Effects of elevated ozone on maize under varying soil nitrogen levels: Biomass, nitrogen and carbon, and their allocation to kernel

Effects of ozone (O-3) on maize have been increasingly studied, but only few studies have focused on the combined impacts of O-3 and nitrogen (N) on this important crop with C-4 carbon (C) fixation. In this study, a maize cultivar with the largest acreage in China was exposed to two O-3 treatments (NF: ambient air O-3 concentration; NF60: NF plus 60 ppb O-3) and four N levels (farmers' N practice: 240 kg N ha(-1) yr(-1); 150%, 50% and 25% of farmers' N practice). Generally, O-3 and N significantly influenced biomass, N and C, but did not change their allocation to kernel. There were significant interactions between O-3 and N in , C concentration and uptake, and leaf biomass and C uptake, with significant O-3 effects mainly occurring at N120 and N240. Based on the coefficient of determination (R-2), root C:N ratio rather than the most commonly used leaf C:N ratio was the best trait to indicate maize productivity. Furthermore, O-3 significantly increased the regression slopes between root C:N ratio and kernel N uptake, kernel C uptake and plant N uptake, strengthened the correlation of C:N ratio and kernel C uptake, and weakened the correlation of C:N ratio and hundred-kernels weight. These suggest that O-3 pollution can change the relationship of C:N ratio and productivity in maize. The weak correlation between kernel harvest index (HI) and N harvest index (NHI) indicated that future breeding researches should consider how to improve the coupling between biomass and N-related nutrition allocations in crop edible parts. Our results not only are helpful to accurately estimate O-3 impacts on maize with consideration of N but also provide a new insight into the relationship between plant traits and its productivity under O-3 pollution. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

This study examines the combined impacts of ozone (O-3) and nitrogen (N) on maize, revealing significant effects on biomass, nitrogen, and carbon elements, as well as changes in the relationship between C:N ratio and productivity due to O-3 pollution. Breeding research should focus on improving the coupling between biomass and N-related nutrition allocations in crop edible parts to enhance maize productivity under O-3 pollution.