Evidence that Invasion by Cheatgrass Alters Soil Nitrogen Availability

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 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 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.