Beyond the Enzyme-Latch systematic review and meta-analyses

Peatlands are globally important carbon stores, because carbon cycling of plant matter in peat soils is impaired leading to accumulation. The mechanisms that underlie this impairment are not clear, nor why damaging peatlands leads to carbon release. Twenty-five years ago, the Enzyme-latch hypothesis proposed a mechanism of enzymatic controls on carbon cycling in peatlands. Here a review of the evidence for this hypothesis is presented. In the narrative part of this review some of the fundamental premises of the Enzyme-latch hypothesis are considered in light of broader biochemical work, providing a more complex and nuanced framework for the operation of the proposed mechanism. In the second section a systematic review identifies 70 studies in peatlands looking at four key variables to the Enzyme-latch hypothesis. Six meta-analyses of the interactions between these variables, each analysing 2250-11 700 data points, show weak to negligible effects, and therefore do not support the Enzyme-latch hypothesis as a dominant driver controlling carbon cycling in peatlands. Newer conceptual models have already begun to present ideas to move the field beyond the Enzyme-latch hypothesis, and this review presents an evidential basis which these ideas can be built upon this to develop new and better mechanistic understandings of carbon cycling in peatlands. This is an urgent question, as the preservation and restoration of peatlands is essential to meeting the challenges of the climate crisis.