Peatlands sequester up to 30% of global carbon (C) and are vulnerable to losses in C storage due to climate change. The vertical zone of active peat is migrating downward due to climate-driven water table suppression, and an understanding of the mechanisms governing organic matter cycling in the context of changing environments remains elusive. To improve our ability to predict future peatland C destabilization, we investigate peat active profiles using ultrahigh resolution metabolomics, extracellular enzyme assays, microbial community sequencing, and novel multi ‘omic analytical approaches that elucidate C cycling under simulated climate change at Spruce and Peatland Response Under Changing Environments (SPRUCE).
Results/Conclusions
We reveal that (1) the mechanisms governing C metabolism are intertwined with organic nitrogen (N), sulfur (S), and phosphorous (P) cycling and (2) climate responses are distinct in mesotlem peat (30-40 cm) as compared to the more frequently-studied acrotelm (0-10 cm). Warming strongly impacted the mesotlem where changes in water table height have a direct effect on redox status. Mesotelm peat supported decomposition of chemically-complex organic matter containing N, in contrast to rapid cycling of highly bioavailable compounds in the acrotelm where organic P and S were linked to C cycling. The mesotelm showed an association of anaerobic and nitrogen cycling organisms with metabolite transformations, whereas metabolite transformations were associated with heterotrophic organisms and extracellular enzyme activity in acrotelm peat. Both zones experienced a sharp decline in biogeochemically-relevant microbial diversity in response to simulated climate change, though shifts towards specific classes of organisms were distinct by layer. We therefore advance that changes in the predominate zone of biogeochemical investigation – the acrotelm – are not reflective of activity in deeper peat. In light of predicted climate-driven changes in the vertical distribution of biogeochemical activity, our work demonstrates that environmental attributes that are poorly-represented in models––including organic matter biochemistry and interconnectivity across elemental cycles ––are critical considerations for accurately predicting losses in peatland C storage due to climate change.