Abstract Detail



Ecology

Cowan, Jacob [1], Gehring, Catherine [2].

Invasive and native grasses exert negative plant-soil feedback effects on Artemisia tridentata whereas conspecific effects are neutral.

The displacement of high diversity big sagebrush (Artemisia tridentata) dominated communities by cheatgrass (Bromus tectorum) invasion, an annual grass which supports much less diverse communities, is widely recognized to represent a major threat to regional biodiversity in the shrub-steppe communities of the western US. Once established, cheatgrass maintains dominance by altering fire regimes and because of its early germination, which makes it a very effective competitor for soil water and nutrients. Additionally, there is increasing recognition that cheatgrass may be altering soils in a way that suppresses sagebrush germination and regrowth. To assess the role that cheatgrass-induced plant-soil feedbacks may be playing in the maintenance of dominance by this invasive, we grew sagebrush seedlings without direct competition in soils conditioned with either cheatgrass, Elymus elymoides (a common native perennial bunchgrass) or conspecifics. Seedling growth was compared with controls to determine the direction and magnitude of feedbacks being exerted by the different conditioning plants. We found that cheatgrass and Elymus exerted negative feedback on sagebrush, and the effect of the invasive was not significantly different than that of the native. Surprisingly, negative feedbacks did not increase with increasing biomass of the conditioning plant (no density-dependent effect). Despite averaging 6 times larger than Elymus, cheatgrass had no greater suppressive effect on sagebrush growth. Conspecific feedbacks were neutral to slightly positive, which is typical of a climax species. To explore some potential mechanisms driving these feedback patterns, we looked at nutrient depletion and reduction in colonization by arbuscular mycorrhizal fungi (AMF), important symbionts of sagebrush. Neither of these seems to be playing a role in sagebrush suppression. Additionally, we are in the process of using next-generation amplicon sequencing to characterize root microbial communities, so they may be compared between conditioning treatments. These data will likely be included in the presentation. Alteration of root microbial communities away from compositions beneficial to natives has been implicated in other invasions and could be driving the observed feedback patterns. We discuss aspects of cheatgrass biology that allow it to more extensively alter soils that do native bunchgrasses. Finally, we consider implications for restoration.   


1 - Northern Arizona University, School of Forestry, 2179 W Adirondack Ave, Flagstaff, AZ, 86001-2403, United States
2 - Northern Arizona University, Department Of Biological Sciences, 617 S Beaver Street, Flagstaff, AZ, 86011, United States

Keywords:
Plant-Soil Feedbacks
cheatgrass
sagebrush
invasion biology
indirect effects.

Presentation Type: Oral Paper
Number: 0004
Abstract ID:435
Candidate for Awards:None


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