Plants have evolved a vast array of secondary metabolites that help defend them against natural enemy attack. The production of these secondary metabolites is influenced by environmental factors, such as temperature, rainfall (soil water availability) and atmospheric [CO₂], which may be altered under climate change. This study aimed to test how two of these environmental factors, namely soil water availability and [CO₂], will affect secondary metabolite and biomass production in Eucalypts. To investigate this, we measured secondary metabolite and biomass production of three Eucalypt species (Eucalyptus grandis, E. moluccana, E. saligna) grown under ambient and elevated [CO₂] (400 and 600 ppm, respectively) and water-stressed and well-watered conditions, in a fully factorial glasshouse experiment. The secondary metabolites measured were foliar phenolic concentration as well as terpene and green leaf volatile emissions. We found that water stress did not alter secondary metabolite production. Unsurprisingly, the water-stressed plants maximised their water uptake potential by reducing shoot biomass but maintaining root biomass. The detrimental effects of water stress on shoot biomass production were not reduced under elevated [CO₂] compared to ambient [CO₂], despite all species experiencing significant reductions in stomatal conductance. Further, [CO₂] as a single factor did not have a significant effect on species’ net carbon gain, with an increase in green leaf volatile emissions under elevated [CO₂] being mitigated by a reduction in shoot biomass production. These results suggest that reductions in carbon gains due to water stress will affect the growth of Eucalypts rather than their chemical defence capabilities.

中文翻译：

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桉树物种在水分胁迫条件下以生长为代价维持次生代谢产物的产生

植物进化出大量次生代谢物，帮助它们抵御天敌的攻击。这些次生代谢物的产生受环境因素的影响，例如温度、降雨量（土壤水分可用性）和大气 [CO ₂ ]，这些因素可能会在气候变化下发生改变。本研究旨在测试其中两个环境因素，即土壤水分可用性和 [CO ₂ ]，将如何影响桉树的次生代谢物和生物量生产。为了研究这一点，我们测量了次级代谢产物和生物质生产的3种桉树（巨桉，E。栗，E.柳桉）环境下生长，并升高[CO ₂]（分别为 400 和 600 ppm）以及缺水和充分浇水的条件，在全析因温室实验中。测量的次生代谢物是叶面酚浓度以及萜烯和绿叶挥发物排放量。我们发现水分胁迫不会改变次生代谢物的产生。不出所料，受水胁迫的植物通过减少枝条生物量但保持根生物量来最大化其吸水潜力。尽管所有物种都经历了气孔导度的显着降低，但与环境 [CO ₂ ]相比，在升高的 [CO ₂ ]下，水分胁迫对地上部生物量产生的不利影响并未减少。此外，[CO ₂] 作为单一因素对物种的净碳增益没有显着影响，在升高的 [CO ₂ ]下绿叶挥发性排放量的增加被地上部生物量产量的减少所缓解。这些结果表明，由于缺水造成的碳增加减少将影响桉树的生长，而不是它们的化学防御能力。