Trophic cascades in a changing climate: elevated CO 2 and trophic interactions.

1. Trophic cascades in a changing climate: elevated CO2 and trophic interactions. William T. Hentley1,2,3, Email - wihen@ceh.ac.uk Tel - 0131 445 8431 T. Hefin Jones2, Rosie S. Hails1, Scott N. Johnson3,4, Adam J. Vanbergen1 Introduction By 2050 atmospheric CO2may increase from the current 390ppm to 650ppm, increasing plant biomass and water use efficiency, possibly reducing the nutritional value of plant tissue for herbivores. It is largely unknown if reduced nutritional quality of plant tissue in elevated CO2 will cascade through the trophic levels. This study attempts to fill this gap in our understanding of multi-trophic interactions at elevated CO2 (eCO2). Results 3) Aphid protein content 1) Plant dry mass 2) Initial aphid abundance a a c b a a b a b b a b a a d c Hypothesis Plants will directly respond to eCO2by increased growth rate and biomass. Aphids can compensate for reduced plant quality by increasing throughput of phloem. Aphid abundance will, therefore, show little response to eCO2. eCO2 will reduce total protein content in aphids via altered plant nutritional quality . Predators feeding on prey with lower total protein content will develop slower and emerge as smaller adults. No CO2 effect, but aphids had higher total protein on susceptible cultivar Dry mass in eCO2 was significantly greater compared to aCO2 Significantly more aphids on the resistant cultivar in eCO2 compared to aCO2 4) Ladybird pupal mass Methods Three raspberry (Rubusideaeus) cultivars with varying resistance to the aphid (Amphorophoraidaei) were exposed to ambient CO2 (aCO2) (390ppm) or eCO2 (600ppm) Plants were inoculated with 3 adult aphids which remained on the plant for 2 weeks. A ladybird (Harmonia axyridis) was then introduced for 72h. Total protein content of aphids from different host plants was determined using the Bradford assay. Ladybird progeny were reared using a diet of aphids from either aCO2 or eCO2 and susceptible or intermediate raspberry cultivar. Raspberry cultivar and/or CO2 treatment does not alter ladybird pupal mass Conclusions 3. 2. 1. • The break down of aphid resistance in eCO2 may result in aphid outbreaks in the next fifty years. However, this may be offset by the presence of natural enemies. • Changes to the plant in eCO2 does not appear to cascade to higher trophic levels. • The impact of eCO2 over multiple generations of herbivores and natural enemies remains untested. 4.