|Ziska, Lewis - USDA-ARS|
|Reeves, James - USDA-ARS|
|White, Robert - USDA-FS|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 15, 2005
Publication Date: February 15, 2006
Citation: Blank, R.R., Ziska, L.H., Reeves, J., White, R.H. 2006. Bromus tectorum: interactive effects of atmospheric CO2 and elevation ecotype on plant growth, tissue biochemistry, and tissue combustibility [abstract]. Range Management, Feb. 2006, Vancouver, B.C., Canada. Technical Abstract: Bromus tectorum (cheatgrass) invasion of rangelands in the western United States is an immense ecological and economic concern. We investigated the interactive effects of atmospheric CO2 concentration (270, 320, 370, 420 'mol mol-1) and elevation ecotype (low, mid, high) on its growth, tissue biochemistry, and tissue combustibility. From 25 until 87 days after sowing, aboveground biomass for these ecotypes increased 1.5-2.7 g per plant for every 10 'mol mol-1 increase above the 270 'mol mol-1 pre-industrial baseline. Carbon dioxide sensitivity among ecotypes was proportional to elevational gradient, with the lowest elevation showing the strongest response, notably an increase in leaf area. Among all ecotypes, the ratio of digestible (hemi-cellulose) to undigestible (lignin) in vegetation declined with increasing [CO2]. In addition, the ratio of C:N increased with age, with [CO2], and was highest for the lower elevational ecotype. Tissue combustion measurements using the cone calorimeter indicate that plants exposed to 270 ppm CO2 had significantly less average heat released than plants exposed to higher CO2 concentrations. Significant negative correlation of heat released to tissue lignin, xylan, and other mineral concentrations suggest that combustion of plants grown in pre-industrial CO2 produced more char. Overall, these data suggest that rising CO2 could contribute significantly to the impact of B. tectorum on fire ecology by: (a) reducing the time for a minimum fuel load to be reached, (b) increasing the amount of fuel (biomass) present at maturity, (c) more efficient combustion, (d) decreasing rates of herbivory, and (e) decreasing decomposition rates.