The Mechanisms of Plant Interactions: To the Root of the Problem

Abstract

This PhD thesis explores the interactions among plants from a mechanistic approach with a special focus on belowground interactions. The first chapter is an introduction presenting a novel framework to study plant interactions as an emergent property of plant communities. We suggest addressing the biophysical mechanisms mediating the interaction among two individual plants. We defend the use of ‘Plant Interaction Models’ (PIMs), defined as spatially explicit, game theory models of interacting individuals in which interactions emerge. The second chapter, based in this idea, addresses the belowground competition among pairs of plants based in a spatial game theory model. We predict the ESS to be an ‘exploitative segregation of plant roots’ (ESPR) potentially leading to a tragedy of the commons in crowded populations, yet root underinvestment when populations are more spaced. We tested the model predictions in a greenhouse experiment, finding support for the ESPR. One of the major challenges that root ecologists must face when trying to validate PIMs are methodological hassles. This is particularly due to the difficulty of obtaining plant roots data at the individual-level, and this is addressed in chapters three and four. The third chapter presents a review of the exiting methods to study in the field plant roots with a special focus on which methods can yield spatial root density distribution of individual plants. The fourth chapter is a test of some of the most promising of these methods, namely DNA microsatellite analysis, multicolor staining, and soil coring, in a Mediterranean shrubland in central Spain, with promising results from the staining methods, allowing us to collect individual-level spatially explicit root density data. Finally, in a fifth chapter, we present potential extensions for the ESPR' model, including some results. This chapter outlines some of the projects in which I am currently working and that I may pursue during my next career steps.