Optimal root proliferation strategies: the roles of nutrient heterogeneity, competition and mycorrhizal networks

Background and Aims Plants proliferate roots in order to acquire nutrients, typically contending with heterogeneous resources and competing neighbours. A mathematical model was developed to identify optimal root proliferation strategies in patchy nutrient environments. The impact of joining mycorrhizal networks was also assessed. Methods A simple model of growth and competition in one spatial dimension was implemented within a genetic algorithm to obtain optimal proliferation strategies under different scenarios of resource distribution, and in the presence or absence of local competition and large-scale mycorrhizal networks. Results A strong proliferation response emerged for isolated plants in heterogeneous environments with low resources, and also for plants growing in competition. Even in statistically homogeneous environments, the presence of competition conferred a selective advantage to plants proliferating in the direction of the most recently acquired patch. In the presence of mycorrhizal networks, the optimal strategy switched from symbiosis to proliferation driven growth as the relative cost of acquiring resources through the networks increased. Conclusions The optimal proliferation response in a given scenario was governed by a hierarchy of factors: resource levels and distribution; the presence or absence of competition; and the marginal benefit of obtaining resources via symbiotic relationships with mycorrhizas.