Characterization of Microbial Communities in Vineyard Soils

The purpose of this study was to characterize soil microbial communities in vineyard soils and to determine if particular kinds of microbial communities are associated with specific wine regions or soil properties. Representative soil samples were collected from twelve Pinot Noir vineyards in Anderson Valley, Russian River Valley, Los Carneros, Chalone, and Santa Maria Valley at the time of first bloom. These samples were analyzed for microbial community biomass and composition using phospholipid fatty acid (PLFA) analysis. A subset of samples were also analyzed at times of veraison and harvest. PLFA analysis provides a measure of living microbial biomass, a “fingerprint” of the soil community; and biomarkers for specific groups of microorganisms. Physical and chemical properties of the soils were also measured, including pH, electrical conductivity, cation exchange capacity, total nitrogen, total carbon, carbonate carbon, sulfate, particle size distribution, total phosphorus, potassium, nitrate nitrogen, and ammonium nitrogen. Microbial biomasses ranged from 72.2 to 234 nanomoles per gram soil and the total number of fatty acids detected ranged from 39 to 56. Although some samples from within a particular region were similar to one another, overall there was not a strong relationship between wine region and a particular kind of microbial community. At the subset of sites sampled at different times over the growing season, seasonal changes in microbial communities were detectable, but smaller than the differences between sites. There appeared to be small seasonal changes in the community that were common to all soils. The texture of the soils reflected considerable variation with clay contents ranging from 7% to 38% and sand contents from 23% to 68%. Soil pH also varied substantially from 4.8 (in pastureland adjacent to a vineyard) to 7.4. Total organic carbon ranged five-fold from 0.82% to 4.85%. Ammonium levels were for the most part lower than 13 ppm and nitrate less than 18 ppm. As we continue to catalog differences in microbial communities across a larger set of vineyard soils and at additional times, we will have better information to answer questions such as whether there are unique traits common to all vineyard communities, or whether region has a stronger influence than crop on microbial communities. Also this information will help us begin to understand how vineyard management practices and seasonal fluctuations affect microbial community composition.