Impacts of the Interaction between Viral Pathogens and Mutualistic Fungi on Plant Performance Under Elevated CO2

To fully understand how increases in atmospheric CO2 concentrations will impact future ecosystem productivity and carbon storage requires that we understand how the strength and nature of multiple, co-occurring species interactions are altered. Specifically, since both microbial mutualists and plant pathogens can modulate plant-carbon cycles, the growth, fecundity and population dynamics of these two groups of widespread microbes may modify plant performance in response to elevated CO2. Using arbuscular mycorrhizal fungi (AMF) and barley yellow dwarf virus PAV (BYDV) we investigated microbial impacts on plant performance due under changes in atmospheric CO2 and phosphorous addition. We grew the invasive species Avena fatua (wild oats) and Bromus hordeaceus (soft brome) in individual pots in replicated continuous flow chambers. We factorially manipulated atmospheric CO2 (585 PPM), soil phosphorous, AMF association, and BYDV infection. To assess plant performance, we measured survivorship, above and belowground biomass, tiller number, BYDV infection, aphid reproduction, AMF colonization, seed production, and photosynthetic capacity. BYDV inoculation reduced B. hordeaceus photosynthetic capacity by 30% compared to mock inoculated plants. Additionally, rates of transpiration for B. hordeaceus were 34% lower when plants were both infected with BYDV and phosphorous addition while A. fatua rates of transpiration were lower when plants were infected with BYDV. Thus, effects of BYDV infection depended on phosphorus supply, but did not interact together, or with atmospheric CO2 concentration.