clade and functional distribution with simulated climate change.

Microbes are essential for the functioning of all ecosystems, and as global warming and anthropogenic pollution threaten ecosystems, it is critical to understand how microbes respond to these changes. We investigated the climate response of , a widespread gram-negative bacterial genus, during an 18-month microbial community reciprocal transplant experiment across a Southern California climate gradient. We hypothesized that after 18 months, the transplanted clade and functional composition would correspond with site conditions and reflect the composition of native communities. We extracted sequences from metagenomic data across the gradient and assessed their clade and functional composition. Representatives of at least 12 major clades were found at varying relative abundances along the climate gradient, and transplanted clade composition shifted after 18 months. Site had a significant effect (PERMANOVA; < 0.001) on the distribution of both functional (R = 0.465) and clade composition (R = 0.400), suggesting that composition depends on climate parameters. Additionally, for both clade and functional composition, ordinations revealed that the transplanted communities shifted closer to the native composition of the grassland site compared with the site they were transplanted into. Overall, our results indicate that climate and substrate collectively determine clade and functional composition.IMPORTANCE is the most abundant gram-negative bacterial genus in litter-degrading microbial communities of desert, grassland, shrubland, and forest ecosystems in Southern California. We aimed to determine whether responds to climate change in the same way as gram-positive bacteria and whole bacterial communities in these ecosystems. Within , both clade composition and functional genes shifted in response to climate and litter chemistry, supporting the idea that bacteria respond similarly to climate at different scales of genetic variation. This understanding of how microbes respond to perturbation across scales may aid in future predictions of microbial responses to climate change.