Phylogeny overrides environmental effects in explaining leaf and root nutrient concentrations in Fabaceae

Plant nutrients are essential for plant growth and ecosystem functioning.
While Fabaceae plants are ecologically and economically significant, the
phylogenetic and environmental controls on their leaf and root nutrient
concentrations at a large scale have not been extensively studied. We
measured six nutrient concentrations (N, P, S, K, Ca, and Mg) in both the
leaves and roots of 121 Fabaceae species across various vegetation types
in China. The scaling exponents between leaves and roots showed that N-N
and P-P were significantly less than 1, Ca-Ca was significantly greater
than 1, and S-S, K-K, and Mg-Mg did not significantly differ from 1,
indicating divergent nutrient allocation strategies between leaves and
roots. For most nutrients, phylogeny explained a larger proportion of the
variation than environmental factors. However, for leaf P and K,
environmental variables accounted for more variation than phylogeny, with
mean annual temperature being the strongest environmental predictor for
both. This suggests that these two nutrients may play a particularly
important role in the environmental adaptation of Fabaceae species.
Synthesis. This study revealed contrasting nutrient allometries
between leaves and roots of Fabaceae plants, clarified the relationships
between nutrients and environmental variables, and highlighted the
dominant role of phylogeny in explaining nutrient variation. Together,
these findings enhance our understanding of the biogeographic distribution
of Fabaceae species and offer insights into their adaptive responses to
environmental change across broad spatial scales.