COS 312-1 - Microbial physiology as a key control of organic matter decomposition in peatlands

Abstract: Peatlands are the most carbon dense ecosystem on earth, meaning they have an important role in climate change mitigation. However, around 10% of peatlands globally have been drained or mined, which emit 5% of anthropogenic greenhouse gas emissions. Recent restoration of peatlands has led to the return of soil carbon sequestration, and associated climate benefits. Ecosystem functioning in peatlands is driven in large part by microbial communities. Their growth and activity or the lack of it largely control the fate of carbon inputs; organic matter accumulates due to the waterlogged and therefore anoxic nature of the system. However, the exact microbial physiological mechanisms involved in peatland organic matter decomposition are poorly understood. A mechanistic understanding of these processes is required to both predict and manage carbon cycling in peatlands.

Here we sampled seven peatland sites across the UK, each containing near natural, degraded, and restored areas to investigate the effect of drainage and dissolved oxygen on microbial physiology and its consequences for organic matter decomposition. We quantified the following key microbial carbon cycling traits using a combination of shotgun metagenomics and stable isotope analysis: growth rate, carbon use efficiency, resource breakdown and uptake, and stress tolerance. We then linked these traits to carbon flux in peatlands at varying stages of ecosystem health.

We have found that drainage of peatlands leads to decreased soil moisture and increased oxygen concentration when compared with near-natural peatlands, this removes physiological constraints on microbial communities leading to higher activity and growth rates. Restoration seems to re-establish these constraints leading to lower activity and growth rates. We also demonstrate that microbial communities face metabolic trade-offs due to ‘stresses’ in peatlands. In drained peatlands they possess fewer genes for anaerobic metabolism and stress tolerance and more genes for breaking down carbon compounds when compared to near natural peatlands, leading to more decomposition and carbon loss from these systems. Restoration leads to substantial changes in the microbial community and metabolic processes, however even 10 years post restoration microbial processes still differ from near natural peatlands. We conclusively demonstrate that microbial physiology is central is driving decomposition rates in peatlands and the shift from anaerobic metabolism in near natural peatlands to aerobic metabolism in damaged peatlands is largely responsible for the increased carbon loss due to drainage. This highlights the need to consider microbial processes when designing restoration projects aimed at enhancing the capacity of peatlands to store carbon.