Effects of whole-ecosystem atmospheric carbon dioxide concentration manipulation on abundance and species diversity of arthropods in a post-fire chaparral community

This study examined the in situ effects of elevated CO₂ on arthropod abundance in a chaparral community using a series of controlled CO₂, ambient L&barbelow;ight, controlled T&barbelow;emperature (CO₂ LT) null-balance chambers and a F&barbelow;ree A&barbelow;tmosphere C&barbelow;arbon dioxide E&barbelow;nrichment (FACE) ring. Abundance of most arthropod groups, including parasitic wasps (Hymenoptera), decreased with elevated CO₂, resulting in reduced total arthropod abundance. However, abundance of moths (Lepidoptera, primarily Geometridae and Microlepidoptera) appeared to increase. The relationship of springtail (Collembola) and predatory arachnid abundance vs. CO₂ concentration was curvilinear, with abundance peaking near 450–550 ppmv, and lowest at 750 ppmv. While other studies have shown that plant biomass typically increases with elevated CO₂ concentrations, our results suggest that arthropod biomass may decrease. Arthropod species diversity was also measured, using the modified Coleman's rarefaction function to estimate species richness. In contrast to decreasing abundance, diversity of arthropods appeared to increase with elevated CO₂, although the relationship was not significant. A separate study examined the effect of elevated CO ₂ and host plant density on psyllids collected from lilac shrubs. Psyllid densities increased on lilac shrubs under elevated atmospheric CO₂, and there was evidence of an interaction between shrub density and CO ₂ effects. Results of this study suggests that ecosystem function is likely to be affected by CO₂-mediated alteration of arthropod services, such as nutrient cycling and energy flow to higher trophic levels.