How some plants “help” their competitors in extreme situations

Photo: Mediterranean scrub. Author: Ciro Cabal

An international collaborative project, in which the Global Change Research Institute (IICG) of the URJC participates, has developed a mathematical model that simulates the competition between plants for a soil resource. For the first time, a model of this type incorporates the action mechanisms of ecosystem engineering plants, capable of extracting nutrients from the soil from which other adjacent plants benefit.

Irene Vega

Traditionally, the study of plant communities has focused on competition between plants without considering the existence of a positive relationship. However, in recent decades, facilitation has gained importance, that is, the ecological interaction that occurs between an engineering plant, capable of obtaining resources from the soil, and the rest of the beneficiary plants that grow around it and compete for it.

An international study, published in the scientific journal New phytologist, shows that the situation in which a plant “helps” a competing neighbour is stable over time and gives rise to positive interactions between plants. The authors of this work have developed a new mathematical model that simulates competition between plants for the exploitation of a soil resource. This model incorporates ecosystem engineering plants, which are capable of extracting nutrients present in the soil, but which are not available to other plants. In this way, the engineering plants make the resources available to the community. “This trait of the engineering plants is only activated in the model when it brings net benefits to said carrier plant despite attracting and benefiting opportunistic competitors,” highlights Ciro Cabal, co-author who led the study and researcher at the Institute for Research on Global Change (IICG) of the URJC.

In this sense, facilitation emerges as an optimal strategy in the model and this study has observed that it is stable in stressful environments. “Among all the possible causes of stress considered in the model, the most important environmental parameter to explain facilitation is the proportion of the resource that is available, and not the absolute amount of the resource existing in the soil as is usually assumed in empirical studies,” adds the researcher.

New approach to the stress gradient hypothesis

The stress gradient hypothesis is a theory that predicts that facilitation is a dominant interaction in habitats subject to high environmental stress such as drought or poor soils.

Another objective of this study was to determine whether facilitation could be an optimal and, therefore, stable strategy for a plant capable of increasing the availability of soil resources, thereby attracting competitors.

This work thus offers a new approach for future empirical studies on the stress gradient hypothesis, by showing that the type of stress taken into account and the way of determining the positive or negative sign of the interaction are fundamental.

figure study plants