Effects of CO2 enrichment on four Great Basin grasses

Plants of four Great Basin grass species were grown from seed in two greenhouses at low (340 mu l 1(-1)) and high (680 mu l 1(-1)) CO2 concentration. In all four species, high CO2 promoted mean increases in the number of basal stems, leaf area, specific leaf weight and above-ground dry weight. High CO2 resulted in an increase in CO2 assimilation in two C-3 grasses but not in a C-4 grass, while all three species showed decreases in stomatal conductance. Mean increases of 60% in above-ground dry weight and 80% in water-use-efficiency are consistent with previously reported high CO2 effects on grasses. No consistent differential effects of high CO2 were observed when comparing annual vs perennial species. Global CO2 enrichment may alter the competitive balance of Great Basin plant communities, possibly enhancing the dominance of Bromus tectorum L. on degraded rangelands.