Final Report Summary - PRIMA (Priming in an aquatic ecosystem - Stream biofilms as hotspots for carbon cycling)
PRIMA was conceived to study microbial biofilms in streams as potential sites where priming of assumedly recalcitrant dissolved organic matter occurs. Addressing this topic is crucial given that we now recognize streams as major contributors to the global carbon cycle on the one hand, but not understanding how organic carbon that was protected in soils over extended periods becomes available to the heterotrophic metabolism in streams. It was the initial hypothesis of PRIMA, in fact, that terrestrial organic carbon is subject to priming in stream microbial biofilms.
The core findings of PRIMA are as follows:
• Priming seems not to occur in the hyporheic zone of the streambed. This is intuitive as this zone is largely heterotrophic with assumedly little contributions of labile dissolved organic matter as the primer.
• Priming seems to occur in the benthic biofilms. This makes sense. Here microbial heterotrophs co-exist in close spatial proximity with algae. Algal exudates are generally considered labile and may serve as primer.
• The interactions between recalcitrant and labile organic compounds are complex and may also involve inorganic compounds.
• Biofilm metabolism and reworking of labile dissolved organic carbon may contribute to the generation of recalcitrant organic matter.
PRIMA exclusively worked with 13C-labeled material to properly track and quantify carbon fluxes, which we consider the most robust approach possible to test for priming.
We were able to connect PRIMA with a sibling project on that same topic. PRIMA itself greatly benefited from this. Thereby we were able to pair PRIMA work on mass fluxes and imaging with metatranscriptomics and even proteomics. These data are still being processed but preliminary results are most promising already. We have also initiated collaborative work with Dr Kainz (WasserCluster Lunz, Austria) and Prof. Robert Findlay (University of Alabama) on compound-specific stable isotope analyses. Finally we also initiated collaborative work with Dr Dick van Oeveln (NIOO, NL) on inverse modeling. No doubt, PRIMA has triggered a wealth of research in the lab all centered around the topic of priming in microbial biofilms. As PI of these projects, I am confident that we will help illuminate the molecular mechanisms of priming in microbial biofilm.
PRIMA work involved two major experiments. A first experiments mimicked hyporheic biofilms in 25 bioreactors that were amended different potential primers in a factorial design. Among these potential primers were also algal exudates. A second experiment mimicked benthic phothotrophic biofilms grown under varying light regimes to yield various algal biomass and therefore various potentials of primers. For both experiments, we used made Salix grow under 13CO2-enriched atmosphere thereby gaining fully labeled plant tissue. From this tissue, we produced a complex mix of 13C-labeled organic matter that we decomposed to remove the bulk labile moieties. The residual material was considered recalcitrant and used in both experiments. Thereby we were able to assess the fraction of respiratory CO2 from the degradation of recalcitrant dissolved organic matter.
During PRIMA, Dr. Mia Bengtsson has had the opportunity to expand her skills in aquatic biogeochemistry and ecology, and in metatranscriptomics. She also attended an international course on biofilms in Delft and a mentoring course at the University of Vienna to improve various soft skills. She also co-supervised one MSc student (Judith Rosentreter) and one PhD student (Karoline Wagner). Dr. Bengtsson greatly contributed to the management of PRIMA and the sibling project on that same topic.
The core findings of PRIMA are as follows:
• Priming seems not to occur in the hyporheic zone of the streambed. This is intuitive as this zone is largely heterotrophic with assumedly little contributions of labile dissolved organic matter as the primer.
• Priming seems to occur in the benthic biofilms. This makes sense. Here microbial heterotrophs co-exist in close spatial proximity with algae. Algal exudates are generally considered labile and may serve as primer.
• The interactions between recalcitrant and labile organic compounds are complex and may also involve inorganic compounds.
• Biofilm metabolism and reworking of labile dissolved organic carbon may contribute to the generation of recalcitrant organic matter.
PRIMA exclusively worked with 13C-labeled material to properly track and quantify carbon fluxes, which we consider the most robust approach possible to test for priming.
We were able to connect PRIMA with a sibling project on that same topic. PRIMA itself greatly benefited from this. Thereby we were able to pair PRIMA work on mass fluxes and imaging with metatranscriptomics and even proteomics. These data are still being processed but preliminary results are most promising already. We have also initiated collaborative work with Dr Kainz (WasserCluster Lunz, Austria) and Prof. Robert Findlay (University of Alabama) on compound-specific stable isotope analyses. Finally we also initiated collaborative work with Dr Dick van Oeveln (NIOO, NL) on inverse modeling. No doubt, PRIMA has triggered a wealth of research in the lab all centered around the topic of priming in microbial biofilms. As PI of these projects, I am confident that we will help illuminate the molecular mechanisms of priming in microbial biofilm.
PRIMA work involved two major experiments. A first experiments mimicked hyporheic biofilms in 25 bioreactors that were amended different potential primers in a factorial design. Among these potential primers were also algal exudates. A second experiment mimicked benthic phothotrophic biofilms grown under varying light regimes to yield various algal biomass and therefore various potentials of primers. For both experiments, we used made Salix grow under 13CO2-enriched atmosphere thereby gaining fully labeled plant tissue. From this tissue, we produced a complex mix of 13C-labeled organic matter that we decomposed to remove the bulk labile moieties. The residual material was considered recalcitrant and used in both experiments. Thereby we were able to assess the fraction of respiratory CO2 from the degradation of recalcitrant dissolved organic matter.
During PRIMA, Dr. Mia Bengtsson has had the opportunity to expand her skills in aquatic biogeochemistry and ecology, and in metatranscriptomics. She also attended an international course on biofilms in Delft and a mentoring course at the University of Vienna to improve various soft skills. She also co-supervised one MSc student (Judith Rosentreter) and one PhD student (Karoline Wagner). Dr. Bengtsson greatly contributed to the management of PRIMA and the sibling project on that same topic.