Meet an Ecology PhD-student: Carina Rofner

FWF-project: Heterotrophic freshwater bacterial groups and the biogeochemical cycle of phosphorus in mountain lakes

samplingThe main aim of my thesis is to understand the role played by heterotrophic freshwater bacteria in the uptake of inorganic and organic phosphorus compounds as well as the strategies used of individual bacterial taxa to cope with low phosphorus concentrations.

Heterotrophic bacteria play a central role in the biogeochemical cycle of elements in aquatic ecosystems. They (re-) cycle dead organic material to biomass and thus, provide energy and nutrients to higher trophic levels (zooplankton, fish). Although phosphorus (P) is a key nutrient limiting bacterial growth in freshwater ecosystems, knowledge on inorganic and organic P utilization by individual bacterial taxa is scarce.

By applying cultivation-independent approaches (uptake of radiolabelled-substrates at the community and taxon-specific level, 16S rDNA sequencing), we gained first insights in the P dynamics of low-productive lakes and identified strategies used by bacterial members to cope with low P concentrations. For instance, it seemed that different bacterial taxa have variable P requirements when related to their growth activity, which means that bacteria differ in their needs for P to maintain growth.

In experiments carried out in a high altitude and latitude lake, we further assessed whether climate-induced changes in plant cover (treeline) and soil chemical composition alter lake bacterial community composition and function. The results obtained in this study are of particular relevance as changes in lake catchments affecting the availability of P in soils, impact bacterial growth rates and thus, the flux of C and P to higher trophic levels.

Carina Rofner

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