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Abstract:
During a 10-month study in Plusssee Si, N, and light were found as potentially limiting resources for phytoplankton growth rates. Therefore, three ratios of essential resources (Si : N, Si : light, N : light) and one ratio of substitutable resources (nitrate: ammonium) were compared to changes in species composition to test the hypothesis that the seasonal change of phytoplankton species composition was a response to changing resource ratios. The relationship was analyzed by a rank correlation analysis between the relative contribution of individual species to total biomass and resource ratios. Allowance was made for time lags between changes in resource ratios and changes in relative biomass. Of 16 species, 14 showed a significant response to at least one resource ratio. Time lags ranged from 0 to 6 weeks. Most species seemed to be favored either by minimal or maximal ratios; optimal ratios in the middle of the range were rare.
