The winter annual, Bromous tectorum (cheatgrass) has become widespread throughout semi-arid western North America. Invasion seriously alters biodiversity, species composition and nutrient cycles, disrupting ecosystem functions. Near monocultures of cheatgrass have occasionally been observed to experience emergence failure, termed a die-off, which presents a window of opportunity for restoring native species. Die-offs are controlled by natural processes that are not readily understood.
Two pathogens in particular are hypothesized to contribute to natural die-offs, Rutstroemia sp. and Fusarium sp. The Rutstroemia sp. infects established juvenile plants through the root-crown interface of already established seedlings or young plants. Rutstroemia sp. pathogen infected plants usually survive to bolting, but the pathogen causes the stunting, sterility, and premature maturation that characterize the bleach blonde syndrome. We hypothesize that bleach-blonde syndrome litter may contain high labile carbon and total nitrogen as a result of seed production failure in the host. This may result in a carbon pulse during the first autumn rains, providing key nutrition for the soil-borne Fusarium sp, and allow this fungus to kill large numbers of germinating cheatgrass seeds, resulting in a die-off event.
The objectives of this project are to determine whether bleach-blonde symptomatic plants contain more labile carbon than cheatgrass plants that have completed their life cycle through seed production, and whether there are any other clear differences between these two categories of standing cheatgrass litter.
This study will be conducted to (1) analyze and compare labile carbon concentration through a water extraction procedure and total organic carbon analysis of life stages for non-diseased and bleach-blonde symptomatic cheatgrass tissue, (2) assess C:N ratios of life stages for non-diseased and bleach-blonde symptomatic cheatgrass tissue through combustion methods, (3) compare structural carbon (cellulose, lignin, hemicellulose) differences in non-diseased and bleach-blonde symptomatic cheatgrass tissue by acid and neutral detergent fiber procedures, and (4) conduct field experiments to track labile carbon and total nitrogen changes throughout the growing season from bleach-blonde symptomatic tissue and normal non-diseased cheatgrass tissue and understand how it influences litter dynamics.
Preliminary data support the hypothesis that labile carbon concentrations are higher in bleach-blonde symptomatic plant tissue. Continued research will aim to understand how bleach-blonde symptomatic cheatgrass influences litter dynamics.