Minimum conductance (g_w,min) in leaves is important for water relations in land plants. Yet, its regulation is unclear due to measurement constraints. Cuticle conductance to water vapor (g_cw) was estimated from the difference between calculated and direct measurement of CO₂ concentration in the leaf airspace (C_i) of amphi-stomatous tobacco and sunflower. We estimated g_cw in a series of light and dark experiments, and partitioned g_w,min into cuticle and stomatal components. Some leaves were detached to simulate severe drought through desiccation conditions where g_w,min is generally determined. Between light and dark experiments each g_cw was in close agreement, and successfully corrected the discrepancies of calculations from direct measurements. In the dark, either stomatal or cuticle conductance dominated the g_w,min, suggesting either of them can control the minimum water loss. In the detached leaves, g_cw could not be estimated likely due to unsaturation in the leaf airspace, and g_w,min was progressively underestimated. Besides cuticle, leaf water status is a potential pitfall of the standard gas exchange model. Our technique is useful to study the minimal gas exchange as well as to refine the model.

中文翻译：

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叶片表皮，气孔渗漏或水蒸气饱和度的电导最小？

叶片中的最小电导（g _w，min）对于陆地植物中的水关系很重要。然而，由于测量限制，其调节尚不清楚。通过计算和直接测量两口烟草和向日葵叶片气隙（C _i）中的CO ₂浓度之间的差异，可以估算表皮对水蒸气的电导率（g _cw）。我们在一系列明暗实验中估计了g _cw，并将g _w，min分为表皮和气孔成分。通过干燥条件（g _w，min通常是确定的。在明暗实验之间，每g _cw都非常吻合，并且成功地校正了直接测量的计算差异。在黑暗中，任一或气孔角质层电导为主的克_{瓦特，最小}，这表明它们中的可控制的最低水分损失。在离体的叶片中，由于叶片气隙中的不饱和度，无法估计出g _cw，并且逐渐低估了g _w，min。除表皮外，叶片水分状态是标准气体交换模型的潜在陷阱。我们的技术对于研究最小的气体交换以及完善模型非常有用。