Role of DOP on the alkaline phosphatase activity of size fractionated plankton in coastal waters in the NW Mediterranean Sea (Toulon Bay, France)

The particulate material was fractionated into 5 size classes (>90 mu, 50-90 mu, 6-50 mu, 1-6 mu, and <1 mu). DOP was analysed as easily (DOPh, DOPpa) and less easily hydrolysable compounds (DOPox). Based on Vmax, 94% of the high affinity AP activity was due to <50 mu cells and 77% to <1 mu cells. 83% of the low affinity activity was due to >90 p. cells. The high affinity activities were negatively correlated with DOP for the <50 mu classes. These correlations came mostly from DOPox. They were more significant when NO3 + NO2 concentrations were high, when DIP concentrations were low and when N/P ratio was >10. At lower N/P ratios, AP was more significantly correlated with DIP. The low affinity activities showed significant negative correlation with DIP and with DOP and DOPox for the >90 mu class. The inhibition of AP activities by DOPox may originate from stable compounds interfering with DIP for the control of AP synthesis. (C) 2017 Elsevier Ltd. All rights reserved.