Phosphorus–Limited Growth Dynamics of Lotic Periphytic Diatom Communities: Areal Biomass and Cellular Growth Rate Responses

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Abstract
Three long-term phosphate enrichment experiments were conducted at the Experimental Troughs Apparatus (EXTRA), South Thompson River British Columbia to determine the relationship between external orthophosphate (PO43−) concentration and peak areal biomass (PB) of periphytic diatom communities. Levels of PO43−which saturated PB were two orders of magnitude greater than those required to saturate specific growth rates in thin film periphyton communities of similar taxonomic composition. With PO43−additions between 0.1 to 1.0 μg P∙L−1, PB responded in a hyperbolic fashion, initially increasing rapidly, then showing signs of saturation PB continued to increase in a slow, linear manner above 1.0 μg P∙L−1. Maximum PB (PBmax) was calculated to occur at ca. 28 μg P∙L−1. At higher PO43−concentrations (> 30–50 μg P∙L−1) PB was no longer P limited. Below the saturation point, PB was approximated by a log–linear function of PO43−.