Cheatgrass Invasion - The Below-Ground Connection

Abstract

Plant-soil microbial feedback loops play an important role in the establishment and development of plant communities. Microbial soil communities, including pathogens, plant-growth-promoting rhizobacteria and their reciprocal interactions, can influence plant health and nutrient cycling in many ways. We are proposing a model that accounts for cheatgrass (Bromus tectorum) invasion success and long-term persistence in both disturbed and undisturbed sites. In this model cheatgrass alters soil microbial communities that favor nitrifying microorganisms, resulting in elevated NO₃^- levels. Increased NO₃^- levels, coupled with B. tectorum life history and climatic and edaphic conditions in the semi-arid western U.S., result in long-term persistence of this invasive annual. In ecosystems that lack major precipitation during the growth season, B. tectorum induced shifts in the nitrifier community result in accumulation of plant available nitrogen during the summer when native perennials are primarily dormant. Increased NO₃^- levels can be efficiently utilized by cheatgrass ahead of native perennials during fall and winter. Restoration and management efforts must be guided by a thorough understanding of soil microbe-cheatgrass interactions to avoid nutrient flushes resulting from freeze-thaw and wet-dry cycles that benefit this invasive grass.