Pore structure controls on microbial decomposition of peat organic matter and GHG production

Organic soils can contribute significantly to greenhouse gas (GHG) emissions, particularly when drained. In the Netherlands, large areas of peat soils have been drained for agricultural use, resulting in peat oxidation, increased CO₂ emissions, and land subsidence. Microorganisms are the driving force behind peat degradation at a landscape scale, yet their activity is determined by the conditions at the pore scale. Understanding peat decomposition dynamics across landscapes therefore requires mechanistic understanding of microscale controls that link microbial processes to larger-scale subsidence and GHG emission patterns.

One factor shaping microscale conditions is the peat pore space and its architectural properties, including pore size distribution and connectivity. In the field, these properties are dynamic and respond to drainage and rewetting, as well as to microbial decomposition. Microorganisms are therefore both constrained by pore space properties and actively modify them. In contrast to natural peatlands, drained Dutch peatlands commonly exhibit a compacted, well-decomposed top layer with low pore volume that transitions into more porous and less decomposed peat with depth.

In this study, we aim to investigate how the volume and architecture of the peat pore space affect microbial metabolism and the resulting peat organic matter decomposition and GHG production. Using intact peat samples, we will establish field-relevant pore space volumes and architectures, as well as the microbial communities that inhabit them. In addition, we test a controlled laboratory setup in which homogenised peat is repacked to generate contrasting levels of pore space volume, while pore architecture is manipulated to create different pore size distributions. This design allows us to disentangle the effects of pore space volume from those of pore architecture. Pore structures will be resolved using X-ray microtomography, complemented by microbial community analysis and measurements of basal respiration.

We expect that variation in total pore volume, pore size distribution, and pore connectivity will alter microscale chemical and biological conditions, thereby impacting microbial metabolism, peat organic matter decomposition, and GHG emissions. By linking peat physical structure to microbial processes, this work seeks to provide mechanistic insights into peat decomposition, CO₂ emissions, and land subsidence.