The importance of testing multiple environmental factors in legume-insect research : replication, reviewers and rebuttal

Investigating the impacts of predicted changes in our atmosphere and climate change on insect-plant interactions is a widely pursued area of research. To date, the majority of experimental studies have tested the impacts of single environmental factors on insect-plant interactions, but meta-analyses have clearly illustrated the importance of investigating multiple factors in tandem (Zvereva and Kozlov, 2006; Robinson et al., 2012). In particular, environmental change factors often interact with each other which can either strengthen or mitigate the effects of environmental factors acting alone (Robinson et al., 2012). For example, the positive effects of elevated atmospheric carbon dioxide concentrations (e[CO2]) on plant growth are stronger under high nitrogen (N) conditions compared to low N conditions (+32% and +19%, respectively) (Robinson et al., 2012). Likewise, from the limited number of studies available, Robinson et al. (2012) showed that e[CO2] had different impacts on plant nitrogen, plant biomass and secondary metabolites under elevated air temperature (eT) conditions. This does not invalidate single factor studies, of which we have published numerous examples, but this is an important consideration for making realistic predictions about how plants and insects will respond to future climates (Facey et al., 2014).