Liming experiments in acid forest soils reveal short-term and long-term pH-driven changes in soil microbial community composition and carbon cycling

Abstract:

Soil pH is one of the best predictors of microbial community structure and function, and large-scale, long-term changes in soil pH resulting from anthropogenic activity are expected to significantly alter ecosystem functions. Here, we characterized the response of the microbial community in northern hardwood forest soils at two watershed-scale liming experiments conducted 2 years (short-term) and 25 years (long-term) earlier. Samples were collected post-liming at the long-term site and both pre- and post-liming at the short-term site, from the Oe and Oa soil horizons in both limed and control plots. Microbial structure was assayed with 16S rRNA gene and ITS region amplicon sequencing, together with measurements of microbial biomass and activity. Liming increased organic horizon pH by one unit at both the short- and long-term sites and reduced microbial biomass-specific respiration by 75% at the short-term site and 28% at the long-term site. In addition, liming was associated with significant accumulation of soil organic carbon, which doubled at the long-term site, where oxidative enzymes were also markedly reduced. Bacterial and fungal community composition changed significantly within two years after liming, and these shifts were amplified over the long-term. The majority of taxa (73%), whose relative abundance was either enhanced or suppressed in response to liming at the long-term site had a similar response in the short-term. Liming reduced the abundance of dominant ectomycorrhizal fungi including Amanita, Russula, and Cenococcum, suggesting direct pH-driven negative responses. Long-term negative responses to liming were observed in actinomycetes related to Actinomadura spp., which taken together with the fungal responses at the long-term site, may have driven forest floor C accumulation. We show that liming can have both rapid and lasting pH-driven effects on microbial community structure, and that these changes are likely to alter community function with respect to the forest soil C cycle.