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Oxygen availability regulates the quality of soil dissolved organic matter by mediating microbial metabolism and iron oxidation

Citation

Li, Ye et al. (2022), Oxygen availability regulates the quality of soil dissolved organic matter by mediating microbial metabolism and iron oxidation, Dryad, Dataset, https://doi.org/10.5061/dryad.c2fqz61cf

Abstract

Dissolved organic matter (DOM) plays a vital role in biogeochemical processes and in determining the responses of soil organic matter (SOM) to global change. Although the quantity of soil DOM has been inventoried across diverse spatio-temporal scales, the underlying mechanisms accounting for variability in DOM dynamics remain unclear, especially in upland ecosystems. Here, a gradient of SOM storage across twelve croplands in northeast China was used to understand links between DOM dynamics, microbial metabolism, and abiotic conditions. We assessed the composition, biodegradability and key biodegradable components of DOM. In addition, SOM and mineral-associated organic matter (MAOM) composition, soil enzyme activities, oxygen availability, soil texture, iron (Fe), Fe-bound organic matter and nutrient concentrations were quantified to clarify the drivers of DOM quality (composition and biodegradability). The proportion of biodegradable DOM increased exponentially with decreasing initial DOM concentration due to larger fractions of depolymerized DOM that was rich in small-molecular phenols and proteinaceous components. Unexpectedly, the composition of DOM was decoupled from that of SOM or MAOM, but significantly related to enzymatic properties. These results indicate that microbial metabolism exhibited a dominant role in DOM generation. As DOM concentration declined, increased soil oxygen availability regulated DOM composition and enhanced its biodegradability mainly through mediating microbial metabolism and Fe oxidation. The oxygen-induced oxidation of Fe(II) to Fe(III) removed complex DOM compounds with large molecular weight. Moreover, increased oxygen availability stimulated oxidase-catalyzed depolymerization of aromatic substances, and promoted production of protein-like DOM components due to lower enzymatic C/N acquisition ratio. As global changes in temperature and moisture will have large impacts on soil oxygen availability, the role of oxygen in regulating DOM dynamics highlights the importance of integrating soil oxygen supply with microbial metabolism and Fe redox status to improve model predictions of soil carbon under climate change.

Funding

Strategic Priority Research Program of Chinese Academy of Sciences, Award: XDA28010302

Natural Science Foundation of Jiangsu Province, Award: BK20211610

Youth Innovation Promotion Association of Chinese Academy of Sciences, Award: 2022313

Young Elite Scientist Sponsorship Program by CAST, Award: YESS20200124

National Natural Science Foundation of China, Award: 41730753

National Natural Science Foundation of China, Award: 42077029

National Natural Science Foundation of China, Award: U1906220