Breaking new ground: Decoding the root's molecular circuits to penetrate compacted soil

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.

Alfalfa Responses to Intensive Soil Compaction: Effects on Plant and Root Growth, Phytohormones and Internal Gene Expression

The perennial legume alfalfa (Medicago sativa L.) is of high value in providing cheap and high-nutritive forages. Due to a lack of tillage during the production period, the soil in which alfalfa grows prunes to become compacted through highly mechanized agriculture. Compaction deteriorates the soil's structure and fertility, leading to compromised alfalfa development and productivity. However, the way alfalfa responses to different levels of soil compaction and the underlying molecular mechanism are still unclear. In this study, we systematically evaluated the effects of gradient compacted soil on the growth of different cultivars of alfalfa, especially the root system architecture, phytohormones and internal gene expression profile alterations. The results showed that alfalfa growth was facilitated by moderate soil compaction, but drastically inhibited when compaction was intensified. The inhibition effect was universal across different cultivars, but with different severity. Transcriptomic and physiological studies revealed that the expression of a set of genes regulating the biosynthesis of lignin and flavonoids was significantly repressed in compaction treated alfalfa roots, and this might have resulted in a modified secondary cell wall and xylem vessel formation. Phytohormones, like ABA, are supposed to play pivotal roles in the regulation of the overall responses. These findings provide directions for the improvement of field soil management in alfalfa production and the molecular breeding of alfalfa germplasm with better soil compaction resilience.