Climate change scenarios predict increasing atmospheric CO2 concentrations ([CO2]), temperatures and droughts in tropical regions. Individually, the effects of these climate factors on plants are well established, whereas experiments on the interactive effects of a combination of factors are rare. Moreover, how these environmental factors will affect tree species along a wet to dry gradient (e.g., along tropical forest-savanna transitions) remains to be investigated. We hypothesized that under the simulated environmental conditions, plant growth, physiological performance and survivorship would vary in a manner consistent with the species' positions of origin along this gradient. In a glasshouse experiment, we raised seedlings of three Eucalyptus species, each occurring naturally in a wet forest, savanna and forest-savanna ecotone, respectively. We evaluated the effect of drought, elevated temperature (4 °C above ambient glasshouse temperature of 22 °C) and elevated temperature in combination with elevated [CO2] (400 ppm [CO2] above ambient of 400 ppm), on seedling growth, survivorship and physiological responses (photosynthesis, stomatal conductance and water-use efficiency). Elevated temperature under ambient [CO2] had little effect on growth, biomass and plant performance of well-watered seedlings, but hastened mortality in drought-affected seedlings, affecting the forest and ecotone more strongly than the savanna species. In contrast, elevated [CO2] in combination with elevated temperatures delayed the appearance of drought stress symptoms and enhanced survivorship in drought-affected seedlings, with the savanna species surviving the longest, followed by the ecotone and forest species. Elevated [CO2] in combination with elevated temperatures also enhanced growth and biomass and photosynthesis in well-watered seedlings of all species, but modified shoot:root biomass partitioning and stomatal conductance differentially across species. Our study highlights the need for a better understand of the interactive effects of elevated [CO2], temperature and drought on plants and the potential to upscale these insights for understanding biome changes.

中文翻译：

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升高的温度和CO2会导致来自相反生境的桉树物种的差异性生长刺激和干旱存活响应。

气候变化情景预测热带地区的大气CO2浓度（[CO2]），温度和干旱将增加。单独地，这些气候因素对植物的影响是公认的，而有关多种因素的相互作用影响的实验却很少。此外，这些环境因素如何影响从湿到干的梯度（例如，沿着热带森林-热带稀树草原过渡）的树种仍有待研究。我们假设，在模拟的环境条件下，植物的生长，生理性能和存活率将以与该物种沿着该梯度的起源位置一致的方式发生变化。在温室实验中，我们种植了三种桉树的幼苗，每种自然生于湿林，稀树草原和森林稀树草原过渡带中，分别。我们评估了干旱，高温（高于温室温度22°C的4°C）和高温与升高的[CO2]（高于环境400 ppm的400 ppm [CO2]）结合对幼苗生长，存活的影响和生理反应（光合作用，气孔导度和水分利用效率）。在环境[CO2]下升高温度对灌溉良好的幼苗的生长，生物量和植物性能影响不大，但受干旱影响的幼苗的死亡率加快，对森林和生态交错带的影响比热带草原物种更大。相比之下，升高的[CO2]结合高温会延缓干旱胁迫症状的出现，并增强受干旱影响的幼苗的生存能力，其中稀树草原物种的生存时间最长，其次是过渡带和森林物种。升高的[CO2]结合高温也增强了所有物种灌溉良好的幼苗的生长，生物量和光合作用，但不同物种的地上部生物量分配不同，枝条：根生物量分配和气孔导度有所不同。我们的研究强调需要更好地了解升高的[CO2]，温度和干旱对植物的相互作用影响，以及潜在地扩大这些见解以了解生物群落变化的潜力。