Researchers at the Universities of Bristol and Exeter in the United Kingdom have found that tiny hairs on plant roots play a pivotal role in reducing soil erosion and increasing soil cohesion.
“I have been a root hair biologist since 1993,” said professor Claire Grierson, head of school in Life Sciences with the University of Bristol.
The team studied Arabidopsis thaliana, thale cress native to Eurasia and Africa and widely used in plant biology studies.
The plant was compared with an almost identical Arabidopsis subspecies that does not grow the same root hair structure. Researchers found that, when planted in sufficient density, the plant with root hairs reduced soil loss almost completely, while the plant without the microscopic hairs could not stop soil erosion.
The team developed three different assays. One included placing roots in a sterile gel in a petri dish and subjecting them to increasing centrifugal force. A second assay placed young plants in pots and the researchers measured their resistance when they were slowly pulled out. A third test focused on erosion using simulated flood waters and how much soil washed away.
The hairless seedlings were far easier to remove from the gel than those with microscopic hairs; the root hairs of potted plants showed that they stabilized the plants since they increased the force needed to uproot the plant. In the experimental landscapes laboratory, root hairs reduced water erosion to almost zero.
“The root hairs had a massive effect in all three assays, which was a real surprise,” said Grierson.
She said the findings could be key to tackling soil erosion and there are three possible ways root hairs function. Either the soil might bind directly to root hair surfaces, root hairs might release material that reinforces soil, or root hairs might release material that is processed by microbes into something that can reinforce soil.
She said about 70 percent of plants likely have these tiny root hairs, they tend to disappear later in the plant’s life, either from shrivelling or rotting away. At the same time, the plant also develops a symbiotic relationship with fungi.
“Mycorrhizal fungi, also known as root fungi, is doing a similar job holding soil and roots together,” she said. “The fungi are literally growing through the roots, connecting physically, and the roots are growing into the soil. I think in some cases they are doing the job instead of the hair.”
Plant roots secrete compounds that have been shown to promote soil binding, but until now there has been no clear evidence of the role of root hairs in soil cohesion.
Grierson also suspects that proteins are involved.
“We are looking at the role of the proteins and there are at least 60 proteins secreted by root hairs. But they are not present in the secretions of the roots that don’t have hairs. We have actually got work going on right now with mutant plants where the root hairs look completely normal but we’ve (deliberately) damaged the gene that affects one of these proteins that would normally be secreted by the root hairs. We could see that those plant roots were no longer sticking to soils.”
Researchers are now trying to determining exactly how these tiny hairs control and bind soil. They are looking at leads such as molecules.
“A lot of the control is directly through binding with soil particles but we haven’t proved that yet,” she said. “I think the roots are also modifying the soil by secreting material that is changing the soil, sticking it together. This is our ongoing research. There are often hairs on root tips and, as the root matures, the hairs are modifying the soil around the root in a way that it is more stable and more likely to stay attached. We don’t know how long that effect lasts. We haven’t tested this yet.”
With a deeper understanding of the role of tiny root hairs, it could produce better crops to minimize erosion, which would be helpful for farmers.
The research was published in Communications Biology.