Stomatal closure during water deficit is controlled by below-ground hydraulics

• Published in: Annals of botany Vol. 129; no. 2; pp. 161 - 170
• Main Authors: Abdalla, Mohanned, Ahmed, Mutez Ali, Cai, Gaochao, Wankmüller, Fabian, Schwartz, Nimrod, Litig, Or, Javaux, Mathieu, Carminati, Andrea
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 28.01.2022
• Subjects: Original; Plant Leaves - physiology; Plant Roots - physiology; Plant Stomata - physiology; Plant Transpiration - physiology; Soil; Water - physiology; Xylem - physiology; water stress; hydraulic limitations; root system; hydraulic signal; modelling; Solanum lycopersicum
• DOI: 10.1093/aob/mcab141
• ISSN: 0305-7364; 1095-8290

Stomatal closure allows plants to promptly respond to water shortage. Although the coordination between stomatal regulation, leaf and xylem hydraulics has been extensively investigated, the impact of below-ground hydraulics on stomatal regulation remains unknown. We used a novel root pressure chamber to measure, during soil drying, the relation between transpiration rate (E) and leaf xylem water pressure (ψleaf-x) in tomato shoots grafted onto two contrasting rootstocks, a long and a short one. In parallel, we also measured the E(ψleaf-x) relation without pressurization. A soil-plant hydraulic model was used to reproduce the measurements. We hypothesize that (1) stomata close when the E(ψleaf-x) relation becomes non-linear and (2) non-linearity occurs at higher soil water contents and lower transpiration rates in short-rooted plants. The E(ψleaf-x) relation was linear in wet conditions and became non-linear as the soil dried. Changing below-ground traits (i.e. root system) significantly affected the E(ψleaf-x) relation during soil drying. Plants with shorter root systems required larger gradients in soil water pressure to sustain the same transpiration rate and exhibited an earlier non-linearity and stomatal closure. We conclude that, during soil drying, stomatal regulation is controlled by below-ground hydraulics in a predictable way. The model suggests that the loss of hydraulic conductivity occurred in soil. These results prove that stomatal regulation is intimately tied to root and soil hydraulic conductances.