Background
In describing the rationale for their study, the authors write that "three important anthropogenic changes, a loss in plant biodiversity, elevation of atmospheric CO2 and increased nitrogen deposition, are likely to occur simultaneously, so interactive effects among them seem likely."

What was done
To better understand how "elevated atmospheric CO2 and higher rate of nitrogen (N) input may influence grasshopper growth by changing food plant quality and how such effects may be modified by species diversity of the plant community," Strengbom et al. reared grasshopper nymphs (Melanoplus femurrubrum) on Kentucky bluegrass (Poa pratensis) produced by field-grown monocultures or 16-species polycultures that were subjected to either ambient or elevated levels of CO2 (370 or 560 ppm, respectively) and N (ambient or ambient plus 4 g N m^-2 per year, applied as NH4NO3) at the BioCON FACE facility at the Cedar Creek Natural History Area in east-central Minnesota, USA.

What was learned
The three researchers report that "grasshopper growth rate was higher on P. pratensis leaves grown in monocultures than in polycultures, higher on P. pratensis grown under elevated than under ambient CO2, and higher on P. pratensis grown under elevated than under ambient N."

What it means
Strengbom et al. conclude that because they found interactive effects among the three factors they studied (CO2, N and biodiversity), "these parameters may influence plant-insect interactions in a complex way that is not predictable from the sum of single factor manipulations." We hasten to add, however, that because elevated CO2 led to greater grasshopper growth, because elevated N led to greater grasshopper growth, and because reduced biodiversity led to greater grasshopper growth (which three anthropogenic-induced environmental changes are what they foresee for the future), it is reasonable to presume that the combination of these three changes will also lead to greater grasshopper growth in the future.