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

Abstract 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 EO 3 ). Linear regressions between the response ratio of each variable (i.e. EO 3 /NF) and the increments of exposure- or flux-based ozone indices (i.e. EO 3 - NF) were conducted. The results showed that the response ratios of soil microbial biomass C and N, as well as cumulative CO 2 and N 2 O effluxes significantly correlated with the increments of ozone indices. The ΔPOD 0 (increment of integrated phytotoxic ozone dose with no threshold) and the ΔAOT40 (increment of accumulated hourly O 3 concentrations over a threshold of 40 nL·L −1 ) performed better than ΔSUM06, ΔW126 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.