Chair of Soil Physics, Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Bayreuth, Germany.
Department of Horticulture, Faculty of Agriculture, University of Khartoum, Khartoum North, Sudan.
Plant Physiol. 2022 Sep 28;190(2):1228-1241. doi: 10.1093/plphys/kiac229.
Salinity and soil drying are expected to induce salt accumulation at the root-soil interface of transpiring plants. However, the consequences of this on the relationship between transpiration rate (E) and leaf xylem water potential (ψleaf-x) are yet to be quantified. Here, we used a noninvasive root pressure chamber to measure the E(ψleaf-x) relationship of tomato (Solanum lycopersicum L.) treated with (saline) or without 100-mM NaCl (nonsaline conditions). The results were reproduced and interpreted with a soil-plant hydraulic model. Under nonsaline conditions, the E(ψleaf-x) relationship became progressively more nonlinear as the soil dried (θ ≤ 0.13 cm3 cm-3, ψsoil = -0.08 MPa or less). Under saline conditions, plants exhibited an earlier nonlinearity in the E(ψleaf-x) relationship (θ ≤ 0.15 cm3 cm-3, ψsoil = -0.05 MPa or less). During soil drying, salinity induced a more negative ψleaf-x at predawn, reduced transpiration rate, and caused a reduction in root hydraulic conductance (from 1.48 × 10-6 to 1.30 × 10-6 cm3 s-1 hPa-1). The model suggested that the marked nonlinearity was caused by salt accumulation at the root surface and the consequential osmotic gradients. In dry soil, most water potential dissipation occurred in the bulk soil and rhizosphere rather than inside the plant. Under saline-dry conditions, the loss in osmotic potential at the root surface was the preeminent component of the total dissipation. The physical model of water flow and solute transport supports the hypothesis that a buildup of osmotic potential at the root-soil interface causes a large drop in ψleaf-x and limits transpiration rate under drought and salinity.
盐度和土壤干燥预计会在蒸腾植物的根-土界面诱导盐分积累。然而，这种情况对蒸腾速率 (E) 和叶片木质部水势 (ψleaf-x) 之间关系的影响尚未被量化。在这里，我们使用非侵入式根压室来测量番茄（Solanum lycopersicum L.）在处理（盐水）或不处理 100-mM NaCl（非盐水条件）时的 E(ψleaf-x) 关系。结果使用土壤-植物水力模型进行了重现和解释。在非盐水条件下，随着土壤变干（θ ≤ 0.13 cm3 cm-3，ψsoil = -0.08 MPa 或更低），E(ψleaf-x) 关系变得越来越非线性。在盐水条件下，植物在 E(ψleaf-x) 关系中表现出更早的非线性（θ ≤ 0.15 cm3 cm-3，ψsoil = -0.05 MPa 或更低）。在土壤干燥过程中，盐度导致黎明前的 ψleaf-x 更负，蒸腾速率降低，并导致根水力传导率降低（从 1.48 × 10-6 减少到 1.30 × 10-6 cm3 s-1 hPa-1）。该模型表明，明显的非线性是由根表面盐分积累和随之而来的渗透压梯度引起的。在干燥的土壤中，大部分水势耗散发生在土壤基质和根际中，而不是在植物内部。在盐干条件下，根表面的渗透势损失是总耗散的主要组成部分。水流和溶质运移的物理模型支持了这样一种假设，即在根-土界面处渗透压的积累会导致 ψleaf-x 的大幅下降，并限制干旱和盐度下的蒸腾速率。
