Understanding nitrogen and microbial dynamics associated with two degraded grassland systems in Big Bend National Park

Desertification is responsible for diminishing land productivity in the Chihuahuan Desert and over much of the southwestern United States. Current research indicates that the ongoing degradative loss of land productivity globally will increase as the human population continues to grow and as these systems undergo climatic changes (i.e., precipitation,temperature).

The ongoing effects of desertification of formally productive grasslands, as evidenced by nitrogen dynamics and microbial processes in the Dog Canyon and Airport sites at Big Bend National Park were determined in this investigation. The objectives for this thesis were to: (1) determine seasonal patterns in soil nitrogen (extractable NH4-N and extractable NO3-N) and N-mineralization in intact versus fragmented Tabossa grass {HHaria mutica) areas in Big Bend N.P., and (2) examine the relationship between grassland fragmentation dynamics and seasonal variations in microbial biomass dynamics.

The field experimental sites were located in the northernmost part of Big Bend National Park. The Dog Canyon and Airport sites were established to examine and compare microbial and nitrogen dynamics in vegetated versus bare soil areas of desertified grasslands. Soils in both sites are classified as Chalkdraw with Tabossa grass as the dominant plant species. Soils were collected from both sites during February, April, June, August, October, and December 2003, and February, April, and June 2004. Upon collection, soil samples were analyzed for soil moisture, microbial biomass, available and extractable nitrogen, net N-mineralization, soil organic matter and soil pH.