In habitats with low water availability, a fundamental challenge for plants will be to maximize photosynthetic C‐gain while minimizing transpirational water‐loss. This trade‐off between C‐gain and water‐loss can in part be achieved through the coordination of leaf‐level photosynthetic and hydraulic traits. To test the relationship of photosynthetic C‐gain and transpirational water‐loss, we grew, under common growth conditions, 18 C₄ grasses adapted to habitats with different mean annual precipitation (MAP) and measured leaf‐level structural and anatomical traits associated with mesophyll conductance (g_m) and leaf hydraulic conductance (K_leaf). The C₄ grasses adapted to lower MAP showed greater mesophyll surface area exposed to intercellular air spaces (S_mes) and adaxial stomatal density (SD_ada) which supported greater g_m. These grasses also showed greater leaf thickness and vein‐to‐epidermis distance, which may lead to lower K_leaf. Additionally, grasses with greater g_m and lower K_leaf also showed greater photosynthetic rates (A_net) and leaf‐level water‐use efficiency (WUE). In summary, we identify a suite of leaf‐level traits that appear important for adaptation of C₄ grasses to habitats with low MAP and may be useful to identify C₄ species showing greater A_net and WUE in drier conditions.

中文翻译：

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适应低降水量生境的C4草表现出与更高的叶肉电导和较低的叶水导率相关的性状。

在水资源匮乏的生境中，植物面临的基本挑战将是最大程度地提高光合作用的C增益，同时最大程度地减少蒸腾作用的水分流失。通过叶片水平的光合和水力性状的协调，可以部分实现碳增益与水分损失之间的权衡。为了测试光合作用C增益与蒸腾水分损失的关系，我们在共同的生长条件下生长了18 C ₄草，这些草适应了具有不同年平均降水量（MAP）的生境，并测量了与叶肉相关的叶级结构和解剖特征电导率（g _m）和叶片水力传导率（K _leaf）。C ₄适应较低MAP的草显示出更大的叶肉表面积暴露于细胞间空隙（S _mes）和轴气孔密度（SD _ada），从而支持更大的g _m。这些草还显示出较大的叶片厚度和静脉至表皮距离，这可能导致较低的K_叶片。此外，具有更大的g _m和更低的K_叶片的草还表现出更高的光合速率（A _net）和叶片级水分利用效率（WUE）。总而言之，我们确定了一组叶水平性状，这些特征对于使C ₄草适应低MAP的生境显得很重要，并且可能对识别C ₄有用。在较干燥的条件下，这些物种显示出更高的A_净值和WUE。