Alkalization-induced disintegration increased redox activity of solid humic acids and its soil biogeochemical...

Solid humic acids (HA_solid) plays a significant role in maintaining soil ecosystem services, especially in alkaline soil. The unique chemical structures and electrochemical properties are the cores that HA_solid works. In this study, the alkalization-induced variations of particle morphology, functional groups and redox activity of HA_solid were investigated and its soil biogeochemical implications were discussed. Atomic force microscopy (AFM) deflection images and zeta potential results showed that alkalization induced disintegration of HA_solid, with particle size reducing to 200 nm when pH value reached 10.0. This result suggested that HA_solid could exist in alkaline soil. AFM-IR along with fluorescence intensity of HA_solid at different pH further proved that the supramolecular aggregation of HA_solid became loose and dispersive with more redox-active functional groups exposure after alkalization, which could lead to HA_solid susceptible to degradation in alkaline soil. Conductivity of HA_solid decreased 42.86 % when pH increased from 5.0 to 10.0, while electron exchange capacity (EEC) of HA_solid increased 45.30 %, indicating the increase of redox activity of HA_solid. Increase of redox activity of HA_solid by alkalization-induced disintegration not only can accelerate organic pollutant degradation via enhancing microbial co-metabolism, but also speed up the organic carbon loss. This study contributes to a better understanding of the role of HA_solid in organic carbon stocks and fluxes of alkaline soils and has great implications for soil biogeochemical process.