Plant & zo
The science of plants and more
Compact soil protocol
For good rooting a not to close packed soil is a must for plants. When the ground is to compact it costs the roots more effort to find a way through. In agriculture, this is increasingly a problem. Here, intensive use of the ground results in compact soils. More difficult to access for the plant. Resulting in a lower yield. Long was thought that this was just a consequence of more resistance. But it turns out, this is not the whole story.
To find out the compactness of the soil a plant uses the volatile hormone ethylene. The roots release ethylene. Ethylene, as a gas, evaporates through all possible holes, trying to find a way up. Is this impossible, because there are hardly any holes, then ethylene stays near the roots. Then, it is noticed by the ethylene receptor, turning on the compact soil protocol.
Long it was unclear how exactly the compact soil protocol works. Only its output, a slower root growth and thicker roots, was known. Now British researchers uncovered in rice how the compact soil protocol works. The researchers observed higher amounts of the plant hormone ABA, in roots growing in compact soil. This, noticed the researchers, was the cause for the swollen roots. Unexpectedly, the thinner roots of a mutant that does not make any ABA were growing with ease through compact soils.
Through slowing down growth and increasing root thickness, the compact soil protocol makes it difficult to grow through compact ground
Another well known plant hormone to influence root growth is auxin. Ethylene, it turned out, was also influencing this hormone. Roots growing in compact soils had more auxin, but not those of a mutant without ethylene production. In compact soil increases ethylene the production of auxin.
One of auxin jobs is preventing cells stretching out too soon. Nearby the root growth region, auxin levels are high, but the further away the cell gets, the lower the auxin levels. Eventually, when far enough from the growth region, auxin levels are low enough that the cell is permitted to stretch. Ethylene, through promoting auxin production, is preventing cells from stretching out for even longer. So, slowing down the growth. Just like mutants without ABA, mutants that don’t make any auxin are growing more easily through compact soil.
The compact soil protocol is actively causing slower root growth. Through slowing down growth and increasing root thickness. In mutants were this didn’t occur the resistance of compacter soil was not enough to slow down the growth. Begs the question: Do we still need a compact soil protocol? Or could we start with breeding crops that cleave through the ground with ease?
Literature
Guoqiang Huang, Azad Kilic, Michal Karady, Jiao Zhang, Poonam Mehra, Xiaoyun Song, Craig J. Sturrock, Wanwan Zhu, Hua Qin, Sjon Hartman, Hannah M. Schneider, Rahul Bhosale, Ian C. Dodd, Robert E. Sharp, Rongfeng Huang, Sacha J. Mooney, Wanqi Liang, Malcolm J. Bennett, Dabing Zhang, Bipin K. Pandey (2022) Ethylene inhibits rice root elongation in compacted soil via ABA- and auxin-mediated mechanisms. PNAS, 119 (30) e2201072119, https://doi.org/10.1073/pnas.2201072119
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