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Critical soil suctions (threshold, tipping point, and permanent wilting) corresponding to initial drought response, near-death stage, and complete mortality, respectively; is essential for formulating irrigation schemes of vegetation grown in compacted soil under drought conditions. The effect of soil types on these critical soil suctions are unexplored and is crucial in understanding the soil-specific plant water functions. This study aims to establish the drought response of Axonopus compressus (grass), based on stomatal conductance (g s ) and chlorophyll fluorescence parameters (CI) grown in different soil types. A. compressus were grown in six soil types (2 coarse-grained and 4 fine-grained soils) for 8 weeks, followed by continued drought condition. The g s and CI were monitored along with soil suction and moisture content. Both leaf and root growth were observed to be higher in coarse-grained soils than fine-grained soils, even though the water retention of the coarse-grained soils were comparatively less. Drought stress initiation in plants was captured by ψ threshold from the CI (especially in fine-grained soils) before the g s response. The three critical soil suctions estimated from the correlation between CI and ψ were found to be increasing with higher soil clay fraction. Corresponding plant available water contents (based on v/v volumetric water content) with each of three critical soil suctions were found to be dependent on the relative growth of canopy to root growth that occurred in different soil medias. Especially, plant available water in 'tipping suction' was dependent on the soil clay fraction (i.e., higher fraction could restrict root water uptake) and is presented with a simple empirical correlation for A. compressus., Competing Interests: Declaration of competing interest All authors state that they have no competing interest to declare., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Aims: Gradients in water potential of soil and plant system drives the water movement in soil-plant-atmospheric continuum. Here, we demonstrate how root water potential measured directly from the roots upon changes in soil water potential would contribute to the understanding of the drought response in Chrysopogon zizanoides. Methods: Plants of Chrysopogon zizanoides L. were sampled at different soil water status (inducing drought) and growth periods (3-, 4- and 5- months). The roots and leaves of the plants were dissected to measure the root water potential and specific leaf area, respectively. The root water potential was measured in a WP4C dew-point potentiometer. Root diameter corresponding to the roots measured for root water potential was also measured. Results: Our findings showed a logarithmic increase in gradient between soil and root water potential under the induced drought stress, similar to the existing findings of root hydraulic conductance. Specific leaf area significantly decreased with root water potential, indicating the hydraulic continuity between roots and leaves. A new power law correlation between root diameter and root water potential established a trait-based understanding of root water uptake. Conclusion: The aggregation of such root water potential measurements using potentiometer would offer strategies to explore the implications of below-ground plant behaviour in applications such as slope stability and irrigation. [ABSTRACT FROM AUTHOR]

Permanent wilting point (PWP) is generally used to ascertain plant resistance against abiotic drought stress and designated as the soil water content (θ) corresponding to soil suction (ψ) at 1500 kPa obtained from the soil water retention curve. Determination of PWP based on only pre-assumed ψ may not represent true wilting condition for soils with contrasting water retention abilities. In addition to ψ, there is a need to explore significance of additional plant parameters (i.e., stomatal conductance and photosynthetic status) in determining PWP. This study introduces a new framework for determining PWP by integrating plant leaf response and ψ during drought. Axonopus compressus were grown in two distinct textured soils (clayey loam and silty sand), after which drought was initiated till wilting. Thereafter, ψ and θ within the root zone were measured along with corresponding leaf stomatal conductance and photosynthetic status. It was found that coarse textured silty sand causes wilting at much lower ψ (≈ 300 kPa) than clayey loam (≈ 1600 kPa). Plant response to drought was dependent on the relative porosity and mineralogy of the soil, which governs the ease at which roots can grow, assimilate soil O2, and uptake water. For clay loam, the held water within the soil matrix does not facilitate easy root water uptake by relatively coarse root morphology. Contrastingly, fine root hair formation in silty sand facilitated higher plant water uptake and doubled the plant survival time. [ABSTRACT FROM AUTHOR]