Imagine you are a pepper plant. You need water and nutrients. Fortunately, you can grow roots that grab that stuff from the ground and spray it back to you. So far so good.
There is only one problem. Your neighbor – also a pepper plant – needs the same things. There is only so much to do. What is your move?
Researchers have spent years looking at the complex problem of root competition and came up with diverse and sometimes conflicting findings about how plants strategically arrange their roots. when the dirt becomes overfilled. An article published in Science earlier this month describes a new model that appears to reconcile this confusion by taking into account the spatial distribution of roots along with their prevalence. In the initial tests conducted by the paper’s authors, real plants played according to the rules set by the model.
It takes energy and materials to grow and maintain a root. Ideally, a plant gets more resources from its roots than it spends on their construction and maintenance. Plants can sense the concentration of water and nutrients in certain soils and divide the roots accordingly to maximize their yield.
This is easy enough for a solitary. But if there are other plants around, the calculus changes. Researchers have borrowed tools from game theory – a way to analyze and optimize decision making, used by everyone, from financial analysts for real gamers – to try to figure out how.
A model published in 2001 predicted that plants growing close together would end in a “tragedy of the commons,” where each individual in a shared space makes more roots than a solitary plant, but also receives fewer rewards. Some real world experiments matched this model and found that plants with neighbors created more root mass than plants that grow alone.
But other studies have found the opposite: that competing plants invested less in roots. And others still didn’t find a noticeable difference.
“There was all this controversy,” said Ciro Cabal, a PhD student in ecology and evolutionary biology at Princeton University and the lead author of the new study.
Mr. Cabal wondered if that model, and other similar models, might be missing a part. They treated all roots the same regardless of their distance from the trunk of the plant. But in reality, the farther a root grows from the plant, the more expensive it is to produce and maintain.
So he and his co-authors built a new model to take that into account. “We’ve built in space,” he said. “And we have found this new theory.”
In their model, a plant facing competition will under-produce those more expensive, wide-spread roots that would otherwise overlap with a neighbor’s. But it will overproduce carrots closer to home, effectively consolidating power and avoiding any “I-drink-your-milkshake” style.
Whether plants with neighbors produce too many or too few roots compared to solo plants depends on how far apart the two competing plants are, Mr Cabal said. So those findings from previous studies that seemed to contradict each other are “all possible according to our model.”
Then the researchers brought this hypothetical math to Earth. They planted peppers in containers – some alone, and some about four inches apart by two – and colored the roots of the rival peppers with dyes to distinguish them. After a few months, they mapped where and how closely the roots of each plant had grown, and found that it matched the model. The paired peppers grew more roots that stayed close to home, and fewer that went further away, compared to the peppers that had containers to themselves.
The new model “provides an excellent basic prediction of how root systems might behave in the presence of neighbors,” bringing together hypotheses and findings that previously seemed contradictory, said Jochen Schenk, a professor of plant biology at California State University Fullerton who does not. used to be. involved in the investigation.
But he warns against generalizing about his findings.
“I wouldn’t accept the claim that a single test with one plant species can tell us what plants will do in general,” he said.
Different species can react to each other in different ways. Recent research also suggests that other life forms, such as fungi and microbes, influence the way some plants interact with each other underground.
Even Mr. Cabal did not expect his model and experiment to match so neatly. While he expects real-life cases to challenge the specifics of the model, “I truly believe the principle we are presenting is true,” he said. Next, he plans to try out his experiment in the wild, on a few types of Mediterranean shrubs.
If it turns out that this strategy is widely used by plants, humans could use it to include more accurate estimates of plant biomass in climate models, Mr Cabal said. And if possible, breeding some of the competitiveness from plants could also improve agricultural yields. Farmers are often hindered by selfish crops that put their energy into roots rather than fruit.
Mr. Cabal and his co-authors also modeled what he called a “cooperative solution” to the nutrient sharing problem. In this scenario, “any plant is not selfish – it is not maximizing its own reward,” he said. Instead, the plants collectively position their roots to produce the most nutrient absorption for the least investment overall.
Unfortunately, experimentally, “we didn’t find it in these plants,” he said.
For now it is every pepper for itself.