Polyphenols comprise a large percentage of plant detritus such as leaf litter, and polyphenols released from plant matter can affect many soil processes. To fully understand the roles of tannins in soil ecology, this work investigated the sorption / desorption of tannins from soil, the effects of tannins on microbial communities, and the mobilization of soil metals by polyphenols.
This dissertation is divided into three parts. First, I studied the sorption and desorption of tannins from soils. I determined that tannin polarity plays the most important role in dictating sorption of tannins to soil by examining six specific polyphenols with a range of polarities and differing molecular structures. The maximum amount sorbed and the rate of sorption were determined for the six model compounds. Using the concept of polarity an extraction method was developed that allowed reliable determination of the amount of tannin in soils even for tightly sorbed compounds.
In the second part of my dissertation, I describe how microbial communities are affected by different tannins. This was tested by amending soil with three different model polyphenols and evaluating soil microbial populations with molecular and physiological methods. The abundances of three genes that reflect populations of total microbial species, ammonia oxidizing bacteria, and ammonia oxidizing archea were measured using DNA extracted from soils and qPCR. Changes in physiology as determined by Community Level Physiology Profile indicated that the small polyphenol, methyl gallate had the greatest affect on community physiology.
In the last part of my dissertation, I determined the effects of tannins on soil metal mobilization. This was tested by determining the maximum binding and binding affinities of two model polyphenols to Al(III) and Fe(III) using micelle-mediated separation and Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). The larger polyphenol (oenothin B) was able to bind more metal then the small polyphenol (EGCg). I then built a model of how each polyphenol would bind to Al(III) and Fe(III) in a multiple metal model system and used that model to predict metal mobilization in soils. The effect of tannins on soil process can be related to the chemical properties of the compound.