The complexity of carbon cycling in peatlands: a biogeochemical perspective

Peatlands store a substantial fraction of the global soil carbon pool. Widespread drainage and land-use change have accelerated peat decomposition, while current restoration efforts aim to slow or reverse peat carbon oxidation and associated greenhouse gas emissions through rewetting. Understanding when and to what extent rewetting restores carbon sequestration and long-term peat accumulation remains a key scientific and management challenge.

Over recent decades, substantial progress has been made in identifying the biogeochemical controls on peat carbon turnover in rewetted systems. Water table dynamics, hydrological connectivity, redox conditions, substrate availability, nutrient status, and vegetation composition jointly regulate microbial processes driving organic matter decomposition and carbon fluxes. Yet, key questions remain: what really drives carbon turnover in peatlands? Is it “the overriding role of the water table”, the “iron gate” of mineral interactions, or the “iron wheel”? Could there even be a single enzyme controlling global carbon storage (Wen et al., 2019)? These questions highlight how peat carbon cycling defies simple explanations and directly challenges long-standing paradigms. Classical concepts emphasizing intrinsic substrate recalcitrance, single inhibitory controls (e.g., phenolics or water table position), or strictly separated aerobic–anaerobic microbial pathways fail to capture the complexity of carbon stabilization and turnover observed in rewetted peatlands (Zak et al., 2019). Instead, emerging evidence points to a network of interacting, context-dependent processes, including microbial community turnover, mineral–organic interactions, and dynamic redox condition changes, underpinning peat carbon persistence.

Yet, these mechanisms are typically studied at micro- to plot scales, while restoration success and climate feedbacks are evaluated at ecosystem to landscape scales, posing persistent challenges for upscaling. In this contribution, we synthesize current insights into carbon cycling in rewetted riparian peatlands by explicitly linking microbial and biogeochemical controls on carbon decomposition with restoration approaches aimed at managing carbon fluxes. Emphasis is placed on spatial and temporal heterogeneity in peat properties, hydrology, and microbial functioning, and on how this variability propagates uncertainty in carbon balance assessments and model predictions.

By integrating process-based understanding with measurements and modeling perspectives, both recent advances and remaining knowledge gaps in predicting peat carbon cycling under restoration will be highlighted. Re-assessing prevailing paradigms and strengthening cross-scale linkages are essential for designing effective rewetting strategies.

 

References

Wen, Y., Zang, H., Ma, Q., Evans, C. D., Chadwick, D. R., & Jones, D. L. (2019). Is the ‘enzyme latch’or ‘iron gate’the key to protecting soil organic carbon in peatlands?. Geoderma, 349, 107-113.

Zak, D., Roth, C., Unger, V., Goldhammer, T., Fenner, N., Freeman, C., & Jurasinski, G. (2019). Unraveling the importance of polyphenols for microbial carbon mineralization in rewetted riparian peatlands. Frontiers in Environmental Science, 7, 147.