Characteristics of dissolved organic matter during decomposition of different organic materials in the black soil region of Northeast China.

Dissolved organic matter (DOM) is the most active component of organic materials, which plays a crucial role in soil organic matter accumulation and soil manuring during the decomposition. We conducted a five-site (Changtu of Liaoning, Dehui of Jilin, Harbin, Hailun and Heihe of Heilongjiang) in-situ experiment with six different organic materials (chicken manure, pig manure, fungal bran, soybean straw, maize straw and rice straw), in Northeast China's black soil belt from south to north. We aimed to characterize the DOM properties by spectroscopic techniques and to uncover the influencing factors. Results showed that after a two-year decomposition, the dissolved organic carbon concentration decreased notably, while the aromaticity index, content of hydrophobic fraction, concentration of colored dissolved organic matter and humification index of the organic materials increased, and differed among the organic materials. The fluorescence index values of all DOM were <1.4, and the autochthonous index values ranged 0.4-0.7, showing a characteristics of exogenous input and low bioavailability. Parallel factor analysis revealed that the relative contents of fulvic acid-like and protein-like fractions in organic manure and fungal bran DOM decreased, while the relative content of humus-like fraction increased. For crop straw DOM, there was a significant decrease in the relative content of protein-like fraction. The properties of DOM exhibited regional variations. The aromaticity and humification degree of DOM increased with the increasing cumulative temperature. From Heihe with the lowest accumulated temperature to Changtu with the highest temperature, the aromaticity and humification indexes of DOM increased by 6.9%-42.7% and 23.9%-59.0%, respectively. The properties of DOM of organic materials were significantly influenced by the type of organic materials, experiment site, and their interactions. Principal component and correlation analyses indicated that the characteristics of organic materials DOM after decomposition linked more to their intrinsically chemical structure of organic carbon than to experiment site. In conclusion, after two-year decomposition, the active components within DOM of all the organic materials converted into more stable components, leading to increased aromaticity and humification degree. The inherent characteristics of organic materials was the predominant factor influencing the changes in DOM characteristics.