Following publications have been announced. Fur further information please contact the marked authors.
Van Dam, B.R., Lopes, C., Osburn, C.L., & Fourqurean, J.W. (2019): Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows. Biogeosciences, 16, 4411–4428, doi:10.5194/bg-16-4411-2019
The net ecosystem productivity (NEP) of two seagrass meadows within one of the largest seagrass ecosystems in the world, Florida Bay, was assessed using direct measurements over consecutive diel cycles during a short study in the fall of 2018. We report significant differences between NEP determined by dissolved inorganic carbon (NEPDIC) and by dissolved oxygen (NEPDO), likely driven by differences in air–water gas exchange and contrasting responses to variations in light intensity. We also acknowledge the impact of advective exchange on metabolic calculations of NEP and net ecosystem calcification (NEC) using the “open-water” approach and attempt to quantify this effect. In this first direct determination of NEPDIC in seagrass, we found that both seagrass ecosystems were net heterotrophic, on average, despite large differences in seagrass net above-ground primary productivity. NEC was also negative, indicating that both sites were net dissolving carbonate minerals. We suggest that a combination of carbonate dissolution and respiration in sediments exceeded seagrass primary production and calcification, supporting our negative NEP and NEC measurements. However, given the limited spatial (two sites) and temporal (8 d) extent of this study, our results may not be representative of Florida Bay as a whole and may be season-specific. The results of this study highlight the need for better temporal resolution, accurate carbonate chemistry accounting, and an improved understanding of physical mixing processes in future seagrass metabolism studies.
Sanders, T., Fiencke, C., Hüpeden, J., Pfeiffer, E.M., & Spieck, E. (2019): Cold Adapted Nitrosospira sp.: A Potential Crucial Contributor of Ammonia Oxidation in Cryosols of Permafrost-Affected Landscapes in Northeast Siberia. Microorganisms 2019, 7, 699, doi:10.3390/microorganisms7120699
Permafrost-affected landscape soils are rich in organic matter and contain a high fraction of organic nitrogen, but much of this organic matter remains inaccessible due to nitrogen limitation. Microbial nitrification is a key process in the nitrogen cycle, controlling the availability of dissolved inorganic nitrogen (DIN) such as ammonium and nitrate. In this study, we investigate the microbial diversity of canonical nitrifiers and their potential nitrifying activity in the active layer of different Arctic cryosols in the Lena River Delta in North-East Siberia. These cryosols are located on Samoylov Island, which has two geomorphological landscapes with mineral soils in the modern floodplain and organic-rich soils in the low-centered polygonal tundra of the Holocene river terrace. Microcosm incubations show that the highest potential ammonia oxidation rates are found in low organic soils, and the rates depend on organic matter content and quality, vegetation cover, and water content. As shown by 16S rRNA amplicon sequencing, nitrifiers represented 0.6% to 6.2% of the total microbial community. More than 50% of the nitrifiers belonged to the genus Nitrosospira. Based on PCR amoA analysis, ammonia-oxidizing bacteria (AOB) were found in nearly all soil types, whereas ammonia-oxidizing archaea (AOA) were only detected in low-organic soils. In cultivation-based approaches, mainly Nitrosospira-like AOB were enriched and characterized as psychrotolerant, with temperature optima slightly above 20 °C. This study suggests a ubiquitous distribution of ammonia-oxidizing microorganisms (bacteria and archaea) in permafrost-affected landscapes of Siberia with cold-adapted AOB, especially of the genus Nitrosospira, as potentially crucial ammonia oxidizers in the cryosols.
Bellou, N., Garcia, J.A.L., Colijn, F., & Herndl, G.J. (2019): Seasonality combined with the orientation of surfaces influences the microbial community structure of biofilms in the deep Mediterranean Sea. In: Deep Sea Research Part II: Topical Studies in Oceanography, 2019, 104703, doi:10.1016/j.dsr2.2019.104703
Attachment to surfaces represents an important life strategy for microbial communities as indicated by the rapid colonization of biotic and abiotic surfaces in marine waters. However, little attention has been paid to the development of biofilm-associated microbial communities and the environmental parameters influencing biofilm development in the deep sea. In this study, a deep-sea experimental setup was used to follow the development of the microbial community colonizing solid surfaces deployed at 4500 m depth at the deepest point of the Mediterranean Sea. The experiment was performed during summer (May to October 2007) and winter (October 2007–May 2008), each lasting for 155 d. The phylogenetic composition of the biofilm community was determined by tag sequencing of the 16S rRNA gene. We investigated whether the composition of the deep-sea microbial biofilms is influenced by seasonality. Based on tag sequencing, operational taxonomic units were identified and diversity indices calculated. Seasonality combined with the orientation of the solid surface on which the biofilms were growing was the main factor influencing the structure of the microbial community. The most abundant phyla of deep-sea biofilm communities attached to the solid surfaces were Gammaproteobacteria (range: 10.8%–92.6%), Alphaproteobacteria (range: 34.9%–92.6%) and Betaproteobacteria (range: 0.3%–2.1%), irrespective of the variables (surface, orientation, season). Flavobacteria and Epsilonbacteria show a clear preference with respect to the orientation of the deployed surfaces during the winter, however, they were essentially absent at the surfaces during the summer. Some bacterial classes such as Campylobacterales and Rhodobacterales showed distinct preferences for specific seasons or orientation of the substrate. Taken together, we conclude that even on deep-sea biofilms, there is to some extent seasonality detectable in the composition of the surface associated prokaryotic community, despite the fact that the deep-sea is, in terms of physico-chemical parameters, a fairly stable environment.