IMPACTS OF GLOBAL CHANGES AND BIOLOGICAL CONTROL OF INVASIVE WEEDS ON WESTERN RANGELANDS
Location: Grassland, Soil and Water Research Laboratory
Title: Climatic regulation of seasonal and inter-annual variability in net ecosystem exchange of CO2 on rangelands
Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: November 13, 2008
Publication Date: February 8, 2009
Citation: Polley, H.W., Emmerich, W.E., Bradford, J.A., Johnson, D.A., Svejcar, A.J., Angell, R.F., Phillips, B.L., Snyder, K.A., Morgan, J.A. 2009. Climatic regulation of seasonal and inter-annual variability in net ecosystem exchange of CO2 on rangelands. In: Proceedings of the Society for Range Management, February 8-12, 2009, Albuquerque, New Mexico. 2009 CDROM.
Net ecosystem exchange of CO2 (NEE) from terrestrial ecosystems varies seasonally and inter-annually because of temporal variation in climate. If we are predict climate-caused variation in NEE, we must understand how climatic variation influences NEE and its components, CO2 uptake and CO2 loss. We partitioned variation in weekly values of growing season measurements of NEE, daytime ecosystem CO2 exchange (Pd), and nighttime respiration (Re) from 8 rangeland sites in the western U.S. into two components - variation between means of CO2 fluxes for each week and the grand mean of fluxes across all weeks (seasonal variation) and variation between weekly values of fluxes and the average of flux measurements for each particular week (inter-annual variation). We used regression analysis to determine contributions of variation in Pd and Re to seasonal and inter-annual variation in NEE and to identify climatic correlates of variability in fluxes. Seasonal and inter-annual variability in NEE and Pd were highly correlated at all sites, indicating that within-year and among-year variation in NEE resulted mainly from shifts in net photosynthesis of rangeland vegetation rather than from shifts in ecosystem respiration. Seasonal trends in NEE followed the seasonal pattern of net radiation on rangelands with greatest precipitation and the seasonal pattern of precipitation on drier rangelands. By contrast, inter-annual variability in NEE was not well-explained by climatic variation. Averages of NEE for each rangeland were well described by variation in a single climatic variable, but inter-annual differences in rangeland carbon balance were not predictable from climatic variability alone.