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.

Biotic interactions mediate soil microbial feedbacks to climate change

“…The inclusion of fungal cords increased the total fungal biomass in plots (Fig. 2), but these values were well within the natural range observed at this site (4,38). This plot allowed the formation of a complete microbial community in the absence of macroinvertebrates (+fungal cords,−isopods).…”

Historical climate controls soil respiration responses to current soil moisture

“…High resistance has also been found in long-term climate change experiments. In temperate forests, microbial acclimation to warming was only evident after 15-18 y based largely on reductions in microbial biomass and substrate depletion (24,25), whereas the microbial community shifted between 12 and 20 y as the organic horizon came to resemble the mineral horizon (26). A similar time frame was also required to see effects of warming on microbial communities in subarctic heath (27).…”

Direct and indirect effects of climate change on soil microbial and soil microbial‐plant interactions: What lies ahead?

“…The direct effects of climatic change on microbial composition and function have been reviewed extensively (Blankinship et al 2011, Henry 2012, Manzoni et al 2012, A'Bear et al 2014. Warming by 58C in a temperate forest, for example, altered the relative abundances of soil bacteria and increased the bacterial to fungal ratio of the community (DeAngelis et al 2015). Microbial communities respond to warming and other perturbations through resistance, enabled by microbial trait plasticity, or resilience as the community returns to an initial composition after the stress has passed (Allison and Martiny 2008).…”