In this synthesis project, we tackle the complex relationships between autotrophic and heterotrophic macro- and micro-organisms that determine whether rewetted peatlands are sources or sinks of the GHG CO₂, CH₄, and N₂O. Generally, C is fixed by plants and autotrophic microbes, while heterotrophic microorganisms are the main decomposers, ultimately controlling the C and N emissions. All microbial processes are governed by (1) physico-chemical properties and (2) biotic interactions. Thus, the quality and quantity of plant biomass are important determinants of the substrate for the below-ground (micro-)biota, which in turn control biomass decomposition (Zak et al. 2019; Hinzke et al. 2021) and mineralization, supplying nutrients to the plants and producing/consuming the GHG CO₂, CH₄ and N₂O.

We aim to understand the complex interactions between physico-chemical properties, plants and below-ground (micro-)biota composition/activity, and the production and consumption of organic matter and GHG. We hypothesize that a) plant growth dynamics as well as trophic interactions drive GHG production, and b) that a microbiome-based proxy for the methane sink or source status of wetscapes can be developed. For this purpose, S1 aims to integrate information from subprojects spanning all project areas to obtain a comprehensive picture of the various players and their interactions. (1) We will assess the effect of plant exudates and root aeration on microbial composition/activities and GHG production. (2) We will carry out an integrated multidimensional analysis of available data on factors controlling mineralization and GHG production. (3) We will develop a simple microbiome-based proxy for the methane sink or source status of rewetted fens using eDNA and/or eRNA approaches.