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University of Texas at El Paso (2013)

Carbon emissions from soil respiration in the northern Chihuahuan Desert shrubland

Ortiz, Anna Cristina

Titre : Carbon emissions from soil respiration in the northern Chihuahuan Desert shrubland

Auteur : Ortiz, Anna Cristina

Université de soutenance : University of Texas at El Paso

Grade : Doctor of Philosophy (PhD) 2013

The United States Department of Agriculture’s Jornada Experimental Range (JER), is located in the northern Chihuahuan Desert in southern New Mexico and historically functioned as an experimental rangeland for cattle grazing. Historical grazing in the US Southwest has been identified as a leading, but not the sole, factor that has led to the conversion of pristine grasslands to shrublands, such has been the case on the JER. The estimated increased variability in precipitation intensity and frequency that is predicted to occur with climate warming will likely affect ecosystem responses from ecological processes including primary productivity, microbial decomposition, and thus respiration. This reinforces the importance of improving our understanding of ecosystem properties and processes that control uptake and release of CO 2 in desert rangelands. The contribution of CO2 flux originating from soils in desert shrublands is largely unknown, yet may contribute substantially to ecosystem level fluxes. Soil flux plots were situated along a soil litter gradient around the dominant shrub species (Prosopis glandulosa and Larrea tridentata) and lichen crusts and were measured weekly or bi-weekly between August 2012 and May 2013 for soil temperature (5cm cm depth), soil volumetric water content, and C flux using an INNOVA 1312 Photoacoustic Analyzer. Seasonal composite samples from soil plots were taken to assess microbial functional diversity with the Biolog Ecoplate assays. Flux data was analyzed with ANOVA, ANCOVA, regression tree analysis, and NMS. Community-level physiological profiling (CLPP) determined microbial functional diversity with NMS. Soil total organic carbon (TOC) was measured with Lachat IL 550 TOC-TN analyzer from each plot seasonally. We found soil respiration ranging from 20-154.7 mg CO2 m-2 hr-1. Abiotic environmental factors such as temperature, solar radiation and barometric air pressure were found to have a significant effect on carbon efflux seasonally. Significant differences among or between shrub species and lichen crusts were not found and did not have an effect on carbon efflux. CLPP was found to depend on TOC concentrations available and showed unique functional diversity within and between shrub and lichen crust soils. Therefore, the release of carbon to the atmosphere during the dry season was not attributed to microbial activity, rather to abiotic environmental effects. The completion of biweekly soil carbon efflux measurements spanning a full year in Chihuahuan Desert shrublands is an important research component to an ongoing study that is focused on further understanding the patterns and controls carbon budgets in desert landscapes.^

Mots clés : Biology, Ecology|Biogeochemistry|Environmental Sciences


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