title: Long-term forest soil warming alters microbial communities in temperate forest soils.
abstract: Soil microbes are major drivers of soil carbon cycling, yet we lack an understanding of how climate warming will affect microbial communities. Three ongoing field studies at the Harvard Forest Long-term Ecological Research (LTER) site (Petersham, MA) have warmed soils 5°C above ambient temperatures for 5, 8, and 20 years. We used this chronosequence to test the hypothesis that soil microbial communities have changed in response to chronic warming. Bacterial community composition was studied using Illumina sequencing of the 16S ribosomal RNA gene, and bacterial and fungal abundance were assessed using quantitative PCR. Only the 20-year warmed site exhibited significant change in bacterial community structure in the organic soil horizon, with no significant changes in the mineral soil. The dominant taxa, abundant at 0.1% or greater, represented 0.3% of the richness but nearly 50% of the observations (sequences). Individual members of the Actinobacteria, Alphaproteobacteria and Acidobacteria showed strong warming responses, with one Actinomycete decreasing from 4.5 to 1% relative abundance with warming. Ribosomal RNA copy number can obfuscate community profiles, but is also correlated with maximum growth rate or trophic strategy among bacteria. Ribosomal RNA copy number correction did not affect community profiles, but rRNA copy number was significantly decreased in warming plots compared to controls. Increased bacterial evenness, shifting beta diversity, decreased fungal abundance and increased abundance of bacteria with low rRNA operon copy number, including Alphaproteobacteria and Acidobacteria, together suggest that more or alternative niche space is being created over the course of long-term warming.
authors.affiliation: Department of Microbiology, University of Massachusetts Amherst, MA, USA.
authors.forename: Kristen M
authors.initials: KM
authors.lastname: DeAngelis
authors.affiliation: Department of Microbiology, University of Massachusetts Amherst, MA, USA.
authors.forename: Grace
authors.initials: G
authors.lastname: Pold
authors.affiliation: Department of Microbiology, University of Massachusetts Amherst, MA, USA.
authors.forename: Begüm D
authors.initials: BD
authors.lastname: Topçuoğlu
authors.affiliation: Department of Natural Resources and the Environment, University of New Hampshire Durham, NH, USA.
authors.forename: Linda T A
authors.initials: LT
authors.lastname: van Diepen
authors.affiliation: Department of Microbiology, University of Massachusetts Amherst, MA, USA.
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Varney
authors.affiliation: Department of Biology, University of Massachusetts Amherst, MA, USA.
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Blanchard
authors.affiliation: Marine Biological Labs Woods Hole, MA, USA.
authors.forename: Jerry
authors.initials: J
authors.lastname: Melillo
authors.affiliation: Department of Natural Resources and the Environment, University of New Hampshire Durham, NH, USA.
authors.forename: Serita D
authors.initials: SD
authors.lastname: Frey
keywords: climate change; microbial ecology; ribosomal RNA; rrn operon copy number; trophic strategy