ARS | Publication request: Tannic Acid Affects Extraction of Water Soluble Carbon and Nitrogen from Soil, and Carbon and Nitrogen Composition of Bradford Reactive Protein

Submitted to: Ecological Society of America Abstracts
Publication Type: Abstract
Publication Acceptance Date: April 12, 2006
Publication Date: August 1, 2006
Citation: Halvorson, J.J., Gonzalez, J.M., Smith, J.L. 2006. Tannic Acid Affects Extraction of Water Soluble Carbon and Nitrogen from Soil, and Carbon and Nitrogen Composition of Bradford Reactive Protein. In: Ecological Society of America Abstracts, August 6-11, 2006, Memphis, Tennessee. CDROM.

Technical Abstract: Tannins, plant-derived polyphenolic compounds that precipitate proteins, bind to metals and other important biomolecules, may be particularly important in soil ecosystems. However, more information is needed to determine their role in soil nutrient cycling and organic matter transformations. We treated soil from 5 farms, each containing samples of forest, pasture, and cultivated land with hydrolyzable tannin (tannic acid), and then measured water-soluble carbon (SOC), nitrogen (SN), and total Bradford reactive protein (BRP). Tannic acid-C added with water was not completely recovered from soils. Compared to untreated controls, tannic acid reduced total SOC in 0-5 cm samples and total SN in 0-5 and 10-20 cm samples. Recovery of less SN after adding tannic acid to soil is apparently a partial result of abiotic complexing reactions. Recovery of BRP from soil appeared to increase after treatment with tannic acid, but formation of dark-colored substances during extraction suggests the colorimetric Bradford assay may overestimate soil protein when tannins are present. Tannin-treated BRP extracts contained less SN than untreated controls and exhibited a lower ratio of absorbance at 465 and 665 nm (E4/E6), associated with the formation of larger or heavier molecules. Carbon concentrations of BRP were highest when soils were treated with tannic acid, but effects were influenced by land use and depth. Tannic acid also increased the nitrogen content of BRP in soil from 10-20 cm but had little or no effect on nitrogen content of BRP from 0-5 cm. The C:N ratio of BRP increased when tannic acid was added to soil. Recovery of less water soluble-C and -N and lower E4/E6 ratios suggests tannins may bind with soil constituents themselves or form non-extractable N-containing complexes. Varying carbon and nitrogen content and C:N ratios of recovered BRP suggest that additions of tannins may affect the quality of soil organic constituents and support the proposition that tannins are important mediators of soil organic matter.