Many tropical planted forests are being subjected to drier conditions due to climate change, but the interaction between drought and species diversity on species' response to drought is poorly understood. We took advantage of a historic El Niño drought in Central Panama to test drought responses of two species—Terminalia amazonia and Dalbergia retusa—in simplified, planted forests. We asked whether and how species adjust strategies when grown in monocultures and mixtures with reduced precipitation. We collected sap flux density, volumetric water content, litterfall, leaf physiology traits and leaf water potential before and during the drought. The main drivers of sap flux density (J_s) in monocultures and mixtures changed from radiation, vapour pressure deficit (VPD) and air temperature to volumetric water content or precipitation towards the end of the drought. The exception was for D. retusa in the mixtures, where VPD was the main driver (0.73–0.77) of J_s during the normal year and switched to precipitation during the drought year (0.47–0.72). Increasing VPD led to increases in J_s until air temperature exceeded 32°C, at which point J_s declined for D. retusa and stabilized for T. amazonia. T. amazonia's litterfall doubled during the drought, whereas D. retusa's litterfall peaked at the start of the dry seasons and was unaffected by the drought. D. retusa, however, delayed leaf flush until the drought ended, whereas T. amazonia transitioned through a series of water‐conserving strategies until prematurely shedding leaves prior to the peak of the drought.

中文翻译：

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单一物种和混合物种人工林对厄尔尼诺现象的差异和动态水调节响应

由于气候变化，许多热带人工林正处于较干燥的条件下，但人们对干旱与物种多样性之间的相互作用缺乏了解，而这些相互作用对物种对干旱的反应也知之甚少。我们利用巴拿马中部历史悠久的厄尔尼诺旱情，在简化的人工林中测试了Terminalia amazonia和Dalbergia retusa这两种物种的干旱反应。我们询问了在单一栽培和降水减少的混合物中生长时，物种是否以及如何调整策略。我们收集了干旱前和干旱期间的汁液通量密度，体积水含量，凋落物，叶片生理特性和叶片水势。液流密度的主要驱动力（J _s），在干旱结束前，混合物的辐射，蒸气压亏缺（VPD）和气温从辐射，蒸气压亏缺（VPD）变为体积水含量或降水。混合物中的D. retusa是例外，在正常年份中，VPD是J _s的主要驱动因素（0.73-0.77），而在干旱年（0.47-0.72）则转向降水。VPD的增加导致J _s的增加，直到气温超过32°C为止，此时D. retusa的J _s下降，而T. amazonia的J _s稳定。T.亚马逊的凋落在旱季增加了一倍，而D.婆罗 的凋落物在干旱季节开始时达到顶峰，不受干旱影响。然而，D。retusa推迟了叶子冲洗直到干旱结束，而T. amazonia则通过一系列节水策略进行了过渡，直到在干旱高峰之前过早地使叶子脱落。