Carlisle, Eli (Univ. of California, Davis, University of California, Dept. of Viticulture, Davis, CA, 95616; Phone: 530-754-7144; Email: ecarlisle@ucdavis.edu)

 

Conversion of Oak Woodlands to Vineyards Alters Physical Constraints on Soil CO2 Respiration in a Mediterranean Climate Ecosystem

 

E.A. Carlisle *, K.L. Steenwerth, D.R. Smart

 

We examined constraints on annual soil CO2 respiration at unmanaged oak woodlands and adjacent vineyards that were converted from oak woodlands approximately 30 years ago in the Oakville Region of Napa Valley, California. All sites were located on the same soil type, a Bale (variant) gravelly loam (Fine-loamy, mixed, superactive, thermic Cumulic Ultic Haploxeroll) and dominated by C3 vegetation. Seasonal soil CO2 efflux was greatest at the oak woodland sites, although during the dry summer periods the rates measured from oak sites were at times similar to those measured from vineyards. In spite of the fact that CO2 efflux rates were higher, soil profile CO2 concentrations were lower at the oak-woodland sites, except at the shallowest depth (15cm). Soil gas diffusion coefficients for the oak sites were larger than for the vineyard sites. Long-term annual cultivation of the vineyard soils apparently increased bulk density, diminished porosity, and thus altered the effective gas diffusivities. In addition to lower CO2 production, lower diffusion coefficients may help account for the lower rates of CO2 efflux and higher CO2 concentrations in vineyard soil profiles. Vineyard soil CO2 was more depleted in 13C throughout the soil profile below 30 cm as indicated by more negative d13C ratios, and points to different respiratory C sources in vineyard soils. Annual C losses were less from the vineyard soils (7.02 0.58 Mg C ha-1 yr -1) as compared to the oak soils (15.67 1.44 Mg C ha-1 yr-1), and both were comparable to losses reported in previous investigations.