Microbial, enzymatic, and soil nutrient dynamics associated with debris dam revegetation efforts of low degraded tobosa grasslands in the Chihuahuan Desert at Big Bend National Park
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With the increase of temperature and the amount of land lost to desertification, scientists must learn to monitor, control, and reestablish the land for future generations. This study,conducted innorth part of Big Bend National Park, Chihuahuan Desert examined the ability of the debris dam approach to reestablish critical soil microbial activity and community structure in conjunction with revegetation efforts of low elevation arid grasslands. Debris dams previously established by resource managers at Big Bend National Park in 2006 were sampled in January, May, August and October 2010 and January 2011 along with bare soil and an ajacent intact tabosa grassland. For all locations, a 7cm diameter by 15cm long bucket auger was used to take soil samples at 15cm increments to a depth of 45cm total (3 increments per core). At each sample date microbial biomass carbon and FAME analyses were conducted to ascertain microbial community structure. Functional characteristics of the soil bacteria and fungi were evaluated using BIOLOG and FUNGILOG procedures and key microbial enzymes (Phosphodiesterase, β-Glucosidase, and Phenol oxidase). Soil nutrient and edaphic properties were also obtained for each sample date. The debris dam approach did reestablish important microbial activity in these degraded low desert grasslands. Microbial biomass carbon levels had increased substantially as compared with the bare soils and were even higher than the natural grassland possible. Microbial community structure was similar between the natural vegetation and the debris dams after 4 years. Although fungi dominated all three locations, Gram Negative bacteria and Actinomycetes dominated the bare soil while Gram Positive Bacteria dominated the natural vegetation and debris dam soils. Soil nutrient dynamics were similar between the debris dams and natural vegetation areas as important microbial and plant linkages were reestablished. Importantly, the high levels of extractable NO3-N that characterize the bare soils in this region of Big Bend National Park with the loss of vegetation were reduced under the debris dams as nitrogen becomes immobilized in the vegetation and with greater microbial biomass. All microbial enzyme activities were higher under the natural vegetation with the debris dams intermediate in activity levels between the natural vegetation and the bare soil. Microbial carbon use was also similar in that microbial functional capabilities were intermediate between the natural vegetation and the bare soil. The microbial and nutrient data indicates that debris dams can be effective in restoring plant cover to formally bare regions in the Chihuahuan Desert without the need for supplemental water. Once plants are reestablished, regardless of species, important microbial dynamics and associated ecosystem processes are increased above levels that had been occurring in the bare or disturbed soils. Moreover the trajectory of the microbial and soil nutrients suggests that these vegetated bands are sustainable as critical aspects of nutrient mineralization coupled with increased microbial activity have been promoted. In addition from a practical standpoint, the debris dams will be more effective than the intensive investment of planting drought tolerant plants that can become evasive and threatening to the naturally occurring plants within Big Bend National Park.