Document: LAR-3-30-12

Interannual variation in ecosystem carbon exchange in a northern grassland.

FLANAGAN, L.B.*, P.J.CARLSON and L.A.WEVER

University of Lethbridge, Lethbridge, Alberta, CANADA ¹

Abstract:
We used the eddy covariance technique to measure exchanges of carbon dioxide in an Agropyron smithii dominated grassland near Lethbridge. Our objectives were to analyze the effects of interannual climate variation on ecosystem metabolism, and to quantify net carbon sequestration on a seasonal and annual basis. In contrast to 1998 when precipitation during May and June was about 67% higher than normal, 1999 was a very dry year with about 40% lower than normal precipitation during May and June. As a consequence, above ground plant biomass and leaf area index in 1999 were 114 g/m² and 0.549, approximately one-half the values measured in 1998. The water deficit and reduced plant growth severely decreased gross photosynthesis and net ecosystem carbon uptake. Integration of the daily carbon gain from the start of our eddy covariance measurements on June 20/98 to the end of the main growing season August 31/98, indicated a net carbon uptake of 146.9 g C/m². During the fall and winter months (Sept 1/98 - March 31/99) the system lost 39.8 g C/m² to the atmosphere. The dry growing season of 1999 (April 1 - Aug 31) resulted in a total carbon uptake of only 43.3 g C/m². When moisture availability is high, this grassland ecosystem can sequester carbon at rates comparable to Aspen parkland forests in Canada. However, primary production and net carbon uptake is strongly constrained by moisture availability.

Keywords: eddy covariance, climate, carbon sequestration

This abstract is being presented at: 10:30 AM in session:
GAS EXCHANGE