We investigated the role of N 2 -fixation by the colony-forming cyanobacterium, Aphanizomenon spp., for the plankton community and N-budget of the N-limited Baltic Sea during summer by using stable isotope tracers combined with novel secondary ion mass spectrometry, conventional mass spectrometry and nutrient analysis. + fluxes to Aphanizomenon colonies at low bulk concentrations (o250 nM) as compared with N 2 -fixation within colonies. No N 2 -fixation was detected in autotrophic microorganisms o5 μm, which relied on NH 4 + uptake from the surrounding water. Aphanizomenon released about 50% of its newly fixed N 2 as NH 4 + . However, NH 4 + did not accumulate in the water but was transferred to heterotrophic and autotrophic microorganisms as well as to diatoms (Chaetoceros sp.) and copepods with a turnover time of 5 h. We provide direct quantitative evidence that colony-forming Aphanizomenon releases about half of its recently fixed N 2 as NH 4 + , which is transferred to the prokaryotic and eukaryotic plankton forming the basis of the food web in the plankton community. Transfer of newly fixed nitrogen to diatoms and copepods furthermore implies a fast export to shallow sediments via fast-sinking fecal pellets and aggregates. Hence, N 2 -fixing colony-forming cyanobacteria can have profound impact on ecosystem productivity and biogeochemical processes at shorter time scales (hours to days) than previously thought.

The present research looked at the importance of the concept of grit in University students based on a mixed-method approach. Study 1 comprised 440 University students. All were given the Grit Scale, the Perceived Stress Scale, the short Warwick–Edinburgh Mental Well-being Scale, the Office of National Statistics Well-being items and the Self-Control Scale. Levels of grit were significantly higher in female students, older students and postgraduates. Grit correlated highest with self-control. Study 2 looked at 340 University students. In addition to measuring self-control, mental well-being and grit, measures of resilience and mindsets were also added. A construct validity test of the Grit Scale showed that high grit scorers had significantly higher levels of self-control and mental well-being, were more resilient and were more likely to have a more growth oriented mindset. Grit varies with age and is most closely associated with the concept of self-control. The third study was a qualitative investigation with 10 successful graduates. Semi-structured interviews were coded using thematic analysis. Three broad themes emerged. The first, Passion and Perseverance, included themes of having short and long terms goals, resilience, dedication, and endurance. The second, Self-Control, included time management, self-awareness, prioritizing tasks and knowing strengths and weaknesses. The third theme identified was Positive Mindsets. This included having a positive attitude toward learning, the importance of feedback and constructive criticism and that success is not materialistic. The qualitative research has helped “unpack” concepts from the grit research and may enable University tutors to guide students better. Though these studies were only conducted in one English University, they have been stepping stones in our quest to discover what are the most important factors in determining student academic success? The development and piloting of our new Uni-Stride Scale, is the next step in this process.

SummaryThe mechanistic basis of feather moss-cyanobacteria associations, a main driver of nitrogen (N) input into boreal forests, remains unknown. Here, we studied colonization by Nostoc sp. on two feather mosses that form these associations (Pleurozium schreberi and Hylocomium splendens) and two acrocarpous mosses that do not (Dicranum polysetum and Polytrichum commune). We also determined how N availability and moss reproductive stage affects colonization, and measured N transfer from cyanobacteria to mosses.The ability of mosses to induce differentiation of cyanobacterial hormogonia, and of hormogonia to then colonize mosses and re-establish a functional symbiosis was determined through microcosm experiments, microscopy and acetylene reduction assays. Nitrogen transfer between cyanobacteria and Pleurozium schreberi was monitored by secondary ion mass spectrometry (SIMS).All mosses induced hormogonia differentiation but only feather mosses were subsequently colonized. Colonization on Pleurozium schreberi was enhanced during the moss reproductive phase but impaired by elevated N. Transfer of N from cyanobacteria to their host moss was observed.Our results reveal that feather mosses likely secrete species-specific chemo-attractants when N-limited, which guide cyanobacteria towards them and from which they gain N. We conclude that this signalling is regulated by N demands of mosses, and serves as a control of N input into boreal forests.

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.

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