| 英文摘要: | Dissolved Organic Matter (DOM) is a component that is sensitive to climate change in soil and plays an important role in environmental chemical behaviors such as transportation and transformation of heavy metals and carbon release. Meanwhile, the Qinghai-Tibet Plateau is one of the most sensitive region to climate change all over the world. However, few researches are focusing on the application of fluorescence spectroscopy to ascertain the impact of climate change on soil DOM and to reveal the response of environmental chemical behaviors of DOM to climate change. In this study, fluorescence spectral characteristics of DOM in meadow soils in Daban Mountain, Qinghai, under different altitudes (2 800, 3 000, 3 300, 3 600 and 3 900 m) was determined by using three-dimensional fluorescence spectroscopy and parallel factor analysis to reveal the response of the sources, compositions and properties of DOM to climatic conditions at different altitudes. The results showed that altitude had an important influence on the physical and chemical properties of the soil. With the increase of altitude, the soil pH decreased significantly, while the average organic matter increased from 6. 32% to 13. 75%. However, there was no significant change in the content of dissolved organic carbon at different altitudes. Additionally, altitude also had an impact on the origin and nature of DOM.
The BIX index of DOM increased with the rise of altitude, indicating a more contribution to DOM in high-altitude soils by microbial sources, which may be due to a lower decomposition of plant residues and the mineralization of organic matter induced by low temperature at high altitudes. The FI index (1. 332 similar to 1. 621) was found to be lower than the eigenvalue indicating an autogenous source (FI=- 1. 9) and the one indicating a terrestrial source (FI=1. 4) , showing that the DOM not only derived from the autogenous microbial activity, but also terrestrial input, such as plant residue and root exudates. However, the HIX index had no significant difference in soil DOM at different altitudes, indicating that elevation of altitude did not significantly change the degree of DOM humification. The results of parallel factor analysis showed that there were six organic components (C1-C6) in the DOM of meadow soil in Qinghai : which are two humic acid components (C2 and C4) , two fulvic acid components (Cl and C3) and one water-soluble microbial by-product (5) and one protein-like component (6). Among them, fulvic acid-like and protein-like were the components with the highest proportion (54. 69 % similar to 5 9. 78%) and the lowest proportion (5. 42% similar to 8. 47%) of DOM, respectively, while humic acids accounted for an average of 25. 08% of DOM. The principal component analysis of the organic components in DOM at different altitudes showed that the samples of DOM at different altitudes were basically dispersed, indicating that the composition of DOM was responsive to altitude. The fulvic acid-like component (C3) , the humic acid-like component (C4) and the protein-like component (C6) contributed the most to the differences in DOM compositions. With the increasing altitude, the relative proportions of C3 and C6 increased significantly, while the C4 decreased significantly. This indicated that the climate conditions at high altitude enhanced the production of fluvic acid and protein, but limited the production of humic acids. It could be concluded that the source, nature and composition of DOM in meadow soils of Qinghai have significant differences under different altitude conditions. And the results may provide theoretical basis for the assessment of soil carbon pool in Qinghai-Tibet Plateau and for the prediction of the transportation and transformation of heavy metals and carbon cycle under global climate change.
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