Under pressure: How do plants strike a balance between growth and defense?

How do plants allocate biomass when simultaneously competing with their neighbors for above- and belowground resources and defending against insect herbivory? How do these selection pressures affect natural selection of plant traits?

The interactions between competition for resources and defense against herbivory are complex, difficult to investigate through experiments. Recent advances in model configuration and integration have made it possible to understand the role of such complex interactions on plant selection in silico.

Drs. Jorad de Vries of ETH Zürich along with Jochem Evers, Erik Poelman, and Niels Anten, of Wageningen University developed a novel modeling method to understand how different levels of resource availability, competition pressure, and herbivore pressure drive selection on the balance between the acquisition and protection of resources over multiple generations.

The authors developed a simulation model that combines a functional-structural plant model of plant growth in a 3D light climate with a model of natural selection. “By combining these two established methodologies we’re able to explore the complex behavior that emerges from interactions between multidimensional plants and their multidimensional environments driven by mechanisms that range from plant physiological to eco-evolutionary scales,” according to de Vries.

The evolutionary functional-structural plant model presented in this study was able to recreate the functional equilibria predicted by principal ecological theories on the effects of resource availability and resource-driven trade-offs. These results were:

• Resource limitation increased biomass allocation towards plant parts that acquire that resource (light: leaves and stems, N: roots).
• Plants in nitrogen-poor environments expressed higher levels of defense due to the reduced capacity for re-growth in these environments.
• Dense stands selected for tall plants due to the inherent asymmetry of height-driven competition for light.
• Selection optimized defense distribution in the canopy to protect the most valuable leaves in terms of current resource allocation and future resource acquisition.

This work demonstrates that the value of plants’ investment in the acquisition or the protection of resources is a dynamic problem that is influenced by multiple ecological interactions, trade-offs and tragedies of the commons, and therefore requires an eco-evolutionary context to be fully understood. Mechanistic modelling approaches, such as the one presented here, have the potential to help researchers better understand plant responses to dynamic and variable environments.

The model code and data generated by the model is publicly available in the dryad repository at https://doi.org/10.5061/dryad.bnzs7h474.