Effects of elevated atmospheric CO 2 and N fertilization on abundance, diversity and C-isotopic signature of collembolan communities in arable soil

Abstract

Rising atmospheric CO 2 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, CO 2 enrichment will indirectly affect soil faunal communities. In the present study we investigated how elevated atmospheric CO 2 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 CO 2 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 δ 13C 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 CO 2 conditions. Our results revealed significant effects of both treatments (CO 2 enrichment and N fertilization) on density and species diversity of collembolans. Overall, collembolans were stimulated under elevated CO 2 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 CO 2 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.