Tuesday, November 14, 2006
203-7

Biogeochemical Cycling in a Mohave Desert Ecosystem.

Giles Marion, Paul Verburg, Bryan Stevenson, and Jay Arnone. DEES, Desert Research Inst, 2215 Raggio Pkwy, Reno, NV 89512

The distribution of chemical species in desert ecosystems is a complex function of climatic inputs (aeolian and precipitation), rock weathering, soil leaching, and plant cycling.  In this study at the Nevada Test Site (NTS), we examined the distribution of soluble soil elements beneath plant canopies and in intershrub zones. We extracted soluble chemistries using saturation extracts that were allowed to equilibrate overnight. All soil horizons were supersaturated with respect to calcite.  Essential cations (K, Ca, and Mg) were highest in concentration in surface soils beneath plant canopies.  Na, Cl, NO3-N, and SO4 were generally highest in concentration at 1.0 m depth.  The NTS desert NO3-N pattern is similar to some previous desert work, but at variance with other desert sites and the majority of global NO3-N patterns, which are highest in concentration near the surface. The dissimilar patterns of essential nutrient accumulations between the cations: Ca, K, and Mg, and the anions: NO3-N and SO4 are likely due to the greater mobility of anions like NO3-N and SO4 compared to cations, which are likely limited in their mobility by exchange reactions with solid phases such as clay minerals.  Furthermore, once NO3-N or SO4 have leached to deeper soil depths, they may be relatively unavailable for plant uptake due to low root mass at depth and a general lack of water at depth that is necessary for plant uptake. Based on the current, variable patterns of nutrients in desert ecosystems, global climate change (temperature and precipitation) will likely play critical roles in controlling and altering desert ecosystems in the future.

Handout (.pdf format, 589.0 kb)