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| Mechanism of dissolved organic matter transformation in paddy soil with the application of fertilizer and straw return driven by oxidation of reduced nontronite |
| Received:June 01, 2024 |
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| KeyWord:reduced chlorite;straw turnover;hydroxyl radicals（·OH）;DOM transformation |
| Author Name | Affiliation | E-mail | | FU Junhong | College of Resources, Hunan Agricultural University, Changsha 410128, China | | | XIAO Yanqi | College of Resources, Hunan Agricultural University, Changsha 410128, China | | | NING Yaqi | College of Resources, Hunan Agricultural University, Changsha 410128, China | | | XIE Wenjing | College of Environment and Health, Jianghan University, Wuhan 430000, China | | | ZHANG Na | Hebei Key Laboratory of Wetland Ecology and Conservation, Hengshui University, Hengshui 053000, China | | | CUI Haojie | College of Resources, Hunan Agricultural University, Changsha 410128, China | hjcui@hunau.edu.cn | | LIAO Wenjuan | College of Resources, Hunan Agricultural University, Changsha 410128, China | 13207124692@163.com |
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| Abstract: |
| In order to investigate the transformation mechanisms of two types of dissolved organic matter（DOM）under straw return and fertilizer application during the oxidation of Fe（Ⅱ）in iron-containing clay mineral structures. The study used iron-rich reduced nontronite （rNAu-2）as a representative clay mineral and extracted DOM from paddy soils subjected to long-term chemical fertilization（CF）and organic manure with straw returning（HOF）practices（referred to as DOMCF and DOMHOF, respectively）. It investigated the effects of DOMCF and DOMHOF on the oxidation of rNAu-2, leading to · OH production, as well as DOM transformation. The study revealed that, DOMHOF undergoes easier mineralization during the oxidation process of rNAu-2[Fe（Ⅱ）=1.2 mmol·L-1]. Specifically, after 8 h of oxidation, the cumulative concentration of CO2（calculated by C）formation from DOMHOF（29.6 μg）exceeds that from DOMCF（16.9 μg）. Both DOMCF and DOMHOF inhibit the oxidation of rNAu-2 to produce ·OH, with DOMHOF exhibiting a more pronounced inhibitory effect. In the absence of DOM, the cumulative amount of ·OH produced from the aerobic oxidation of rNAu-2 after 8 hours is 26.06 μmol·L-1, which is higher than that in the rNAu-2/DOMCF（19.83 μmol·L-1）and rNAu-2/DOMHOF（17.07 μmol·L-1）systems（DOM concentration at 50 mg·L-1）. Solidliquid separation results indicated that the electron transfer between rNAu-2 and DOM or DOM-Fe3+ inhibits the structural Fe（Ⅱ） oxidation and ·OH production. Three-dimensional excitation-emission matrix spectroscopy（3DEEMs）revealed that straw return promoted the accumulation of humic substances and fulvic acids in paddy soil. After oxidation, significant changes were observed in the humic substances and fulvic acids, whereas their presence was scarcely detected in DOMCF. X-ray photoelectron spectroscopy（XPS）analysis indicates that ·OH can add to aromatic structures or olefins through ring-opening and hydroxylation mechanisms, leading to the generation of more oxygen-containing groups（C—O and C＝O）. Therefore, the presence of DOM inhibits the oxidation of Fe（Ⅱ）in the rNAu-2 structure and thus inhibits the formation of ·OH, while the DOM in the soil where the straw is returned to the field contains more easily decomposed organic matter components, which is more likely to consume ·OH and release more CO2. |
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