Nitrogen limitation of photosynthesis and growth: Comparison across aquatic plant communities in a Danish Estuary (Roskilde Fjord)

Abstract

Abstract Dominance of different plant communities in coastal marine ecosystems changes predictably from large perennial benthic plants to small ephemeral macroalgae and pelagic phytoplankters during eutrophication. It is suggested that these changes result from a stronger nutrient limitation among the uni- and thin multi-cellular algae. This hypothesis is tested by in situ nutrient enrichment experiments in a shallow estuary during mid-summer when irradiance is high, nutrient availability, especially that of N, is low and, therefore, nutrient limitation should be most pronounced. Tissue-N, chlorophyll content, maximum photosynthetic rate (Pmax) and growth rate tended to increase following N-enrichment in the phytoplankton community and the two ephemeral macroalgae Ulva lactuca and Chaetomorpha linum. Although tissue-N and chlorophyll content also increased in the two perennial macrophytes Fucus vesiculosus and Zostera marina, N-enrichment had no significant effect on Pmax or growth rate. P-enrichment incr...