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

Abstract

properly cited. Bromus tectorum L. (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 of B. tectorum. Using rhizotrons, the experiment was conducted over 5 growth cycles: (1) B. tectorum planted between perennial grasses; (2) perennials clipped and B. tectorum planted; (3) perennials clipped and B. tectorum planted into soil mixed with activated carbon; (4) perennials clipped, B. tectorum planted, and top-dressed with fertilizer, and; (5) perennial grasses killed and B. tectorum planted. 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. tectorum without competition), established perennial grasses significantly hindered the growth of B. tectorum. Overall, biomass of B. tectorum, grown between established perennials, increased considerably after fertilizer addition and dramatically upon death of the perennials. Potential mechanisms involved in the suppression of B. tectorum include 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 against B. tectorum.

Resilience to Stress and Disturbance, and Resistance to Bromus tectorum L. Invasion in Cold Desert Shrublands of Western North America

“…Seedlings of native perennial species are generally poor competitors with cheatgrass, but adults of native, perennial herbaceous species, especially those with similar growth forms and phenology, can be highly effective competitors (Booth and others 2003;Chambers and others 2007;Blank and Morgan 2012). Disturbances or management treatments that reduce the abundance of perennial herbaceous species, shrubs, or trees can increase resource availability and expand the realized niche of cheatgrass given climate suitability and a propagule supply.…”

“…Both perennial and invasive annual C 3 grasses exhibit higher growth rates with increased N availability at both seedling (James and others 2011) and adult life stages (Schwinning and others 2005). Higher growth rates, coupled with early germination and establishment, give invasive annual grasses a competitive advantage over native grass seedlings in both low and high nitrogen environments (James and others 2011), but may have little effect on competition with mature native herbaceous species especially grasses (Blank and Morgan 2012). Thus, low levels of N deposition may increase the ability of native grasses to compete with annual bromes in ecosystems with relatively high resilience and resistance, but will likely give annuals a competitive advantage in systems with depleted herbaceous species or low resistance.…”

Root Growth of Two Perennial Grass Types and Musk Thistle (Carduus nutans) in Temperate Grasslands of North America

“…In these regions, native perennial grass resistance to nonindigenous plant species invasion depends on resource acquisition timing aboveground (e.g., light, moisture) and belowground (e.g., soil moisture, nutrient, biological soil space) (Blank and Morgan 2012;Daehler 2003;DiTomaso et al 2003;Young et al 2011). Root distribution patterns of native perennial grasses and invasive plants are often influenced by the dominant habitat type and variations in carbon and nutrient cycles (Aerts et al 1989;Jackson 1997).…”

“…The overlap in resource acquisition occurs when the native and invasive plants compete for the same spatially or temporally available resources at specific phenological growth stages (Suding et al 2003;Zavaleta and Hulvey 2007). An established, healthy, and diverse native perennial grass stand has an extensive root system that allows for the efficient uptake of resources with few open niches (Blank and Morgan 2012).…”

“…DiTomaso et al (2003) reported that a decrease in the availability of light aboveground corresponds to a reduction in root productivity for yellow starthistle (Centaurea solstitialis L.), an invasive plant species in California. Blank and Morgan (2012) indicated that early season root growth of CS grasses reduced biological soil space for competitors and increased resistance to invasion by Bromus tectorum L.…”