Viral Pathogen Production and Virus-plant Interactions are Controlled by Nitrogen and Phosphorus Supply

Background/Question/Methods Inter- and intra-specific competition for nutrient resources governs life-history traits in organisms of all shapes and sizes. This includes the reproduction of viral pathogens and the growth of their respective hosts. Though traditionally understudied due to their inherently small size, nutrient limitation is as theoretically justifiable for viruses as it is for any other organismal group. The outcome of virus-interactions with the host is also likely to be dictated by nutrient availability, albeit via a more complex process. While high nutrient availability should induce direct benefits to host growth, it may also stimulate viral production, thereby indirectly reducing host fitness. Host biomass itself may feedback to alter viral titer. In order to test these relationships, we manipulated soil nitrogen and phosphorus availability under greenhouse conditions for a model virus-host system consisting of the annual grass species Bromus hordeaceus and viral pathogen Barley Yellow Dwarf Virus-PAV. Five levels of soil nitrogen and phosphorus were factorially crossed in order to achieve a broad range of representative nutrient conditions and address whether external nutrient availability altered viral production and virus-host interactions. Results/Conclusions Both nitrogen and phosphorus played a role in altering virus-host interactions. The influence of soil nitrogen addition depended on final host biomass. Specifically, at low soil nitrogen concentrations, larger plants supported greater relative titer than smaller ones, whereas at high nitrogen, comparatively smaller plants supported greater relative titer (F1,64=12.6, p\u3c0.01). Also, viral titer was greatest in hosts with high leaf nitrogen concentrations and greater final biomass (F1,64=7.21, p\u3c0.01). Similarly, viral titer was greatest in hosts with greater final biomass and high leaf phosphorus concentrations (F1,64=7.44, p\u3c0.01). However, we did not detect an effect of soil phosphorus addition on viral titer (F1,64=0.134, p=0.72). Interestingly, infected individuals that supported greater viral titer grew to larger final mass under high soil nitrogen and phosphorus addition than their low-titer counterparts grown under limiting nutrient conditions (F1,64=11.2, p\u3c0.01). Our results suggest that virus-host-nutrient interactions are multifaceted and that viral population growth may be particularly augmented under conditions of high nitrogen in the host or surrounding environment