摘要：Rising atmospheric CO2 has resulted in declining tissue nutrient concentrations and leaf biochemicals, which has potential ramifications for animal nutrition, herbivory and litter decomposition rates. We investigated the interacting effects of atmospheric CO2 concentrations (270, 320, 370, and 420 ppmv), plant age (42, 57, 75, and 87 days), and elevation ecotype (salt desert, sagebrush steppe, and mountain brush) on aboveground tissue nutrient levels and biochemistry of cheatgrass (Bromus tectorum), an important range grass in the Great Basin. Most nutrients were affected by significant (P < 0.05) interactions between CO2 level and plant age, and plant ecotype and plant age. At 87 days growth, tissue C:N ratios increased significantly and concentrations of P, K, and Mg declined, with rising CO2 levels suggesting declining forage nutrition. Tissue concentrations of Mn, K, Mg, and Ca increased with plant age and, in general, the low elevation ecotype had greater tissue nutrient concentrations than the high elevation ecotype. Hemicellulose concentration was influenced by a significant CO2 level by ecotype interaction; overall, the high elevation ecotype had greater concentrations of hemicellulose, which increased with increasing CO2 levels. The high elevation ecotype had significantly less acid detergent fiber than the low or mid elevation ecotypes. These data suggest that increasing atmospheric CO2 levels may have a profound effect on the nutritional value of cheatgrass forage, and this effect may differ among elevational ecotypes.
