Water Table and Vegetation Shape Peatland CO₂ and CH₄ Fluxes With Water Table Modulating Temperature Sensitivity

Peatland rewetting can reduce CO₂ loss but increase CH₄ emissions. How vegetation shapes this trade-off and how the water table modifies temperature sensitivity remain unclear. We analysed 14,643 observations from 285 peatland sites. CH₄ emissions increased more steeply with rising water-table level (WTL) under graminoid dominance, while the pattern of declining ecosystem respiration differed between vegetation classes. Combined CO₂-equivalent emissions (GHGE; respiration + CH₄ at GWP₁₀₀ = 28) declined by 73.9% as WTL rose from 60 cm below to 15 cm above the peat surface and were still declining at the wet end of the analysed range. The decline persisted under GWP₂₀, although the magnitude of the decline above the peat surface depended strongly on the CH₄ weighting. The within-site analysis further showed that apparent CH₄ temperature sensitivity (Q₁₀) increased by 14.9% per 10 cm rise in WTL (95% CI 6.9%-23.5%), whereas respiration Q₁₀ showed no detectable WTL dependence. A supplementary comparison within non-graminoid-dominated bogs showed that fitted CH₄ Q₁₀ increased with WTL where graminoids were present and decreased where graminoids were absent or negligible. Under +3°C warming, fixing CH₄ Q₁₀ at its value at WTL = -10 cm gave a predicted warming multiplier that was 24.7% larger at WTL = -63 cm and 11.8% smaller at +20 cm than the WTL-dependent formulation. These results suggest that assessments of peatland rewetting under warming should consider both vegetation differences in emission responses and the WTL dependence of CH₄ temperature sensitivity.