The existence of microbial biogeographic patterns is now well established. Two challenges now are to understand the drivers of this variation and its consequences for ecosystem functioning. Both of these topics can be greatly informed by the consideration of microbial traits – the phenotypic characteristics of microorganisms. As the environment varies over space, it selects for different microbial taxa based on their traits – specifically, their preferences for particular environmental conditions. In turn, the resulting communities alter ecosystem functioning depending on their traits, such as the ability to use particular nutrient resources. A focus on traits therefore provides a framework for interpreting biogeographic patterns as well as predicting whether these patterns will correlate with functional changes. Another promising direction is the investigation of the biogeographic patterns of traits themselves. I will present an example of nitrogen-cycling traits in soils across the globe.
We characterized the biogeography of microbial N traits, defined as eight N-cycling pathways, using publically available soil metagenomes. The relative frequency of N pathways varied consistently across soils, such that the frequencies of the individual N pathways were positively correlated across the soil samples. Habitat type, soil carbon, and soil N largely explained the total N pathway frequency in a sample. In contrast, we could not identify major drivers of the taxonomic composition of the N functional groups. Further, the dominant genera encoding a pathway were generally similar among habitat types. Finally, phylogenetic analysis showed that some microbial groups seem to be N-cycling specialists or generalists. Despite some methodological challenges, the application of metagenomics data to a trait-based framework offers a powerful avenue for elucidating the role that microbial communities play in regulating biogeochemical processes.