Fig. 4
Summary of feedbacks between NO2/NOx, NO3, plants and herbivores. Direct effects are denoted by solid arrows and indirect interactions by dashed arrows. NO2 caused significant increases in total foliar alkaloids, e.g. nicotine (solid green arrow), and a corresponding decrease in herbivore performance. In turn, feeding by herbivores caused a decrease in foliar NO2 uptake. Plants in high NO3 conditions decreased investment in C-based defensive metabolites, but herbivores on these plants performed relatively poorly. NO2 exposure and NO3 level did not strongly influence C-based and N-based defensive secondary metabolite production, respectively
