PARENT SESSION
Contributed Oral Session 29: Climate Dynamics: Arid Land Responses to Variability in Rainfall
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 520 A, Level 5, Palais des congrès de Montréal
Ecosystem responses to rainfall quantity and variability in model grassland assemblages.
Kaufman, Dawn*,1, Harper, Christopher1, Nippert, Jesse2, Fay, Philip3, Blair, John1, 1 Kansas State University, Manhattan, KS, USA2 Colorado State University, Ft. Collins, CO, USA3 Natural Resources Research Institute, Duluth, MN, USA
ABSTRACT- Global climate change scenarios and climate observations suggest increased variability in the total quantity, frequency, and event sizes in future precipitation patterns. Resulting changes in photosynthetic carbon gain, net primary production, or soil respiration are likely to have important consequences for climate-biosphere linkages, carbon and water budgets, and species ranges–depending on changes in the total quantity of rainfall inputs and in individual event size and frequency. The effects of rain-event frequency, size and totals have been extensively studied in strongly water-limited arid systems, but also are likely important in more mesic grasslands. We implemented a watering quantity/interval experiment in an outdoor microcosm facility in a tallgrass prairie in NE Kansas, USA (39.1°N, 96.9°W), where 64 2.6-m3 microcosms were planted with native C4 grasses and C3 forbs. Four annual "rainfall" quantities (400, 600, 800, and 1000 mm yr-1) were combined with four "rain-event" intervals (3, 6, 10, and 15 d) to produce 16 treatments (n = 4 microcosms trt-1), yielding individual event sizes from 4 to 53 mm. Mean soil water content increased with total water added, but larger individual events yielded progressively smaller increases in soil water content, suggesting less efficient capture and storage of large events by the soil column. Several measures of ecosystem response (photosynthetic carbon gain, aboveground net primary production, soil respiration) showed similar gains in performance with increased event size that declined with decreased event frequency, which suggests decreased rainfall use efficiency despite differing sensitivity to soil moisture variation. In this relatively mesic grassland, carbon gain, growth, and overall productivity, are limited by efficiencies of rainfall conversion to soil moisture and subsequent plant utilization. This supports previous findings of lower productivity with increased rainfall variability in these grasslands.
Key words: precipitation variability, pulse event, pulse size, Konza Prairie Biological Station