Respiration characteristics differ among cheatgrass (Bromus tectorum L.) populations

Cheatgrass (Bromus tectorum L.) is a dominant weed that has increased the f requency of wildfire in the Great Basin since its introduction about 100 yr ago. This study examines characteristics of respiratory metabolism in seve ral different populations. Seeds from 6 populations were germinated and met abolic heat rates (q) and dark respiration rates (R-CO2) of all seedlings w ere measured calorimetrically at 15 degrees and 25 degrees C or (for 3 popu lations) at 5 degrees intervals from 5 degrees to 35 degrees C. Growth rate s, substrate carbon conversion efficiencies, and Arrhenius temperature coef ficients were calculated from the data. Results show that cheatgrass metabo lism is most efficient at temperatures near 0 degrees C; at temperatures ab ove 20-25 degrees C, efficiency goes to zero. Cheatgrass populations differ in their temperature dependencies of substrate carbon conversion efficienc y and predicted growth rate. Measurements of respiratory heat and CO2 rates as functions of temperature can be made relatively quickly and used to aid understanding of metabolic adaptation by invasive and native species to th e environment.