PARENT SESSION
Oral Session 3: Biogeochemistry I: Litter and Decomposition.
Presiding: J Dilustro
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room A 107.

Decomposition in a desert environment: Abiotic regulators and thresholds.

Fernandez, Daniel^{*,1, 2}, Neff, Jason^{1, 2}, Belnap, Jayne ³, Reynolds, Richard¹, ¹ US Geological Survey, Denver, CO, United States² University of Coloado, Boulder, CO, United States³ US Geological Survey, Moab, UT, United States

ABSTRACT- Three major abiotic factors influencing microbial decomposition in mesic environments are soil moisture, temperature, and texture. However, uncertainty remains as to how these three variables interact and influence the rate of decomposition in xeric ecosystems. We investigated the influence of soil moisture, temperature, texture, depth, and soil organic carbon and nitrogen content, in relation to soil respiration and decomposition in a semiarid/cold desert environment. Regression tree analysis of soil respiration measurements showed volumetric soil moisture to be significant at or below 15.175 deg. At this threshold temperature average soil moisture was 9.5%. Above the threshold temperature, soil respiration was regulated by soil organic carbon and nitrogen and average soil moisture was 6.3%. Results also show an increase in soil respiration as soil organic carbon, nitrogen, and % fines (silt + clay) increase. Decomposition cloth results show significant differences in microbial decomposition rate relative to time of year, soil depth, and texture. Decomposition rate was greatest in spring/summer and lowest in fall/winter. Greatest decomposition rate in summer was 0.565% loss at a depth of 4-6cm whereas greatest decomposition rate in fall/winter was 0.397% loss at a depth of 12-14cm. Influence of soil texture varied throughout the year. Coarse textured soils had the greatest overall spring/summer decomposition rate (0.576% loss) and the lowest overall fall/winter rate (0.337% loss). The highest fall/winter decomposition rate (0.424% loss) and highest annual average rate (0.496% loss) occurred in soils with the highest proportion of silt and clay. Results also show decomposition rate to be influenced soil texture at the surface (0-2cm). Overall our study suggest that factors regulating decomposition in a xeric ecosystem have complex and variable influence but may be understood by examining thresholds at which they become significant.

Key words: soil respiration, thresholds, semiarid/cold desert, decomposition