Key Laboratory of Urban Environment and Health, Ningbo Urban Environment Observation and Research Station, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China.
CAS Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
Environ Sci Technol. 2022 Nov 15;56(22):16419-16427. doi: 10.1021/acs.est.2c03799. Epub 2022 Oct 12.
Microbially mediated iron redox processes are of great significance in the biogeochemical cycles of elements, which are often coupled with soil organic matter (SOM) in the environment. Although the influences of SOM fractions on individual reduction or oxidation processes have been studied extensively, a comprehensive understanding is still lacking. Here, using ferrihydrite, MR-1, and operationally defined SOM components including fulvic acid (FA), humic acid (HA), and humin (HM) extracted from black soil and peat, we explored the SOM-mediated microbial iron reduction and hydroxyl radical (OH) production processes. The results showed that the addition of SOM inhibited the transformation of ferrihydrite to highly crystalline iron oxides. Although FA and HA increased Fe(II) production over four times on average due to complexation and their high electron exchange capacities, HA inhibited 30-43% of the OH yield, while FA had no significant influence on it. Superoxide (O) was the predominant intermediate in OH production in the FA-containing system, while one- and two-electron transfer processes were concurrent in HA- and HM-containing systems. These findings provide deep insights into the multiple mechanisms of SOM in regulating microbially mediated iron redox processes and OH production.
微生物介导的铁氧化还原过程在元素的生物地球化学循环中具有重要意义，这些过程通常与环境中的土壤有机质（SOM）耦合。尽管已经广泛研究了 SOM 分数对单个还原或氧化过程的影响，但仍缺乏全面的了解。在这里，我们使用水铁矿、MR-1 和从黑土和泥炭中提取的操作定义的 SOM 成分，包括腐殖酸（FA）、腐殖酸（HA）和腐殖质（HM），探索了 SOM 介导的微生物铁还原和羟基自由基（OH）产生过程。结果表明，SOM 的添加抑制了水铁矿向高结晶氧化铁的转化。虽然 FA 和 HA 由于螯合作用和高电子交换能力平均将 Fe(II) 的生成增加了四倍，但 HA 抑制了 30-43%的 OH 产率，而 FA 对此没有显著影响。在含有 FA 的系统中，超氧阴离子（O）是 OH 产生的主要中间体，而在含有 HA 和 HM 的系统中则同时存在单电子和双电子转移过程。这些发现深入了解了 SOM 调节微生物介导的铁氧化还原过程和 OH 产生的多种机制。
