Impact of multiple climate stressors on microbial processes and carbon sequestration in peatlands

Peatlands represent one of the largest stores of terrestrial carbon, accounting for ~21% of the global total soil carbon stock. Drained peatlands contribute to around 4% of UK's estimated total anthropogenic greenhouse gas emissions each year. Climate warming, increased drought occurrences and fires in these fragile ecosystems exacerbate uncertainty over the fate of peatland carbon. Increased effort is therefore required to develop sustainable management approaches for peatlands, which is expected to make an important contribution to climate change mitigation in Scotland.

Drainage and climate stressors such as drought and warming impact the hydrology of wetlands such that the removal of water-logged anoxic conditions leads to increased decomposition of the otherwise preserved peat organic matter and release of CO2 back to the atmosphere (Kitson & Bell, 2020; Tiemeyer et al., 2016). Such conditions may reduce methane emissions but increased CO2 release outweighs the climate benefits of methane reduction in terms of long-term global warming potential (Huang et al., 2021). Fires, on the other hand, primarily affect belowground carbon cycling through change in aboveground organic matter and therefore decomposition rates and CO2 flux.

Microbes (bacteria, archaea, viruses, fungi and other microeukaryotes) act as gatekeepers of soil-atmosphere carbon exchange because their growth, activity and interactions with the environment control the fate of carbon inputs (Malik et al., 2018). However, there is a lack of mechanistic understanding of the microbial physiological processes in peatlands that are responsible for carbon cycling, and their sensitivity to multiple climate stressors such as warming, drought and fire (Ritson et al., 2021). Therefore, there is an urgent need to understand the ecology and physiology of soil decomposer communities in response to changes in land use and climate together.

The project aims to investigate microbial carbon cycling processes in intact and degraded systems that are under the influence of climate extremes, which are becoming increasingly frequent. There is a general consensus that degraded peatlands are less resilient to climate extremes such as severe droughts, heatwaves and fires in comparison to intact peatlands (Page & Baird, 2016). This PhD project will rigorously test the response of microbial functions and carbon sequestration rates to climate extremes. A combination of genotypic and phenotypic measurements will enable the project to link microbial traits to carbon sequestration rates under different treatment combinations. Taken together, this knowledge will provide the basis for better prediction and management of microbial processes in peatlands to enhance carbon storage under future climate.