The interplay between root morphological plasticity and mucilage production facilitates drought adaptation across soil textures

The interplay between root functional traits, such as mucilage secretion and root morphology, in plant response to combined edaphic and atmospheric drought, particularly under contrasting soil texture, remains unknown.

We leveraged two cowpea genotypes differing in mucilage production (high mucilage [HM] and low mucilage [LM]) to investigate plant water use and root morphological responses to two contrasting soil textures (sand and loam).

Both genotypes adapted their root morphological traits in response to soil textures. In contrast to HM, the LM genotype exhibited a twofold increase in root length in sand compared to loam, which resulted in a fourfold increase in root-to-shoot area ratio and specific root length. During soil drying and increasing vapor pressure deficit (VPD), the HM genotype exhibited transpiration limitation at lower transpiration rates compared to LM, hereby promoting more conservative water use, particularly in sand. We further found that the critical soil moisture (SM) threshold, the SM at which plants started to downregulate transpiration, is soil-texture specific.

Our findings suggest that high mucilage production promotes water saving strategy during soil drying. Increasing root length and high root-to-shoot area ratio emerge as compensatory drought-adaptive strategies to coarse-textured soil, especially in LM genotype. Future studies should investigate the interplay between different root functional traits across species and climates.