9527722 Dahlgren Pygmy Forest species on the northern California coast contain some of the highest levels of foliar polyphenols ever reported. Data show that foliar polyphenol contractions in coniferous species increase as soil acidity increases and fertility decreases. It is believed that plants produce polyhenols in a response to increased acidity as a positive feedback mechanism. This feedback may control the dominant form in which litter N is mobilized (dissolved organic N vs mineral N), facilitating recovery of DON by adapted mycorrhizal associations, minimizing N availability to competing organisms, and attenuating N losses from leaching an denitrification. Specific objectives of this research are to I) determine soil acidity and nutrient limitation effects on foliar polyphenol production, ii) examine the influence of polyphenol-rich litter on regulating release of mineral and organic N forms, iii) to determine whether polyphenol production is a phenotypic response to soil conditions, iv) to examine mycorrhizal changes and rhizosphere conditions along the acidity/nutrient gradient, and v) determine DON utilization by vegetation and their associated mycorrhizae. This research will use landscape units which have undergone leaching for 100,00 to 500,000 years and which impose increasingly acidic conditions and nutritional stress on plant communities. Controlled growth chamber studies using quartz sand will examine acidity and nutritional effects on foliar polyphenol levels in Pinus muricata (Bishop pine) and Cupressus pygmaea (Mendocino cypress). In the field, foliar nutrient applications to single branches of Bishop pine and Mendocino cypress and fertilizer and lime applications to individual trees will evaluate the response of foliar polphenol levels to changing nutrient and acidity conditions. The forms of N released (NH4, NO3, DON) from Bishop pine, Mendocino cypress and ericaceous litter differing in phenol and tannin levels both in field and laboratory incubation studies w ill be examined. The forms of dissolved organic carbon (DOC) and DON in soil solutions and leachates from the incubation studies will be fractionated into hydrophobic/hydrophilic, acid/base/neutral fractions. Release rates of mineral N and DON will be evaluated in relation litter polyphenol, nutrient, lignin contents. Mycorrhizal species composition and infection levels will be determined across vegetation types and soil conditions, and rhizosphere versus bulk soil will be evaluated acrtoss the edaphic gradient. Utilization of DON by acid-adapted plant species and their mycorrhizae will be evaluated in solution cultures using natural and synthetic soures of DON.
