274-7 Impact of Precipitation Dynamics On Net Ecosystem CO2 Exchange.



Tuesday, October 18, 2011: 3:00 PM
Henry Gonzalez Convention Center, Ballroom C-2, Ballroom Level

Stephen Del Grosso1, William Parton2, Jack Morgan3, David Smith3, Lara Prihodko2, Dan LeCain3 and Robin Kelly2, (1)Soil Plant Nutrient Research, USDA ARS, Fort Collins, CO
(2)Colorado State University, Fort Collins, CO
(3)USDA-ARS, Fort Collins, CO
Anthropogenic climate change is expected to alter both the frequency and size of rainfall events. Our results suggest that this will likely affect the net carbon balance of semi-arid grasslands. Net ecosystem carbon dioxide (CO2) exchange (NEE) was measured on shortgrass steppe (SGS) vegetation in northeastern Colorado. As expected, nighttime NEE was positive (CO2 source) throughout the year and daytime NEE was positive during the non-growing season. But during the growing season, daytime NEE could be positive or negative (CO2 sink), depending on the size of precipitation events in this water limited system.  Large precipitation events (> 10 mm day-1) promoted carbon uptake because increased soil water content in sub-surface layers promoted plant photosynthesis, while small precipitation events (5 - 10 mm day-1) that only wet the surface soil enhanced heterotrophic respiration and resulted in a loss of carbon from the system. Although the growing season extends from April - October, more than 95% of the net carbon uptake occurred during the April - June time period. Live aboveground plant biomass, solar radiation, and soil water content were the major variables that controlled daytime net CO2 uptake and nighttime respiration losses.
See more from this Division: S07 Forest, Range & Wildland Soils
See more from this Session: Carbon and Nutrient Cycling