Effects of elevated CO₂ and O₃ on soybean N₂ fixation and total N in the surface soil.

Values shown for N inputs to soil from N2 fixation exclude seeds. Values are mean ± s.e.m. *** (P<0.001) and ** (P<0.01) denote statistically significant main treatment effects, ANOVA mixed models. ND, not determined. NS, not significant. CF, charcoal-filtered ambient air. +O3, elevated O3.+CO2, elevated CO2.+CO2+O3, elevated CO2+O3. The main treatment effects of CO2, O3 and the CO2×O3 interaction on soil N were not statistically significant for any years.经生物固氮（N₂ fixation）途径向土壤输入的氮素相关数值，未计入种子所含氮素。 数据以均值±标准误（s.e.m.）表示；***（P<0.001）与**（P<0.01）分别代表方差混合模型（ANOVA mixed models）检验下处理主效应具有极显著与显著统计学差异。ND：未测定（not determined）；NS：无统计学显著性（not significant）。CF：炭滤净化的环境空气（charcoal-filtered ambient air）；+O₃：臭氧浓度升高处理（elevated O₃）；+CO₂：二氧化碳浓度升高处理（elevated CO₂）；+CO₂+O₃：二氧化碳与臭氧浓度同时升高处理（elevated CO₂+O₃）。各观测年份中，二氧化碳、臭氧的处理主效应以及二者的交互作用对土壤氮素的影响均未达到统计学显著性水平。