Environmental Controls on Carbon Stability in Peatlands: Integrating Microbial, Geochemical, and Organic Matter Variation

Peatlands are significant terrestrial ecosystems that play a large role in regulating many global processes, resulting in a high social, environmental, and cultural importance. Despite this global distribution, these systems are far from uniform with differences in their hydrology, geochemistry, vegetation, and microbial communities, all shaping carbon processing pathways. This study investigates how contrasting peatland types across tropical and temperate zones differ in their biogeochemical characteristics, and to identify the dominant environmental and microbial drivers underpinning this variation. We examined microbial community composition, nutrient profiles, dissolved porewater gases, and detailed organic matter (OM) characterisation of eight peatlands from Colombia (n=4), Uganda (n=1), and the United Kingdom (n=3) to determine the influence on carbon cycling. First, we find that peat, which serves as microbial substrate, becomes enriched in aromatic and alkyl macromolecules with depth, which correlates with an increase abundance of Bathyarchaea and Spirochaeta, whilst a decrease in Methanobacterium and Burkholderia. This is consistent with a shift towards more processed OM and decreased substrate availability. Results also indicate a pH control, in relation to peatland type, on the abundance of Acidobacteriota. Sites with lower pHs (~ 4) are observed to have more Acidobacteriota in comparison to higher sites (~ 6) where Chloroflexi dominate more. Together, these results suggest that local geochemistry exerts a stronger influence on microbial community structure than latitude, further influencing OM decomposition pathways and carbon preservation. Overall, our data indicates that peat carbon stability is governed primarily by site-specific geochemistry rather than regional climate alone, highlighting the need for process-based constraints in predicting peatland carbon emissions under future environmental changes.