New theory of root competition reveals rules governing growth

In the presence of competitors, plants overproduce roots to snatch up nearby resources but avoid foraging for nutrients near their neighbors, according to a new study, which provides a new theoretical foundation for understanding the rules that govern competitive root behavior. Plant roots represent much of Earth’s biomass, and understanding how they compete for limited soil nutrients has broad implications, including our ability to optimize agricultural efficiency and productivity. However, observing intact root systems in their natural subterranean environments is difficult, and as a result, very little is known about how a plant’s roots respond to underground competition. Previous research has produced a range of seemingly conflicting results, adding further confusion to understanding root behavior. Some studies report that neighboring plants tend to minimize overlap between their root systems (root segregation) by keeping roots nearer to their stem. Others suggest a type of soil-bound “tragedy of the commons” between nearby competitors. “Whether and when it pays for plants to selfishly overproduce roots and preempt resource capture by competitors or cooperate by restraining root growth has been the subject of extended debate,” writes Marina Semchenko in a related Perspective. According to Ciro Cabal and colleagues, however, few studies have considered both the total amount of roots produced by competing plants and their spatial distribution of root systems together. Cabal et al. developed a game theory-based model, which accounts for the increasing fitness cost of foraging for nutrients further away from the plant stem, to predict how one plant’s roots react to nearby plants’ roots. The authors then tested the predictions in experiments using greenhouse-grown pepper plants. The model and experimental results revealed that plants adjust their root growth strategies according to how close competing plants are by overinvesting in nearby roots and reducing their foraging range when it overlaps with neighboring root systems. The authors suggest that the new findings reconcile conflicting hypotheses and demonstrate they are likely different parts of a complex response.


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