Effects of elevated carbon dioxide (CO₂)and ozone (O₃)concentrations on ectoenzyme activities in rice rhizospheric...

Rising atmospheric carbon dioxide (CO₂) and ozone (O₃) concentrations are the main global change drivers. Soil ectoenzymes play an important role in maintaining soil ecosystem services. Exploring the responses of soil ectoenzymes to elevated CO₂ and O₃ concentrations is important for combating global climate change. In this study, we simulated elevated CO₂ concentrations (+200 μmol·mol^-1, eCO₂), elevated O₃ concentrations (0.04 μmol·mol^-1, eO₃), and their combination (eCO₂+eO₃) in open-top chambers (OTCs), and investigated the responses of rhizospheric soil ectoenzyme activities. The results showed that eCO₂ significantly increased the β-D-Glucosidase (βG) activity by 73.0%, and decreased that of polyphenol oxidase (PHO), peroxidase (PEO), and acid phosphatase (AP) by 48.9%, 46.6% and 72.9% respectively, but did not affect that of cellulose hydrolase (CBH) and β-N-Acetylglucosaminidase (NAG). eO₃ significantly reduced the activities of CBH and AP by 34.2% and 30.4%, respectively. The activities of PHO and AP were reduced by 87.3% and 32.3% under the eCO₂+eO₃ compared with the control, respectively. Results of the principal coordinate analysis, permutation multivariate analysis of variance and redundancy analysis showed that both elevated CO₂ and O₃ significantly affected soil ectoenzyme activities, with stronger effects of elevated CO₂ than elevated O₃. Root nitrogen content, root carbon to nitrogen ratio, soil microbial biomass carbon and nitrate nitrogen were the main drivers of soil ectoenzyme activities under elevated CO₂ and O₃. Elevated O₃ could partially neutralize the effects of elevated CO₂ on soil ectoenzyme activities. In conclusion, elevated CO₂ and O₃ restrained the activities of most soil ectoenzyme, suggesting that climate change would threat soil ecosystem services and functions in the agroecosystem.