Root hairs offer benefit during drought without decreasing yield in good years

Root hairs – tiny protrusions from the root that increase root surface area and interaction between the plant and the soil – are thought to provide several benefits to the plant. In addition to increasing water and nutrient uptake, the hairs, which make up about 2% of the total root mass, increase the diffusion of root exudates and promote the diversification of microbiota. They may also be important for anchorage during growth in certain soil types, despite growing to a maximum of only 1.5mm in angiosperms. While these functions have often been studied in the context of laboratory experiments, they are rarely validated under realistic field conditions, making it difficult to know what effect root hairs have on actual crops.

In a new article published in Annals of Botany, lead author M. Marin and colleagues conducted a field experiment designed to test the impact of root hairs on plant growth and yield under different moisture and soil conditions. To do this, they used five barley genotypes with contrasting root hair length and density. Following growth in the field, the plants’ shoot biomass, water status, and grain yield, among other factors, were measured. Of the two years the crops were studied, the first, 2017, had typical moisture conditions, while the second, 2018, was the driest June-July period in over a century for that location, creating an ideal contrast in moisture levels.

The researchers found that under ideal conditions, root hairs didn’t confer a significant advantage to the barley plants. Under drought conditions, however, the hairs improved plant water status, stress tolerance, phosphorous accumulation, and yield. Soil type had an effect on root hair length, with hairs as much as 46% longer in clay loam compared to sandy loam. Drought itself also affected root hair length, decreasing it progressively through the dry growing season. In fact, the change in root hair length throughout both the drought and non-drought growing seasons was large enough to eclipse the initial differences attributable to genotype.

One notable finding was that under ideal moisture conditions, while root hairs didn’t improve plant performance, neither did they decrease yield. This makes root hairs a valuable target for breeding, such that breeders stand to increase yield stability in dry years without decreasing grain production in good years. Findings such as this have increased value as climate change takes its toll.

“Although Scotland is generally considered a wet country, a large interannual variability of precipitation is predicted for the next decades, which may cause drought stress in crops unless more resilient genotypes are developed,” write the authors. “We may expect root hairs to contribute to drought tolerance in other crops too, but further investigation is needed as root hair traits vary largely between species and there is a lack of field investigations looking at their role under water deficit conditions.”