Temperature-dependent kinetics of microbial particulate organic matter reduction and its regulatory effect on CH4 emissions in peatlands

• POM reduction followed pseudo-first-order kinetics. • 120–860 µmol e- (g peat C) -1 ) of electrochemically reducible EAC POM was microbially accessible. • The Q10 30-15℃ of POM reduction was comparable to that of inorganic electron acceptors. • Faster POM reduction resulted in an earlier onset of CH 4 formation. Particulate organic matter (POM) is increasingly recognized as an important electron acceptor influencing methane (CH 4 ) dynamics in peatland soils. However, the temperature-dependent kinetics of microbial POM reduction remain unclear. In this study, peat soils collected from five poor fens in China were incubated under anoxic conditions at 15 and 30°C. Microbial reduction of POM was assessed by tracking its electron accepting capacities (EAC POM ) over time using mediated electrochemical reduction (MER). The effect of POM reduction on net CH 4 formation was examined in peat soils from the Tibetan Plateau. Results demonstrated that EAC POM decreased exponentially, following pseudo-first-order kinetics (R 2 = 0.86–0.99). On average, 58 ± 12% (120–860 µmol e- (g peat C) -1 ) of the electrochemically reducible EAC POM was microbially accessible. This fraction remained largely invariant with temperature and was comparable to values previously reported for DOM. The first-order rate constants (k red ) at 30°C (0.08 to 0.28 d -1 ) were, on average, three times higher than at 15°C. Temperature sensitivity (Q10 30-15℃ ) ranged from 1.8 to 2.5, consistent with Q10 values involving inorganic electron acceptor reductions. The CH 4 formation became significant only after ∼ 90% of the microbially available EAC POM (△EAC POM ) was depleted. Elevated temperatures accelerated POM reduction, resulting in an earlier onset of CH 4 formation. These findings provide insights into the temperature-dependent kinetics of microbial POM reductions and underscore its gatekeeping role in CH 4 emissions from peatland ecosystems.