Comparing the classical permanent wilting point concept of soil (−15,000 hPa) to biological wilting of wheat and barley plants under contrasting soil textures

Abstract

Recent studies have shown that the permanent wilting point is influenced by soil properties and plant drought-tolerance mechanisms. This study was designed to evaluate the soil matric potential at which the biological wilting point (BWPplant) of wheat and barley cultivars occurs compared to the classic concept of the permanent wilting point at a matric potential of -15,000 hPa for soils (PWPsoil) with contrasting textures. The study was performed under greenhouse conditions with the experiment arranged in a completely randomised design in a double factorial scheme with three soil textures (sandy loam - SL, sandy clay loam - SCL and clay - C) and four plants (two crops (wheat and barley) and two cultivars for each crop). The 95 % confidence intervals were used to compare treatment means. The results revealed that BWPplant could occur at matric potential values > −15,000 hPa, i.e. wetter conditions than for the classical PWPsoil. Plants cultivated in clay soils withered at lower matric potentials than those in sandy soils, which could be related to a hydraulic cut-off that occurs at higher matric potentials in sandy soils. Barley plants were more sensitive to water deficits than wheat plants. The BWPplant for barley plants could occur at matric potentials values > −15,000 hPa, independently of soil texture, whereas wheat plants wilted at matric potentials > −15,000 hPa only in sandy soils (e.g. −1,637 to −2,417 hPa). Our results suggest that wilting depends on soil texture, with an occurrence of wilting at higher matric potentials (i.e. at wetter soil conditions) for sandy soils than for clay soils. Furthermore, plants/cultivars exhibit various tolerance mechanisms to drought, and wheat is able to take up water at considerably lower matric potentials (at dryer soil conditions) than barley. Thus, the wilting matric potential threshold across various species and cultivars is not uniform.