Leaf economics fundamentals explained by optimality principles

The life span of leaves increases with their mass per unit area (LMA). It is unclear why. Here, we show that this empirical generalization (the foundation of the worldwide leaf economics spectrum) is a consequence of natural selection, maximizing average net carbon gain over the leaf life cycle. Analyzing two large leaf trait datasets, we show that evergreen and deciduous species with diverse construction costs (assumed proportional to LMA) are selected by light, temperature, and growing-season length in different, but predictable, ways. We quantitatively explain the observed divergent latitudinal trends in evergreen and deciduous LMA and show how local distri-butions of LMA arise by selection under different environmental conditions acting on the species pool. These results illustrate how optimality principles can underpin a new theory for plant geography and terrestrial carbon dynamics.

Automated summary

The life span of leaves is positively correlated with their mass per unit area (LMA), but the underlying mechanism remains unclear. By analyzing large leaf trait datasets, we found that this empirical generalization is a result of natural selection, which maximizes average net carbon gain over the leaf life cycle. We demonstrated how evergreen and deciduous species with different construction costs (assumed proportional to LMA) are selected by light, temperature, and growing-season length in predictable ways. Moreover, we explained the observed divergent latitudinal trends in evergreen and deciduous LMA and showed how local distributions of LMA arise from selection under different environmental conditions acting on the species pool. These findings highlight how optimality principles can contribute to a new theory for plant geography and terrestrial carbon dynamics.