SOIL DEVELOPMENT AND THE ECOHYDROLOGY OF WATER-LIMITED SYSTEMS

Soils are intimately connected to ecosystems, particularly in arid and semi-arid regions where water is the key limitation on primary productivity. Soil architecture develops from fluxes of moisture, energy and solute over time. These temporal morphological features of arid soils, including desert pavement, vesicular (V) horizon and subsoil horizonation are the accumulatory result of eolian input and redistribution within the profile which ultimately limit plant-available water. For this study, we use continuous soil moisture monitoring along a soil chronosequence in the Sonoran Desert to assess soil moisture stability patterns in plant and interspace microsites. Results found that V horizon thickness increased modestly with surface age with concomitant increase in water retention and surface runoff potential. The developing soil architecture reduces infiltration into the subsoil, thus decreasing both temporal variability and plant available water on older soil surfaces. Vegetation is interspersed and larger on young surfaces lacking a V horizon and focused in low-order drainages once a pavement begins to form and reroute moisture. Vegetated microsites on the youngest surface had the highest temporal variability and lowest mean due to both lower water holding capacity and higher root-water uptake. Despite higher mean moisture contents and temporal stability, soil water potentials were lowest on older surfaces limiting plant available water. Recent drought over the past century appears to have enhanced the contraction of Sonoran vegetation on geomorphically older, inter-pavement surfaces in the Sonoran Desert which can ultimately be tied to soil development.