Soil-plant water relations in a Mojave Desert mixed shrubcommunity: a comparison of three geomorphic surfaces

Comparative plant water relations and soil moisture content of three geomorphic surfaces were assessed in a northern Mojave Desert mixed shrub community. The adjacent geomorphic surfaces studied were an ephemeral wash (Wash), a dissected alluvial fan remnant (Bench), and a montane slope (Slope). Perennial vegetation transpired for 2-6 months during a typical precipitation year. Plant water relations differed between species (on the same geomorphic surface) and between surfaces (for the same species). Plant water stress was greatest on the Bench, which had the finest textured soils and was underlaid by an indurated petrocalcic layer. Plants from the Wash and Slope sites had higher water potentials and stomatal conductances, presumably due to coarser textured, deeper soils in the Wash and water storage in fractured bedrock on the Slope. Soil water uptake patterns closely approximated relative transpiration on each surface. No evidence of deep percolation below the rooting zone was found on any of the three surfaces during a normal rainfall year.