The functioning of microbial communities in response to elevated atmospheric carbon dioxide (eCO₂) is one of the most important, but poorly understood, contributors to climate change feedbacks. The effect of soil moisture caused by eCO₂ on soil microbial communities and functioning may be of high importance in water limited ecosystems. To address this knowledge gap, we measured the functional composition, structure, and functional processes of soil microbial communities under eCO₂ and an irrigation treatment simulating water availability with eCO₂ at two soil depths (0–5 cm and 5–15 cm) in a mixed-grass semiarid prairie. The overall functional diversity increased and the microbial composition and structure were significantly (P < 0.01) altered in response to eCO₂ and irrigation treatments. A greater number of key functional genes involved in soil, i.e. carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) cycling were stimulated under eCO₂ than under irrigation treatment. Structural equation modeling (SEM) suggested that eCO₂ significantly impacted soil microbial community structure by mediating both soil moisture and plant biomass, while irrigation influenced soil microbial community structure merely via regulation of soil moisture. Moreover, in this water-limited system, soil moisture mediated eCO₂ effects on soil microbial functional structure were relatively more important than those mediated by plant activity. The present study further improves our understanding of how global climate change regulates soil microbial functional processes in a semiarid grassland ecosystem.

微生物群落对大气中二氧化碳（eCO ₂）升高的响应是导致气候变化反馈的最重要但知之甚少的因素之一。在缺水的生态系统中，eCO ₂引起的土壤水分对土壤微生物群落和功能的影响可能非常重要。为了解决这一知识鸿沟，我们测量了eCO ₂下土壤微生物群落的功能组成，结构和功能过程，以及在两个土壤深度（0-5 cm和5-15 cm）下模拟eCO ₂水分利用的灌溉处理。混草半干旱大草原。整体功能多样性增加，微生物组成和结构显着（P  <0.01）响应eCO ₂和灌溉处理而改变。与灌溉处理相比，eCO ₂刺激了更多的土壤关键功能基因，即碳（C），氮（N），磷（P）和硫（S）循环。结构方程模型（SEM）表明，eCO ₂通过介导土壤水分和植物生物量显着影响土壤微生物群落结构，而灌溉仅通过调节土壤水分来影响土壤微生物群落结构。此外，在这种限水系统中，土壤水分介导的eCO ₂对土壤微生物功能结构的影响比由植物活性介导的影响更为重要。本研究进一步增进了我们对全球气候变化如何调节半干旱草原生态系统中土壤微生物功能过程的理解。