POLYPHENOLS AS REGULATORS OF PLANT-LITTER-SOIL INTERACTIONS IN NORTHERN CALIFORNIA PYGMY FOREST - A POSITIVE FEEDBACK

The convergent evolution of polyphenol-rich plant communities has occu rred on highly acidic and infertile soils throughout the world. The py gmy forest in coastal northern California is an example of an ecosyste m on an extremely infertile soil that has exceptionally high concentra tions of polyphenols. Many 'negative feedbacks' have been identified w hereby plants degrade fertile soils through production of polyphenol-r ich litter, sequestering soil nutrients into unavailable form and crea ting unfavorable conditions for seed germination, root growth, and nut rient uptake. But in the context of plant-litter-soil interactions in ecosystems adapted to soils that are inherently acidic and infertile ( such as the pygmy forest), there are also many 'positive feedbacks' th at result from polyphenol production. By inhibiting decomposition, pol yphenols regulate the formation of a mor-humus litter layer, conservin g nutrients and creating a more favorable medium for root growth. Poly phenols shift the dominant pathway of nitrogen cycling from mineral to organic forms to minimize potential N losses from the ecosystem and m aximize litter-N recovery by mycorrhizal symbionts. Polyphenol complex ation of Al, Mn and Fe reduce potential Al toxicity and P fixation in soil. Polyphenols regulate organic matter dynamics, leading to the acc umulation of organic matter with cation exchange capacity to minimize leaching of nutrient cations. Humic substances derived from polyphenol ic precursors coat rhizosphere soil surfaces, improving physical and c hemical conditions for root growth and nutrient cycling. Although thei r long-accepted adaptive value for antiherbivore defense is now in dou bt, polyphenol alteration of soil conditions and regulation of nutrien t cycling illustrate how fitness can be influenced by the 'extended' p henotype in plant-litter-soil interactions.