Ozone dose-response relationships for soil microbial dynamics of winter wheat in North China

Dynamic responses of soil microbial properties of winter wheat (Triticum aestivum L.) to elevated ozone concentration have never been quantified. In this study, the winter wheat was cultivated under two contrasting ozone treatments: non-filtered ambient air (hereinafter called NF) and elevated ozone (effective increase in 9-h mean ozone concentration of 34.91 +/- 1.42 nL.L-1 (mean +/- SE) above ambient, hereinafter called EO3). Linear regressions between the response ratio of each variable (i.e. EO3/NF) and the increments of exposure- or flux-based ozone indices (i.e. EO3 - NF) were conducted. The results showed that the response ratios of soil microbial biomass C and N, as well as cumulative CO2 and N2O effluxes significantly correlated with the increments of ozone indices. The Delta POD0 (increment of integrated phytotoxic ozone dose with no threshold) and the Delta AOT40 (increment of accumulated hourly O-3 concentrations over a threshold of 40 nL.L-1) performed better than Delta SUM06, Delta W126 and the increments of other flux-based ozone indices. They showed stronger linear relationships with soil microbial biomass than that with gas effluxes. The expanded deviations from the effect-free line indicated distinct cumulative detrimental ozone impacts on soil microbial properties. Ammonia nitrogen content and nitrite reductase activity showed non-significantly adaptive and self-adjustment responses to accumulative ozone stress. The ozone dose-response relationships obtained here will benefit the ecological modeling that evaluates the dynamic responses or predicts the feedback effects of sustainable agro-ecosystems under global climate change.