Despite multiple studies of the impact of climate change on temperate tree species, experiments on tropical and economically important tree crops such as cacao (Theobroma cacao L.) are still limited. Here, we investigated the combined effects of increased temperature and [CO2] on the growth, photosynthesis, and development of juvenile plants of two contrasting cacao genotypes: SCA 6 and PA 107. The factorial growth chamber experiment combined two [CO2] treatments (410 and 700 ppm) and three day/night temperature regimes (control: 31/22°C, control+2.5°C: 33.5/24.5°C, and control+5.0°C: 36/27°C) at a constant vapour pressure deficit of 0.9 kPa. At elevated [CO2], final dry weight, total and individual leaf area increased in both genotypes, whilst duration for individual leaf expansion declined in PA 107. For both genotypes, elevated [CO2] also improved light-saturated net photosynthesis (Pn) and intrinsic water-use efficiency (iWUE), whereas leaf transpiration (E) and stomatal conductance (gs) decreased. Under a constant low vapour pressure deficit, increasing temperatures above 31/22°C enhanced rates of Pn, E, gs, in both genotypes suggesting that photosynthesis responds positively to higher temperatures than previously reported for cacao. However, dry weight, total and individual leaf area declined with increases in temperature being more evident in SCA 6 than PA 107, suggesting the latter genotype was more tolerant to elevated temperature. Our results suggest that the combined effect of elevated [CO2] and temperature is likely to improve the early growth of high temperature-tolerant genotypes, while elevated [CO2] appeared to ameliorate the negative effects of increased temperatures on growth parameters on more sensitive material. The evident genotypic variation observed in this study, demonstrates scope to select and breed cacao varieties capable of adapting to future climate change scenarios.

中文翻译：

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温度升高和 [CO2] 模拟气候变化条件对热带树木作物 Theobroma cacao L. 早期生长和生理的影响。

尽管对气候变化对温带树种的影响进行了多项研究，但对可可 (Theobroma cacao L.) 等热带和经济重要树种作物的实验仍然有限。在这里，我们研究了温度升高和 [CO2] 对两种对比可可基因型（SCA 6 和 PA 107）幼苗生长、光合作用和发育的综合影响。因子生长室实验结合了两种 [CO2] 处理（410和 700 ppm）和三个昼/夜温度范围（控制：31/22°C，控制+2.5°C：33.5/24.5°C，控制+5.0°C：36/27°C）在恒定蒸气压下赤字0.9 kPa。[CO2] 升高时，两种基因型的最终干重、总叶面积和单叶面积均增加，而 PA 107 中单叶扩张的持续时间下降。对于这两种基因型，[CO2] 升高还改善了光饱和净光合作用 (Pn) 和内在水分利用效率（iWUE），而叶片蒸腾量（E）和气孔导度（gs）下降。在恒定的低蒸气压赤字下，温度升高到 31/22°C 以上会增强两种基因型中 Pn、E、gs 的速率，这表明光合作用对比先前报道的可可更高的温度有积极的反应。然而，干重、总叶面积和单叶面积随温度升高而下降，在 SCA 6 中比 PA 107 更明显，表明后者基因型对高温更耐受。我们的结果表明，升高的 [CO2] 和温度的综合作用可能会改善耐高温基因型的早期生长，而升高的 [CO2] 似乎可以改善温度升高对更敏感材料的生长参数的负面影响。本研究中观察到的明显基因型变异证明了选择和培育能够适应未来气候变化情景的可可品种的范围。