Growth & Development

Groping in the soil for nutrients encourages root growth

In addition to root proliferation, the root response to a nutrient-rich patch was also accompanied by root hair elongation.

Plants hunt in the soil for nutrients, and grabbing nitrogen or phosphorus can improve a plant’s chances to survive or thrive. But nutrients are often not evenly distributed in the earth. Plants allocate resources to lateral roots and root hairs when they find nutrients. It’s not clear how they do this, so Liyang Wang and colleagues in China and Germany have studied how maize grows below the soil surface.

Maize roots. Image: Canva.

Often the problem with phosphorus for plants isn’t that it’s missing from the soil. It’s that it’s fixed where it is in the soil. It doesn’t move easily in solutions, so the plant has to find it. A plant hunts for nutrients by growing lateral roots or root hairs. When it finds them it can exude chemicals to help break down the soil for phosphorus.

Root hairs, the finest roots, are thought to be the easiest for a plant to make. They can expand the volume of soil that a plant can pick up nutrients from. But there’s no point making them where the soil is barren. So what triggers root hair formation?

Wang and colleagues compared how two types of maize plants coped with a heterogeneous nutrient supply. One was a wild-type. The other was a hairless mutant rth3. They supplied phosphorus in localised patches in the soil. They expected that the plants without root hairs would have lower growth, and that where the plants found phosphorus, there would be more root hairs, or for the hairless plant, more roots to gather the phosphorus.

They found that phosphorus increased root hair density as expected. However, for the mutant plants, it appears that the more expensive lateral roots compensated for the lack of root hairs.

“Root hair traits are critical for maize growth and P acquisition, especially under P-limited conditions,” the authors write. “In terms of nutrient management, localized application of nutrients could greatly improve P uptake and maize growth (both in WT and rth3), but this also depends on external nutrient supply intensity. This study also confirmed that root hairs could respond to heterogeneous nutrients in the soil, manifested as significant increases in root hair length, which were largely regulated by local nutrient signals. In addition, plants can regulate the combination of root traits, and enhanced root proliferation in nutrient-rich patch compensates for the negative effects of the absence of root hairs on nutrient acquisition.”

RESEARCH ARTICLE

Wang L, Li X, Mang M, Ludewig U, Shen J. 2021. Heterogeneous nutrient supply promotes maize growth and phosphorus acquisition: additive and compensatory effects of lateral roots and root hairs. Annals of Botany 128: 431–440. https://doi.org/10.1093/aob/mcab097

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