Do shrubs destroy or build peat soil carbon pools?

Abstract

Dwarf shrubs naturally form dense growths in some peatland types, but their presence is increasing and spreading across the Northern Hemisphere due to climate change. Their role as ecosystem engineers – particularly through their symbiotic ericoid mycorrhizal fungi – has been explicitly recognized in peatland ecology only recently. However, whether they build or destroy peat carbon pools remains debated, with contrasting evidence suggesting that shrubs may enhance either the decomposition or stabilization of peat carbon pools. Regardless of whether shrubs are “bad” or “good” for peat carbon storage, the mechanisms through which they influence peat carbon pools remain the same. Shrubs modify soil carbon and nutrient cycling via inputs of above- and belowground litter, leachates, root exudates, and the plant-soil interactions mediated by their fungal partners. We postulate that the shrub effect on peatland carbon pools depends on the shrub species and/or the environment they grow in. In this perspective, we identify key knowledge gaps related to shrub effects and emphasize the need to better account for variation in shrub functional traits and environmental context. Understanding how shrubs shape their peaty environment is basic knowledge that is, unfortunately, lacking, despite being essential for predicting how shrubs shape peatland carbon dynamics under the ongoing climate change.