THE EFFECTS OF PARENTAL CO2 ENVIRONMENT ON SEED QUALITY AND SUBSEQUENT SEEDLING PERFORMANCE IN BROMUS-RUBENS

Seeds were collected and compared from parent plants of Bromus rubens L. (Poaceae), an exotic Mojave Desert annual grass, grown in ambient ( 360 mu mol mol(-1)) and elevated (700 mu mol mol(-1)) CO2 to determine if parental CO2 growth conditions affected seed quality. Performance of seeds developed on the above plants was evaluated to determine the influence of parental CO2 growth conditions on germination, growth rat e, and leaf production, Seeds of B. rubens developed oil parents grown in elevated CO2 had a larger pericarp surface area, higher C:N ratio, and less total mass than ambient-developed seeds, Parental CO2 enviro nment did not have an effect on germination percentage or mean germina tion timer as determined by radicle emergence. Seedlings from elevated -CO2-developed seeds had a reduced relative growth rate and achieved s maller final mass over the same growth period. Elevated-CO2-developed seeds had smaller seed reset-yes than ambient seeds, as determined by growing seedlings in sterile media and monitoring senescence. It appea rs that increased seed C:N ratios associated with plants grown under e levated CO2 may have a major effect on seed quality (morphology, nutri tion) and seedling performance (e.g., growth rate and leaf production) . Since the invasive success of B. rubens is primarily due to its abil ity to rapidly germinate, increase leaf area and maintain a relatively high growth rate compared to native annuals and perennial grasses, re ductions in seed duality and seedling performance in elevated CO2 may have significant impacts on future community composition in the Mojave Desert.