Quercus agrifolia (Nee) and Quercus durata (Jeps.) are evergreen oaks that co-occur on serpentine-derived soils at the Jasper Ridge Preserve in northern California (San Mateo county, 37$spcirc$ 24$spprime$ N 122$spcirc$ 13$spprime$ W). Measurements of soil and pre-dawn xylem water potentials made late in the summer drought indicate that the two species differ substantially in rooting depth. Additional investigations have established that over the year water availability increases and nitrogen availability decreases with soil depth. As a result of the spatial interaction between soil resources and root distribution, I hypothesized that neighboring individuals of the two species: (2) differ in their seasonal courses of water and nitrogen acquisition, and (3) differ in the efficiencies with which they use water and nitrogen. Measurements of sap-flow, pre-dawn xylem water potential, stem water content, leaf gas-exchange, canopy gas-exchange, and leaf carbon isotope composition were made between September 1989 and January 1991 on representatives of the two species. The seasonal patterns of sap-flow, water potential, stem water content, and leaf gas-exchange established that for the shallowly rooted species, Q. agrifolia, transpiration was confined primarily to the relatively wet period between April and June, while the deeply rooted species, Q. durata, maintained access to water throughout the summer drought. When integrated over the study period, individuals of Q. agrifolia transpired less, but used water more efficiently than did neighboring individuals of Q. durata, resulting in approximately equal total carbon assimilation between the species. In contrast, leaf, xylem-sap and litter-fall nutrient analyses indicated that the two species had similar seasonal courses of foliar and sap nitrogen, and comparable rates and efficiencies of above-ground nitrogen turnover. This result implies that the roots of Q. durata were sufficiently active near the soil surface to permit access to ample nitrogen. Ecosystem level models of nutrient cycling and hydrological processes have traditionally assumed physiologically homogeneous plant communities. These findings indicate that interspecific differences in rooting depth may need to be considered in models of community evapo-transpiration, but are probably less critical for treatments of ecosystem nutrient cycling.