The impact of creosote bush (Larrea tridentata) and biological soil crust on calcium distribution in arid soils of the Mojave Desert

Ca is an important nutrient that plays a role in membrane stability and cell repair in plant life. This study examines the impact of creosote bush (Larrea tridentata) and biological soil crust on calcium cycling and distribution in desert soils in order to explore the use of Ca as a biosignature. Samples of creosote bush, biological soil crust and eolian dust were taken at two field sites in the Mojave Desert. The first site is located in Eldorado Valley, NV, a soil formed on a young (800--1200 years) alluvial fan deposit; the second site is located on a late Holocene-aged alluvial fan from the Lucy Gray Mountain Range in Ivanpah Valley, NV. Both sites are dominated by creosote bush, have a granitic parent material and contain biological soil crust. Soil and dust samples were subjected to three sequential extractions of BaCl2, CH3OOH, and HNO3; creosote bush was digested with HNO3. All solutions were analyzed for Ca content by flame AAS. Results show that soils in the rhizosphere also contain higher amounts of exchangeable Ca but lower amounts of CaCO3, relative to soils at the same depth in the interspaces. Soil immediately beneath the biological soil crust is depleted in exchangeable Ca but shows no effect on CaCO3 relative to the soils in the interspaces. These results may be useful for identifying past vegetative life in desert paleosols in which this pattern of Ca is preserved.