To sustain high production of alfalfa (Medicago sativa) with limited water resource in many areas, cultivars with improved water use efficiency (WUE) are urgently needed. We recently conducted greenhouse experiments and identified an alfalfa collection, River side (RS) that is naturized to the environment in the Grand River National Grassland in South Dakota, with a greater water use efficiency (WUE) under drought than other ten alfalfa accessions. To understand the mechanisms that may contribute to the higher WUE in RS, we examined physiological and morphological traits in comparison with Alfagraze (AF), a commercial variety with lower WUE under drought under greenhouse conditions. RS showed a greater reduction of water loss through transpiration despite more stomata per unit area under drought. Both RS and AF showed a reduction of stomatal aperture under drought compared to respective well-watered plants but stomatal aperture in RS was smaller compared to AF regardless of irrigation status. Leaves of RS showed a more rapid accumulation of abscisic acid (ABA), at 14 days versus at 28 days in AF under drought. RS also closed stomata more rapidly when treated with 10 ÂµM ABA. In addition, leaves of RS showed denser but shorter leaf hairs under drought. A correlation analysis points to a greater stomatal sensitivity to ABA in RS as a key factor contributing to its greater WUE under drought.

中文翻译：

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苜蓿高水分利用生理和形态特征的鉴定

维持苜蓿（Medicago sativa）的高产) 在许多地区水资源有限，迫切需要提高水资源利用效率 (WUE) 的品种。我们最近进行了温室试验，并确定了一种苜蓿藏品，河边 (RS)，它在南达科他州格兰德河国家草原的环境中自然化，在干旱条件下的水分利用效率 (WUE) 比其他 10 种苜蓿品系更高。为了了解可能导致 RS 中 WUE 较高的机制，我们检查了与 Alfagraze (AF) 相比的生理和形态特征，Alfagraze (AF) 是一种在温室条件下干旱时 WUE 较低的商业品种。尽管在干旱条件下每单位面积有更多的气孔，但 RS 显示通过蒸腾作用减少的水分流失更多。与灌溉充足的植物相比，RS 和 AF 在干旱条件下的气孔孔径均减小，但无论灌溉状态如何，RS 的气孔孔径均小于 AF。在干旱条件下，与 AF 中的 28 天相比，RS 的叶子在 14 天时表现出更快的脱落酸 (ABA) 积累。当用 10 µM ABA 处理时，RS 也会更快地关闭气孔。此外，RS 的叶子在干旱下表现出更浓密但更短的叶毛。相关性分析指出，RS 中对 ABA 的更大气孔敏感性是导致干旱条件下其 WUE 更大的关键因素。当用 10 µM ABA 处理时，RS 也会更快地关闭气孔。此外，RS 的叶子在干旱下表现出更浓密但更短的叶毛。相关性分析指出，RS 中对 ABA 的更大气孔敏感性是导致干旱条件下其 WUE 更大的关键因素。当用 10 µM ABA 处理时，RS 也会更快地关闭气孔。此外，RS 的叶子在干旱下表现出更浓密但更短的叶毛。相关性分析指出，RS 中对 ABA 的更大气孔敏感性是导致干旱条件下其 WUE 更大的关键因素。