Metal-rich soils increase tropical tree stoichiometric distinctiveness

Background and aims Ultramafic soils have high metal concentrations, offering a key opportunity to understand if such metals are strong predictors of leaf stoichiometry. This is particularly relevant for tropical forests where large knowledge gaps exist. Methods On the tropical island of Sulawesi, Indonesia, we sampled forests on sand, limestone, mafic and ultramafic soils that present a range of soil metal concentrations. We asked how variation in 12 soil elements (metals and macronutrients) influenced leaf stoichiometry and whether stoichiometric distinctiveness (the average difference between a species and all others in a multivariate space, the axes of which are the concentrations of each leaf element) is influenced by increasing soil metal concentrations. Results Positive correlations between corresponding elements in soils and leaves were only found for Ca and P. Noticeably, soil Cr had a negative effect upon leaf P. Whilst most species had low stoichiometric distinctiveness, some species had greater distinctiveness on stressful metal-rich ultramafic soils, generally caused by the accumulation of Al, Co, Cr or Ni. Conclusions Our observation of increased stoichiometric distinctiveness in tropical forests on ultramafic soils indicates greater niche differentiation, and contrasts with the assumption that stressful environments remove species with extreme phenotypes.

Automated summary

This study in tropical forests on Sulawesi Island, Indonesia found that metal elements in ultramafic soils can affect leaf stoichiometry, leading to greater distinctiveness in some species in these environments. This indicates greater niche differentiation among species in stressful environments.