Solubility characteristics of soil humic substances as a function of pH: mechanisms and biogeochemical perspectives

作者：Xuemei Yang, Jie Zhang, Khan M. G. Mostofa, Mohammad Mohinuzzaman, H. Henry Teng, Nicola Senesi, N. Senesi, Jie Yuan, Yu Liu, Si‐Liang Li, Xiaodong Li, Baoli Wang, Cong‐Qiang Liu · 发表于：Biogeosciences · 年份：2025 · DOI：10.5194/bg-22-1745-2025 · 被引用次数：21 · 研究领域：Soil Carbon and Nitrogen Dynamics、Heavy metals in environment、Geology and Paleoclimatology Research

Abstract. Soil humic substances (HSs) typically alter their electrochemical behaviours in the pH range of 1–12, which simultaneously regulates the stability of organo-minerals by modifying the HS functionalities. This process facilitates both biotic and abiotic transformations, which consequently leads to the export of degradative byproducts (e.g. HS components, nutrients) from soils into surrounding aquatic environments through water and/or rainwater discharges. However, the solubility features, environmental consequences, and mechanisms of HSs, including humic acids (HAs), fulvic acids (FAs), and protein-like substances (PLSs), under different pHs remain unclear. To respond to these issues, we used two soil extracts which were fractionated in the pH range from 12–1. The pH-dependent presence or absence of fluorescence peaks in the individual HS components reflected their functional group proton/electron exchange features at both low and high pH values, which were related to their solubility or insolubility. In particular, alkaline pH (≥pH 9) yielded the anionic forms (-O- and -COO-) of phenolic OH and carboxyl groups of HACS, resulting in decreased electron/proton transfer from HS functionalities, as indicated by the decline of fluorescence peak maxima, whereas the protonic functionalities (e.g. –COOH, –OH) of HSs at lower pH resulted in the formation of highly available and remaining uncomplexed HS forms. The solubility of HA fractions increases with increasing pH, whereas...