Global changes can interact to affect photosynthesis and thus ecosystem carbon capture, yet few multi‐factor field studies exist to examine such interactions. Here, we evaluate leaf gas exchange responses of five perennial grassland species from four functional groups to individual and interactive global changes in an open‐air experiment in Minnesota, USA, including elevated CO₂ (eCO₂), warming, reduced rainfall and increased soil nitrogen supply. All four factors influenced leaf net photosynthesis and/or stomatal conductance, but almost all effects were context‐dependent, i.e. they differed among species, varied with levels of other treatments and/or depended on environmental conditions. Firstly, the response of photosynthesis to eCO₂ depended on species and nitrogen, became more positive as vapour pressure deficit increased and, for a C₄ grass and a legume, was more positive under reduced rainfall. Secondly, reduced rainfall increased photosynthesis in three functionally distinct species, potentially via acclimation to low soil moisture. Thirdly, warming had positive, neutral or negative effects on photosynthesis depending on species and rainfall. Overall, our results show that interactions among global changes and environmental conditions may complicate predictions based on simple theoretical expectations of main effects, and that the factors and interactions influencing photosynthesis vary among herbaceous species.

中文翻译：

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CO5浓度升高，变暖，降雨量减少和氮元素对5种多年生草地物种叶片气体交换的相互作用。

全球变化可能相互作用以影响光合作用，进而影响生态系统的碳捕获，但很少有多因素田间研究来检验这种相互作用。在这里，我们在美国明尼苏达州的一项露天实验中评估了四个功能组的五个多年生草地物种对个体和互动全球变化的叶片气体交换响应，包括升高的CO ₂（eCO ₂），变暖，降雨减少和土壤增加氮气供应。所有这四个因素均影响叶片的净光合作用和/或气孔导度，但几乎所有影响均取决于具体情况，即它们在物种之间不同，随其他处理水平的不同和/或取决于环境条件。首先，光合作用对eCO ₂的响应取决于物种和氮，随着蒸气压亏缺的增加，正值变得更正；对于C ₄草和豆类，在减少降雨的情况下，正值变得更正。其次，降雨减少可能会通过适应低土壤水分增加三个功能上不同的物种的光合作用。第三，变暖对光合作用有正面，中性或负面影响，具体取决于物种和降雨。总体而言，我们的结果表明，全球变化和环境条件之间的相互作用可能会使基于主要作用的简单理论预期而使预测变得复杂，并且影响光合作用的因素和相互作用在不同草种之间也有所不同。