Sensitivity of nematode feeding types in arable soil to free air CO 2 enrichment (FACE) is crop specific

Abstract

The study was part of a long-term CO 2 enrichment field experiment (FACE: free air CO 2 enrichment), using isotopically labelled CO 2 , at the Federal Research Institute for Rural Areas, Forestry and Fisheries (vTI) in Braunschweig (Germany). Impacts of elevated atmospheric CO 2 concentration (550 ppm) on nematode abundance, feeding type composition and the stable C-isotopic signatures (δ 13 C) of feeding types were analysed in an arable soil of a luvisol soil type and a loamy sand texture under cultivation of sugar beet and winter wheat. Two different crop growth stages were considered. The total nematode abundance was significantly higher under winter wheat compared to sugar beet cultivation and tended to increase under CO 2 -enriched conditions. The feeding type composition of nematodes significantly differed between crops and their growth stages. CO 2 enrichment increased the relative abundance of fungivorous nematodes under winter wheat, and the relative abundance of bacterivores under sugar beet cultivation. Accordingly, under FACE conditions, the nematode channel ratio (NCR) indicated a shift towards a more fungal-based food chain under winter wheat, but towards a more bacterial-based energy pathway under sugar beet cultivation. The stable C-isotopic signatures of nematodes confirmed the ingestion of labelled C used for atmospheric CO 2 enrichment. The δ 13 C values indicated significant FACE effects on all nematode feeding types. CO 2 impacts depended on either crop type or crop growth stage, or on the combination of both. According to their food specificity, nematode feeding types were specifically affected by atmospheric CO 2 enrichment due to different food qualities and quantities in the rhizosphere. The present results indicate that fungivores benefit from CO 2 enrichment in arable soils under winter wheat, and bacterivores under sugar beet cultivation. Due to these changes, the soil C-cycle and decomposition processes might change as well. Generally, FACE effects differed strongly between crops and their growth stages, revealing the need to introduce more than one plant type and sampling date when CO 2 enrichment effects on soil faunal communities are studied.