Impact of Piling and Long-Term Topsoil Storage On Potential Soil Microbial Activity in the Northern Chihuahuan Desert.

Cryptobiotic soil crusts in arid regions contribute to ecosystem stability through increased water infiltration, soil aggregate stability, and nutrient cycling between the soil community and vascular plants. Natural gas mining involves removal of the topsoil, including surface crust, and storage of the removed topsoil in piles at the edge of the operation. Often this topsoil is stored for extended periods ranging from a few years to decades. During removal and piling the soil layers are often mixed and reversed. During storage the soil-pile surface is rarely vegetated. Currently we have no understanding of the significance of these practices on the microbiological metabolic potential of these soils. Since little vegetation is able to reestablish on the piles during extensive storage periods it is generally assumed that the soil’s biologic potential degrades. Soil microbial activity within such storage piles around a natural gas well pad in the Northern Chihuahuan desert was investigated. Surface and subsurface soil samples were taken from different layers of the topsoil stockpile (fallow 12yr). Microbial activity was measured using the MicroResp™ system, which measures respiration of microbes within whole soil samples supplemented with various carbon sources (simple and polymeric sugars, amino acids, carboxylic acids, and fatty acids). Heterotrophic microbial growth was evaluated by plating soil subsamples on agars aimed at recovering copiotrophes and oligotrophes. Genetic diversity of the recovered and directly extracted DNA was evaluated via 16S PCR-DGGE targeting the V3 and V6 variable regions. Preliminary results indicate that, interestingly, the greatest microbial activity was measured in the soil stockpile at a depth of 5-30cm.