COS 38-8
Influence of C and N availability on repeated wetting-induced pulses of soil respiration in a southern California desert

Tuesday, August 12, 2014: 4:00 PM
309/310, Sacramento Convention Center
Jennifer R. Eberwein, Botany and Plant Sciences, University of California Riverside, Riverside, CA
G. Darrel Jenerette, Department of Botany and Plant Sciences, University of California, Riverside, CA

            Wetting-induced pulses of soil respiration (Rsoil) dominate annual emissions in arid environments, and climate change-induced shifts in precipitation patterns make understanding regulation of these pulses increasingly important.  We investigated the influence of carbon (C) and nitrogen (N) availability on Rsoil pulse responses in two desert sites, representing high and low anthropogenic N deposition.   We hypothesized that C and N availability would influence both the timing and the magnitude of the pulse response.  Collars placed under the canopy of the dominant vegetation, Larrea tridentata, received a 3 cm artificial rain event with one of the following treatments: water only, N (45 kg N ha-1 NH4NO3), C (90 g/L dextrose) and both N and C.  Additional collars served as a control (no addition) and to monitor soil temperature and moisture after water addition.  Rsoil was measured before treatment additions and then at 5, 15, 30 and 60 minutes after.  On subsequent days, Rsoilwas measured before and one hour after another 3 cm wetting event to follow the length of the pulse response for each treatment, with and without the influence of soil moisture.


            Rsoil at the low N deposition site (Low) ranged from 0 to 19.52 µmol m-2 s-1 across all treatments.  The Low site demonstrated peak flux rates of 7±5, 10±2, 17±3, 13±5  (mean ± standard deviation) within 5 minutes of treatment additions for water, nitrogen, dextrose and both, respectively.  The high N deposition site (High) demonstrated Rsoil from 0.18 to 42.16 µmol m-2 s-1.  Unlike the Low site, peak fluxes at High occurred at different times depending on treatment.   Peaks were 10±3 at 15 minutes for water only and 8±2 for the N treatment.  The two treatments that included dextrose peaked 48 hours after addition at 17±11 for C alone and 27±13 for both C and N.  At both High and Low, C addition resulted in fluxes that were significantly greater than water alone (p<0.05), but N had no effect.  On the first day of study, the Low site demonstrated higher fluxes, but peak fluxes were significantly greater at the High site (p<0.05).  Vegetation at the High site was larger with a deeper litter layer than the Low site, consistent with the effects of N deposition.  These results highlight the importance of a potential legacy effect from vegetation productivity and soil C and N status on influencing both the magnitude and the timing of wetting-induced pulses of soil respiration.