Production-ecological analysis of a plant community dominated by Elodea canadensis michx

Abstract

The seasonal changes in biomass, mineral nutrient content in the plants, water and sediments, diurnal changes of oxygen and carbon dioxide concentrations in the water and light conditions were followed in a plant community dominated by Elodea canadensis Michx. in a shallow bay of a managed fishpond. The surface layers of mud were more acidic in the bay colonized by the Elodea community (pH 5.1) than in the open water of the pond, and a higher content of magnesium and a lower nitrogen content were found in the bottom sediments in the Elodea community. Substantial changes were observed in the biological and chemical oxygen demands, and nitrogen, phosphorus and potassium concentrations in the water. Diurnal changes in oxygen concentration, pH and vertical profiles of photosynthetically active radiation (PhAR) were followed in this plant community. The daily photosynthetic production of oxygen increased and decreased with the biomass of the macrophyte community. The maximum biomass was 450 g m −2 (dry mass) in the middle of August. The estimate of annual net production was about 500 g m −2. The ash content in dry mass ranged between 10 and 24% during the growing season. The growth-curve of the stand was constructed on the basis of 28 biomass samples taken between May and October, each from a 0.5-m 2 plot. The growth characteristics relative growth rate (RGR), crop growth rate (CGR), net assimilation rate (NAR) and chlorophyll index (CI) were calculated. A characteristic feature was the accumulation of biomass in the upper water layers. The light and pH dependences of photosynthesis were also measured in Elodea plant-segments to obtain data for the construction of a mathematical model of the oxygen and carbon dioxide régime in the stand.