Anabolic Rates Measured by Calorespirometry for Eleven Subpopulation of Bromus tectorum Match Temperature Profiles of Local Microclimates1

Bromus tectorum L. (cheatgrass) is a dominant weed that has increased the frequency of wildfire in western North America since being introduced about 120 years ago from Central Asia. Cheatgrass germinates in the fall, overwinters as young seedlings, grows rapidly in early spring, and completes the life cycle by early June. The dead grass then serves as fuel for wildfires. Cheatgrass seeds survive fire well while competing native perennials do not. Cheatgrass subpopulations have adapted to the thermal environments of different habitats in little more than a century. Calorespirometry was employed to study the effects of temperature (from 5 to 45°C) on growth rate, defined as net anabolic rate. Growth rate versus temperature curves tend to be bimodal for eleven subpopulations of cheatgrass. There are different growth rate responses to temperature among subpopulations, which appear to match the temperature profile of the native environment during the growth season and maximize growth. Both respiratory rates and efficiencies differ according to microclimate.