PARENT SESSION
Wednesday, August 9, 8:00-11:30 am
COS 46 - Climate and global change I: carbon cycling
Chickasaw, Mezzanine Level, Cook Convention Center
Presiders: A Dikou and K Treseder

Net ecosystem exchange of carbon dioxide and water vapor in an annual grassland exposed to multiple global change factors.

Lunch, Claire^{*,1, 2}, Field, Christopher², ¹ Stanford University, Stanford, CA² Carnegie Institution of Washington, Stanford, CA

ABSTRACT- Global environmental change has the potential to alter both the timing and magnitude of growth and activity in plant species worldwide. The Jasper Ridge Global Change Experiment (JRGCE) explores the effects of elevated carbon dioxide (CO₂), warming, increased precipitation, and nitrogen deposition on a California annual grassland. These four factors have been manipulated at two levels, in a full factorial design replicated eight times, starting in the fall of 1998. In the 2005-06 growing season, net ecosystem exchange of carbon dioxide and water vapor was measured in six replicates of all treatments throughout the season. Open-top dynamic chambers were used to minimize pressurization and heating by the chamber, and to allow long-term chamber installation. Chambers were placed to monitor a single set of replicates at a time, and were moved between replicate blocks once every five days. At the beginning of the growing season, shortly after the first rainfall, fluxes of CO₂ were low and respiratory, averaging 1.3 mol m^-2 s^-1. The ecosystem became a daily net sink for CO₂ in early February, on average, approximately two months after the start of the season. This transition occurred slightly later in the elevated CO₂ treatment than under ambient conditions, as did subsequent increases in daily uptake rates. Variability in flux rates was considerably higher in the elevated CO₂ treatment, most likely due to the difficulty of measuring fluxes at elevated concentrations. Both uptake and respiration rates were higher in the N-fertilized treatment, while the warming and precipitation treatments had small effects.

Key words: global change biology, net ecosystem exchange, grassland