Microbial community responses to elevated temperature and CO2 in peatland soil decomposition ladders

Background/Question/Methods

Peatlands are ecosystems where plant primary production has outpaced microbial decomposition over millennia, and, as a result, are estimated to store approximately one-third of terrestrial soil carbon. As climate change accelerates, increased temperature and CO2 have the potential to alter the processes involved in organic matter accumulation and degradation. Specifically, warming may alter microbial decomposer communities and activity, leading to increased decomposition and production of the greenhouse gases CO2 and CH4. To investigate how increased temperature and CO2 may impact soil microbial communities associated with organic matter decomposition, we utilized the Spruce and Peatland Responses Under Changing Environments (SPRUCE) site in northern Minnesota, which varies belowground and aboveground temperature at five levels from +0 to +9°C above ambient. Peatland soil decomposition ladders consisting of known quantities of peat in discrete mesh bags attached to a rigid “ladder” support frame, with four exposed depths below the surface in 10 cm from 0-40 cm. Three replicate ladders were inserted into the acrotelm in each SPRUCE treatment chamber and allowed to decompose in situ for three years. Peat mass loss and carbon:nitrogen (C:N) changes were quantified, and characterization of the microbial communities was completed using 16S rRNA (bacterial/archaeal) and ITS (fungal) amplicon sequencing.

Results/Conclusions

Our results show that peat microbial community composition, including bacteria, archaea and fungi are significantly impacted by soil depth, temperature, and CO2 treatment across the SPRUCE experimental chambers. We found that bacterial/archaeal and fungal alpha-diversity were highest in the layer closest to the surface (0-10 cm) of the peat acrotelm and in the plots with the highest warming treatment (+9° C). Numerous microbial phyla were significantly differentially abundant across both depth increments and temperature treatments within depths, indicating selection of specific microbes over three years of warming. In contrast, we did not find a significant correlation between microbial community composition and peatland soil mass loss or C:N ratio. This may be due to a lag between community shifts and decomposition process responses to warming, or possibly the selection of microbial communities with similar decomposition activities and rates. Additional planned outyear collections of peat decomposition ladders will be used to further test these hypotheses. Collectively, our results indicate that increased temperature and CO2 as a result of climate change can alter near surface microbial communities in peatlands, potentially contributing to increased decomposition rates and greenhouse gas emissions.