Drought and Competition Mediate Mycorrhizal Colonization, Growth Rate, and Nutrient Uptake in Three Artemisia Species

The genus Artemisia includes several keystone shrub species that dominate the North American sagebrush steppe. Their growth, survival, and establishment are negatively affected by exotic invasive grasses such as Taeniatherum caput-medusae. While the outcomes of symbiotic relationships between Artemisia spp. and arbuscular mycorrhizal fungi (AMF) are ambiguous, the benefits of ameliorated nutrient and drought stress may be cryptic and better revealed under competition. We evaluated the effects of a commercial AMF inoculum on ameliorating biotic (competition with T. caput-medusae) and abiotic (drought) stress of Artemisia tridentata ssp. wyomingensis, Artemisia arbuscula, and Artemisia nova when grown in sterile and microbially active field soil. Stress amelioration was measured as an increase in biomass production and nutrient acquisition. Mycorrhizal colonization of roots was lower in Artemisia plants grown in competition, while T. caput-medusae colonization was higher in plants with greater moisture. Both types of stress negatively affected plant biomass. Commercial AMF inoculation did not increase biomass. Colonization from field soil increased average phosphorous concentration under drought for A. tridentata ssp. wyomingensis by 36% and A. nova by 125%. While commercial inoculum and live soil led to AMF colonization of T. caput-medusae, only the commercial inoculum increased average phosphorus uptake by 71%.