Photosynthetic responses of 15 phytoplankton species to ammonium pulsing

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Abstract
In a series of short-term experiments on marine phytoplankton no evidence was found that transient exposure to high NH4+ concentration led to suppression of initial photosynthesis in 13 spp. previously grown to steady state under NH4+-limitation in continuous culture. Under similar conditions up to 60% initial suppression of photosynthesis in the chlorophyte Nannochloris sp. and up to 32% suppression in the prasinophyte Platymonas sp. were found. Recovery followed and was up to 90% complete by 60 min. These results point toward rather diverse modes of coupling between transient CO2 fixation and NH4+ uptake, but are consistent with an earlier conclusion that rapid NH4+ uptake, but relatively undisturbed photosynthesis is the common response of marine phytoplankton exposed to ephemeral patches of NH4+ in the pelagic environment.