The potential effect of high atmospheric CO2 on soil fungi–invertebrate interactions

Litter mixtures of four meadow plant species, Cardamine hirsuta, Poa annua, Senecio vulgaris, and Spergula arvensis, were produced from laboratory model terrestrial ecosystems maintained at either ambient or enriched (ambient + 200 µmol mol^?1) CO₂ concentrations. The effect of litter source on the oviposition attractivity of fungi to the sciarid fly Lycoriella ingenua was tested for seven fungal species (Absidia glauca, Cladosporium cladosporioides, C. herbarum, Fusarium oxysporum, Penicillium arenicola, P. chrysogenum, and P. janthinellum). For all species, except F. oxysporum, oviposition attractivity increased when the fungi were growing on litter derived from CO₂‐enriched environments. The relative increase of the oviposition attractiveness of fungi growing on CO₂‐enriched litter differed substantially and resulted in a shift in sciarid fly oviposition preference. For example, when P. chrysogenum and C. herbarum grew on ambient litter, P. chrysogenum was more attractive; the opposite was true for mycelia growing on enriched litter. The effect of litter source on the suitability of four fungal species for larval development was also tested. In two species of fungi (A. glauca and C. herbarum) suitability was significantly higher if growing on CO₂‐enriched litter. With P. chrysogenum the opposite was true. The consequences of these rarely considered CO₂‐induced trophic interactions on ecosystem processes such as nutrient feedback cycles between plants and soil decomposition are considered.