Plant Trait-Mediated Water-table Thresholds in Peatland Carbon Flux Dynamics

Peatlands are central to climate mitigation strategies; however, existing management approaches and process-based modelling methods often rely on oversimplified assumptions about how water table depth (WTD) regulates carbon fluxes. This study used long-term flux observation data spanning distinct peatland ecosystems and vegetation functional traits to quantify the nonlinear response of methane and carbon dioxide emissions to the water-table gradient. We employed a hierarchical, segmented linear mixed-effects model accounting for site heterogeneity and identified consistent, transition-state-like variations in the flux-water table relationship that across peatlands.

Methane exhibited stronger threshold behaviour (~-15.2 cm) than carbon dioxide, with trait-related variations suggesting plant-mediated gas transport prolongs methane sensitivity at deeper water levels. In contrast, ecosystem respiration (Rs) exhibited a more gradual response until reaching the surface, with less separation between trait groups, highlighting differences in the control mechanisms of CH₄ and CO₂ emission processes.

Our findings provide an observation-based foundation for defining hydrological “windows” capable of balancing greenhouse gas emissions. This trait-based WTD-flux approach offers actionable targets for ecological restoration and water level management, while establishing a generalisable method for diagnosing ecohydrological controls on greenhouse gas exchange. Moreover, the results help explain why similar hydrological interventions may yield markedly different climate outcomes across varying vegetation compositions and wetland environments.