Drought is a global threat, increasing in severity and frequency throughout tropical ecosystems. Although plants often face drought in conjunction with biotic stressors, such as herbivory or disease, experimental studies infrequently test the simultaneous effects of drought and biotic stress. Because multiple simultaneous stressors may have non‐additive and complex effects on plant performance, it is difficult to predict plant responses to multiple threats from research examining one stress at a time. Using an experimental approach in the greenhouse, we investigated potential non‐additivity in seedling growth and survival to simulated drought and herbivory across a phylogenetically diverse pool of ten Hawaiian plant species. Overall, seedlings showed limited tolerance, defined as similar growth and survival in stressed compared with control (non‐stressed) plants, to simulated herbivory and drought, with the combined effects of both stressors to be generally additive and negative across species. Significant variation in stress tolerance was detected among species, and species variation was explained, at least in part, by functional traits such that species with larger root/shoot ratios and smaller seeds, tended to demonstrate greater herbivory and drought tolerance. Future research incorporating additional trait analysis and different stressors could shed light on mechanisms underlying seedling stress tolerance and clarify whether additivity, as detected in this study, extends across other combinations of stressors. Such work will provide needed insights into the regeneration of seedlings in tropical forests under threats of herbivory and climate change.

中文翻译：

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幼苗对模拟食草和干旱的加性和非加性响应

干旱是全球性威胁，在整个热带生态系统中，干旱的严重性和频率不断增加。尽管植物经常面临干旱和生物胁迫，例如食草或疾病，但实验研究很少测试干旱和生物胁迫的同时影响。由于多个同时存在的胁迫因素可能对植物的生长性能产生非累加和复杂的影响，因此难以通过一次研究一种胁迫的研究来预测植物对多种威胁的反应。我们使用温室中的一种实验方法，研究了在十种夏威夷植物物种的系统发育多样性库中，幼苗生长和存活对模拟干旱和草食的潜在非添加性。总体而言，幼苗显示出有限的耐受性，定义为：与对照（非胁迫）植物相比，胁迫下植物的生长和存活率与模拟食草和干旱相似，并且两种胁迫源的组合效应在整个物种中通常是累加的，并且是负面的。在物种之间检测到胁迫耐受性的显着变化，并且至少部分地通过功能性状解释了物种变化，即具有较大根/茎比和较小种子的物种倾向于表现出较高的食草和干旱耐受性。结合其他性状分析和不同胁迫因素的未来研究可以阐明幼苗胁迫耐受性的潜在机制，并阐明本研究中检测到的可加性是否跨越了其他胁迫因素组合。