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Effects of Elevated CO2 on Plant-Herbivore Interactions
Stiling, P. and Cornelissen, T. 2007. How does elevated carbon dioxide (CO2) affect plant-herbivore interactions? A field experiment and meta-analysis of CO2-mediated changes on plant chemistry and herbivore performance. Global Change Biology 13: 1823-1842.

What was done
First of all, the authors "report the results of the longest-known field study (9 years) to examine the effects of elevated carbon dioxide on leaf miner densities in a scrub-oak community at Kennedy Space Center, Florida [USA]." Secondly, they describe the results of various meta-analyses they employed to determine "the effects of elevated CO2 on both plants (n = 59 studies) and herbivores (n = 75 studies)," where ambient CO2 concentrations ranged between 350 and 420 ppm and elevated concentrations ranged between 550 and 1000 ppm.

What was learned
With respect to the first subject of their review, Stiling and Cornelissen report that "the densities of all leaf miner species (6) on all host species (3) were lower in every year in elevated CO2 than they were in ambient CO2." With respect to the second subject, they say that "elevated CO2 significantly decreased herbivore abundance (-21.6%), increased relative consumption rates (+16.5%), development time (+3.87%) and total consumption (+9.2%), and significantly decreased relative growth rate (-8.3%), conversion efficiency (-19.9%) and pupal weight (-5.03%)," while noting that "host plants growing under enriched CO2 environments exhibited significantly larger biomass (+38.4%), increased C/N ratio (+26.57%), and decreased nitrogen concentration (-16.4%), as well as increased concentrations of tannins (+29.9%)."

What it means
With plant biomass increasing and herbivorous pest abundance decreasing (by +38.4% and -21.6%, respectively, in response to an approximate doubling of the atmosphere's CO2 concentration), it would appear that in the eternal struggle to produce the food that sustains all of humanity, either directly or indirectly, man's crops will fare ever better as the air's CO2 content continues its upward climb. Likewise, it would appear there will be a concomitant expansion of the vegetative food base that sustains all of the biosphere.

Reviewed 2 January 2008