Leaf metabolic traits reveal hidden dimensions of plant form and function

The plant metabolome encompasses the biochemical mechanisms through which evolutionary and ecological processes shape plant form and function[1][1],[2][2]. However, while the metabolome should thus be an important component of plant life-history variation[3][3], we know little about how it varies across the plant kingdom. Here, we use the plant functional trait concept[4][4] – a powerful framework for describing plant form and function[5][5]–[7][6] – to interpret leaf metabolome variation among 457 tropical and 339 temperate plant species. Distilling metabolite chemistry into five discriminant metabolic functional traits reveals that plants vary along two major axes of leaf metabolic specialization – a leaf chemical defense spectrum and an expression of leaf longevity. These axes are qualitatively consistent for tropical and temperate species, with many trait combinations being viable. However, axes of leaf metabolic specialization vary orthogonally to life-history strategies described by widely used functional traits[5][5]–[7][6], while being at least equally important to them. Our findings question classical trait[6][7] and plant defense[8][8] theory that predicts relationships between the leaf chemical phenotype, plant productivity, and pace of life. Moreover, we show that metabolic functional traits describe unique dimensions of plant life-history variation that are complementary to, and independent from, those captured by existing plant functional traits. ### Competing Interest Statement The authors have declared no competing interest. [1]: #ref-1 [2]: #ref-2 [3]: #ref-3 [4]: #ref-4 [5]: #ref-5 [6]: #ref-7 [7]: #ref-6 [8]: #ref-8