Responses of root hairs to soil compaction: A review

In recent years, many studies have investigated the effects of soil compaction on plant root growth. However, root hairs, which are important parts of plants that anchor the soil and absorb nutrients and water, under compacted conditions have received limited attention. We reviewed the responses of root hair structure (behaviors), the rhizosheath, water and nutrient uptake by root hairs, plant hormones and crop species associated with root hairs to soil compaction and proposed potential solutions to mitigate the impacts of soil compaction on root hairs. Soil compaction generally reduces root hair length and density; however, a few studies have reported opposite results for reasons that are unclear. Root hairs exhibit limited water and nutrient uptake capacity, whereas high levels of ethylene have been observed in response to soil compaction. The scales of the effects described above are closely related to genotype. Bio-tillage, the application of ethylene inhibitors, the use of microorganisms and the breeding of soil compaction-tolerant crops may be effective methods to promote root hair growth under soil compaction. High-resolution computed tomography (CT) techniques are needed in the future to study root hair interactions with non-homogeneous soils over large scales.