Negative effects of elevated ozone levels on soil microbial characteristics: a meta-analysis

Background and aimsThe effects of elevated tropospheric ozone (O3) concentrations on terrestrial ecosystems have been extensively researched by numerous O3 fumigation experiments and syntheses. While the detrimental impacts of O3 stress on aboveground plant physiological traits are well-documented, there remains a gap in our understanding of how elevated O3 influences soil microbes and plant-microbe interactions.MethodsHere, we synthesized data from 71 O3 fumigation experiments conducted globally to evaluate the effects of elevated O3 on soil microbial characteristics, including biomass, community composition, and extracellular enzyme activities (EEAs).ResultsElevated O3 led to an average reduction of 14.2% in microbial biomass carbon (MBC). It was largely attributable to decreased plant carbon input, as the effect size of MBC was closely correlated with declines in both aboveground and root biomass. Fungal communities appeared more vulnerable to O3 stress than bacterial communities, as evidenced by a 10.7% decrease in fungal phospholipid fatty acids (PLFAs), while total and bacterial PLFAs were only marginally affected. Furthermore, the negative impacts on microbes intensified with increasing O3 concentrations but tended to diminish over time. In addition, elevated O3 significantly reduced hydrolytic EEAs, which target simple compounds, by 12.9%, while increasing oxidative EEAs, which degrade recalcitrant compounds, by 12.0%. It suggests that O3 stress would affect the decomposition of soil organic matter by shifting EEAs.ConclusionElevated O3 impairs soil microbial growth and changes microbial C utilization strategies, which could profoundly impact C cycling in terrestrial ecosystems.