The response of tropical ecosystems to elevated carbon dioxide (CO₂) remains a critical uncertainty in projections of future climate. Here, we investigate how leaf trait plasticity in response to elevated CO₂ alters projections of tropical forest competitive dynamics and functioning. We use vegetation demographic model simulations to quantify how plasticity in leaf mass per area and leaf carbon to nitrogen ratio alter the responses of carbon uptake, evapotranspiration, and competitive ability to a doubling of CO₂ in a tropical forest. Observationally constrained leaf trait plasticity in response to CO₂ fertilization reduces the degree to which tropical tree carbon uptake is affected by a doubling of CO₂ (up to −14.7% as compared to a case with no plasticity; 95% confidence interval [CI_95%] −14.4 to −15.0). It also diminishes evapotranspiration (up to −7.0%, CI_95% −6.4 to −7.7), and lowers competitive ability in comparison to a tree with no plasticity. Consideration of leaf trait plasticity to elevated CO₂ lowers tropical ecosystem carbon uptake and evapotranspirative cooling in the absence of changes in plant‐type abundance. However, “plastic” responses to high CO₂ which maintain higher levels of plant productivity, many of which fall outside of the observed range of response, are potentially more competitively advantageous, thus, including changes in plant type abundance may mitigate these decreases in ecosystem functioning. Models that explicitly represent competition between plants with alternative leaf trait plasticity in response to elevated CO₂ are needed to capture these influences on tropical forest functioning and large‐scale climate.

中文翻译：

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叶片特征可塑性改变模拟的热带树木对二氧化碳含量升高的竞争能力和功能

热带生态系统对二氧化碳（CO ₂）升高的响应仍然是未来气候预测中的关键不确定因素。在这里，我们调查了如何应对高CO ₂引起的叶片性状可塑性改变热带森林竞争动态和功能的预测。我们使用植被人口统计学模型模拟来量化热带森林中单位面积叶片质量的可塑性和叶片碳氮比如何改变碳吸收，蒸散和竞争能力以使CO ₂倍增。观察到的受限制的叶片性状对CO ₂施肥的响应降低了CO ₂倍增对热带树木碳吸收的影响程度（与没有可塑性的情况相比，最高为-14.7％； 95％的置信区间[CI _95％ ] -14.4至-15.0）。与没有可塑性的树相比，它还减少了蒸散量（高达-7.0％，CI _95％ -6.4至-7.7），并降低了竞争能力。在植物类型丰度没有变化的情况下，考虑到叶片性状对CO ₂含量升高的可塑性会降低热带生态系统的碳吸收和蒸散量。但是，对高​​CO _2的“塑性”反应保持较高水平的植物生产力（其中许多不属于所观察到的响应范围）的植物具有潜在的竞争优势，因此，包括改变植物类型的丰度可能减轻生态系统功能的这些下降。需要模型来明确表示具有交替的叶片性状可塑性的植物之间的竞争，以响应CO _2的升高，以捕捉这些对热带森林功能和大规模气候的影响。