Suppression ofBromus tectorumL. by Established Perennial Grasses: Potential Mechanisms—Part One

Bromus tectorumL. (cheatgrass) is an Eurasian annual grass that has invaded ecosystems throughout the Intermountain west of the United States. Our purpose was to examine mechanisms by which established perennial grasses suppress the growth ofB. tectorum. Using rhizotrons, the experiment was conducted over 5 growth cycles: (1)B. tectorumplanted between perennial grasses; (2) perennials clipped andB. tectorumplanted; (3) perennials clipped andB. tectorumplanted into soil mixed with activated carbon; (4) perennials clipped,B. tectorumplanted, and top-dressed with fertilizer, and; (5) perennial grasses killed andB. tectorumplanted. Water was not limiting in this study. Response variables measured at the end of each growth cycle included above-ground mass and tissue nutrient concentrations. Relative to controls (B. tectorumwithout competition), established perennial grasses significantly hindered the growth ofB. tectorum. Overall, biomass ofB. tectorum, grown between established perennials, increased considerably after fertilizer addition and dramatically upon death of the perennials. Potential mechanisms involved in the suppression ofB. tectoruminclude reduced nitrogen (possibly phosphorus) availability and coopting of biological soil space by perennial roots. Our data cannot confirm or reject allelopathic suppression. Understanding the mechanisms involved with suppression may lead to novel control strategies againstB. tectorum.