A long-standing question in ecology is whether there exists a feedback between the root traits and soil foraging strategies employed by plants and the biogeochemical cycles that emerge at the scale of biomes. We will here take a combined perspective of empirical observations (10 functional root traits across 369 species in 7 biomes) and first-principle theoretical analysis based on the adaptive dynamics of root growth and soil exploration.
Results/Conclusions
Our empirical analysis suggests that plants have evolved thinner roots since they first emerged in land ecosystems, roughly 400 million years ago. At the same time, plants have progressively shed their dependence upon mycorrhizal fungi symbionts, and adjusted the density of their root tissue to greatly improve the volume of soil explored for each gram of root biomass. These global trends have allowed plants to develop opportunistic strategies, by which they have stayed competitive in the face of highly unpredictable soil environmental conditions. As a result, predictable combinations of root traits have accompanied the invasion of plants into new biomes over evolutionary time. Our first-principle model analysis suggests that these global evolutionary trends have resulted from (i) intense competition within plant communities for soil nutrients, and (ii) a highly strategic below-ground game in which plants have evolved the ability to invest carbon in acquiring soil nutrients. Our findings imply that, at the global scale, plant communities not only define the local properties of biogeochemical cycles (nitrogen and phosphorus, chiefly), but also that root traits and strategies have been selected as a consequence of local nutrient conditions.