Going underground: soil hydraulic properties impacting maize responsiveness to water deficit

Abstract

Purpose Although the coordination between stomatal closure and aboveground hydraulics has extensively been studied, our understanding of the impact of belowground hydraulics on stomatal regulation remains incomplete. Here, we investigated whether and how the water use of maize (Zea mays L.) varied under hydraulically contrasting soil textures. Our hypothesis is that a textural-specific drop in the hydraulic conductivity is associated with a distinct decrease in transpiration during soil drying. Methods Maize plants were grown in contrasting soil textures (sand, sandy loam, loam) and exposed to soil drying. We measured the relationships between transpiration rate, soil water content as well as soil and leaf water potential. We used a soil-plant hydraulic model to reproduce the experimental observations and infer the hydraulic conductance of the soil-plant system during soil drying. Results We observed the impact of soil texture on plant response to soil drying in various relationships. The soil water potentials at which transpiration decreased were more than one order of magnitude more negative in loam than in sand. The soil-plant conductance decreased not only abruptly but also at less negative soil water potentials in sand than in sandy loam or loam. Stomata closed at less negative leaf water potentials in sand than in loam. The model predictions matched well the experimental observations. Conclusion The results elucidated that the critical soil water content and potential at which plants close stomata depends on the soil texture. These findings support our plea to include soil properties for understanding and predicting stomatal regulation during soil drying.

The effect of root hairs on root water uptake is determined by root–soil contact and root hair shrinkage

“…Nevertheless, the extent to which the hydraulic conductivity of hairs decreases after shrinkage still needs to be investigated. Note that the soil matric potential range of −1 to −0.1 MPa coincides with the water potential range in which transpiration rate decreases due to stomatal closure (Koehler et al ., 2022). The authors carried out a soil column experiment using the same maize genotype grown in the same soil texture as in our experiment and measured the relationship between soil water potential and transpiration rate.…”

Soil‐plant hydraulics explain stomatal efficiency‐safety tradeoff

“…In this region, plants with higher g max show more negative midday leaf water potential than plants with lower g max . As the soil dries, the loss in soil hydraulic conductivity induces stomatal closure (Abdalla et al, 2022; Cai, König, et al, 2022; Carminati & Javaux, 2020; Koehler et al, 2022) and maintains midday leaf water potential very close to the SOL curve. Plants with high g max reach the SOL curve at less negative predawn leaf water potential (i.e., in wetter soils) than species with low g max , but the corresponding midday leaf water potential of species with high g max was not as negative as species exhibiting lower g max (Figure 2e,f).…”

Special issue: Rhizosphere spatiotemporal organisation: an integrated approach linking above and belowground

“…Experimental data on the role of soil texture and root hairs for the development of drought stress have been interpreted using modelling approaches at the laboratory scale for the juvenile phase (Köhler et al, 2022) and at field scale during the whole growing period in two consecutive years (Jorda et al, 2022). Jorda et al (2022) show that the root capacity was large enough to absorb all available soil water and that the onset of drought stress was primarily related to shoot size.…”