Hard to crack research reveals how crop roots penetrate hard soils

Scientists have discovered a signal that causes the roots of plants to stop growing in hard soils, which can be ‘switched off’ to allow them to punch through compacted soil – a discovery that could help plants to grow in even the driest of climates. Scientists from Utrecht University publish their findings, together with an international research team on 15 January in Science.

Hard (compacted) soils represent a major challenge facing modern agriculture that can reduce crop yields over 50% by reducing root growth, causing significant losses annually. Europe has over 33-million-hectares of soil prone to compaction which represents the highest area in the world. Soil compaction triggers a reduction in root penetration and uptake of water and nutrients. Despite its clear importance for agriculture and global food security, the mechanism underpinning root compaction responses has been unclear until now.

“Understanding how roots penetrate hard soils has huge implications for agriculture, as this knowledge will be crucial for breeding crops more resilient to soil compaction”, says Professor Malcolm Bennett from the University of Nottingham School of Biosciences, who led the research. “Our team’s identification that the plant signal ethylene controls root responses to hard soil opens up new opportunities to select novel compaction-resistant crops.”

Switch-off

The research utilised X-ray Computed Tomography scanners available at the Hounsfield Facility at the University of Nottingham to visualise in situ how plant roots responded to compacted soil. “Prior to this research we assumed that the hardness of the soil prevented roots growing deeper. By using our imaging approach, we were able to see that roots continued growing in very hard soils when the ethylene signal was switched off”, explains Prof. Sacha Mooney from the University of Nottingham and Director of the Hounsfield Facility. “The potential for new crops that can now go deeper in soils and capture previously unavailable resources is really exciting!”

A crucial finding described in the Science publication is the extremely hampered diffusion of the gaseous hormone ethylene. “The resulting entrapment of ethylene in roots growing in compacted soils made it possible for ethylene to act as an early warning signal for compaction”, explains Sjon Hartman, who performed the ethylene work at Utrecht University, together with Prof. Rens Voesenek. “When plants can no longer perceive ethylene, the ethylene alarm bells won’t ring in hard soils and the roots will continue to grow,” says Voesenek.

The international team involved in this new Science paper includes researchers drawn from nine universities based in Europe, China and USA, integrating expertise spanning plant and soil sciences, bioimaging and mathematics.