engleski

Pseudo-nitzschia: the physiology of success in a highly structured and dynamic phytoplankton ecosystem

The northern Adriatic is a very convenient ecosystem to observe phytoplankton under a variety of different conditions. Steep gradients of nutrient concentration/ availability in this shallow basin allow the observation of the very same species under changing nutrient regimes on small temporal and spatial scales. The genus Pseudo-nitschia is among the most abundant and most frequent diatoms in the northern Adriatic phytoplankton community over the last four decades. After studying in situ behaviour of this genus along the aforementioned gradients, we set out and isolated key species for in vitro experiments, where we analyzed their reactions to contrasting nutrient regimes. In earlier studies, we found that alkaline phosphatase extracellular activity as well as membrane lipidremodeling are major reactions of phytoplankton to phosphate limitations. However, each species is using those functions in its own way to ensure survival and success within the phytoplankton community. Having identified phosphate limitation as a major shaping factor, we here present how harmful algae species of the genera Pseudo-nitzschia ensure successful competition within the phytoplankton community. Here we report data on species-specific growth rates under different nutrient regimes, phosphate uptake rates, alkaline phosphatase activity, localization and activation patterns and characteristics of alkaline phosphatase activity in four Pseudo-nitzschia species regularly occurring in the basin. Our results demonstrate a high interspecific variation in metabolic responses to phosphate limitation in sympatric congeneric species. The ecological significance and function appears hence to be defined on the species level andappears far from homogeneous within genera.

diatoms ; alkaline phosphatase ; northern Adriatic ; phosphorus limitation

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