生態系と生態学のジャーナル

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Seasonal Variation in Arbuscular Mycorrhizal Fungi Root Colonization of Cheatgrass (Bromus tectorum), an Invasive Winter Annual

Ryan R. Busby,Mark W. Paschke, Mary E. Stromberger and Dick L. Gebhart

Cheatgrass is a highly invasive winter annual grass that is most aggressive in the semi-arid steppe region of western North America. In this region, cheatgrass invasion becomes so severe that virtual monocultures can result. Due to its strategy for growth from autumn to spring, cheatgrass remains active during winter months when most native vegetation is dormant. This shift in host activity could be important for beneficial soil microbes, particularly the arbuscular mycorrhizal fungi (AMF), as they are adapted for coincidental growth with host plants. Many native plant species that are utilized for restoring areas invaded by cheatgrass associate with AMF, so any reduction in these symbiotic fungi could reduce the successful establishment of desirable plant species. Although cheatgrass is recognized as a facultative associate of AMF, its associations with AMF across seasons and throughout its lifespan are not known. We measured AMF colonization of cheatgrass roots from soon after germination through senescence. We found that cheatgrass remains colonized throughout its life. Colonization drops dramatically once soil temperatures approach freezing, but was highest late in the growth cycle of cheatgrass during flowering and seed set. Colonization by AMF never attained levels comparable to highly mycorrhizal plant species. This indicates that cheatgrass is a poor host for AMF throughout its life, and long-term dominance by cheatgrass could alter AMF in soils. Restoring highly invaded sites quickly following invasion might reduce the negative effects of cheatgrass on this important soil microbial community.