Photosynthesis acclimation to high temperature differs among and within species. Grapevine intra-specific variation in photosynthetic acclimation to elevated temperature has been scarcely assessed. Our objectives were to (i) evaluate the mechanisms underlying long-term acclimation of photosynthesis to elevated temperature in grapevine, and (ii) determine whether these responses are similar among two varieties. A warming experiment with well irrigated Grenache and Syrah field-grown plants was performed during two growing seasons comparing plants exposed at ambient temperature (control) with plants in open-top chambers (heating) that increased mean air temperature between 1.5 and 3.6°C. Photosynthetic acclimation was assessed through the response of net assimilation (A_n), Rubisco carboxylation rate (V_cmax) and electron transport rate (J_max), at leaf temperatures from 20 to 40°C. Our results evidenced different mechanisms for photosynthetic acclimation to elevated temperature. Compared with control, Grenache heated increased A_n, maintaining higher V_cmax and J_max at temperatures above 35°C. By contrast, Syrah heated and control presented similar values of A_n, V_cmax and J_max, evidencing an adjustment of photosynthesis without increasing C assimilation. Both varieties increased the optimum temperature for A_n, but to a lesser extent when growth temperature was higher. Our study provides evidence that grapevine varieties present different acclimation mechanisms to expected warming.

物种之间和物种内部对高温的光合作用适应不同。几乎没有评估过葡萄在光合适应高温下的种内变化。我们的目标是（i）评估葡萄光合作用长期适应高温的机制，以及（ii）确定两个品种之间的反应是否相似。在两个生长季节中，对灌溉良好的歌海娜（Grenache）和西拉（Syrah）田间生长的植物进行了升温试验，比较了暴露于环境温度下的植物（对照）和敞口室内（加热）的植物，该植物的平均气温升高了1.5至3.6°C。通过净同化（A _n在20至40°C的叶片温度下，Rubisco羧化速率（V _cmax）和电子传输速率（J _max）。我们的结果证明了光合作用适应高温的不同机制。与对照相比，歌海娜在35°C以上的温度下加热的A _n增加，保持较高的V _cmax和J _max。相比之下，西拉（Syrah）加热和控制得到的A _n，V _cmax和J _max值相似，证明在不增加C同化的情况下可以调节光合作用。两种品种均提高了A _n的最佳温度，但当生长温度较高时，其幅度较小。我们的研究提供了证据，表明葡萄品种对预期的变暖表现出不同的适应机制。