Vesicular Pore Formation: The Effect of Microbes and Soil Temperature.

Vesicular horizons regulate the infiltration and runoff of rain in desert ecosystems, where water is the most limiting resource.  Our understanding of the resilience of vesicular horizons following disturbance is limited by our knowledge of the fundamental drivers for vesicular pore formation.  This study was conducted in order to evaluate the mechanism of vesicular pore formation.  While vesicular pores have been attributed to expansion of trapped air during wetting and drying cycles at the surface of desert soils, the mechanism of air expansion has not been thoroughly addressed.  Laboratory regeneration of vesicular pores was examined in sterile and non-sterile sieved soil material in order to test competing hypotheses regarding the mechanism of vesicular pore formation.  A purely physical expansion in response to temperature was compared with a biologically-driven expansion, attributed to the pulse of microbial respiration associated with wetting of the soil surface.  The results of this study suggest that resilience of vesicular horizon properties and ecosystem functions may vary depending on the physical and biological conditions of the disturbed soil.