Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 13, 2005
Publication Date: October 9, 2005
Citation: Halvorson, J.J., Gonzalez, J.M. 2005. Tannins can affect measurement of soil proteins and recovery of soluble carbon and nitrogen from soil. Proceedings of 2nd International Conference on Mechanisms of Soil Organic Matter Stabilization and Destabilization, Monterey, CA, October 9-13-2005. Technical Abstract: Tannins, plant-derived polyphenolic compounds that precipitate proteins, bind to metals and other important biomolecules, may be particularly important in soil ecosystems but more information is needed to determine their roles in soil nutrient cycling and organic matter transformations. We treated soil from 5 farms, each with samples of forest, pasture and cultivated land with condensed (quebracho) and hydrolyzable (tannic acid) tannins and then measured total Bradford reactive protein (BRP), water-soluble carbon (SOC) and nitrogen (SN). Apparent recovery of BRP increased after treatment with tannic acid, but less soluble-N was recovered from tannin-treated samples than from untreated controls and a lower ratio of absorbance at 465 and 665 nm (E4/E6) was observed, associated with the formation of larger or heavier molecules. Additions of tannic acid resulted in extraction of less SOC or SN from surface soil (0-5 cm) than from control or quebracho-treated soil. Formation of dark-colored substances during extraction suggests the colorimetric Bradford assay may overestimate soil protein when tannins are present. Recovery of less soluble-C and -N and lower E4/E6 ratios suggests tannins may bind with soil constituents themselves or form non-extractable N-containing complexes. The data support the proposition that tannins are important mediators of soil organic matter and provide an initial framework upon which to build future research.