In the McMurdo Dry Valleys of Antarctica (MDV) nematodes and other microinvertebrates make up the top levels of the food chain, while the biotic function of soils is dominated by microbial taxa performing most bio-geochemically important functions in the ecosystem. Abiotic factors have been considered as the drivers for community composition in these systems, yet as this simple ecosystem undergoes the effects of climate change and the resulting abiotic changes affect individual species and their interactions, the underestimated role of biotic interactions is slowly coming to light. A long-term experiment in the McMurdo Dry Valleys of Antarctica (MDV) was established to identify the biotic components of community assembly and primary succession in this purely microbial ecosystem. Soils containing viable microinvertebrate communites and with known abiotic conditions were sterilized by autoclave and replaced into their original environment to measure the rate and order of microbial and microinvertebrate succession. Microinvertebrates were extracted from soils after 1, 4 and 15 years and the microbial communities were analysed by shotgun metagenomics to reveal the functional groups present in soils over time and between samples.
Strikingly, both one and four years after sterilization no live microinvertebrates were found to have colonized the sterilized soils, and after 15 years only five out of eight plots showed nematode colonization at numbers much lower than neighbouring control plots. Previous experiments have shown that dispersal is not a limiting factor in MDV environments, even if most metazoans in these ecosystems require more than one year to complete a single life cycle. While microbial communities are shown to have recovered to some extent as measured by respiration of the treated soils even after a single year, the metagenomic results reveal which specific metabolic or environmentally crucial functions are currently lacking in the microbial community profile. The specific functional groups absent in uncolonized soils provides direct insight into the reliance of these microinvertebrates on microbial facilitation in an extreme environment.