Department of Viticulture & Enology, University of California, Davis, CA, USA.
Faculty of Land and Food Systems, The University of British Columbia, Vancouver, British Columbia, Canada.
Ann Bot. 2022 Mar 23;129(4):389-402. doi: 10.1093/aob/mcab132.
Living root tissues significantly constrain plant water uptake under drought, but we lack functional traits to feasibly screen diverse plants for variation in the drought responses of these tissues. Water stress causes roots to lose volume and turgor, which are crucial to root structure, hydraulics and growth. Thus, we hypothesized that root pressure-volume (p-v) curve traits, which quantify the effects of water potential on bulk root turgor and volume, would capture differences in rootstock drought tolerance.
We used a greenhouse experiment to evaluate relationships between root p-v curve traits and gas exchange, whole-plant hydraulic conductance and biomass under drought for eight grapevine rootstocks that varied widely in drought performance in field trials (101-14, 110R, 420A, 5C, 140-Ru, 1103P, Ramsey and Riparia Gloire), grafted to the same scion variety (Vitis vinifera 'Chardonnay').
The traits varied significantly across rootstocks, and droughted vines significantly reduced root turgor loss point (πtlp), osmotic potential at full hydration (πo) and capacitance (C), indicating that roots became less susceptible to turgor loss and volumetric shrinkage. Rootstocks that retained a greater root volume (i.e. a lower C) also maintained more gas exchange under drought. The rootstocks that previous field trials have classified as drought tolerant exhibited significantly lower πtlp, πo and C values in well-watered conditions, but significantly higher πo and πtlp values under water stress, than the varieties classified as drought sensitive.
These findings suggest that acclimation in root p-v curve traits improves gas exchange in persistently dry conditions, potentially through impacts on root hydraulics or root to shoot chemical signalling. However, retaining turgor and volume in previously unstressed roots, as these roots deplete wet soil to moderately negative water potentials, could be more important to drought performance in the deep, highly heterogenous rooting zones which grapevines develop under field conditions.
在干旱条件下，活体根系极大地限制了植物对水分的吸收，但我们缺乏功能特征来切实筛选不同植物在这些组织对干旱响应方面的差异。水分胁迫会导致根系失去体积和膨压，而这对根系结构、水力和生长至关重要。因此，我们假设，量化水势对整体根系膨压和体积影响的根压-体积（p-v）曲线特征，可以捕捉砧木耐旱性的差异。
我们使用温室实验，评估了 8 种不同抗旱性的葡萄砧木（101-14、110R、420A、5C、140-Ru、1103P、Ramsey 和 Riparia Gloire）的根 p-v 曲线特征与气体交换、整株水力导度和生物量之间的关系，这些砧木在田间试验中表现出广泛的耐旱性差异（101-14、110R、420A、5C、140-Ru、1103P、Ramsey 和 Riparia Gloire），并嫁接到相同的接穗品种（Vitis vinifera 'Chardonnay'）上。
这些特性在砧木之间差异显著，干旱条件下，葡萄藤的根膨压损失点（πtlp）、完全水合时的渗透压（πo）和电容（C）显著降低，这表明根系对膨压损失和体积收缩的敏感性降低。保持较大根体积（即较低 C）的砧木在干旱条件下也能维持更多的气体交换。在田间试验中被归类为耐旱的砧木，在水分充足的条件下表现出明显较低的 πtlp、πo 和 C 值，但在水分胁迫下，表现出明显较高的 πo 和 πtlp 值，而被归类为耐旱性较差的砧木则表现出明显较低的 πtlp、πo 和 C 值。
这些发现表明，根 p-v 曲线特征的适应可以改善持续干旱条件下的气体交换，这可能是通过对根水力或根到梢的化学信号的影响。然而，在葡萄在田间条件下形成的深层、高度异质的根系区保留膨压和体积，对于在较深、高度异质的根系区中保持干旱性能可能更为重要，因为这些根系会耗尽湿润土壤到中等负的水势。
