Content area
Full text
ABSTRACT
We hypothesized that cheatgrass (Bromus tectorum), an exotic invasive annual, may alter soil nitrogen availability. In the Honey Lake Valley of northeastern, California, we have monitored soil and vegetation along a chronosequence of cheatgrass invasion. In 2007, we measured total C, total N, and ∂^sup 15^N in tissue of cheatgrass, winterfat (Krascheninnikovia lanata), freckled milkvetch (Astragalus lentiginosus), and Indian ricegrass (Achnatherum hymenoides) in areas invaded for 1, 4, and >10 years. As time since invasion increased, tissue N increased and C/N decreased significantly for cheatgrass and winterfat. Time since invasion significantly affected ∂^sup 15^n, which declined significantly for winterfat and increased significantly for Indian ricegrass and freckled milkvetch. These data suggest that cheatgrass invasion has altered soil nitrogen availability and that other plants respond to this altered availability.
In Monaco, T.A. et al. comps. 2011. Proceedings - Threats to Shrubland Ecosystem Integrity; 2010 May 18-20; Logan, UT. Natural Resources and Environmental Issues, Volume XVII. S.J. and Jessie E. Quinney Natural Resources Research Library, Logan Utah, USA.
INTRODUCTION
Plants that can engineer the soil or create positive plant-soil feedbacks to enhance nutrient availability can elevate their competitive stature (Ehrenfeld 2003; Kulmatiski and others 2008). Such tipping of competitive stature may be responsible for turning an exotic species into an invasive one (Crooks 2002). The invasive success of Bromus tectorum (cheatgrass) is predicated on myriad factors, but soil nutrient availability, particularly of nitrogen (N), is an important determinant (Adair and others 2007; Vasquez and others 2008). The literature is conflicting regarding the effects of cheatgrass invasion on soil N resources. Rimer and Evans (2006) reported that after 2 years invasion by cheatgrass in Canyonlands National Park, Utah, the labile N pool decreased 50 percent. Over a 2-year period, few consistent differences in N mineralization, extractable soil N, or total soil C or N were found between native and cheatgrass invaded sites in Oregon (Svejcar and Sheley 2001). On the other hand, in northern Utah, soil beneath cheatgrass was shown to increase N availability relative to native species (Booth and others 2003).
We...