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United States Department of Agriculture

Agricultural Research Service

Title: Long-Term Dynamics of Production, Respiration, and Light-Use Efficiency in Two Sagebrush Steppe Ecosystems of the U.S. Intermountain West in Relation to Ndvi:scaling Up Co2 Fluxes

item Gilmanov, Tagir - S. DAKOTA UNIV.
item Svejcar, Anthony
item Johnson, Douglas
item Angell, Raymond
item Saliendra, Nicanor
item Wylie, Bruce - USGS

Submitted to: Agricultural and Forest Meteorology Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: April 26, 2004
Publication Date: June 16, 2004
Citation: Gilmanov, T., Svejcar, A.J., Johnson, D.A., Angell, R.F., Saliendra, N.Z., Wylie, B. 2006. Long-term dynamics of production, respiration, and light-use efficiency in two sagebrush steppe ecosystems of the u.s. intermountain west in relation to ndvi:scaling up CO2 fluxes [abstract]. Agricultural and Forest Meteorology Conference Proceedings. Paper No. 2.11.

Technical Abstract: We continuously measured the net ecosystem CO2 exchange (Fc) of two sagebrush steppe ecosystems in the USDA-ARS AgriFlux network (Burns, OR, 1995-2001 and Dubois, ID, 1996-2001) using the Bowen ratio-energy balance technique. For all sites and years, photosynthetically active radiation (Q) was the most important driver of the CO2 flux during daytime, followed by soil temperature (Ts), as described by ecosystem-scale light-response functions Fc(Q, al, ..., am) and Fc(Q,Ts,al,....,an), where {ai} are empirical parameters. Using nonlinear identification of the light-response functions parameters, we partitioned Fc into two components, gross primary productivity (Pg) and total ecosystem respiration (Re), thus Fc=Pg-Re (physiological sign convention). For years when winter-time measurements were not available, winter-time fluxes were gap-filled using relationships established from data collected during 1999/2000 and 2000/2001 winter periods. Seven year average annual gross primary production (GPP) at the Burns site was 1111 (range 475-1716) g CO2/m2/yr, average ecosystem respiration (RE) was 1029 (range 581-1544) g CO2/m2/yr, and average net ecosystem CO2 exchange (NEE) was 82 (range -424 to +621) g CO2/m2/yr. At the more productive Dubois site, six year average GP was 1602 (range 963-2162) g CO2/m2/yr, RE was 1349 (range 786-1778), and NEE was 273 (range -118 to +867) g CO2/m2/yr.

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