HR: 10:50h
AN: B21H-03    [PDF]
TI: Interannual Variation in the Relationship Between Aboveground Net Primary Productivity and Net Ecosystem Productivity in a Northern Temperate Grassland
AU: * Flanagan, L B
EM: larry.flanagan@uleth.ca
AF: University of Lethbridge, Department of Biological Sciences, 4401 University Drive, Lethbridge, AB T1K 3M4 Canada
AB: Measurements of aboveground net primary productivity (ANPP) and net ecosystem carbon dioxide exchange (NEE) have been made in a native Canadian grassland during 6 years (1998-2003) of contrasting weather. The eddy covariance technique was used to measure NEE and these measurements were integrated to calculate net ecosystem productivity (NEP). Variation in summer precipitation input was the major environmental factor influencing ANPP and NEP in this ecosystem. Annual ANPP ranged from 40 to 100 g C/m$^{2}$ with a strong positive correlation to the amount of summer (April-August) precipitation (107-412 mm range). However, ANPP varied asymmetrically in response to changes in precipitation, with increases in ANPP during a wet year being much more pronounced than reductions in a drought year. Strong increases in plant water-use efficiency contributed to the resilience of ANPP during times of drought. Annual NEP ranged from a net loss of 18 g C/m$^{2}$ to a net gain of 288 g C/m$^{2}$. The NEP in a year with normal precipitation was 21 g C/m$^{2}$, while years with below normal precipitation had either a net gain of 19 g C/m$^{2}$ or a net loss of 18 g C/m$^{2}$. Differences in soil respiration were responsible for whether the ecosystem was a carbon sink or source in years of low precipitation. Late summer rain, received after most of the plant canopy had gone dormant, can stimulate soil respiration more than photosynthesis, with a resulting net loss of carbon from the ecosystem. Soil moisture was also observed to have strong control on the temperature sensitivity of ecosystem respiration. ANPP and NEP were closely linked when moisture was abundant. However, in years with normal or lower precipitation, variation in soil respiration strongly influenced NEP and disrupted the correlation with ANPP.
DE: 0400 Biogeosciences
DE: 3300 METEOROLOGY AND ATMOSPHERIC DYNAMICS
DE: 3307 Boundary layer processes
DE: 3322 Land/atmosphere interactions
SC: Biogeosciences [B]
MN: 2003 Fall Meeting