Elevated carbon dioxide alters impacts of precipitation pulses on ecosystem photosynthesis and respiration in a semi-arid grassland.

Predicting net C balance under future global change scenarios requires a comprehensive understanding of how ecosystem photosynthesis (gross primary production; GPP) and respiration (Re) respond to elevated atmospheric [CO(2)] and altered water availability. We measured net ecosystem exchange of CO(2) (NEE), GPP and Re under ambient and elevated [CO(2)] in a northern mixed-grass prairie (Wyoming, USA) during dry intervals and in response to simulated precipitation pulse events. Elevated [CO(2)] resulted in higher rates of both GPP and Re across the 2006 growing season, and the balance of these two fluxes (NEE) accounted for cumulative growing season C uptake (-14.