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The present study investigated the relative importance of leaf and root carbon input for soil invertebrates. Experimental plots were established at the Swiss Canopy Crane (SCC) site where the forest canopy was enriched with (13)C depleted CO(2) at a target CO(2) concentration of c. 540 p.p.m. We exchanged litter between labelled and unlabelled areas resulting in four treatments: (i) leaf litter and roots labelled, (ii) only leaf litter labelled, (iii) only roots labelled and (iv) unlabelled controls. In plots with only (13)C-labelled roots most of the soil invertebrates studied were significantly depleted in (13)C, e.g. earthworms, chilopods, gastropods, diplurans, collembolans, mites and isopods, indicating that these taxa predominantly obtain their carbon from belowground input. In plots with only (13)C-labelled leaf litter only three taxa, including, e.g. juvenile Glomeris spp. (Diplopoda), were significantly depleted in (13)C suggesting that the majority of soil invertebrates obtain its carbon from roots. This is in stark contrast to the view that decomposer food webs are based on litter input from aboveground.

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Summary• Vesicular-arbuscular mycorrhiza (VAM) and earthworms are known to affect plant and herbivore performance. However, surprisingly few studies have investigated their interactions.• In a glasshouse experiment we investigated the effects of earthworms ( Aporrectodea caliginosa ) and VAM ( Glomus intraradices ) on the growth and chemistry of Plantago lanceolata and the performance of aphids ( Myzus persicae ).• Earthworms did not affect VAM root colonization. Earthworms enhanced shoot biomass, and VAM reduced root biomass. VAM increased plant phosphorus content, but reduced the total amount of N in leaves. Earthworms led to a preferential uptake of soil N compared with 15 N from the added grass residues in the absence of VAM. Earthworm presence reduced the concentration of catalpol. Earthworms and VAM combined accelerated the development of M. persicae , while the development tended to be delayed when only VAM or earthworms were present.• We suggest that earthworms promote plant growth by enhancing soil N availability and may affect herbivores by influencing concentrations of secondary metabolites. VAM enhances the P uptake of plants, but presumably competes with plant roots for N.