Pedosphere 30(2): 159--167, 2020
ISSN 1002-0160/CN 32-1315/P
©2020 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Are humic substances soil microbial residues or unique synthesized compounds? A perspective on their distinctiveness
Sen DOU1, Jun SHAN2, Xiangyun SONG1,3, Rui CAO4, Meng WU2, Chenglin LI2, Song GUAN1
1College of Resources and Environmental Sciences, Jilin Agricultural University, Changchun 130118 (China);
2State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China);
3College of Resources and Environment, Qingdao Agricultural University, Qingdao 266109 (China);
4Jiangsu Key Laboratory for Eco-Agricultural Biotechnology around Hongze Lake, Huaiyin Normal University, Huaian 223300 (China)
Corresponding Author:Sen DOU
      Humic substances (HS), which are defined as a series of highly acidic, relatively high-molecular-weight, and yellow to black colored substances formed during the decay and transformation of plant and microbial remains, ubiquitously occur in nature. Humic substances represent the largest stable organic carbon pool in terrestrial environments and are the central characteristic of the soil. However, the validity of the HS concept and the justification of their extraction procedure have been recently debated. Here, we argue that the traditional humic paradigm is still relevant. Humic substances are distinctive and complex because the extracted HS formed during the humification are chemically distinct from their precursors and are heterogeneous among soils. By reviewing the concept, formation pathways, and stabilization of HS, we propose that the key question facing soil scientists is whether HS are soil microbial residues or unique synthesized compounds. Without revealing the distinctiveness of HS, it is impossible to address this question, as the structure, composition, and reactivity of HS are still poorly known owing to the heterogeneity and geographical variability of HS and the limits of the currently available analytical techniques. In our view, the distinctiveness of HS is fundamental to the soil, and thus further studies should be focused on revealing the distinctiveness of HS and explaining why HS hold this distinctiveness.
Key Words:  heterogeneity,humic acid,humification,humus,microbial biomass,soil organic matter
Citation: Dou S, Shan J, Song X Y, Cao R, Wu M, Li C L, Guan S. 2020. Are humic substances soil microbial residues or unique synthesized compounds? A perspective on their distinctiveness Pedosphere. 30(2): 159-167.
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