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Rezumat articol ediţie STUDIA UNIVERSITATIS BABEŞ-BOLYAI
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Rezumat: The identification of environmental barriers that govern species distribution is a fundamental concern in ecology. Salt was previously identified as a major transition boundary for micro- and macroorganisms alike, selecting for organisms adapted to this environmental stressor and probably also preventing their dispersal. The salinities causing species turnover in protistan communities, however, remained unknown. We analysed protistan plankton community structures in various salt ponds from different geographic regions. Salinity in these habitats ranged between 4 to >40%. Partitioning of diversity pointed to a niche differentiation, suggesting distinct salinity classes defining the boundaries for protistan community turnover. Regardless of their geographic origin, protistan communities in these salinity categories displayed different taxonomic memberships. Laboratory experiments using halophile ciliates were conducted to investigate physiological constraints for the observed protistan community turnover in hypersaline waters. Using proton nuclear magnetic resonance spectroscopy, the use of two compatible solutes to combat high-salt conditions could be shown, and, furthermore, significant positive correlations of intracellular concentrations of the compatible solutes and external salinity could be revealed. This is the first experimental evidence that heterotrophic protists use the salt-out strategy as haloadaptation. However, the observation of varying relative proportions of compatible solutes within the four ciliates points to slight differences in haloadaptive strategies by regulatory action of the ciliates. Based on this finding, we provide an explanatory hypothesis for the distribution of protistan diversity along salinity gradients.
Keywords: ciliates, compatible solutes, haloadaptation, protists, transition boundaries |
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