engleski

How diatoms win: Life strategies of diatoms in the Northern Adriatic

The northern Adriatic Sea is a highly structured and shallow ecosystem. It is characterized by steep, spatiotemporal ecological gradients. These characteristics allow us sampling strategies with reasonably good spatiotemporal coverage both, across longitude and latitude as well as throughout the water column. The northern Adriatic hence is particularly suited for ecological observations of phytoplankton, here we can observe its behavior and succession as it travels through a multitude of ecological conditions while climate stays a constant. Growth of phytoplankton in the area is generally controlled by light, temperature and Phosphorous limitation, while nutrient availability is governed by the river Po, the largest freshwater input into the Mediterranean. The phytoplankton of the northern Adriatic is largely dominated by diatoms. To understand the in situ performance of marine planktonic diatoms, we here present the analysis of long term monitoring data on transects across the most pronounced ecological gradients. Our results demonstrate that the phytoplankton succession and growth is mainly governed by light availability, temperature and the species capability to cope with phosphorous limitation. In situ measurements demonstrated that the expression of alkaline phosphatase activity as a tool to access the organic phosphate pool is a key reaction of the phytoplankton community to phosphorous limitation. We then analyzed key species from the northern Adriatic phytoplankton in vitro with respect to their reaction to nutrient availability and phosphorous limitation. We characterized growth curves and morphological alterations. Additionally, we characterized nutrient uptake rates, lipids profiles, chlorophyll content and the expression of alkaline phosphatase activity as a reaction to phosphorous limitation. To further compare the expressed alkaline phosphatase activity, we characterized the dynamics of its expression across growth phases as well as the kinetic parameters of the enzyme activity. Combining all our results we formulated strategies for each examined species that explain how the respective species competes within the phytoplankton community for resources. Our results support the notion that success in competition for the limiting nutrient salt (phosphorous) as well as relative performance with respect to temperature and light availability explains the succession and composition of marine phytoplankton. Our results also demonstrate a high diversity of ecological niches in marine phytoplankton ultimately explaining the resulting biodiversity. Phylogenetic analyses of our results uncovered a surprisingly low phylogenetic restraint of the analyzed physiological adaptations and further helps understanding the biodiversity paradox of planktonic ecosystems.

phytoplankton ; Adriatic Sea ; diatoms ; APA ; P LIMITATION

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