Effects of elevated atmospheric CO2 and N fertilization on abundance, diversity and C-isotopic signature of collembolan communities in arable soil

Rising atmospheric CO2 concentrations are expected to have marked impacts on the carbon (C) turnover in agro-ecosystems through increased plant photosynthetic rates, leading to an enhanced biomass, and wider plant C/N ratios. Through increased carbon allocation below-ground, as well as through changed litter quality, CO2 enrichment will indirectly affect soil faunal communities. In the present study we investigated how elevated atmospheric CO2 and two different levels of N fertilization may affect abundance and diversity of collembolans, as important catalysts in decomposition processes, within an agro-ecosystem under winter wheat cultivation. The investigations were carried out in 2002 within a field experiment using the “Free Air CO2 Enrichment” technique (FACE) at the Federal Agricultural Research Centre (Braunschweig, Germany). Stable C-isotopic analysis of collembolans, soil, and crops gave insight into C translocation. During our investigations δ13C values of all components analysed were significantly more negative under FACE compared to ambient air conditions. Stable C-isotopic signatures of collembolans were similar to those of soil under ambient air, but in between those of soil and roots under elevated CO2 conditions. Our results revealed significant effects of both treatments (CO2 enrichment and N fertilization) on density and species diversity of collembolans. Overall, collembolans were stimulated under elevated CO2 conditions, showing an increased abundance of more than 50% (11 240 ind m−2) as well as a higher biodiversity (Shannon Weaver index = 2.5; evenness = 0.75) compared to ambient air conditions (7520 ind m−2; Shannon Weaver index = 2.2; evenness = 0.72). With regard to N supply, a decrease of about 20-30% under CO2 enrichment and 45-55% under ambient air conditions in collembolan abundance with no alteration in diversity was recorded under reduced N fertilization. The observed impacts were species-specific.