Recovery of methanogenic community and its activity in long-term drained peatlands after rewetting

Peatland rewetting is a widely used restoration technique, yet the recovery of anaerobic processes is poorly characterized. Microbes involved in anaerobic processes, especially methanogens, could reflect the stabilization of anaerobic conditions, vegetation succession and overall restoration success. We investigated the effect of long-term drainage and hydrological rewetting on methanogenic abundance, community composition and CH4 production potential in bogs and spruce swamp forests. Additionally, the substrate limitation of methanogens was tested with a focus on original peatland plant species and their spreading after rewetting by addition of natural substrates. Drainage strongly reduced the abundance and diversity of the methanogenic community. After rewetting, methanogenic abundance and community composition reached almost a pristine-like state, however their CH4 production remained as low as in the drained sites. Substrate addition confirmed the substrate limitation of methanogens due to strongly decomposed peat and the slow spreading of original peatland vegetation. The addition of natural substrates supported methanogenesis close to a pristine-like level. The limited CH4 production reflected not fully recovered anaerobic microbial community composition and vegetation structure 7-16 years after rewetting, although anaerobic conditions seemed to stabilize. Thus, the reestablishment of peatland vegetation structure is crucial for the recovery of methanogenic activity and microbial processes in rewetted peatlands. Moreover, methanogenic community composition, abundance and activity could be used as indicators of restoration success. Originality significant statement: Peatland drainage is increasingly recognized as a major problem affecting the status of valuable natural habitats, water quality and global carbon balance. Rewetting projects are set up to combat and mitigate the losses; yet not enough is known about the recovery of anaerobic processes, especially methanogenesis, which are assumed to reflect stabilization of anaerobic conditions and overall restoration success. Forestry-drained spruce swamp forests and bogs, common in northern Europe, are currently rewetted for both nature conservation purposes and for their anticipated function as hydrological buffers, but information on the recovery of anaerobic microbial communities and especially methanogens are only partly known. Our study concerns the effect of long-term drainage and hydrological rewetting on methanogenic abundance, community composition and activity (CH4 production potential) in undrained, drained and rewetted bogs and spruce swamp forests in the Bohemian Forest, Central Europe. We searched for a reason of limited methanogenic activity in rewetted sites by addition of natural substrates simulating the spreading of original peatland plants (Sphagnum, sedges). This paper contributes to scientific understanding on how long it takes for rewetted peatlands to recover anaerobic microbial communities, anaerobic processes and what are the crucial factors in this process. These results provides a basis for further studies on the trophic relations between anaerobic microbes and recovery of the drained peatlands after rewetting. This study can also extend a set of indicators which should be use for restoration progress evaluation.