Environmental controls on soil respiration in the northern Chihuahuan Desert

Background/Question/Methods

Historical grazing in the US Southwest has converted pristine grasslands to shrublands, including those at the Jornada Experimental Range (JER), located in the northern Chihuahuan Desert. Given the dominance of desert landscapes throughout the world and predicted increased variability in precipitation intensity and frequency, which will affect ecosystem responses such as primary productivity biotic decomposition, and microbial respiration, understanding the ecosystem properties and processes that control uptake and release of CO₂ in desert shrublands is of vital importance. Soil microbiota are extremely important to soil ecological functioning as they regulate nutrient cycling through the decomposition of organic matter. The goal of this project was to determine changes in carbon emissions from soil both seasonally and as a function of precipitation pulses.  Soil plots situated along a litter gradient associated with dominant shrub species (Prosopis glandulosa and Larrea  tridentata) and lichen crusts were measured weekly for carbon flux using the INNOVA Multi-gas analyzer 1312. 

Results/Conclusions

Preliminary results from regression tree analysis indicate that an initial 25% of the variation in soil respiration was explained by temperature, where soils with mean temperatures greater than 28.6 C released the most CO₂. At higher temperatures, soils with VWC>12 tended to release the greatest amount of CO2 (54 mg/m2/hr). Carbon uptake increases immediately following rain events, with the relative contribution by soil respiration gradually increasing until a threshold  soil moisture is reached. This threshold likely depends on microbial community structure and food availability.  Analysis of covariance indicated that the relationship between respiration and temperature did not differ between shrub types; however, different litter quantities did affect the rates of respiration. Differences in labile carbon as a source of decomposition for microbiota might be able to explain soil respiration and microbial community with PCA analysis.