Semiarid and arid ecosystems are pulse driven systems. At the daily time scale, the nearly continuous dry soil is irregularly interrupted by brief wet periods. The duration of these wet periods depends on the size of the precipitation event.  The precipitation regimes in semiarid and arid environments, and therefore the pulsing regimes, are dominated by small events (≤ 10 mm).  The goal of our research was to determine how small precipitation events (2mm, 5mm, and 10mm) affected the dynamics of soil respiration and water loss in the shortgrass steppe.  Since landuse change has resulted in a patchwork of large-scale disturbances in this region, we estimated respiration and water loss from sites that varied in time since cultivation disturbance (4 and 20 years after cultivation, and undisturbed shortgrass steppe). 

Results/Conclusions

Total carbon respired and duration of elevated soil respiration increased as event size increased in all sites.  Total carbon loss ranged from 0.3 g C/m² (0.01% of carbon in ANPP) after a 2mm pulse in a field 20 years after cultivation to 3 g C/m² (6% of carbon in ANPP) after a 10mm pulse in undisturbed shortgrass steppe.  Time since cultivation did not significantly affect the total carbon respired for 2mm pulses, but increased in importance as event size increased.  The smallest events (2mm and 5mm) caused a respiration response that lasted longer than it took soils to lose water from the pulses, whereas for the largest event (10mm), respiration returned to baseline before the added water had been depleted.  Our results suggest that water is the most limiting factor to soil respiration rates for the smallest events, but becomes less limiting for events above 5 mm.  Small precipitation events have the potential for large short-term losses of carbon in the shortgrass steppe.