Fig. 4: Diazotroph community composition and nifH gene expression.
A Relative abundance of diazotroph classes at each station. CAO Central Arctic Ocean, MIZ marginal ice zone, LF: land-fast ice. L: large size fraction ( > 2 μm), S: small size fraction (0.22–2 μm), T total ( > 0.22 μm) size fractions (equal volume of DNA template from >2 and 0.22–2 μm size fractions for comparability of CAO to MIZ and LF, see methods), R RNA (nifH expression). Note the one to three replicates (A–C) for each station in the CAO. Tr. 1: transect one, Tr. 2: transect two, Other: sequences not annotated at the class level. The asterisk marks the cyanobacterial class category. B Redundancy analysis (RDA) of the diazotroph community composition in the CAO, and (C) MIZ (transects 1 and 2 refer to the transects performed over the MIZ), displaying the top five orders (if the group does not have assigned taxonomy at order level the closest above-lying available taxonomic rank is given, e.g., Gammaproteobacteria Class) and the significant environmental drivers constraining the RDA (in red). POC particulate organic carbon, DOC dissolved organic carbon, NH4 ammonium, TN total nitrogen, Fuco fucoxanthin, DOP dissolved organic phosphorus. The light grey lines from the centre in (B, C) represent the loadings of remaining orders (i.e., beyond the top five displayed orders).
