Photoprotection is a plant functional mechanism to prevent photooxidative damage by excess light. This is most important when carbon assimilation is limited by drought, and as such, it entails a trade-off between carbon assimilation vs stress avoidance. The ecological adaptation of plants to local water availability can lead to different photoprotective strategies. To test this, we used different provenances of Caesalpinia spinosa (Mol.) Kuntze (commonly known as ‘tara’) along a precipitation gradient. Tara is a Neotropical legume tree with high ecological and commercial value, found in dry tropical forests, which are increasingly threatened by climate change. Morphological and physiological responses of tara provenances were analysed under three different treatments of drought and leaflet immobilization, i.e., light stress, in a common garden greenhouse experiment. Tara quickly responded to drought by reducing stomatal conductance, evapotranspiration, photochemical efficiency, carbon assimilation and growth, while increasing structural and chemical photoprotection (leaflet angle and pigments for thermal dissipation). Leaflet closure was an efficient photoprotection strategy with overall physiological benefits for seedlings as it diminished the evaporative demand and avoided photodamage, but also entailed costs by reducing net carbon assimilation opportunities. These responses depended on seed origin, with seedlings from the most xeric locations showing the highest dehydration tolerance, suggesting local adaptation and highlighting the value of different strategies under distinct environments. This plasticity in its response to environmental stress allows tara to thrive in locations with contrasting water availability. Our findings increase the understanding of the factors controlling the functional ecology of tara in response to drought, which can be leveraged to improve forecasts of changes in its distribution range, and for planning restoration projects with this keystone tree species.

中文翻译：

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局部适应优化干旱胁迫下新热带豆科植物的光保护策略

光保护是一种植物功能机制，可防止过量光照引起的光氧化损伤。当碳同化受到干旱限制时，这一点最为重要，因此，它需要在碳同化与避免压力之间进行权衡。植物对当地水资源可用性的生态适应可导致不同的光保护策略。为了测试这一点，我们使用了不同来源的Caesalpinia spinosa(Mol.) Kuntze（通常称为“tara”）沿着降水梯度。塔拉是一种具有很高生态和商业价值的新热带豆科植物，发现于干燥的热带森林中，这些森林越来越受到气候变化的威胁。在普通花园温室试验中，在干旱和小叶固定三种不同处理（即光胁迫）下，分析了 tara 种源的形态和生理反应。Tara 通过降低气孔导度、蒸散量、光化学效率、碳同化和生长，同时增加结构和化学光保护（叶角和用于散热的色素）来快速应对干旱。小叶闭合是一种有效的光保护策略，对幼苗具有整体生理益处，因为它减少了蒸发需求并避免了光损伤，但也通过减少净碳同化机会而带来成本。这些反应取决于种子来源，来自最干旱地区的幼苗表现出最高的脱水耐受性，表明局部适应性并突出了不同环境下不同策略的价值。这种对环境压力反应的可塑性使 tara 能够在水资源供应量相反的地方茁壮成长。我们的发现增加了对控制 tara 响应干旱的功能生态的因素的理解，可以利用这些因素来改进对其分布范围变化的预测，