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

Abstract

Abstract. We experimentally evaluated the temporal (interday and interseason) and spatial variability in microbial plankton responses to vitamin B12 and/or B1 supply (solely or in combination with inorganic nutrients) in coastal and oceanic waters of the northeast Atlantic Ocean. Phytoplankton and, to a lesser extent, prokaryotes were strongly limited by inorganic nutrients. Interday variability in microbial plankton responses to B vitamins was limited compared to interseason variability, suggesting that B-vitamin availability might be partially controlled by factors operating at seasonal scale. Chlorophyll a (Chl a) concentration and prokaryote biomass (PB) significantly increased after B-vitamin amendments in 13 % and 21 %, respectively, of the 216 cases (36 experiments × 6 treatments). Most of these positive responses were produced by treatments containing either B12 solely 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. Negative responses, implying a decrease in Chl a or PB, represented 21 % for phytoplankton and 26 % for prokaryotes. Growth stimulation by B1 addition was more frequent on prokaryotes than in phytoplankton, suggesting that B1 auxotrophy in the sampling area could be more widespread in prokaryotes than in phytoplankton. Negative responses to B vitamins were generalized in coastal surface waters in summer and were associated with 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-vitamin 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-vitamin cycling in marine ecosystems.

Cobalamin and microbial plankton dynamics along a coastal to offshore transect in the Eastern North Atlantic Ocean

“…1A) showed a marked seasonal variability in the response of phytoplankton and bacteria to inorganic nutrient and/or B12 additions in surface waters, with phytoplankton responding at the beginning and at the end of the productive period. A detailed experimental study by Joglar et al (2020) at a shelf and an oceanic station off this area (stn 3 and stn 6 in Fig.1A) also revealed that phytoplankton and prokaryotes frequently respond to B12 and/or B1 additions. Overall, the magnitude of positive responses in the sampling area after external B12 inputs was relatively small (Barber-Lluch et al, 2019;Joglar et al, 2020), and the patterns of microbial responses appeared to be mostly controlled by the prokaryote taxonomic composition (Joglar et al, 2020).…”

“…3) and by changes in the microbial community composition (Fig. 6), particularly by the relative increase of Synechococcus , which tend to be dominant in oceanic waters in this sampling area (Teira et al ., 2009, Joglar et al ., 2020). Interestingly, Synechococcus is a cyanobacteria that produces and uses pseudocobalamin (Helliwell et al ., 2016), which was not measured in this study.…”

“…A detailed experimental study by Joglar et al . (2020) at a shelf and an oceanic station off this area (stn 3 and stn 6 in Fig 1A…”

“…also revealed that phytoplankton and prokaryotes frequently respond to B12 and/or B1 additions. Overall, the magnitude of positive responses in the sampling area after external B12 inputs was relatively small (Barber‐Lluch et al ., 2019; Joglar et al ., 2020), and the patterns of microbial responses appeared to be mostly controlled by the prokaryote taxonomic composition (Joglar et al ., 2020).…”

“…The first few measurements of B12 availability in this area revealed consistently low concentrations of this growth factor (<2.7 pM of CB12 + HB12) (Barber‐Lluch et al ., 2019; Joglar et al ., 2020). Nevertheless, the limited number of samples included in these studies, together with the lack of concomitant measurements of microbial plankton activity and diversity, precluded solid conclusions on the role of B12 in the dynamics of the microbial plankton assemblage in this productive area.…”