Ground-level ozone (O₃) pollution frequently coincides with the deposition of anthropogenic nitrogen (N), and both factors can influence the structure and functionality of both above- and belowground ecosystems. Elevated O₃ levels have been shown to adversely impact plants in many prior reports, but the interacting effects of high O₃ levels and N addition on exposed plants remain to be clearly defined, and the changes in rhizosphere microbial community composition in this context have yet to be studied. The direct and indirect mechanisms and interactions among plants, microbes, and the soil that shape these O₃ and N responses are also poorly understood. Herein, we explored the interactive effects of O₃ exposure (five levels) and soil N (four levels) on the composition of rhizosphere soil microbial communities associated with poplar trees (Populus euramericana cv. ‘74/76’). In these analyses, exposure to higher levels of O₃ was linked to significant decreases in bacteria, fungi, arbuscular mycorrhizal fungi, and to a reduction in the ratio of fungi-to-bacteria, whereas soil N addition had no impact on these parameters. No interactive effects between O₃ and N were observed in the context of alterations in soil microbial community composition, and equivalent performance was observed for concentration-based (AOT40, cumulative exposure to hourly O₃ concentrations >40 ppb) and flux-based [POD₁ and POD₇, cumulative stomatal uptake of O₃ > 1 or 7 nmol O₃ m⁻¹ PLA (projected leaf area) s⁻¹] dose–response analyses. Structural equation modelling revealed that changes in the composition of the microbial community were attributable to changes in soil pH but unrelated to plant characteristics. Overall, these findings indicated that increased O₃ levels can induce soil alkalinisation and thereby influence soil microbial communities such that soil pH is a reliable predictor of O₃ pollution-related changes in these communities.

中文翻译：

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土壤pH驱动杨树根际土壤微生物群落对臭氧污染和氮添加的反应

地面臭氧 (O ₃ ) 污染经常与人为氮 (N) 的沉积同时发生，这两个因素都会影响地上和地下生态系统的结构和功能。在许多先前的报道中，已经证明升高的 O _{3水平会对植物产生不利影响，但是高 O 3}水平和添加 N 对暴露植物的相互作用影响仍有待明确定义，在这种情况下根际微生物群落组成的变化尚未待研究。形成这些 O ₃和 N 响应的植物、微生物和土壤之间的直接和间接机制和相互作用也知之甚少。在此，我们探讨了 O _{3的交互作用}暴露（五个水平）和土壤氮（四个水平）对与杨树相关的根际土壤微生物群落组成（Populus euramericana cv. '74/76'）。在这些分析中，暴露于较高水平的 O ₃与细菌、真菌、丛枝菌根真菌的显着减少以及真菌与细菌的比例降低有关，而土壤 N 添加对这些参数没有影响。在土壤微生物群落组成变化的背景下，没有观察到O _{3和 N 之间的交互作用，并且观察到基于浓度（AOT40，每小时 O 3}浓度累积暴露 >40 ppb）和基于通量的 [POD] 的等效性能₁和 POD_{如图7所示，O 3}  > 1 或7 nmol O ₃ m ^-1 PLA（投影叶面积）s ^-1的累积气孔吸收]剂量反应分析。结构方程模型显示，微生物群落组成的变化可归因于土壤 pH 值的变化，但与植物特性无关。总体而言，这些研究结果表明，增加的 O ₃水平可以诱导土壤碱化，从而影响土壤微生物群落，因此土壤 pH 值是这些群落中 O ₃污染相关变化的可靠预测指标。