Hydrocarbon substrate richness impacts microbial abundance, microbiome composition, and hydrocarbon loss

Manipulating the taxonomic richness of communities can impact numerous community functions. One proposed explanation is that certain taxa can exploit resources or habitat space that others cannot, leading to additive contributions to process rates. It is of interest to learn whether the reverse could also be true. That is, can increasing the richness of resources in an environment impact community size, composition, and function? We mimicked hydrocarbon spills in an uncontaminated soil by introducing individual substrates and all possible combinations of hexadecane, fluorene, and pyrene at four total concentrations, along with a crude oil treatment. We hypothesized that increasing substrate richness would increase microbial abundance, diversity, and function. When a single hydrocarbon substrate was added, we observed lower bacterial and fungal abundance (qPCR) relative to controls receiving no hydrocarbons. Interestingly, however, regardless of total hydrocarbon concentration, microbial abundance increased as the number of added substrates increased. We observed large changes in microbial composition, diversity, and hydrocarbon loss based on specific hydrocarbon substrate combinations, but this was not clearly linked to hydrocarbon substrate richness. These results show that introduced hydrocarbon richness has a strong influence on microbial abundance, but that changes to other soil processes may depend more on other properties of the added compounds.