PARENT SESSION
Poster Session #35: Decomposition and Soil Respiration.
Thursday, August 9, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Response of soil carbon mineralization to moisture pulses under sagebrush, cheatgrass, and crested wheatgrass vegetation in the Great Basin, Utah.

CHOROMANSKA, URSZULA¹, SAETRE, PETER², STARK, JOHN¹, ^{1 2}

ABSTRACT- Human manipulation of vegetation in the Great Basin may considerably alter ecosystem biogeochemistry. Corresponding changes in soil resources can influence available carbon pools and result in plant community composition shifts toward non-native invasive species. Here we report how seasonal carbon (C) dynamics vary among semi-arid plant communities dominated by plants of different life forms and phenologies. Plots were established in annual exotic grass (Bromus tectorum), perennial exotic pasture (Agropyron desertorum), and native shrub (Artemisia tridentata spp. wyomingensis) cover types. Field and lab analyses of soil water content, microbial biomass, available C, respiration rates, and inorganic N concentrations in the 0-10 cm soil layer were performed biweekly for two years. B.tectorum soil had 50% greater CO₂ production rates than the other soils during spring (late March through early June). During the growing season, fluxes of CO₂ from intact soil cores ranged from 0 to 19 ug CO₂-C g^-1 soil d^-1 and were highly correlated with laboratory assays of available C and soil water content. Temporal patterns of C availability to soil microbes resulted in the greatest microbial biomass in B.tectorum soil and the lowest in A.desertorum soil during spring, but little difference during other times of year. These results suggest that B.tectorum alters seasonal patterns in C-availability to microbes, which modifies the timing of nitrogen pulses and increases the ability of B.tectorum to compete with perennial plant species.

KEY WORDS: Agropyron desertorum, Artemisia tridentata, Bromus tectorum, soil respiration