Past research has shown that plants possess the capacity to alter their instantaneous response of photosynthesis to temperature in response to a longer-term change in temperature (i.e. acclimate). This acclimation is typically the result of processes that influence net photosynthesis (A_net), including leaf biochemical processes such as the maximum rate of Rubisco carboxylation (V_cmax) and the maximum rate of photosynthetic electron transport (J_max), stomatal conductance (g_s) and dark respiration (R_d). However, these processes are rarely examined in the field or in concert with other environmental factors, such as precipitation amount. Here, we use a fully factorial warming (active heating up to +4 °C; mean = +3.1 °C) by precipitation (−50 % ambient to 150 % ambient) manipulation experiment in an old-field ecosystem in the north-eastern USA to examine the degree to which Ulmus americana saplings acclimate through biochemical and stomatal adjustments. We found that rates of A_net at ambient CO₂ levels of 400 µmol mol⁻¹ (A₄₀₀) did not differ across climate treatments or with leaf temperatures from 20 to 30 °C. Canopy temperatures rarely reached above 30 °C in any treatment, suggesting that seasonal carbon assimilation was relatively homeostatic across all treatments. Assessments of the component processes of A₄₀₀ revealed that decreases in g_s with leaf temperature from 20 to 30 °C were balanced by increases in V_cmax, resulting in stable A₄₀₀ rates despite concurrent increases in R_d. Photosynthesis was not affected by precipitation treatments, likely because the relatively dry year led to small treatment effects on soil moisture. As temperature acclimation is likely to come at a cost to the plant via resource reallocation, it may not benefit plants to acclimate to warming in cases where warming would not otherwise reduce assimilation. These results suggest that photosynthetic temperature acclimation to future warming will be context-specific and that it is important to consider assimilatory benefit when assessing acclimation responses.

中文翻译：

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没有适应性：在温度升高下，美国榆树的降水梯度对温度的瞬时响应保持稳态光合速率

过去的研究表明，植物具有响应长期温度变化（即适应）而改变其光合作用对温度的瞬时响应的能力。这种适应通常是影响净光合作用（A _net）的过程的结果，包括叶片生化过程，例如Rubisco羧化的最大速率（V _cmax）和最大光合电子传递速率（J _max），气孔导度（g _s）和黑暗呼吸（R _d）。但是，这些过程很少在野外或与其他环境因素（例如降水量）一起检查。在这里，我们通过在东北老田生态系统中进行降水（−50％环境至150％环境）操纵实验，进行了完全因子升温（主动加热至+4°C；均值= +3.1°C）美国通过生化和气孔调节来检查美洲榆树幼树的适应程度。我们发现其中率甲_净在环境CO ₂水平400微摩尔摩尔^-1（甲₄₀₀）在不同气候处理条件下或叶片温度为20至30°C时均无差异。在任何处理中，冠层温度很少会超过30°C，这表明在所有处理中，季节性碳同化作用都是相对稳态的。对A ₄₀₀的组成过程的评估表明，叶片温度从20到30°C ，g _s的降低与V _cmax的增加是平衡的，尽管R _d同时增加，但仍能保持稳定的A ₄₀₀速率。光合作用不受降水处理的影响，可能是因为相对干燥的一年对土壤水分的处理作用很小。由于温度的适应可能会通过资源重新分配而使植物付出代价，因此在变暖不会以其他方式减少同化的情况下，它可能不会使植物适应变暖。这些结果表明，光合作用的温度适应未来的变暖将因环境而异，并且在评估适应性反应时考虑同化益处非常重要。