Biochar induced changes of soil dissolved organic matter: The release and adsorption of dissolved organic matter by biochar and soil

Dissolved organic matter (DOM) is an important organic matter fraction that affects many biological and chemical processes in soil. Biochar can change soil DOM while the effects were paradoxical, and contributions of biochar to soil DOM was not clear yet. In this study, excitation-emission matrix (EEM) fluorescence spectroscopy was applied to determine the biochar-induced changes of DOM composition. Batch experiments were conducted to quantify the contributions of biochar to soil DOM. Biochars were prepared by pyrolyzing wheat straw (S300/700) and cow manure (M300/700) at 300 and 700 degrees C, respectively. Generally, biochar increased the humification of soil DOM possibly by the release of indigenous DOM and selective adsorption of the small molecule DOM. Besides, contributions of 5300 and M300 to soil DOM (37-91%) were higher than that of 5700 and M700 (2-19%) irrespective of application rates. The indigenous DOM released from 5300 and M300 was 6.4-12.1 times more than the soil DOM adsorbed by 5300 and M300, leading to the increase of DOM content. Contrarily, the DOM from 5700 and M700 was only 11-17% of the soil DOM adsorbed by them, resulting in the decrease of DOM content. In acklition, contributions of biochar to soil DOM increased as the application rale increased, especially for 5300 and M 300. This study indicated that the release and adsorption of DOM were the key processes determining the effects of biochar on soil DOM, which were closely related to the pyrolysis temperature and application rate of biochar. (C) 2021 Elsevier B.V. All rights reserved.