Temperature-dependent soil CH₄ fluxes and their drivers across a forest–wetland ecotone in degrading permafrost, Northeast China

Abstract

Methane (CH₄) fluxes in permafrost regions are commonly represented as monotonic functions of temperature, despite pronounced seasonal hydrological variability and habitat heterogeneity. Here, using two years of in situ high-frequency measurements, we examined whether CH₄ fluxes exhibit trajectory-dependent temperature responses across a forest–wetland ecotone in a degrading permafrost landscape, and how hydrological and microbial processes modulated. We found that: (1) Wetland patches consistently acted as CH₄ sources, with an average flux of 5.14 nmol m⁻² s⁻¹, whereas forests exhibited seasonal source–sink shifts and a much lower mean flux of 0.08 nmol m⁻² s⁻¹. Importantly, phase-stratified segmented regressions revealed distinct, nonlinear temperature thresholds and hysteresis in wetlands, with contrasting CH₄–temperature relationships during warming and cooling phases, while forests showed weaker trajectory dependence. (2) Across habitats and seasons, soil methanogenic communities varied more strongly than methanotrophic communities and explained a larger (35%) of CH₄ flux variability than methanotrophic attributes (21%) and soil properties (24%). (3) Soil moisture and inorganic nitrogen emerged as key factors linking hydrological conditions, microbial communities, and CH₄ dynamics. These findings demonstrate that CH₄ fluxes in permafrost ecotones are governed by the interaction of phase-dependent temperature responses, hydrological constraints, and microbial processes. Incorporating warming–cooling asymmetry and hydrological–microbial coupling may improve the prediction of CH₄ dynamics in heterogeneous permafrost landscapes undergoing thaw.

Keywords

CH₄ flux / Permafrost / Forest–wetland ecotone / Temperature response / CH₄-cycling microorganisms

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Funding

National Natural Science Foundation of China(42501119)

China Postdoctoral Science Foundation(2025M770323)

Natural Science Foundation of Heilongjiang Province(PL2024D006)

Heilongjiang Provincial Postdoctoral Science Foundation(LBH-Z24205)

RIGHTS & PERMISSIONS

The Author(s)