Photosynthetic responses of 15 phytoplankton species to ammonium pulsing

Abstract

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