Exogenous nutrient inputs restructure phytoplankton community and ecological stoichiometry of Eastern Indian Ocean

Exogenous nutrient inputs increasingly impact the structure and function of marine food weds through abiotic and biotic ways. The influence of nutrient inputs from atmospheric depositions and intermediate seawater supply on the phytoplankton growth and stoichiometry was studied in the Eastern Indian Ocean through multifactorial mesocosm experiments. Our results indicate that nitrogen inputs from atmospheric deposition and hydrodynamic processes did not only promote chlorophyll a biomass (5.3-58.52 mu g.L-1) to increase the photosynthetically fixed carbon content but also generate a regime shift from picophytoplankton cyanobacteria to microphytoplankton diatom indicated by high relative abundance of microphytoplankton (>50%). These alternations of nutrient status and phytoplankton community structure reduced biodiversity of marine ecosystems (N-cultures, 0.18 to 0.56; control, 0.63) and generated the attendant C/N ratio of 5.6 +/- 0.2 in cultures with nitrogen addition that was significantly lower than cultures with only phosphorus or iron addition. These results provide a thorough insight about the influence of nutrient inputs on marine biogeochemical cycle. Considering the universality of phytoplankton community alteration induced by exogenous nutrient inputs, integrating community compositions with phytoplankton stoichiometry may be helpful for clarify mechanisms of environment events impacting marine food weds.

Automated summary

The external nutrient inputs from atmospheric deposition and hydrodynamic processes not only promoted chlorophyll a biomass increase and generated a shift in phytoplankton community structure, but also reduced biodiversity in marine ecosystems. The C/N ratio in cultures with nitrogen addition was significantly lower than cultures with only phosphorous or iron addition. These results provide insights into the influence of nutrient inputs on marine biogeochemical cycles.