Frontiers in Marine Science (Jul 2014)
Does B12 vitamin limit phytoplankton growth in the new Iberian Peninsula?
Abstract
The effects of increasing nutrient inputs entering to oceanic and coastal environments on primary producers are hardly predictable. Phytoplankton responses to nutrient supply depend on the autotrophic-heterotrophic coupling and a profound understanding of this interaction is required to describe response patterns. A series of microcosm experiments were carried out to assess the response of primary producers to nutrient amendments and to elucidate the role of B-vitamins on phytoplankton growth in coastal waters off the NW Iberian peninsula. Surface autotrophic microbial populations were monthly collected and exposed to known nutrient concentrations and incubated under in situ light and temperature conditions. The experimental addition treatments included: a) inorganic nutrients (nitrate, ammonium and phosphate); b) B12 vitamin (cobalamin) and c) inorganic nutrients and cobalamin. On two occasions, four additional treatments were included: d) organic nutrients (glucose and amino acids); e) a combination of inorganic and organic nutrients; f) organic nutrients and cobalamin; g) inorganic and organic nutrients plus cobalamin. Amendment experiments lasted 4 days. Samples were collected every 24h for Chlorophyll-a concentration, pico- and nanoplankton abundance and heterotrophic bacterial abundance determination. Our results suggest that phytoplankton growth is co-limited by inorganic nutrients and B12-vitamin. This co-limitation varied along the study period likely related to changes in community composition and ambient nutrient and B-vitamins concentrations.
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