Arbuscular mycorrhizal fungi and their associated microbial community modulated by Collembola grazers in host plant free substrate

• Gigaspora gigantea but not Glomus deserticola was consumed by Collembola.
• Collembola feeding strategies varied with their ecological life form.
• Collembola changed the composition of the microbial community accompanying AMF.

Collembola grazing on arbuscular mycorrhizal fungi (AMF) may affect the transfer of mycorrhizosphere C to the soil food web and the regulation of soil mycorrhizal infectivity potential. We used a plant-free mesocosm experimental system with two different mycorrhizal substrates containing either Glomus deserticola or Gigaspora gigantea and three Collembola species (Heteromurus nitidus, Folsomia candida and Protaphorura fimata) to test the hypothesis that Collembola grazing can interfere directly with AMF feeding on the mycorrhizal propagules and/or indirectly changing structure of associated microbial populations. The fatty acid (FA) composition of Collembola grazers and of their mycorrhizal food substrates was assessed. The feeding strategies of H. nitidus and P. fimata varied distinctly between mycorrhizal substrates, whereas the diet of F. candida was invariant to the presence of mycorrhizal propagules. The FA marker for G. deserticola (16:1ω5) was not detected in Collembola lipids, indicating that this AMF was not consumed. In contrast, H. nitidus and P. fimata comprised the marker for feeding G. gigantea (20:1 ω9). Both mycorrhizal substrates were no profitable diet for H. nitidus, resulting in a decline of individuals. Collembola grazed on the bacterial and fungal populations in the mycorrhizal substrate, predominantly H. nitidus that even decreased microbial biomass, resulting in significant changes in the composition of the microbial community. In sum, grazing by microarthropods can directly and indirectly modulate AMF performance as well as interactions with microorganisms, which in turn can impose on the soil infection potential from AMF propagules.