Dissolved organic matter (DOM) is the most active component in the soil environment. Understanding the chemical diversity of DOM and the interaction of the physicochemical properties of the soil are key to managing peatland under succession. In this study, we aimed to understand the effects of peatland succession on soil DOM. We collected soil samples (topsoil: 0–10 cm, subsoil: 10–20 cm) from peatland during different stages of peatland succession in mid–high latitude northern regions, determined the changes in quantity and quality of DOM using fluorescence spectroscopy and parallel factor analysis. We found that peatland succession altered the effectiveness of soil nutrients and water content. During the succession, the content of humus-like substances in the DOM of the topsoil increased and the content of protein-like material decreased, whereas the content of substances in the subsoil remained stable. pH was the key factor affecting the change in the composition of the DOM in the topsoil during peatland succession. The variation of DOM in the subsoil may be related to the vegetation composition. The results suggest that fluorescent DOM components respond significantly to changes in peatland succession, and DOM properties are driven by soil pH and vegetation composition during peatland succession. In conclusion, our results reveal the optical changes and factors that influence DOM in peatlands under succession. This suggests that DOM can be modified by simultaneous changes of the physicochemical properties in the soil and the vegetation cover.
Forest swamp ecosystems play an important role in the global carbon cycle, yet they are often overlooked. With global climate warming, it is inevitable that it will impact the relationship between soil microorganisms and organic matter. Dissolved organic matter (DOM) in the soil environment is extremely sensitive to environmental changes. Understanding the effects of climate change on DOM and microorganisms is crucial for assessing the stability of carbon (C) in forest swamp soils. Therefore, we conducted a 142-day laboratory warming incubation experiment (control: 10 °C, and warming: 20 °C) to investigate the response of forest swamp soil microbial and DOM properties to warming. Excitation-emission matrix (EEM) fluorescence spectroscopy was used to explore the changes in different material compositions of DOM over time at different incubation temperatures, and high-throughput sequencing was used to investigate the changes in soil bacteria. The DOM content (dissolved organic C, DOC) and the degree of humification index (HIX) increased with an increase in incubation time under warming conditions (p < 0.05). In contrast, microbial humic substances (C3) decreased with increasing time. Long-term warming has separated bacterial communities and gradually tightened the degree of connectivity between bacterial networks. The degree of soil humification (Mantel test r = 0.58, p < 0.01) and DOC (r = 0.21, p < 0.05) were the most critical indicators that changed the diversity of the bacterial community. Our findings suggest a degree of interaction between changes in forest swamp soil microbial communities and DOM under warming conditions. The results of this study contribute to our understanding of changes in DOM fluorescence indices in forest swamp soils under the influence of climate change and their associated microbial mechanisms.
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