What was done
The authors measured the amounts of herbivore and pathogen damage done to the common prairie legume Lespedeza capitata growing in ambient and elevated (560 ppm) CO2 treatments in the seventh and eighth full years (2004 and 2005) of the BioCON study (Reich et al., 2001) conducted at the Cedar Creek Natural History Area in Minnesota (USA), where the CO2 treatments were applied during the daylight hours of each growing season. The herbivore damage was inflicted by three types of pests -- (1) generalist chewers (primarily grasshoppers), (2) Pachyschelus laevigatus (Coleoptera: Buprestidae), and (3) Tortriedon sp. (Lepidoptera) -- while the pathogen damage was caused by Pythium or Fusarium spp.

What was learned
Lau et al. report they "detected no evidence that the CO2 treatments affected herbivore damage." With respect to pathogen damage, however, they found that disease incidence "was lower in the elevated CO2 environment, although this difference [10% less in 2004 and 53% less in 2005] was statistically significant only in 2005 (P < 0.01)."

What it means
"Because disease caused major reductions in reproductive output," in the words of the five researchers, "the effects of CO2 on disease incidence may be important for L. capitata evolution and population dynamics," which phenomena should significantly benefit this species in a high-CO2 world of the future. In addition, they note that Strengbom and Reich (2006), "working in the same experimental site ... also found that elevated CO2 ... reduced disease incidence on Solidago rigida."

References
Reich, P.B., Tilman, D., Craine, J., Ellsworth, D., Tjoelker, M.G., Knops, J., Wedin, D., Naeem, S., Bahauddin, D., Goth, J., Bengston, W. and Lee, T.D. 2001. Do species and functional groups differ in acquisition and use of C, N, and water under varying atmospheric CO2 and N availability regimes? A field test with 16 grassland species. New Phytologist 150: 435-448.

Strengbom, J. and Reich, P.B. 2006. Elevated CO2 and increased N supply reduce leaf disease and related photosynthetic impacts on Solidago rigida. Oecologia 149: 519-525.