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

通过对富上湖、木崎湖和三川湾浮游植物群落演替的时空变化特征分析，探讨了浮游植物群落演替的机制。以藻类细胞碳同位素比值及其碳氮吸收速率为指标，分析了环境对藻类生长的限制程度。富上样湖藻类细胞的碳同位素辨别值随水深的增加而增加，与光合速率的降低平行，表明光强的降低限制了光合作用。2. 三川湾藻类细胞光合速率和碳同位素比值均较高，7月变化较大，9月以后变化较小。营养物质供应的时空异质性可能是7月份藻华频繁发生的原因。结果表明，木崎湖的NH - 4吸收和更新速率随季节和深度的变化而变化。再生速率的变化幅度小于吸收速率，表明环境变化对大型藻类光合作用的影响更大，导致了浮游植物群落的演替。

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.