The effect of elevated ozone concentration on enzymes increases NO3− content in the soil at the jointing stage of wheat field

Soil NO3− in the South China Plain has recently received considerable attention because it is closely related to soil leaching. Elevated atmospheric O3 influences soil N through altered rhizosphere C allocation. Little is known about how elevated O3 (eO3) concentrations affect the availability of soil NO3−. Here, we used structural equation modeling (SEM) to investigate the direct and indirect influence of eO3 on soil NO3− in the rhizosphere of Yannong 19 (O3-sensitive) and Yangmai 16 (O3-tolerant) wheat (Triticum aestivum L.) cultivar. Compared with ambient O3 (aO3), eO3 led to a significant decrease in soil pH, soil moisture (SM), nitrification enzymes and protease and an increase in soil NH4+ and NO3−. SEM showed direct and indirect connections between eO3 and increased NO3− through nitrification enzymes, Protestant and total nitrogen. Additionally, based on redundancy analysis (RDA), O3 is the main element among the selected environmental factors, including soil pH, soil moisture (SM), total nitrogen, NH4+ and NO3−, that affects nitrification enzymes and Protestant. In conclusion, in the jointing stage in wheat, enzymes play an important role in determining the direct and indirect influence of eO3 on soil NO3− concentration.