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The Advantages of Having Polyphenols in Soils

Polyphenols are chemicals produced by plants that are not easily decomposed after the death of the plant. Typically, they accumulate in the soil, decomposing very slowly and depriving subsequent generations of the nutrients used to manufacture them. Initially thought to be used to discourage predation, this theory has recently come under heavy pressure. In fact, many species derive health benefits from consuming plant polyphenols, including humans. Pycnogenol is a polyphenol found in pine bark and is one of the most potent natural antioxidants yet discovered.

Nutrient Sequestration
- A great deal of research has already been done demonstrating the negative effects of polyphenols in soils. There are documented cases where polyphenol production has resulted in positive feedback loops, where the plants degrade fertile soils to produce polyphenols, which then become nonbiodegradeable components of forest litter, effectively diminishing soil fertility by sequestering nutrients and creating chemically unfavorable conditions for plant growth. However, the the pygmy forest in coastal northern California has proven to be an exception. There, already relatively infertile soil is invested with extremely high concentrations of polyphenols. Although these polyphenols still function to inhibit further decomposition, this functions to create a more stable layer of humus, preserving nutrient availability, discouraging competition and enhancing the environment for root system development.
Mycorrhizal Association
- In this case, the polyphenols shift the predominant route of nitrogen cycling from mineral to carbon-containing forms to decrease the potential for nitrogen losses and maximizing its recovery from leaf litter through the exploitation of symbiotic fungal species. This is accomplished by the improvement to soil structure caused by the decreased degradation of plant duff in the presence of nonbioavailable polyphenols, producing an environment more readily colonized by filamentous molds.
Toxin Sequestration
- Polyphenol complexation, or composite, of aluminum, iron, and manganese also serve to reduce potential phosphate fixation and aluminum toxicity in the soil. By using these toxins in the metabolism of inert compounds that can then be sequestered in the soil, a plant´s descendants can enjoy a more favorable soil environment than its parents did.
Cation Conservation
- Polyphenols manage the dynamics of the soil's organic matter, causing the accumulation of organic matter with the capacity for cation exchange in order to minimize leaching of essential nutrient cations. Additionally, components of humus that are derived from polyphenolic precursors serve to coat rhizospherous soil surfaces, improving the physical and chemical conditions of the soil for both rootlet development and nutrient cycling. This interpretation of the role of polyphenols in some plant ecosystems dramatically changes our understanding of their metabolic importance to plants as plant duff and soil modulators.

Nature