Studies on the successional mechanism of phytoplankton community by analyzing community metabolism.

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In the present study, the mechanism of phytoplankton community succession was studied based on the analysis of the temporal and spatial variations of the dependency of primary production on NH _4 regeneration and other environmental factors in Lakes Fukami-ike and Kizaki, and Mikawa Bay. Carbon isotope ratio of algal cells and their carbon and nitrogen uptake rates were employed as the measures to analyze the extent of algal growth limitation by environments.1. Carbon isotope discrimination values of algal cells in Lake Fukami-ike increased with water depth in parallel with the decrease of photosynthetic rates, suggesting the limitation of photosynthesis by decreasing light intensity. 2. In Mikawa Bay, the values of both photosynthetic rates and carbon isotope ratio of algal cells were high with their greater variation in July but lower values after September. Temporarily and spatially heterogenous supply of nutrients could account for frequent development of short span-algal blooms in July. 3. It was observed that the rates of NH _4-uptake and -regeneration in Lake Kizaki varied with season and with depth. The range of variation was smaller for the regeneration rate than uptake rate, suggesting a greater effect of environmental variation on the photosynthesis of larger algal species which resulted in the succession of phytoplankton community.