Elevated CO2 and O3t concentrations differentially affect selected groups of the fauna in temperate forest soils

Rising atmospheric CO2 concentrations may change soil fauna abundance. How increase of tropospheric ozone (O3t) concentration will modify these responses is still unknown. We have assessed independent and interactive effects of elevated [CO2] and [O3t] on selected groups of soil fauna. The experimental design is a factorial arrangement of elevated [CO2] and [O3t] treatments, applied using Free-Air CO2 Enrichment technology to 30 m diameter rings, with all treatments replicated three times. Within each ring, three communities were established consisting of: (1) trembling aspen (Populus tremuloides) and paper birch (Betula papyrifera) (2) trembling aspen and sugar maple (Acer saccharum) and (3) trembling aspen. After 4 yr of stand development, soil fauna were extracted in each ring. Compared to the control, abundance of total soil fauna, Collembola and Acari decreased significantly under elevated [CO2] (−69, −79 and −70%, respectively). Abundance of Acari decreased significantly under elevated [O3t] (−47%). Soil fauna abundance was similar to the control under the combination of elevated [CO2+O3t]. The individual negative effects of elevated [CO2] and elevated [O3t] are negated upon exposure to both gases. We conclude that soil fauna communities will change under elevated [CO2] and elevated [O3t] in ways that cannot be predicted or explained from the exposure of ecosystems to each gas individually.