Harnessing the Low-Hanging Fruits: Rewetting Unmanaged Marginal Organic Soils to Achieve Maximal Greenhouse Gas Reduction.

Rewetting drained peatlands is a promising strategy for mitigating carbon dioxide (CO) emissions, transforming these areas from carbon sources to sinks. Despite the well-known climate benefits, practical implementation is often hampered by conflicts between environmental goals and farmers' economic interests. Identifying optimal rewetting locations that maximize greenhouse gas (GHG) reduction while minimizing agricultural disruption is crucial to advancing this process. However, there is currently limited scientific evidence to guide these decisions. To identify "low-hanging fruits", 12 sites were selected for 4-month incubations to investigate the effects of four land uses (grass-cut, grass-graze, arable, and unmanaged) on CO and methane (CH) emissions postrewetting. Results showed that unmanaged sites exhibited the highest potential for GHG reduction (2015 mg CO-eq m day, 89.9%), followed by grass-graze, grass-cut, and arable sites, reflecting a gradient of management intensity. These insights suggest that prioritizing rewetting of unmanaged areas while delaying interventions on arable lands could yield greater climate benefits and enhance farmers' acceptance. Additionally, emission variability across sites was linked to soil properties, indicating that soils with a higher organic carbon content (for greater CO reduction) and lower bacterial diversity (for reduced CH production) offer the greatest GHG reduction potential. This study provides crucial scientific evidence to guide targeted peatland rewetting efforts, supporting net-zero emission goals.