In wheat, night-time transpiration rate (TR_N) could amount to 14–55% of daytime transpiration rate (TR), depending on the cultivar and environment. Recent evidence suggests that TR_N is much less responsive to soil drying than daytime TR, and that such ‘wasteful’ water losses would increase the impact of drought on yields. In contrast, other evidence indicates that pre-dawn, circadian increases in TR_N may enable enhanced radiation use efficiency, resulting in increased productivity under water deficit. Until now, there have been no attempts to evaluate these seemingly conflicting hypotheses in terms of their impact on yields in any crop. Here, using the Mediterranean environment of Tunisia as a case study, we undertook a simulation modelling approach using SSM-Wheat to evaluate yield outcomes resulting from these TR_N trait modifications. TR_N represented 15% of daytime TR-generated yield penalties of up to 20%, and these worsened when TR_N was not sensitive to soil drying TR. For the same TR_N level (15%), simulating a predawn increase in TR_N alleviated yield penalties, leading to yield gains of up to 25%. Overall, this work suggests that decreasing TR_N but increasing pre-dawn circadian control would be a viable breeding target to increase drought tolerance in a Mediterranean environment.

在小麦中，取决于品种和环境，夜间蒸腾速率（TR _N）可能占白天蒸腾速率（TR）的14-55％。最近的证据表明，TR _N对土壤干燥的响应远不如白天TR，而且这种“浪费”的水损失将增加干旱对单产的影响。相比之下，其他证据表明，黎明前，昼夜增加TR _ñ可以提高辐射的利用效率，从而在缺水的情况下提高生产率。迄今为止，还没有尝试根据它们对任何作物的产量的影响来评估这些看似矛盾的假设。在此，以突尼斯的地中海环境为例，我们使用SSM-Wheat进行了模拟建模，以评估这些TR _N性状改良产生的产量结果。TR _N代表白天TR产生的高达20％的产量损失的15％，当TR _N对土壤干燥TR不敏感时，这些损失会恶化。对于相同的TR _N水平（15％），模拟TR _N的黎明前增加减轻了产量损失，导致收益增加高达25％。总的来说，这项工作表明减少TR _N，但增加黎明前的昼夜节律控制将是提高地中海环境中耐旱性的可行育种目标。