Figure 4

Multivariate regression tree (MRT) analyses of the interaction between environmental parameters and (a) AAP bacterial phylogroups and (b) OTUs abundance (in terms of sequence number). The model explained 89% and 61% of the variance in the whole data set for phylogroups and OTUs, respectively. Pies (a) and multiple value bar chars (b) under each leaf represent the mean of normalized phylogroups (a) and OTUs (b) abundance for each lineage significantly correlated with environmental parameters. Number on the bar chars (b) indicated the number of the corresponding OTUs. Asterisks show indicator OTUs at a significance threshold of P = 0.05. C1 to C5 indicated the 5 habitats identified for AAP from the MRT analysis (e.g. habitat C1: salinity ≥35 g.L⁻¹ and temperature ≥17 °C). [Note that stations Z65 and Z59 from ARCTIC and stations ARC2 and PAC2 from MALINA were not used in MRT analyses because of the lack of environmental data (see Table S1)].