Nonmicrobial mechanisms dominate the release of CO_(2)and the decomposition of organic matter during the short-term redox process in paddy soil slurry

Both biotic and abiotic mechanisms play a role in soil CO_(2)emission processes.However,abiotically mediated CO_(2)emission and the role of reactive oxygen species are still poorly understood in paddy soil.This study revealed thatOH promoted CO_(2)emission in paddy soil slurries during short-term oxidation(4 h).OH generation was highly hinged on active Fe(II)content,and theOH contribution to CO_(2)efflux was 10%–33%in topsoil and 40%–77%in deep-soil slurries.Net CO_(2)efflux was higher in topsoil slurries,which contained more dissolved organic carbon(DOC).CO_(2)efflux correlated well with DOC contents,suggesting the critical role of DOC.Microbial mechanisms contributed 9%–45%to CO_(2)production,as estimated byγ-ray sterilization experiments in the short-term reoxidation process.Solid-aqueous separation experiments showed a significant reduction in net CO_(2)efflux across all soil slurries after the removal of the original aqueous phase,indicating that the water phase was the main source of CO_(2)emission(>50%).Besides,C emission was greatly affected by pH fluctuation in acidic soil but not in neutral/alkaline soils.Fourier transform ion cyclotron resonance mass spectrometry and excitation-emission matrix results indicated that recalcitrant and macromolecular dissolved organic matter(DOM)components were more easily removed or attacked by·OH.The decrease in DOM content during the short-term reoxidation was the combined result of ·OH oxidation,co-precipitation,and soil organic matter release.This study emphasizes the significance of the generally overlooked nonmicrobial mechanisms in promoting CO_(2)emission in the global C cycle,and the critical influence of the aqueous phase on C loss in paddy environments.