Abstract Coffee (Coffea arabica L.) is an important global commodity grown in tropical areas where increased drought severity and frequency are believed to become progressively important due to climate changes. Nonetheless, elevated air [CO2] is thought to be able to mitigate heat and drought stresses. In this study, we tested how carbon assimilation and use are affected by elevated [CO2] in combination with a progressive drought, and how this could impact shifts on biomass accumulation and partitioning. For that, we cultivated coffee plants in open top chambers under greenhouse conditions. Plants grown in 12-L pots were then submitted to ambient (386 ± 20 ppm) or elevated (723 ± 83 ppm) [CO2] during approximately seven months, as well as to varying soil water availabilities (100, 50, 37.5, 25 or 20 % of soil field capacity). Our results demonstrate that elevated [CO2] improved carbon assimilation rates (>60 %) with unaltered stomatal conductance and no signs of photosynthetic downregulation. This was accompanied by increases in water-use efficiency, respiration rates and biomass accumulation regardless of watering, and decreased photorespiration rates and oxidative pressure under drought. Improved growth under elevated [CO2] was more evident under drought than under full irrigation, and was unlikely to have been associated with global changes on hormonal pools, but rather with shifts on carbon fluxes. Finally, elevated [CO2] promoted key allometric adjustments linked to drought tolerance, e.g., more biomass partitioning towards roots with greater root length. Collectively, our results offer novel and timely information on the mitigating ability of elevated [CO2] on the photosynthetic performance and growth of coffee plants under drought conditions.

中文翻译：

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升高的空气 [CO2] 提高了光合作用性能并改变了干旱胁迫咖啡植物的生物量积累和分配

摘要 咖啡 (Coffea arabica L.) 是一种重要的全球商品，生长在热带地区，据信由于气候变化，干旱的严重程度和频率日益增加，变得越来越重要。尽管如此，升高的空气 [CO2] 被认为能够缓解高温和干旱压力。在这项研究中，我们测试了碳同化和利用如何受到升高的 [CO2] 以及渐进性干旱的影响，以及这如何影响生物量积累和分配的变化。为此，我们在温室条件下在开顶室中种植咖啡植物。在大约 7 个月内，将种植在 12 升盆中的植物置于环境 (386 ± 20 ppm) 或升高的 (723 ± 83 ppm) [CO2] 环境中，以及不同的土壤水可用性（100、50、37.5、25或土壤田间持水量的 20%）。我们的结果表明，升高的 [CO2] 提高了碳同化率 (>60%)，气孔导度未改变，并且没有光合作用下调的迹象。这伴随着水分利用效率、呼吸速率和生物量积累的增加，而不管浇水，以及干旱下光呼吸速率和氧化压力的降低。在高 [CO2] 条件下的生长改善在干旱下比在完全灌溉下更明显，并且不太可能与全球激素库的变化有关，而是与碳通量的变化有关。最后，升高的 [CO2] 促进了与耐旱性相关的关键异速生长调整，例如，更多的生物量分配给具有更大根长的根。总的来说，