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 Cell Environ. 2021 Feb;44(2):425-431. doi: 10.1111/pce.13939. Epub 2020 Nov 17.
The fundamental question as to what triggers stomatal closure during soil drying remains contentious. Thus, we urgently need to improve our understanding of stomatal response to water deficits in soil and atmosphere. Here, we investigated the role of soil-plant hydraulic conductance (K ) on transpiration (E) and stomatal regulation. We used a root pressure chamber to measure the relation between E, leaf xylem water potential (ψ ) and soil water potential (ψ ) in tomato. Additional measurements of ψ were performed with unpressurized plants. A soil-plant hydraulic model was used to simulate E(ψ ) for decreasing ψ . In wet soils, E(ψ ) had a constant slope, while in dry soils, the slope decreased, with ψ rapidly and nonlinearly decreasing for moderate increases in E. The ψ measured in pressurized and unpressurized plants matched well, which indicates that the shoot hydraulic conductance did not decrease during soil drying and that the decrease in K is caused by a decrease in soil-root conductance. The decrease of E matched well the onset of hydraulic nonlinearity. Our findings demonstrate that stomatal closure prevents the drop in ψ caused by a decrease in K and elucidate a strong correlation between stomatal regulation and belowground hydraulic limitation.
在土壤干燥过程中引发气孔关闭的根本问题仍然存在争议。因此，我们迫切需要提高对土壤和大气中水分亏缺条件下气孔响应的理解。在这里，我们研究了土壤-植物水力传导度（K）对蒸腾作用（E）和气孔调节的作用。我们使用根压室来测量番茄中 E、叶片木质部水势（ψ）和土壤水势（ψ）之间的关系。使用未加压植物进行了额外的 ψ测量。使用土壤-植物水力模型模拟了ψ下降时的 E（ψ）。在湿润的土壤中，E（ψ）具有恒定的斜率，而在干燥的土壤中，斜率减小，随着 E 的适度增加，ψ迅速且非线性地减小。加压和未加压植物中测量的 ψ 值匹配良好，这表明在土壤干燥过程中，茎部水力传导度没有下降，而 K 的下降是由土壤-根传导度的下降引起的。E 的下降与水力非线性的开始很好地匹配。我们的发现表明，气孔关闭防止了由于 K 的下降而导致的 ψ下降，并阐明了气孔调节和地下水力限制之间的强烈相关性。
