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Accueil du site → Doctorat → États-Unis → 2011 → Cheatgrass (Bromus tectorum L.) interactions with arbuscular mycorrhizal fungi in the North American steppe : prevalence and diversity of associations, and divergence from native vegetation

Colorado State University (2011)

Cheatgrass (Bromus tectorum L.) interactions with arbuscular mycorrhizal fungi in the North American steppe : prevalence and diversity of associations, and divergence from native vegetation

Busby, Ryan Ray

Titre : Cheatgrass (Bromus tectorum L.) interactions with arbuscular mycorrhizal fungi in the North American steppe : prevalence and diversity of associations, and divergence from native vegetation

Auteur : Busby, Ryan Ray

Université de soutenance : Colorado State University

Grade : Doctor of Philosophy (Ph.D.) 2011

Résumé partiel
Cheatgrass (Bromus tectorum L.) is a highly invasive winter annual grass that has caused significant changes to the steppe ecosystem of western North America. Cheatgrass is considered a facultative host of arbuscular mycorrhizal fungi (AMF), and has been shown to reduce AMF density in invaded soils and reduce AMF diversity in roots of neighboring grasses. However, specific information about interactions between cheatgrass and AMF remains unknown, as well as how these interactions differ from native vegetation. The research presented here addresses these knowledge gaps. To determine when cheatgrass is colonized by AMF and the magnitude of colonization, two dense cheatgrass patches were identified in invaded shortgrass prairie in Colorado. Individuals were excavated every three weeks, from six weeks after germination through senescence. Roots were collected from individuals, cleared, stained, and observed for AMF colonization. Roots were colonized by AMF at every sampling date, but percent colonization of roots declined dramatically when soil temperatures dropped below 0° C, and colonization remained low from late January through March. Peak colonization occurred in May (15.3%), when florets appeared on the cheatgrass shoots, and colonization dropped in June, once seeds were produced and senescence began. Although mycotrophic, cheatgrass is a poor host for AMF throughout its life, as evidenced by low AMF root colonization. Severe, lasting invasions by cheatgrass could have a negative impact on the AMF community. Cheatgrass invasion is most severe in the sagebrush steppe of western North America, which is dominated by the native shrub big sagebrush (Artemisia tridentata Nutt.). As cheatgrass replaces big sagebrush, it is important to know how this shift affects the AMF community. Two studies were conducted to identify and compare AMF species associating with these two host plant species. Three sites (in Colorado, Utah and Wyoming) were selected where coexisting cheatgrass and big sagebrush populations were interspersed. Soil and root samples from underneath sixteen individuals of each species were collected at each of the sites.

Mots Clés : arbuscular mycorrhizal fungi ; big sagebrush ; cheatgrass ; ecological restoration ; plant-microbe interactions ; plant-soil feedbacks

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