Increases in tropospheric carbon dioxide (CO2) and ozone (O3) have profound effects on both organisms and ecosystem processes. However, our understanding of the effects of these atmospheric changes on many higher trophic level interactions, such as insect-vectored plant diseases, is limited. Plant diseases have an enormous economic impact on agricultural and natural ecosystems and can impact community dominance and evenness and ecosystem properties such as nutrient cycling. Understanding the effects of climate change on diseases will be an important part of predicting how ecosystems will respond into the future. Vectored plant viruses are particularly ecologically complex, because their spread may be determined by complex interactions between virus, vector, and plant. As a model, we used the barley yellow dwarf virus (BYDV), a grass-generalist luteovirus which is obligately transmitted by a variety of aphids and Avena fatua, a highly competent BYDV host plant. We used an open-topped chamber system and exposed Avena plants to factorial combinations of elevated CO2 (~680 ppm) and ozone (~70 ppbv above ambient) in the presence and absence of virus-carrying aphids. We examined the proportion of plants infected, viral concentration within the plants (a measure of virus performance) and plant performance, measured by vegetative and reproductive biomass.
Results/Conclusions:
Our data suggest that the atmospheric changes we examined have relatively weak effects on the probability of infection of Avena by BYDV, but they may change the potential for viral spillover from the excellent host Avena to less competent hosts through effects on virus performance. In this study, there were no significant differences in the proportion of plants infected in the different gas treatments. However, there was a trend towards higher infection rates in the plots receiving both gases. Furthermore, there was a significant interaction between CO2 and ozone in viral concentration, and both gases had significant predictive power alone. The combination of aphids and viral infection significantly suppressed reproduction but had no effect on aboveground vegetative biomass. Ozone had a strong suppressive effect on biomass and reproduction, while elevated CO2 was unable to completely compensate for the damaging effects of ozone. Often only a handful of plants in the ozone + virus treatment reproduced. This has important implications for both conservation and agriculture, as it suggests the virus may be able to dramatically reduce yields of cereal crops in places exposed to high ozone levels, and may limit recruitment of native grasses in ozone polluted areas.