In order to assess the response of cocoa trees to drought, changes in water status, gas exchange, leaf carbon isotopic ratio (δ13C), photochemical activity, and leaf N and chlorophyll content during the rainy and dry season were measured in 31 Venezuelan cocoa clones (17 Trinitarios, 6 Criollos, and 8 Modern Criollos) grown in a common garden. Drought caused a 40% decrease in water potential (ψ) in all but the Modern Criollos, and a reduction in net photosynthetic rate (A) and stomatal conductance (gs) without an increase in instantaneous water use efficiency (WUE) in 93% of clones, and an increase in δ13C (long-term WUE) in 74% of clones; these responses suggest differences in tolerance to drought among clones. A positive correlation between A and both gs and leaf N content was found for all genotypes. Leaf N content, chlorophyll content, and photochemical activity were reduced during drought, suggesting that metabolism was also inhibited. The best performance during drought was shown by Modern Criollos with the highest WUE, while five Trinitario clones seemed to be less sensitive to drought, since neither chlorophyll, N, total soluble protein concentration, nor gs changed with drought, indicating that those Trinitario clones, with lower A, have a conservative water use. Modern Criollos showed no reductions in either ψ or gs; A remained unchanged, as did WUE, which was the highest, suggesting that these clones would be more successful in environments with low water availability. Our results indicate large variation in physiological response to drought over a range of parameters, suggesting possible differences in tolerance among clones.

中文翻译：

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委内瑞拉可可对干旱的生理反应变化

为了评估可可树对干旱的响应，水分状况、气体交换、叶片碳同位素比的变化（δ13C)、雨季和旱季期间的光化学活性以及叶片 N 和叶绿素含量在一个共同的花园中生长的 31 个委内瑞拉可可克隆（17 个 Trinitarios、6 个 Criollos 和 8 个现代 Criollos）中进行了测量。干旱导致水势下降 40% (ψ) 除现代 Criollos 外的所有植物，净光合速率降低 (一种) 和气孔导度 (Gs) 93% 的克隆的瞬时水分利用效率 (WUE) 没有增加，并且δ1374% 的克隆为 C（长期 WUE）；这些反应表明克隆之间对干旱的耐受性存在差异。之间呈正相关一种和两者Gs发现所有基因型的叶 N 含量。干旱期间叶片氮含量、叶绿素含量和光化学活性降低，表明新陈代谢也受到抑制。Modern Criollos 在干旱期间表现最好，WUE 最高，而五个 Trinitario 克隆似乎对干旱不太敏感，因为叶绿素、N、总可溶性蛋白浓度和Gs随着干旱而变化，表明那些 Trinitario 克隆，具有较低的一种，有一个保守的用水。现代 Criollos 两者都没有减少ψ要么Gs;一种保持不变，最高的 WUE 也是如此，这表明这些克隆在水资源可用性低的环境中会更成功。我们的结果表明在一系列参数上对干旱的生理反应存在很大差异，这表明克隆之间的耐受性可能存在差异。