# A war under our feet – basic research

From Pedro Lira

Plants fight quietly underground for water and minerals

* *

How can one study the part of the vegetation that is hidden underground? Does the growth of plant roots follow any rules? Researchers from Brazil, Spain, and the United States came together to answer this fundamental ecology question, and the conclusions were surprising. The trees compete with each other and “calculate” how and where their roots should grow, depending on the proximity of neighboring plants – and competitors.

The logic is simple. A plant will only expand its roots if there are sufficient natural resources at the point at which it is found to be of benefit to it. The physicist Ricardo Martinez-Garcia, professor at the Institute for Theoretical Physics at the State University Jãlio de Mesquita Filho in São Paulo and at the South American Institute for Basic Research in São Paulo, explains this. “It is more expensive for a plant to pick up resources two meters from its stem than ten centimeters from it because it cannot move and has to produce a longer root.” That said, it has to weigh costs and profits.

The level of complexity increases when a second system is nearby. Then the two begin to compete for the available resources. Imagine a certain amount of water at a certain point two meters from one plant and half a meter from another. Even if the two plants shared this available water identically, the one closest to the source would get it at a lower cost.

The researchers came to this conclusion thanks to a simulation of how the plants spread their roots underground. The computation was derived from game theory, a branch of mathematics that studies strategic situations in which the objects of study decide how to act in search of a better outcome.

The study gained prominence after it stamped the cover of Science magazine in December 2020. Up until then, there had been two conflicting theories to explain how a plant’s roots would behave in the presence of a competitor. It is said that plants respond to competition by reducing the size of their root system, i.e. investing less in roots compared to competitors. The other targets the total mass of roots that will either be produced if the plant is growing alone or if it is competing for resources with competitors if it then produces more roots.

Does a plant reduce its root system or produce more roots in the presence of other plants? “Because our work takes into account the number of roots a plant produces and also the position of the space in which it produces, we have succeeded in reconciling the two theories: when they have competitors, plants produce more roots near the trunk and less away from it. ”

From a theoretical point of view, the discovery is fundamental to better understand the planet’s ecosystems. According to Garcia-Martinez, the tool can help predict how biomes optimize water resources and respond to climate change. “In terms of applied science, the model can help us develop optimized plants and distribute the plants to produce more fruit as they use less energy to spread roots,” he explains.

This was only the first phase of the study. The researchers set out to deepen the model and examine the interactions in systems with more than two plants, with different species and under different climatic conditions.

* *

Pedro Lira is a journalist and social media at Instituto Serrapilheira

Sign up for Serrapilheira’s newsletter to receive more news from the institute and the Ciência Fundamental blog. Do you have an agenda? Here’s how you can work together.