Light and Nutrients in the Control of Aquatic Plant Community Structure. I. In Situ Experiments

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Abstract
(1) Maximum summer biomass and morphology of Potamogeton praelongus, Vallisneria americana and Potamogeton robbinsii were influenced by both sediment composition and irradiance when plants were grown in Lake Memphremagog, Quebec-Vermont, at depths of 1.5, 2 and 3 m, in buckets containing mixtures of fertile sediment (100%, 30%, 10%) and sand (0%, 70%, 90% respectively). (2) While all species attained maximum biomass and morphological diversity at 1.5 m in 100% fertile sediment and minimum biomass in the least fertile sediment, the effects of sediment composition and irradiance on growth differed between the species. (3) Biomass of the erect P. praelongus was primarily determined by sediment composition whereas the biomass of the bottom-dwelling P. robbinsii was largely determined by irradiance; the intermediate, rosette-form, V. americana, showed an intermediate response. (4) Sediment and irradiance effects on these species are consistent with their growth form, suggesting that the natural distribution of submerged aquatic plant species is related to plant growth form.