Spatial and temporal variability in the response of phytoplankton and bacterioplankton to B-vitamin amendments in an upwelling system

Abstract

Abstract. We evaluated the temporal (inter-day and inter-season) and spatial variability in microbial plankton responses to vitamins B12 and B1 supply in coastal and oceanic waters. Inter-day variability in microbial plankton responses to B-vitamins was not of great concern, suggesting that B-vitamins availability was controlled by factors operating at larger temporal scales, such as those driving microbial community seasonal succession. Most positive responses were produced by treatments containing either B12 alone or B12 combined with B1 in oceanic waters, which was consistent with the significantly lower average vitamin B12 ambient concentrations compared to that in the coastal station. Growth stimulation by B1 addition was more frequent on bacteria, which is coherent with their widespread dependence on exogenous sources for this growth factor. Negative responses to B-vitamins were generalized in coastal waters in summer, and were associated to a high contribution of Flavobacteriales to the prokaryote community. This observation suggests that the external supply of B12 and/or B1 may promote negative interactions between microbial components when B-vitamins auxotrophs are abundant. The microbial response patterns to B12 and/or B1 amendments were significantly correlated with changes in the prokaryotic community composition, highlighting the pivotal role of prokaryotes in B-vitamins cycling in marine ecosystems.

Coastal upwelling systems as dynamic mosaics of bacterioplankton functional specialization

“…Overall, our results demonstrate that specific functional processes of the prokaryotic community identified from gene expression analyses) are associated with different phytoplankton groups in the upwelling system off the NW Iberian Peninsula. The presence of different phytoplankton and bacterioplankton populations during periods with different environmental conditions has been suggested in previous studies both in the area (Joglar et al, 2020;Costas-Selas et al, 2023) and in other marine ecosystems (Pinhassi et al, 2004;Needham et al, 2017;Bunse et al, 2019). Recent work in the NW Iberian Peninsula suggests a key role of biotic interactions as structuring factors of the eukaryotic community, mostly driven by positive associations between phytoplankton and bacteria (Costas-Selas et al, 2023).…”

“…The observed very low nutrients concentrations during summer in surface waters at the coastal station are probably due to the massive consumption of nutrients by the phytoplankton bloom (Figures 1B; S1-S3; Table S2). At the coastal station, pronounced changes in Chl-a concentration were observed at the end of the winter cruise (Figures 1B; S1, S5) and even more so, at the end of the summer cruise (likely due to the rapid wind relaxation that interrupted the upwelling and disrupted the bloom (Figure S1), see Joglar et al, 2020(Joglar et al, 2020.…”

“…Among the bacteria, Pelagibacterales and Synechococcales showed higher relative proportions at the offshore station, particularly in winter, while other Alphaproteobacteria and Flavobacteria reached higher relative abundances in spring and summer on the coast. At both stations, Oceanospirillales were relatively more abundant in winter, whereas Cellvibrionales increased in summer (Figure S6B) (Joglar et al, 2020).…”

“…The eukaryotic community at both stations was dominated by dinoflagellates and diatoms (Dinophyceae, Thalassiosira, and Chaetoceros, particularly in summer) (Figure S6A) (Joglar et al, 2020). Among the bacteria, Pelagibacterales and Synechococcales showed higher relative proportions at the offshore station, particularly in winter, while other Alphaproteobacteria and Flavobacteria reached higher relative abundances in spring and summer on the coast.…”

“…Finally, the present dataset suggests that different strategies for using light as a source of energy by bacteria occur in this upwelling system. Thus, the relative transcription of photosynthesis related genes by Synechococcales was more important in the offshore station during winter, where the abundance of this group was relatively higher (Joglar et al, 2020). It is important to note here that, as explained in the Methods section, the coastal and offshore stations were sampled at different time points in the daily cycle.…”