Plant root hairs ‘unrecognized heroes’ that hold the soil together, research shows.

A team of researchers, including Professor Tim Quine from the University of Exeter, has revealed the crucial function the microscopic roots hairs play in binding and reinforcing soil.

While the larger-scale root properties such as diameter, length and surface area have been extensively studied to understand their role in preventing soil erosion,  the effect that micro-scale properties, such as root hairs, has is less well documented.

In this new study, researchers tested the effect that root hairs had on preventing soil loss due to rapidly flowing water.

The found that, when planted in sufficient density, plants with root hairs reduced soil loss almost completely - while otherwise identical plants without hairs could not stem the flow of erosion.

The study is published in the journal Communications Biology on Friday, April 3^rd 2020.

Professor Quine, an expert in Earth System Science at the University of Exeter said: “This exciting, truly interdisciplinary project across biology, maths, engineering and environmental science has given us invaluable new insights into the influence of microscopic root structures on the macroscopic behavior of soils.

“I was amazed at the difference that root density made in reducing soil erosion to almost zero, when root density was high, whereas soil loss was still significant when roots at the same density had no hairs.

“We are excited to explore how the hairs exert this extraordinary influence.”

Soil erosion can have a devastating impact across the globe. The increased demand for agriculture has led to forests and natural grasslands being converted to farm fields and pastures.

However, many of the plants grown, such as coffee, cotton and palm oil, can significantly increase soil erosion beyond the soil’s ability to maintain and renovate. It can also lead to increased pollution and sedimentation in streams and rivers or, because these areas are often less able to hold onto water, can worsen flooding.

In the new study, the research team looked at how the Arabidopsis thaliana wild plants, which produced root hairs, compared with an almost identical Arabidopsis with the same root hair structure in reducing soil erosion.

Three methods were used to explore the soil retention benefits of root hairs. First, the samples were placed in a sterile gel, in a petri dish, and then subjected to increasing centrifugal force. 

The study found that the hairless seedlings were easier to remove from the gel compared to seedlings abundant with root hairs. Second, the study found that root hairs were also shown to stabilize the plant in the soil, as they increased the force needed to uproot the plant. Third, in the experimental landscapes laboratory at Exeter, root hairs reduced water erosion to almost zero.

Claire Grierson, lead author and from the University of Bristol explained “There are three possible ways root hairs could enhance soil:  “(i) soil might bind directly to root hair surfaces; (ii) root hairs might release material that reinforces soil; and (iii) root hairs might release material that is processed by microbes into something that can reinforce soil.” The team are now working to distinguish between these hypotheses and identify the molecules involved.

This research was an interdisciplinary collaboration led by Claire Grierson at Bristol, environmental scientist Tim Quine at the University of Exeter, and Tannie Liverpool and Isaac Chenchiah of the School of Mathematics at Bristol. It was supported by a Leverhulme Trust project grant, two BBSRC SWBio PhD studentships and an EPSRC-funded Bristol Centre for Complexity Sciences PhD studentship.