The McMurdo Valley has been one of the ecosystems studied for nearly 30 years as part of the Long Term Ecological Research Project, and due to the monitoring of this ecosystem community composition and distribution is thoroughly sampled. Because of the extreme environmental conditions the diversity of species is low, especially at higher trophic levels. However, there still exists a surprising diversity at the microbial level with a high number of taxonomically unique species. Abiotic factors have historically been considered to be driving community composition in these systems, with organisms occupying broad niches, including high functional diversity within species, and presumed low competition. However, ecological principles such as the Stress-Gradient Hypothesis argue that mutually beneficial interaction should play a disproportionate role in an ecosystem such as the McMurdo Dry Valleys.
We sterilized soil samples and tracked the re-establishment of original microbial communities by sequencing the 16S and 18S genetic barcodes for these communities. Having re-set the biotic environment and allowing natural dispersal to colonize these soils we can not only follow the steps of community assembly but discover the potential facilitative interactions between microbes and microinvertebrates in these Antarctic desert soils.
Results/Conclusions
Strikingly, three years after sterilization no live microinvertebrates were found to have colonized the soils. While microbial communites recovered to some extent, as measured by respiration parameters of the soils, diversity is lower in these soils three years after sterilization compared to the original baseline. 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. The total absence of nematodes and other microinvertebrates indicates that there is a strong biotic component to ameliorating the environmental conditions in these soils, without which these soils are inhospitable to multicellular life. These sterilization experiments thus provide strong support for the Stress-Gradient Hypothesis, indicating that life in extreme environments relies heavily on facilitative interactions between microbes and multicellular life.