Frontiers in Marine Science (Jun 2014)
Response of prokaryotic and eukaryotic community structure to inorganic and organic nutrient additions in a eutrophic coastal ecosystem
Abstract
Coastal oceans are known to receive increasing inputs of reactive N as a result of the anthropogenic alteration of N cycling at the global scale, which may greatly alter nutrient supply to microbial plankton communities. The influence of nutrient availability (mainly inorganic N and P and/or organic C) on species composition has been widely reported for both eukaryotes and prokaryotes. The Ría de Vigo is a eutrophic embayment located in the coastal system of the NW Iberian Peninsula. Previous studies in the area revealed a highly variable response of microbial plankton to nutrient additions, a strong stimulation of phytoplankton growth after inorganic (N and P) and organic (C and N) nutrient addition and a strong carbon limitation of bacterial activity. To gain understanding on the effect of nutrient inputs on the functioning of this coastal ecosystem, the short-term effects of inorganic N and P (nitrate, ammonium, phosphate) and organic C and N (glucose, amino acids) inputs, added separately as well as jointly, on eukaryotic and prokaryotic community composition were studied in microcosm experiments conducted under contrasting hydrographic conditions. Changes in microbial diversity were analyzed by ARISA (automatic rRNA intergenic spacer analysis) and two sets of primers specific for bacteria and eukaryotes. The results obtained in these experiments showed that changes in microbial communities were clearly determined by the initial microbial assemblage. Changes in prokaryotic and eukaryotic community composition were closely related to changes in metabolic rates. In contrast to previous observations, prominent changes in bacterial community composition occurred only after inorganic and organic nutrient additions, which suggest a C and P co-limitation of bacteria during the sampling periods. Major eukaryotic community composition changes were observed in response to inorganic additions.
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