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Background <p>Plants are often classified on a spectrum from isohydric to anisohydric depending on the extent of stomatal regulation of plant water status, but this concept remains controversial. We examined the stomatal behavior of 30 winegrape cultivars with diverse geographic origins and fivefold differences in canopy size. Using controlled irrigation in an arid climate, we imposed soil drydown cycles in each of two years, measured changes in soil moisture, leaf water potential (Ψ<sub>leaf</sub>), and gas exchange, and calculated derived traits that are commonly used to describe plant hydraulic strategies.</p> Results <p>When measured against relative extractable soil water (θ<sub>e</sub>), all cultivars maintained constant stomatal conductance (g<sub>s</sub>) as the soil dried from θ<sub>e</sub> &gt; 1 to 0.33, and decreased g<sub>s</sub> at θ<sub>e</sub> &lt; 0.33. When measured against predawn leaf water potential (Ψ<sub>pd</sub>) as a proxy for soil water potential (Ψ<sub>soil</sub>), all cultivars began lowering g<sub>s</sub> at Ψ<sub>pd</sub> ≈ -0.3&#xa0;MPa (corresponding to θ<sub>e</sub> ≈ 0.33 and Ψ<sub>soil</sub> ≈ -0.2&#xa0;MPa) until the stomata were essentially closed at Ψ<sub>pd</sub> &lt; -0.7&#xa0;MPa. As residual transpiration continued, leaf wilting began at Ψ<sub>pd</sub> &lt; -1.5&#xa0;MPa. Thus, while the rate of soil drying varied depending on canopy size, stomatal regulation of Ψ<sub>leaf</sub> was broadly conserved across cultivars, with common thresholds for stomatal closure and turgor loss. Leaf area-specific whole-plant hydraulic conductance followed the same patterns as g<sub>s</sub> but increased further as g<sub>s</sub> reached a plateau. Cultivar rankings differed for distinct traits used to assess and describe plant hydraulic strategy, and the 30 cultivars did not fall on a continuum from isohydric to anisohydric behavior for any measured trait.</p> Conclusion <p>In winegrapes, stomatal regulation of Ψ<sub>leaf</sub> is similar across cultivars, but cultivars might variously be classified as isohydric or anisohydric depending on the extent of water stress and the choice of driving variables. The similarity of stomatal behavior across 30 cultivars indicates limited potential for using cultivar choice or targeting g<sub>s</sub> in breeding as adaptation strategies to drought.</p>

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Conserved stomatal regulation across winegrape cultivars challenges conclusions regarding hydraulic strategies

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月6日

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  • Charles O. Obiero,
  • Markus Keller

摘要

Background

Plants are often classified on a spectrum from isohydric to anisohydric depending on the extent of stomatal regulation of plant water status, but this concept remains controversial. We examined the stomatal behavior of 30 winegrape cultivars with diverse geographic origins and fivefold differences in canopy size. Using controlled irrigation in an arid climate, we imposed soil drydown cycles in each of two years, measured changes in soil moisture, leaf water potential (Ψleaf), and gas exchange, and calculated derived traits that are commonly used to describe plant hydraulic strategies.

Results

When measured against relative extractable soil water (θe), all cultivars maintained constant stomatal conductance (gs) as the soil dried from θe > 1 to 0.33, and decreased gs at θe < 0.33. When measured against predawn leaf water potential (Ψpd) as a proxy for soil water potential (Ψsoil), all cultivars began lowering gs at Ψpd ≈ -0.3 MPa (corresponding to θe ≈ 0.33 and Ψsoil ≈ -0.2 MPa) until the stomata were essentially closed at Ψpd < -0.7 MPa. As residual transpiration continued, leaf wilting began at Ψpd < -1.5 MPa. Thus, while the rate of soil drying varied depending on canopy size, stomatal regulation of Ψleaf was broadly conserved across cultivars, with common thresholds for stomatal closure and turgor loss. Leaf area-specific whole-plant hydraulic conductance followed the same patterns as gs but increased further as gs reached a plateau. Cultivar rankings differed for distinct traits used to assess and describe plant hydraulic strategy, and the 30 cultivars did not fall on a continuum from isohydric to anisohydric behavior for any measured trait.

Conclusion

In winegrapes, stomatal regulation of Ψleaf is similar across cultivars, but cultivars might variously be classified as isohydric or anisohydric depending on the extent of water stress and the choice of driving variables. The similarity of stomatal behavior across 30 cultivars indicates limited potential for using cultivar choice or targeting gs in breeding as adaptation strategies to drought.