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United States Department of Agriculture

Agricultural Research Service

Title: Tannins Alter Soil Organic Matter Extraction, Solubility of Metals, and Root Physiology

Authors
item Halvorson, Jonathan
item Gonzalez, Javier
item Kinraide, Thomas

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: December 20, 2007
Publication Date: N/A

Technical Abstract: Tannins are common plant-derived polyphenolic compounds that precipitate proteins and react with other biomolecules but knowledge of their effects on soil organic matter, the solubility of metals, and root physiology is incomplete. Soil from forest and pasture systems was treated with tannic acid (TA) or related phenolic compounds, and analyzed for soluble soil-C (WSC), –N (WSN), and metals in solution. Treatment with TA reduced net WSC and WSN suggesting that TA-C sorbed on soil and interacted with labile soil-N. A simple gallotannin inhibited extraction more than TA while non-tannin phenolics had little effect. Effects of a single application of tannin persisted through 13 washings. Multiple applications of tannin resulted in an L-type sorption curve, suggesting that soils had a maximum sorption capacity for TA-C. The amount of Ca and Mn detected in solution also varied among the different phenolic treatments, highest for gallic acid. The higher Ca content may result from the low pH of the phenolic compounds. Higher Mn in solution may result from the redox reaction of Mn (IV) oxides with the phenolic compounds, producing soluble Mn2+and quinones, reactive compounds that can self-polymerize and/or copolymerize with other biomolecules to form humic-like substances. Tannic acid enhanced the electronegativity of seedling root surfaces perhaps reducing the potential for intoxication by toxic anions and favoring adsorption of Al and other cations. The effects of TA on root growth and morphology varied with concentration but, when added together, reduced the toxicity of Al and Cu. This information will contribute to an assessment of the impacts of tannins and other phenolic compounds on soil organic matter formation, nutrient cycling and toxicity risk of some metals and improve the management of forest soils.

Last Modified: 4/18/2014