Figure 5. Overview of the main results on the determinants of pyoverdine (PVD) production in Pseudomonas soil and pond communities.

The upper part of the scheme shows that: soil isolates produce on average less pyoverdine than pond isolates, there are more pyoverdine non-producers in soils than in ponds, and the coefficient of variation for pyoverdine production is higher in soil compared to pond communities. The lower part of the scheme indicates that there were more associations between environmental parameters and variables of pyoverdine production in soil than in pond communities. For isolates from soil communities, relative pyoverdine production was positively associated with community diversity (green circle), whereas variables of pyoverdine non-production all correlated with the environmental trade-off between iron concentration (red circle) and pH (yellow circle) versus carbon concentration (grey circle). Furthermore, the likelihood of non-producers being stimulated by heterologous pyoverdines increased with the relatedness between donor and recipient strain (purple circle). For isolates from pond communities, relative pyoverdine production was negatively associated with pH and carbon concentration. The likelihood of non-producers being stimulated by heterologous pyoverdines correlated with a complex trade-off between community diversity and pH versus carbon and iron concentration. For all isolates, pyoverdine production was scaled relative to laboratory reference strains (see Table S1). Variation in the environmental variables across soil and pond communities is shown in Fig. S3.