Historical contingency maintains biogeographic and microbially driven functional variation in a common garden experiment

We aimed to quantify the relevant scales for which historical contingency shapes microbial structure and function and the magnitude of these effects. We compared distance decay relationships of bacterial (16S) and fungal communities (LSU) from soils collected at local (2m-3000m) and regional (1500m-600km) scales to those from microbial communities after 33-day common garden decomposition microcosm experiments inoculated with microbial communities from the original soils. We also examined the distance decay relationship of soil and microcosm microbial composition with variation in CO2 and dissolved organic carbon (DOC) from the microcosm experiments. We reveal historical contingencies have a strong influence on contemporary microbial distributions. These impacts increase in importance from local to regional scales. We also show historic community composition can influence CO2 and DOC, although the impacts vary with geographic scale and carbon pool. Bacterial, as opposed to fungal communities were more strongly related to both carbon pools. Our results suggest it is imperative to consider historical contingencies when predicting microbial distributions and associated variation in function.