Dispersal of bacteria and stimulation of permafrost decomposition by Collembola

[摘要] Contrary to most soils, permafrost soils have theatypical feature of being almost entirely deprived of soil fauna. Abioticconstraints on the fate of permafrost carbon after thawing are increasinglyunderstood, but biotic constraints remain scarcely investigated. Incubationstudies, essential to estimate effects of permafrost thaw on carbon cycling,typically measure the consequences of permafrost thaw in isolation from thetopsoil and thus do not account for the effects of altered bioticinteractions because of e.g. colonization by soil fauna. Microarthropodsfacilitate the dispersal of microorganisms in soil, both on their cuticle(ectozoochory) and through their digestive tract (endozoochory), which maybe particularly important in permafrost soils, considering that microbialcommunity composition can strongly constrain permafrost biogeochemicalprocesses. Here we tested how a model species of microarthropod (the Collembola Folsomia candida ) affected aerobic CO 2 production of permafrost soil over a 25 dincubation. By using Collembola stock cultures grown on permafrost soil oron an arctic topsoil, we aimed to assess the potential for endo- andectozoochory of soil bacteria, while cultures grown on gypsum and sprayedwith soil suspensions would allow the observation of only ectozoochory. The presence of Collembola introduced bacterial amplicon sequence variants (ASVs) absent in theno-Collembola control, regardless of their microbiome manipulation, whenconsidering presence–absence metrics (unweighted UniFrac metrics), whichresulted in increased species richness. However, these introduced ASVs didnot induce changes in bacterial community composition as a whole (accountingfor relative abundances, weighted UniFrac), which might only becomedetectable in the longer term. CO 2 production was increased by 25.85 % in the presence ofCollembola, about half of which could be attributed to Collembolarespiration based on respiration rates measured in the absence of soil. Weargue that the rest of the CO 2 being respired can be considered apriming effect of the presence of Collembola, i.e. a stimulation ofpermafrost CO 2 production in the presence of active microarthropoddecomposers. Overall, our findings underline the importance of bioticinteractions in permafrost biogeochemical processes and the need to explorethe additive or interactive effects of other soil food web groups of whichpermafrost soils are deprived.

[学科分类] 大气科学