Research Background
In permafrost regions, CH₄ emissions represent a significant potential positive feedback to global warming. However, most existing studies and models assume a monotonic response between CH₄ fluxes and temperature, paying relatively little attention to the possible nonlinear threshold characteristics in CH₄ production and oxidation processes, as well as to the asymmetry in hydrothermal conditions between warming and cooling seasons. This suggests that the same temperature may correspond to different flux states during the warming and cooling phases (i.e., “hysteresis effect”). Yet, this phenomenon has so far lacked long-term, in-situ empirical evidence in forest-wetland transition zones characterized by high hydrological heterogeneity.
To this end, Professor Zang Shuying’s team from Harbin Normal University, drawing on the Arctic Town of Daxing'anling in Northeast China, conducted two years of high-frequency monitoring to systematically examine the temperature threshold for phase-dependent CH₄ fluxes and their hydrological-microbial regulatory mechanisms. The findings have been published in the Journal of Forest Research.
Figure 1. Research area, sample plot location and experimental setup.
Research methods
The study area is located in Beiji Town, Daxinganling, Northeast China, situated on the southern edge of the Eurasian permafrost zone, where permafrost degradation is severe. Three key sampling periods were established: the early stage of active-layer thawing (early May), the peak growing season (mid-July), and the pre-freezing stage of soil (late October). For each habitat, three 0–10 cm soil cores were collected and mixed to form one composite sample; each composite sample was then divided into two subsamples.
Measurement indicators: Soil CH₄ flux, pH, SOC, DOC, NH₄⁺-N, NO₃⁻-N, and other relevant parameters; simultaneously, soil DNA will be extracted for high-throughput sequencing.
It is worth noting that the study employed a portable greenhouse gas analyzer and SF-3500 Long-Term Soil Greenhouse Gas Flux System (Beijing LICA United Technology Limited). The SF-3500 automatically controls the operation of each flux chamber according to the following procedure: “90 s pre-flushing—90 s equilibration—180 s measurement.” It measures the concentrations of CH₄ and H₂O and simultaneously monitors soil temperature and volumetric water content at a depth of 5 cm.
Statistical Analysis: The study identifies the temperature threshold for CH₄ fluxes through segmented regression and, combined with community analysis, co-occurrence networks, and random forests, dissects their driving factors.
Figure 2. Seasonal variations of soil CH₄ fluxes in forest (a) and wetland patches (b) in 2021 and 2022.
Figure 3. Temperature thresholds of soil CH₄ flux in forest (a: heating stage; b: cooling stage; c: aggregated data) and wetland (d: heating stage; e: cooling stage; f: aggregated data) habitats.
Figure 4. Relative contribution of soil-, methanogen-, and methanotrophic-related predictive factors to CH₄ flux (percentage increase in mean squared error).
Figure 5. In the permafrost region, a conceptual framework was constructed that links the temperature change trajectory, hydrological conditions, and the control of methane fluxes in the forest-wetland transition zone by microorganisms.
Core results
Forests and Wetlands—Distinct Source-Sink Dynamics
Wetlands: Throughout the year, they consistently act as net sources of CH₄. The flux gradually increases from near zero in May–June, peaks during the height of summer in July–August, and then slowly declines from September to October.
Forest: Exhibits a distinct seasonal source-sink transition—net uptake occurs in late June, abruptly turns positive in early July and persists through August, then rapidly becomes negative again in mid-to-late September.
lag effect
The temperature thresholds for the warming and cooling phases in forests are relatively close, and their trajectory dependence is weak; in contrast, the thresholds for the warming and cooling phases in wetlands differ significantly, exhibiting a pronounced lag effect.
Microbe-driven: Methanogens dominate, with ammonium nitrogen and water content serving as key links.
1）The microbial community structures involved in the CH₄ cycle in forests and wetlands both exhibit significant differences. Among these, the composition and diversity of methanogens show more pronounced changes, indicating that they are more sensitive to habitat and seasonal variations.
2）Soil moisture, NH₄⁺-N, and the methanogenic microbial community are closely associated with CH₄ flux, among which the predictive importance of methanogenic microbial-related indicators is the highest (35.46%).
Mechanism of the mouth
1）Warming phase: The active layer melts → soil water-holding capacity increases → anaerobic microzones expand → the bioavailability of NH₄⁺-N rises → methanogenic microbial activity intensifies → CH₄ emissions surge;
2）Cooling phase: Drainage and freezing → oxygen recovery → CH₄ production inhibited; even though the temperature remains relatively high, emissions rapidly decline.
Conclusion
Temperature isn't the only answer—hydrology and microorganisms are the real hidden players behind CH₄ fluxes. This two-year field study reminds us that to truly understand carbon emissions from permafrost, we need to move beyond the mindset that temperature alone dictates everything and instead recognize the more complex—and more authentic—processes at work in their interplay.
Journal: Journal of Forestry Research [Impact Factor: 4.1]
Research institutions: Harbin Normal University, Northeast Agricultural University, and others
Study location: Beiji Town, Daxinganling, Northeast China
Equipment used: SF-3500 Long-Term Soil Greenhouse Gas Flux System
DOI: https://doi.org/10.1007/s11676-026-02100-4