Figure 2.

The effect of soil acidity and heavy metal contamination on microbial abundance and siderophore production in natural soils. (a) Heavy metal loadings on the first principal component (PC1), which explained 27% of the observed environmental variation; (b) Positive correlation between soil acidity (pH) and heavy metal contamination (PC1); (c) Proportion of siderophore producers and (d) microbial density (log₁₀‐transformed bacterial cells g⁻¹ soil) as a function of PC1 and pH. Lines and shaded area depict the fitted relationships ± SE.