Cell‐specific nitrogen‐ and carbon‐fixation of cyanobacteria in a temperate marine system (Baltic Sea)

Abstract

SummaryWe analysed N 2 -and carbon (C) fixation in individual cells of Baltic Sea cyanobacteria by combining stable isotope incubations with secondary ion mass spectrometry (SIMS). Specific growth rates based on N 2 -and C-fixation were higher for cells of Dolichospermum spp. than for Aphanizomenon sp. and Nodularia spumigena. The cyanobacterial biomass, however, was dominated by Aphanizomenon sp., which contributed most to total N 2 -fixation in surface waters of the Northern Baltic Proper. N 2 -fixation by Pseudanabaena sp. and colonial picocyanobacteria was not detectable. N 2 -fixation by Aphanizomenon sp., Dolichospermum spp. and N. spumigena populations summed up to total N 2 -fixation, thus these genera appeared as sole diazotrophs within the Baltic Sea's euphotic zone, while their mean contribution to total C-fixation was 21%. Intriguingly, cell-specific N 2 -fixation was eightfold higher at a coastal station compared to an offshore station, revealing coastal zones as habitats with substantial N 2 -fixation. At the coastal station, the cell-specific C-to N 2 -fixation ratio was below the cellular C:N ratio, i.e. N 2 was assimilated in excess to C-fixation, whereas the C-to N 2 -fixation ratio exceeded the C:N ratio in offshore sampled diazotrophs. Our findings highlight SIMS as a powerful tool not only for qualitative but also for quantitative N 2 -fixation assays in aquatic environments.

Leaf-Associated Shifts in Bacterial and Fungal Communities in Response to Chicken Rearing Under Moso Bamboo Forests in Subtropical China

“…A previous study showed that the bamboo species Merostachys neesii had a large number of cyanobacterial 16S rRNA genes per cm 2 of leaf [39]. Cyanobacteria have been suggested to be capable of both nitrogen and carbon fixation [40,41]. We also observed that Ascomycota was the most abundant fungal phylum associated with moso bamboo leaves, followed by Basidiomycota.…”

Nitrogen fixation estimates for the Baltic Sea indicate high rates for the previously overlooked Bothnian Sea

“…Pelagic nitrogen fixation in the Baltic Sea is dominated by three genera of filamentous cyanobacteria (Klawonn et al 2016). The toxic Nodularia spumigena are mostly common in the southern parts and the non-toxic Aphanizomenon sp.…”

Application of the isotope pairing technique in sediments: Use, challenges, and new directions

“…Long (> 3 h) pre‐incubation times may be useful to ensure the 15 NO 3 − has can penetrate through the oxic layer to the zone of NO 3 − reduction; however, this also increases the time available to MPB to continuously take up NO 3 − . Additional experiments are required to specifically assess intracellular NO 3 − uptake, storage, and respiration during light and dark exposure such as spatially resolving isotope measurements by Secondary Ion Mass Spectrometry (SIMS) in combination with labeling experiments (e.g., Klawonn et al ; Bergkvist et al ).…”

“…. Additional experiments are required to specifically assess intracellular NO 3 − uptake, storage, and respiration during light and dark exposure such as spatially resolving isotope measurements by Secondary Ion Mass Spectrometry (SIMS) in combination with labeling experiments (e.g., Klawonn et al 2016;Bergkvist et al 2018).…”