Phytoplankton community growth in enrichment bioassays: Possible role of the nutrient intracellular pools

Examination of published experimental data showed that nutrient addition can sometimes inhibit growth rate of natural algal communities. Such reductions in algal growth might be due to toxic effects of some enrichments. This hypothesis could not however explain inhibitions following moderate additions of nitrate and phosphate. A new hypothesis is proposed to account for such ''unexplained'' results. It considers a limitation of algal community growth by several different resources. Experimental observations are consistent with resource competition determining the coexistence of several species competing for the same resources. Intracellular nutrient storage may reduce bioavailability of many resources involved in algal growth limitation. A simplified mathematical approach, derived from the DROOP growth model (1973), was developed to describe possible relationships between species diversity and algal community growth. Coexistence of several species competing for different resources might provide a partial buffer against large variations in algal community growth following nutrient enrichments.