From the litter layer to the saprolite: Chemical changes in water-soluble soil organic matter and their correlation to microbial community composition

• Published in: Soil biology & biochemistry Vol. 68; pp. 166 - 176
• Main Authors: Gabor, Rachel S., Eilers, Kathryn, McKnight, Diane M., Fierer, Noah, Anderson, Suzanne P.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 01.01.2014; Elsevier
• Subjects: Agronomy. Soil science and plant productions; Biochemistry and biology; Biological and medical sciences; chemical structure; Chemical, physicochemical, biochemical and biological properties; Colorado; community structure; EEM-PARAFAC; fluorescence; fluorescence emission spectroscopy; Fundamental and applied biological sciences. Psychology; landscape position; landscapes; microbial communities; organic horizons; Organic matter; Organic matter/microbe interactions; Physics, chemistry, biochemistry and biology of agricultural and forest soils; saprolite; Soil depth; soil organic matter; soil sampling; Soil science; UV–vis absorbance and fluorescence spectroscopy; vegetation; Water soluble organic matter (WSOM); watersheds; XAD-8 resin fractionation; USA, Colorado; Colorado; Organic matter/microbe interactions; EEM-PARAFAC; Water soluble organic matter (WSOM); UV–vis absorbance and fluorescence spectroscopy; XAD-8 resin fractionation; Soil depth; Community structure; Fractionation; Organic matter; Litter; UV―vis absorbance and fluorescence; Fluorescence; saprolite; Depth; Soils; Absorbance; Chemical modification; Spectrometry; spectroscopy; Water solubility; Soil science; Microorganism; Resins; Microbial community
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2013.09.029

Organic matter content and chemistry is vital to the structure and function of soil systems, but while organic matter is recognized as biogeochemically important, its chemical interaction with soil processes is not well understood. In this study we used fluorescence spectroscopy, which has been used extensively for understanding the role of organic matter in aquatic systems, to identify chemical changes in organic matter with depth in a soil system. Soil was collected from nine different pits in a first-order montane catchment in the Colorado Front Range. The water-soluble soil organic matter was extracted from each sample and fluorescence and UV–vis spectroscopy was used to analyze its chemical character. While organic matter chemistry had little correlation with landscape location and local vegetation, there were noticeable consistent trends between soil horizon and organic matter chemistry in each pit. Total organic matter decreased with depth and became less aromatic with increasing depth. This less aromatic material in the saprolite also had a greater microbial signature. The redox character of the organic matter accompanied this change in source and molecular structure, with more oxidized character corresponding with organic matter with more microbial input and more reduced character corresponding to organic matter with more plant input. A concurrent investigation of the microbial population of the same soil samples also showed microbial population composition varying more with soil depth than landscape position, and depth changes in microbial diversity occurred concomitantly with depth changes in organic matter chemistry. •Chemistry of water-soluble organic matter, as measured by fluorescence spectroscopy, changed noticeably with soil depth.•The degree of microbial input to water-soluble organic matter correlated to the redox state of the organic matter.•Microbial community diversity and organic mater chemistry changed concomitantly with soil depth.