of Environ. Sci., Univ. of Massachusetts, Amherst, MA 01003. The research was supported by the Agric. Exp. Stn., Univ. of Massachusetts, and by grant from the Office of Water Res. and Technol., U.S. Dep. of the Interior.

² The authors are formerly a Graduate Research Assistant and Assistant Professor, Biology Dep., Univ. of Bridgeport; and Professor, Dep. of Environ. Sci., Univ. of Massachusetts, respectively.

Received for publication November 27, 1978.