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Article

The Influence of Seasonal Freeze–Thaw in Northeast China on Greenhouse Gas Emissions and Microbial Community Structure in Peat Soil

State Environmental Protection Key Laboratory of Wetland Ecology and Vegetation Restoration, School of Environment, Northeast Normal University, Changchun 130117, China
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Author to whom correspondence should be addressed.
Water 2025, 17(16), 2395; https://doi.org/10.3390/w17162395
Submission received: 15 May 2025 / Revised: 25 July 2025 / Accepted: 8 August 2025 / Published: 13 August 2025
(This article belongs to the Section Soil and Water)

Abstract

Peat soil is a significant global carbon storage pool, accounting for one-third of the global soil carbon pool. Its greenhouse gas emissions have a significant impact on climate change. Seasonal freeze–thaw cycles are common natural phenomena in high-latitude and high-altitude regions. They significantly affect the mineralization of soil organic carbon and greenhouse gas emissions by altering the physical structure, moisture conditions, and microbial communities of the soil. In this study, through the construction of an indoor simulation experiment of the typical freeze–thaw cycle models in spring and autumn in the Greater Xing‘an Range region of China and the Jinchuan peatland of Jilin Longwan National Nature Reserve, the physicochemical properties, greenhouse gas emission fluxes, microbial community structure characteristics, and key metabolic pathways of peat soils in permafrost and seasonally frozen ground areas were determined. The characteristics of greenhouse gas emissions and their influencing mechanisms for peat soil in northern regions under different freeze–thaw conditions were explored. The research found that the freeze–thaw cycle significantly changed the chemical properties of peat soil and significantly affected the emission rates of CO2, CH4, and N2O. It also clarified the interaction relationship between soil’s physicochemical properties (such as dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonium nitrogen (NH4+), soil organic carbon (SOC), etc.) and the structure and metabolic function of microbial communities. It is of great significance for accurately assessing the role of peatlands in the global carbon cycle and formulating effective ecological protection and management strategies.

1. Introduction

The freeze–thaw cycle is a common abiotic stress factor in the seasonal and permafrost regions of the Northern Hemisphere. On an interannual scale, this region experiences a freeze–thaw alternation period lasting 1 to 2 months in both spring and autumn each year. Although the freeze–thaw period accounts for only 16.7 to 20% of the annual cycle, due to the significant fluctuation characteristics of air temperature and ground temperature during this period, it plays an important regulatory role in the soil development process and the biogeochemical cycle of the ecosystem [1,2]. During the freeze–thaw process of soil, spatial redistribution occurs between water and nutrients, and at the same time, there is a significant interaction between soil water and heat conditions and nutrient availability. The accumulation and enrichment effects caused by this dynamic change in nutrients will significantly affect the activity of soil microorganisms and their community composition, and thereby have a profound impact on the structure and function of the soil ecosystem [3,4].
Peat soils are significant carbon reservoirs in terrestrial ecosystems and play a crucial role in the storage of organic carbon within these environments [5]. Peatland ecosystems are estimated to store approximately 500–600 Pg of organic carbon and play a significant role in carbon sink functions [6]. However, the stability of the carbon sink function of wetlands is vulnerable to the interference of changes in external environmental factors, and this feature is particularly prominent in peat wetlands in middle and high latitudes. Studies show that peat soil is highly sensitive to temperature changes, and its carbon emission process is highly susceptible to the influence of environmental factors, thereby leading to changes in the carbon balance state of wetlands. Although peat soil accounts for only 3% of the world’s land area, it stores approximately 30% of the world’s soil carbon. This means even minor changes in the peat soil carbon pool can potentially trigger significant climate feedback effects [7]. Based on this, peat soil has become a key research object in the field of carbon cycle research.
One of the key effects of freeze–thaw on peat soil is to change the physical properties of the soil [8]. It is generally believed that freeze–thaw alternations can damage the soil structure, and the degree of damage is mainly related to factors such as soil type, moisture conditions, and the frequency and intensity of freeze–thaw cycles [9]. The reaction forces of water phase transitions, ice crystal growth, and water migration on soil particles and pores during the freeze–thaw process are the fundamental reasons for the changes in soil structure caused by freeze–thaw [10]. A study revealed that varying numbers of cycles differentially affect soil strength, showing an increase after 2 cycles but a decrease after 5–10 cycles [11]. However, there is currently a lack of systematic research on the influence of freeze–thaw cycles on the physical properties of peat soil.
Furthermore, the soil matrix in wetland ecosystems, especially peat bogs and peat soil types, constitutes an important biogeochemical source of greenhouse gases [12]. Seasonal freeze–thaw cycles have a significant impact on the emissions of greenhouse gases such as CO2, CH4, and N2O in soil, involving complex ecological and biochemical mechanisms. Multiple studies on different ecosystems have shown that research data from regions including forest ecosystems [13], alpine tundra [14], Arctic deserts [15], grasslands [16], and peat bogs [17] indicate that soil experiences significant peaks in carbon dioxide release during the thawing phase. On the one hand, under low-temperature freezing conditions, microbial cells undergo lysis due to the frost swelling effect caused by the formation of ice crystals. The low-molecular-weight carbohydrates released by cell death can be rapidly assimilated and decomposed by surviving heterotrophic microorganisms. For instance, during the soil thawing process in farmland ecosystems, approximately 65% of the CO2 flux comes from the mineralization and decomposition of organic matter in the microbial biomass [18]. On the other hand, after the soil underwent freeze–thaw cycles, the biomass of root death residues reached 300 kg hm−2, indicating that the damage suffered by plant roots during soil’s freezing and its subsequent decomposition process might be one of the key factors affecting soil CO2 emissions during the thawing period [19].
In terms of CH4 and N2O, as important greenhouse gases, their emissions are also significantly affected by freeze–thaw cycles, and this change may be dominated by soil microbial activity. For example, the formation of methane flux is the result of the dynamic equilibrium of the two processes of methane generation and methane consumption [20]. The methane generation process mainly relies on the anaerobic degradation of organic matter by methanogenic archaea of the Euryarchaeota phylum in an anaerobic environment, while methane consumption is mainly achieved by methanogenic bacteria through metabolic activities to meet their demands for carbon sources and energy [21]. The generation rate of N2O is affected by the metabolic activity of denitrifying microorganisms [22].
There is a close correlation between microbial-mediated carbon emissions and climate change. The changes in microbial activity and community structure during freeze–thaw processes and their regulatory mechanisms of greenhouse gas emissions have become important research directions at present. The anaerobic microbial activity in peat soil is significantly inhibited under freezing conditions. However, studies have shown that even in a low-temperature environment of −16 °C, microorganisms still maintain a certain metabolic activity and continuously participate in the degradation process of organic matter [23]. During the thawing stage, microbial activity shows the characteristic of rapid recovery. It was found through the determination of the 35S sulfate reduction rate that the metabolic activity of microorganisms in peat soil in the frozen state was only 0.25% of the initial state at 4 °C but could recover to more than 60% of the initial activity during the thawing process [24]. However, with the increase in the number of freeze–thaw cycles, the microbial community shows obvious environmental adaptability, and its biomass shows a gradually increasing trend [25].
In conclusion, the emissions of greenhouse gases from soil during freeze–thaw cycles are influenced by multiple factors, including changes in physical properties, alterations in biological metabolism, and variations in environmental conditions. In regard to freeze–thaw, as an important surface process, there are still some scientific issues regarding its impact on carbon emissions from peat wetlands that need to be further explored. The freeze–thaw period in spring is short, and the melting process is usually concentrated and rapid. In autumn, the freeze–thaw period is long, and the freezing process may be slow. Spring freeze–thaw is centered on warming to drive melting, promoting ecosystem activity, but it may intensify carbon loss. Autumn freeze–thaw cycles are mainly driven by cooling to freezing, which inhibits decomposition but may indirectly affect the carbon cycle through physical disturbances (frost heaving). This study simulates the seasonal freeze–thaw process based on the characteristics of a short freeze–thaw and long freeze–thaw in spring and long freeze–thaw and short freeze–thaw in autumn; explores the effects of spring freeze–thaw and autumn freeze–thaw on greenhouse gas emissions and some carbon and nitrogen cycling processes in two types of peat wetlands, namely permafrost and seasonally frozen ground, as well as the microbial mechanisms; and supplements our understanding of the carbon and nitrogen cycling of wetland soil in the middle and high latitudes of the Northern Hemisphere. In this way it can provide data support for accurately assessing the feedback between wetland carbon processes and climate.

2. Materials and Methods

2.1. Collection of Frozen Soil Samples

The peat soil in the permafrost area was taken from Tuqiang Town, Mohe County, Greater Khingan Mountains Region, Heilongjiang Province (52°56′ N, 122°51′ E). The special geographical environment of this area has led to the distribution of permafrost in this region. The cold and humid environment of the permafrost provides natural conditions for the development of peatlands. The thickness of the peat layer in this area is approximately 50 cm. And the peatland soil is all acidic soil [26]. The peat soil in the seasonally frozen ground area was taken from the Jinchuan peat marsh in Longwan National Nature Reserve, Jilin Province. This marsh wetland is located in Jinchuan Town, Huinan County, Tonghua City, Jilin Province (42°20′56″ N, 126°22′51″ E). This area is cold and dry in winter, and the freeze–thaw phenomenon is obvious [27]. In order to maintain the original state of the soil, the root systems in the soil were not removed. After the collected soil was mixed evenly, it was transported to the laboratory for further laboratory simulation culture and analysis testing.

2.2. Soil Freeze–Thaw Experiment

A total of 15 freeze–thaw cycles were set up in this experiment. The experimental temperature was controlled using a high-precision temperature control box (range: −20 °C to 150 °C). The freezing temperature was set to −10 °C, and the soil thawing temperature was set to 5 °C. Humidity was maintained at ≥90% to prevent the soil from drying. The initial soil mass was 100 g, and it was weighed every two days to replenish lost water. The spring freeze–thaw experiment was cultivated for 30 days as the control variable, and the autumn freeze–thaw experiment was also cultivated for 30 days. According to the characteristics of freeze–thaw cycles in spring (short freezing and long thawing) and autumn (long freezing and short thawing), two freeze–thaw modes were set: freezing for 12 h and thawing for 36 h constitutes one spring freeze–thaw cycle (S), and freezing for 36 h and thawing for 12 h constitutes one autumn freeze–thaw cycle (A). Meanwhile, samples at 5 °C that had not undergone freeze–thaw treatment were set as unfreeze–thaw controls (CK) respectively. Sample naming method: Peat soil in permafrost areas is named “T”, and peat soil in seasonally frozen ground areas is named “B”. The sample name is “Freeze–Thaw Model—Soil Type”.

2.3. Determination of Soil’s Soluble Organic Carbon Content

Press water: The ratio of soil to soil is 4:1. Weigh 5 g of fresh soil that has passed through a 2 mm sieve and place it in a centrifuge tube. Add 20 mL of deionized water, shake for 30 min, then centrifuge on a centrifuge at 4000 rpm min−1 for 30 min. Take the supernatant and filter it with a 0.45 μm filter membrane. The filtrate is placed in a reagent bottle for testing. The content of SOC in the soil was determined by a total organic carbon analyzer (TOC-LCPH/CPN, Kyoto, Japan).

2.4. Determination of Greenhouse Gas Emissions from Soil

Close the three-way valve and put the culture flask back into the high-precision temperature control box. After 1 h, open the three-way valve and collect 20 mL of gas with a syringe. After sampling, open the culture flask to replenish the fresh air. The gases were collected after the first, third, fifth, seventh and fifteenth freeze–thaw cycles, and the concentrations of CO2, CH4, and N2O were determined by a gas chromatograph (Agilent 7890A, Santa Clara, CA, USA). The emission rates of CO2, CH4, and N2O in the soil were calculated based on the differences between the concentrations of CO2, CH4, and N2O in the soil sample after 1 h of sealing and those in the blank sample. The specific calculation process is as follows:
F = ρ × C × V × 273 / 273 + T × W
In the formula, F represents the soil CO2 emission rate (mg CO2-c kg−1 h−1), CH4 emission rate (μg CH4-c kg−1 h−1), and N2O emission rate (μg N2O-N kg−1 h−1); ρ is the concentration (g L−1) of standard gases such as CO2, CH4, and N2O; it indicates the concentration difference (ppmv h−1) between the measured sample and the control sample after 1 h in the sealed culture flask; V represents the volume of the culture flask (mL); T represents the fixed temperature of the high-precision temperature control box (°C); W represents the dry weight (kg) of the culture soil [28].

2.5. Microbial Sampling and Detection Methods

After removing the cell wall, the matrix samples were collected. For microbial community analysis, a 10 g sample was mixed with 50 mL PBS (phosphate buffer), shaken at 200 rpm min−1 for 60 min, and filtered through a 0.22 µm filter membrane. The sequencing of the microbial community was completed by Beijing Novogene Technology Co., Ltd., Beijing, China. The V3-V4 region of 16S rRNA was amplified using primer 338F/806R to characterize the composition and structure of the bacterial community, and the ITS1 region was used to identify the structure and composition of the fungal community. After amplifying the extracted DNA, the product was further sequenced using the Illumina Novaseq sequencing platform (Illumina, San Diego, CA, USA). The Paired-End sequencing method was used to construct small fragment libraries for sequencing. By splicing and filtering reads, clustering or denoising, and conducting species annotation and abundance analysis, the species composition of the samples was revealed.

2.6. Analytical Statistical Methods

The soil’s physicochemical properties measured in this study included SOC, total nitrogen (TN), NH4+, nitrate nitrogen (NO3), dissolved organic carbon (DOC), DON, soil microbial biomass carbon (MBC), and soil microbial biomass nitrogen (MBN). Samples were collected under different freeze–thaw conditions, and multiple replicates were conducted to obtain datasets for each parameter. During data processing, the mean values of replicate measurements were first calculated, and obvious outliers were removed to ensure the data’s accuracy and consistency. The Shapiro–Wilk test was used to assess data’s normality. For normally distributed data with a homogeneity of variance, differences between experimental groups were analyzed using one-way ANOVA. Non-normally distributed data were compared using the Kruskal–Wallis nonparametric test. A two-way ANOVA was employed to examine the effects of different freeze–thaw patterns (unfrozen, spring, and fall) and their interactions with freeze–thaw frequency on the physicochemical properties, greenhouse gas (CO2, CH4, and N2O) emission fluxes, and microbial community structure of two peat soil types (perennial permafrost and seasonally frozen ground). Means and standard errors for biologically replicated data were calculated using SPSS 23.0 software (IBM, Armonk, NY, USA). The sequencing data analysis is detailed in Text S2.

3. Results and Discussion

3.1. Seasonal Freeze–Thaw Changes the Carbon and Nitrogen Content in Peat Soil

3.1.1. Total Nitrogen, Ammonium Nitrogen, and Nitrate Nitrogen

Seasonal freeze–thaw has a significant impact on the TN content of peat soil (Figure 1A,B). Without going through the freeze–thaw treatment stage (FT0), the TN content in permafrost peat soil (such as CKT) is higher than that in seasonally frozen ground (such as CKB). This is because low temperatures inhibit nitrogen mineralization and promote the accumulation of nitrogen in organic form [29]. With an increase in freeze–thaw cycles, the TN content decreased significantly in the initial stage (FT1-FT3) (e.g., AT: from 20.66 g/kg to 18.17 g/kg, SB: from 12.21 g/kg to 10.28 g/kg), showing an accelerated decomposition and mineralization of organic nitrogen [30]. During the FT5-FT15 stage, the TN content in some soils increased (e.g., ST rose to 25.66 g/kg, SB rose to 13.96 g/kg), and nitrogen release was promoted due to the destruction of soil structure [31]. In the same section, the TN in the permafrost area was still higher than that in the seasonally frozen ground, indicating that the responses of different permafrost types in the nitrogen cycle vary significantly. Especially during the freezing and thawing in spring, the variation range of TN in permafrost is greater, indicating that it is more sensitive to the freeze–thaw process.
The effects of seasonal freeze–thaw on the content of NH4+ and nitrate nitrogen (NO3) in peat soil are shown in Figures S1 and S2. In the initial stage (FT0), the NH4+ content in permafrost soil was higher than that in seasonally frozen ground. In the early stage of freeze–thaw, the content of NH4+ increased (for example, ST reached 35.68 mg/kg), due to the accelerated decomposition of organic matter [32,33]. During the FT7-FT15 stage, the content of NH4+ decreased and was affected by nitrification. The decrease in NH4+ in permafrost is more significant (such as a 17.04% decrease in ST). The initial content of NO3 was relatively low and was affected by the inhibition of nitrification by soil acidity. In the early stage of freeze–thaw (FT1-FT5), the content of NO3 rose rapidly (for example, SB reached 9.16 mg/kg), indicating the acceleration of nitrification. In the later stage of freeze–thaw (FT5-FT15), the content of NO3 decreased particularly significantly (for example, SB decreased by 22.52%), which was affected by the enhanced absorption by microorganisms in seasonal frozen soil [34,35]. This indicates that seasonal freeze–thaw cycles have a significant impact on nitrification in seasonal frozen soil.

3.1.2. Total Organic Carbon Content

The variation characteristics of SOC content in different types of peat soil under seasonal freeze–thaw conditions are shown in Figure 1C,D. Under the initial state (FT0), the SOC content of CKT was 346.89 g/kg−1, and the SOC content of CKB was 277.94 g/kg−1. This indicates that peatlands in permafrost areas have a higher organic carbon storage. The initial differences in SOC content may be related to the soil formation process, climatic conditions, and microbial activity [36]. With the progress of the freeze–thaw cycle, SOC content at all sampling sites decreased significantly. This downward trend was more significant at FT3 and FT5, especially in the peatlands of the seasonally frozen ground areas (AB and SB). Among them, the SOC content of the SB group decreased from the initial 277.94 g/kg−1 to 220.14 g/kg−1, a decrease of 20.80%. This might be because the temperature changes during the freeze–thaw process in spring affected the activities of microorganisms, enhancing microbial activities in the soil and accelerating the decomposition rate of organic carbon [37]. From the FT7 to FT15 stage, the decline rate of SOC slowed down, and the SOC content tended to stabilize. This indicates that the freeze–thaw cycle has a significant impact on SOC’s decomposition and carbon release, especially in peat soil in seasonally frozen ground areas, where the SOC content is more sensitive to the freeze–thaw process.

3.1.3. Soluble Organic Carbon and Soluble Organic Nitrogen

Seasonal freeze–thaw has a significant impact on the DOC of peat soil (Figure 2A,B). In the initial stage (FT0), the DOC content of seasonal frozen soil (SB and AB) was higher than that of permafrost (AT and ST), because the seasonally frozen ground exhibited higher pH values, which was conducive to the dissolution of organic matter [38]. During the freeze–thaw period in autumn, the DOC of AT and AB increased significantly (AB increased to 72.60% in the FT5 stage), affected by the decomposition of organic matter and the increase in microbial activity [39]. From the FT7 to FT15 stage, the DOC of most soils decreased, but AT rose to 35.47 mg/L at the FT15 stage. Figure 2C,D reveals the influence of different freeze–thaw periods on the DON of peat soil. During the freeze–thaw period in autumn, DON remained stable and rose significantly at the end. During the freeze–thaw period in spring, ST DON was initially stable, and FT5 reached a peak of 2.77 mg/L before declining. SB DON continued to rise to a peak of 4.48 mg/L at FT7 and then decreased by 18.97% at FT15. The increase in DON in permafrost was significantly higher than that in seasonally frozen ground, possibly due to enhanced microbial activity, which promoted the dissolution of organic nitrogen.

3.2. The Freeze–Thaw Cycle Suppresses Greenhouse Gas Emissions from Peat Soil

In recent years, with global warming, the frequency and intensity of freeze–thaw cycles in permafrost regions have changed. This not only affects the physical and chemical properties of peat soil but may also further intensify the emissions of greenhouse gases such as CO2, N2O, and CH4. The research finds that there are significant differences in the CO2 emission characteristics of different types of peat wetlands under freeze–thaw conditions [29]. The CO2 emission rate of the AT group in the permafrost area reached a peak (2.32 ± 0.41 mg CO2-c kg−1 h−1) at FT1 and then remained at a relatively low level (Figure 3C). Conversely, the ST group showed bimodal characteristics at FT1 and FT7 (Figure 3E). The data of the control group (CK) (Figure 3A,B) showed that the CO2 emission intensity of seasonal frozen soil was higher (peak 2.96 ± 0.62 mg CO2-c kg−1 h−1), and the AB group (Figure 3D) rebounded to the initial level (from 1.07 to FT0 level) after the initial emission reduction, while the SB group (Figure 3F) was basically not affected by spring freeze–thaw. The seasonal effect of the freeze–thaw mode is particularly prominent. The inhibitory effect of freeze–thaw in autumn on CO2 emissions is more significant than that in spring, which may be related to the degree of inhibition of microbial activities during the freezing period [40]. The overall discharge intensity of seasonal frozen soil is approximately 28–35% higher than that of permafrost, suggesting that its organic matter is more easily decomposed. It is worth noting that the differences between AT and ST in the permafrost group mainly occurred in the FT3-FT15 stage. This dynamic response may reflect essential differences in the stability of the carbon pool and the structure of the microbial community under different permafrost types.
For CH4, the seasonal freeze–thaw cycle significantly affects the CH4 emission characteristics of different types of peat soils (Figure S3). Studies have shown that there are significant differences in the reference emission rates of peat soil between permafrost (0.21 ± 0.03 mg CH4-C kg−1 h−1) and seasonally frozen ground (0.30 ± 0.04 mg CH4-C kg−1 h−1). Under the autumn freeze–thaw model, the CH4 emissions of permafrost soil increased sharply by 4.53 times after the first round of freeze–thaw (FT1) and then continued to decline. On the contrary, seasonal frozen soil shows a “V” -shaped variation trend and always maintains a relatively low emission level. The spring freeze–thaw experiments show that the peak emission of CH4 in seasonal frozen soil (FT5 stage) not only lags behind that of permafrost, but its peak intensity (about 0.15 mg CH4-C kg−1 h−1) is only 50% of the latter. It is worth noting that the CH4 emissions of both types of soil remained consistently higher than the initial value (FT0) after multiple spring freeze–thaw cycles, indicating that the spring thawing process as a whole inhibited methane release. This inhibitory effect showed significant temporal dynamic differences among different permafrost types (p < 0.05).
In addition, the freeze–thaw cycle has a relatively weak and phased effect on N2O emissions from peat soil (Figure S4). Data show that the benchmark emission rates of N2O in permafrost and seasonally frozen ground were stable at 0.50 ± 0.05 and 0.74 ± 0.08 mg N2O-N kg−1 h−1, respectively. It is notable that only during the first freeze–thaw cycle (FT1) in autumn did the emissions of the two types of soil significantly increase (by 2.45 and 1.57 times, respectively), while there was no statistical difference between the subsequent cycles and FT0 (p > 0.05). The relatively high emissions of seasonal frozen soil during the autumn freeze–thaw period may result from the low initial value of FT0, while the spring freeze–thaw had no significant impact on the N2O fluxes of both types of soil. This inert response characteristic distinct from CO2/CH4 suggests that N2O emissions are more likely to be directly regulated by soil nitrogen availability rather than freeze–thaw physical processes [41,42,43].
Based on the above data, in comparison, the N2O emissions from permafrost peat soil are more significantly stimulated by the freeze–thaw cycle, especially in autumn, showing a higher peak emission rate. This might be related to the higher soil moisture content and the rate of organic matter decomposition in permafrost peat soil [4].
To determine whether there is a significant correlation between ST, SB, AT, and AB and DOC, DON, pH, NH4+, NO3, SOC, TN, MBC, and MBN in CO2 and N2O emission rates, Pearson correlation analysis was conducted. According to Table S1, there is a positive correlation between ST and DOC and a negative correlation between SB and DOC in terms of CO2 emission rates. Additionally, SB shows a positive correlation with TN and a negative correlation with MBC. For N2O emission rates, ST exhibits a positive correlation with pH, and SB shows a negative correlation with pH but a positive correlation with NH4+. AT and AB both demonstrate a positive correlation with pH and a negative correlation with NH4+ (p < 0.05). These results provide important data support for a deeper understanding of the carbon and nitrogen cycling processes in different permafrost wetlands and their response mechanisms to climate change.

3.3. The Freeze–Thaw Cycle Reduces the Global Warming Potential of Greenhouse Gases in Peat Soil in Seasonally Frozen Ground Regions

As can be seen from Figure 4 and Figure 5A, in the peat soil of permafrost and seasonally frozen ground, both the spring cycle and the autumn cycle have reduced the cumulative emission flux of CO2; especially, the autumn freeze–thaw cycle is the most obvious. It is worth noting, however, that seasonal frozen soil shows a higher cumulative CO2 emission flux compared to permafrost peat soil, with the maximum reaching 5786.38 ± 354.25 kg·hm−2. Furthermore, under the conditions of the spring freeze–thaw cycle, the cumulative emission fluxes of CH4 in the peat soil of permafrost and seasonally frozen ground also show a decreasing trend, decreasing by 2.74 and 3.86 times, respectively. Unlike CO2 and CH4, both the autumn and spring freeze–thaw cycles increase the cumulative N2O emission fluxes in peat soils of permafrost and seasonally frozen ground, but this promoting effect is limited. Subsequently, the global warming potential (GWP) of greenhouse gases was further calculated (Figure 5D). The data indicated that the GWP of greenhouse gases produced by permafrost peat soil was not affected by the freeze–thaw cycles in spring and autumn, while the GWP of greenhouse gases produced by seasonally frozen ground peat soil was inhibited by the freeze–thaw cycles in spring and autumn [44].

3.4. The Freeze–Thaw Cycle Has Changed the Microbial Community Structure of Peat Soil

It can be seen from Figure 6A that with the increase in the number of freeze–thaw cycles (from FT0 to FT15), the composition of the peat soil bacterial community has undergone significant changes. In the control group (Ft0) that did not undergo freeze–thaw cycles, the composition of the bacterial community was relatively stable, with Proteobacteria and Acidobacteria dominating. However, the abundance of other groups such as Firmicutes and Bacteroidota is relatively low. With the increase in the number of freeze–thaw cycles, especially in the samples of Ft7 and Ft15, the diversity and abundance of the bacterial community have changed significantly. The abundances of Proteobacteria and Acidobacteriota remain relatively high, but in some treatment groups (such as Ft15), the abundances of Firmicutes and Bacteroidota have significantly increased. It is worth noting that the abundance of Firmicutes in the FT15 samples has significantly increased, indicating that after a relatively long period of freeze–thaw cycles, these groups exhibit a strong adaptive capacity to the changing soil environment. This adaptability may be related to the changes in soil moisture and temperature fluctuations brought about by freeze–thaw cycles [45]. Similarly, Bacteroidota also shows a trend of increasing abundance with the increase in freeze–thaw cycles, especially in the samples of FT7 and FT15. Overall, the increase in the number of freeze–thaw cycles has a significant impact on the bacterial community in peat soil, mainly reflected in changes in the abundance of some bacterial groups; especially, the relative abundance of groups such as Firmicutes and Bacteroidota has increased after more freeze–thaw cycles. This change indicates that the frequent occurrence of freeze–thaw cycles can affect the structure of bacterial communities, which may lead to alterations in the carbon and nitrogen cycling processes of the soil, as well as the generation and emission of greenhouse gases [46].

3.5. The Relationship Between Soil Microbial Community Structure and Greenhouse Gas Emissions

The Typical Correspondence Analysis (CCA) diagram in Figure 6B shows the relationship between the samples and greenhouse gas emissions. CCA1 and CCA2 respectively explained 65% and 18.85% of the variances, demonstrating a significant impact of the number of freeze–thaw cycles on the sample distribution. The T1 sample (permafrost area) was significantly separated from the other samples, indicating that freeze–thaw has a greater impact on the microbial community. The CH4 arrow points to the sample in the upper right corner, indicating active methanogenic conditions. Freeze–thaw cycles affect the composition of the microbial community, which in turn influences methane production. The N2O arrow points to the lower left, which is closely related to some samples, indicating that they are in a strong nitrification environment. The CO2 arrow points downward, revealing its association with the bottom sample.
The spring freeze–thaw samples are close to the CH4 direction, indicating that methanogenic bacteria are active. Their short freezing and long thawing characteristics promote the decomposition of organic matter to produce methane, and the moist soil provides an anaerobic environment to facilitate the activity of methanogenic bacteria. The CO2 emissions of freeze–thaw samples increase in autumn. The long freezing period inhibits microbial activities. The rapid recovery after thawing increases CO2‘s release. Thawing promotes the mineralization of organic matter, affecting denitrification and CO2 emissions.
The microbial community of the freeze–thaw-treated samples (CK) is stable, with less N2O and CO2 emissions. Due to the lack of freeze–thaw, metabolic activities are affected, maintaining low greenhouse gas emissions. In the permafrost region (T), the samples are concentrated on the left side, reflecting high N2O emissions and thawing promoting nitrification and denitrification. The methane production in the samples from the seasonally frozen ground area (B) varies greatly. After thawing, methanogenic bacteria are activated, increasing CH4 emissions [47].

3.6. Prediction and Analysis of Functional Pathways of Soil Microbial Communities Under Seasonal Freezing and Thawing

The key predicted metabolic pathways in this study include methanogenesis, nitrate reduction, nitrogen fixation, fermentation, and aerobic chemoheterotrophy. These pathways are of interest due to their established roles in the emission of greenhouse gases (CH4, N2O, and CO2) and their high predicted functional abundance under various freeze–thaw conditions. Quantitative evidence was derived from functional predictions based on 16S rRNA gene data using bioinformatics tools like FAPROTAX. As can be seen from Figure 7A, the related functions of methane generation have been significantly enhanced in the samples that have undergone multiple freeze–thaw cycles (such as TFt3, TFt7, TFt15, BFt3, BFt7, BFt15). This indicates that during the freeze–thaw cycle, anaerobic conditions and the decomposition of organic matter provide sufficient energy sources for methanogenic bacteria, thereby promoting the generation of more methane. In the BFt3, BFt7, and BFt15 samples, the functions related to methane generation (such as the green and purple parts) are particularly prominent. This might be due to the freeze–thaw pattern in the seasonally frozen ground area, which effectively converts soil organic matter into methane during the thawing process. The nitrate reduction function has a relatively high abundance in all freeze–thaw modes, especially in samples such as TFt0 and TFt3. Nitrate reduction is a key process in the nitrogen cycle in soil, reflecting the important role played by microbial communities in nitrogen transformation [48]. This may affect the emission of N2O, especially during the alternating process of freezing and thawing; the nitrate reduction effect may promote the formation of N2O. With an increase in the number of freeze–thaw cycles, the generation of N2O may also be affected by microorganisms, which is related to the available nitrogen sources in the soil and their microbial treatment capacity [49]. Fermentation and Aerobic_chemoheterotrophy functions also showed certain increases in some samples. These microbial functions involve the degradation of organic matter and may play a role in the release of CO2; especially after thawing, when microbial activity resumes, organic matter in the soil will be rapidly decomposed to produce CO2 [1].
As can be seen from Figure 7B, the relative abundances of functions such as “methane generation” and “hydrogen-nutrient methane generation” are relatively high in the TFt7, BFt7, TFt15, and BFt15 samples. This indicates that with the increase in the number of freeze–thaw cycles, the changes in soil moisture and temperature provide a more suitable environment for methanogenic bacteria, promoting the generation of methane. In the TFt0 and BFt0 samples, the functions related to “nitrate reduction” and “nitrogen fixation” were more active, which was associated with stronger N2O emissions in these samples. Microorganisms reduce nitrate in the soil to nitrous oxide through the nitrate reduction process [50]. Under different freeze–thaw modes, the increase in metabolic functions such as fermentation and aerobic chemical heterotrophic ones also indicates the recovery of organic matter decomposition in the soil during the freeze–thaw process. Especially in samples such as TFt3 and BFt3, the abundance of these functions is relatively high, indicating that the decomposition of organic matter accelerates the release of carbon dioxide.
The distribution and abundance of functional genes in peat soil microbial communities are key factors affecting greenhouse gas emissions. The high abundance of aerobic heterotrophic metabolic genes indicates the importance of oxygen supply driving CO2 emissions under freeze–thaw conditions, while the distribution of nitrogen-fixing genes reflects that microorganisms regulate greenhouse gas release through the nitrogen cycle. The differences between different groups indicate that seasonal freeze–thaw significantly affects the distribution of microbial functional genes, thereby regulating the soil carbon and nitrogen cycle and greenhouse gas emissions. This provides microbiological evidence for understanding the emission mechanism of peat soil under climate change.
Overall, under different freeze–thaw conditions, the correlation between the physical and chemical properties of peatland soil and microbial functional genes shows significant differences. The freeze–thaw process affects the expression of microbial functional genes by altering properties such as soil temperature, moisture, and nutrients, providing a scientific basis for understanding the impact of freeze–thaw on the ecosystem functions of peatlands.

4. Conclusions

This study takes peat soil in typical permafrost and seasonally frozen ground areas in Northern China as the main research object. Different freeze–thaw models (spring freeze–thaw and autumn freeze–thaw) were constructed in combination with the climatic characteristics of the northern region to explore the influence mechanism of seasonal freeze–thaw on greenhouse gas emissions from peat soil. Research has found that seasonal freeze–thaw significantly alters the carbon and nitrogen content in peat soil. Permafrost is more sensitive to the freeze–thaw process, while seasonally frozen ground shows a stronger adaptability during the freeze–thaw process. Seasonal freeze–thaw cycles significantly affect the characteristics of greenhouse gas emissions. Among them, in the autumn freeze–thaw cycle of permafrost peat soil, the CO2 emission rate shows a trend of first decreasing and then increasing, while the CO2 emission rate of seasonally frozen ground peat soil is generally higher than that of permafrost. The emission rate of N2O shows a pulsed release in the spring freeze–thaw cycle, while it exhibits a different trend in the autumn freeze–thaw cycle. The N2O emission in seasonal frozen soil wetlands is more significantly stimulated by the freeze–thaw cycle. The methane emission flux is greatly affected by the freeze–thaw model. The methane emission rate of peat soil in seasonal frozen soil shows an upward “V” shape under the freeze–thaw conditions in autumn, while it shows a trend of first increasing and then decreasing under the freeze–thaw conditions in spring. In addition, seasonal freeze–thaw cycles significantly alter the diversity and composition of peat soil microbial communities. The aerobic heterotrophic metabolic function of bacteria dominates in peat soil, indicating that the aerobic heterotrophic process is the main driving force of carbon metabolism. The nitrogen fixation function shows significant differences under different freeze–thaw modes, indicating that the freeze–thaw process may affect greenhouse gas emissions by altering microorganisms related to the nitrogen cycle. Therefore, under different freeze–thaw mode conditions, the greenhouse gas emission fluxes of the two types of peat soils are mainly closely related to the nitrogen fixation function and the aerobic metabolic function of methane generation. Although this study successfully revealed the core mechanisms of the freeze–thaw cycle on peat soils by tightly controlling experimental conditions, there are several limitations that need to be addressed. For instance, in terms of environmental control, the laboratory temperature was managed with greater precision than the natural fluctuations observed in the field, and the freeze–thaw cycle was fixed at 12/36 h, whereas field monitoring indicated temporal variations in the actual cycle. Additionally, the laboratory setup did not model the role of seasonal plant root growth in regulating the microbiome, even though field studies have shown that root secretions can significantly affect microbial biomass’s distribution. Considering these limitations, future studies are advised to incorporate field observations to validate laboratory findings. We plan to introduce more natural variables in subsequent studies to enhance the ecological applicability of the results.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/w17162395/s1, Text S1: Determination of total nitrogen, ammonium nitrogen and nitrate nitrogen; Text S2: Sequencing data analysis; Table S1: Correlation between CO2 and N2O Emission Rates and Physicochemical Properties of Peatland Soil under Seasonal Freeze-Thaw Cycles; Figure S1: Changes in soil ammonium nitrogen (NH4+) of peatlands under seasonal freeze-thaw cycles; Figure S2: Changes in soil nitrate nitrogen (NO3) of peatlands under seasonal freeze-thaw cycles; Figure S3: The variation of CH4 emission rate in peat soil under seasonal freeze-thaw conditions; Figure S4: The variation of N2O emission rate in peat soil under seasonal freeze-thaw conditions; Figure S5: (a) Bacterial Co-occurrence Network, (b) Fungal Co-occurrence Network.

Author Contributions

Formal analysis, Y.G.; Investigation, T.Y.; Data curation, J.Y.; Writing—original draft, Y.G.; Writing—review & editing, X.Y.; Supervision, X.Y.; Project administration, X.Y.; Funding acquisition, X.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Natural Science Foundation of China grant numbers 42222102, 42171107 and U24A20585, and China Postdoctoral Science Foundation grant number 2024M763242.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Grogan, P.; Michelsen, A.; Ambus, P.; Jonasson, S. Freeze-thaw regime effects on carbon and nitrogen dynamics in sub-arctic heath tundra mesocosms. Soil Biol. Biochem. 2004, 36, 641–654. [Google Scholar] [CrossRef]
  2. Yu, X.F.; Zou, Y.C.; Jiang, M.; Lu, X.G.; Wang, G.P. Response of soil constituents to freeze-thaw cycles in wetland soil solution. Soil Biol. Biochem. 2011, 43, 1308–1320. [Google Scholar] [CrossRef]
  3. Maljanen, M.; Hytönen, J.; Martikainen, P.J. Cold-season nitrous oxide dynamics in a drained boreal peatland differ depending on land-use practice. Can. J. For. Res. 2010, 40, 565–572. [Google Scholar] [CrossRef]
  4. Risk, N.; Snider, D.; Wagner-Riddle, C. Mechanisms leading to enhanced soil nitrous oxide fluxes induced by freeze-thaw cycles. Can. J. Soil Sci. 2013, 93, 401–414. [Google Scholar] [CrossRef]
  5. Cong, J.X.; Gao, C.Y.; Zhao, H.Y.; Han, D.X.; Meng, F.; Wang, G.P. Chemical stability of carbon pool in peatlands dominated by different plant types in Jilin province (China) and its potential influencing factors. Front. Ecol. Evol. 2023, 11, 12. [Google Scholar] [CrossRef]
  6. Gorham, E.; Lehman, C.; Dyke, A.; Clymo, D.; Janssens, J. Long-term carbon sequestration in North American peatlands. Quat. Sci. Rev. 2012, 58, 77–82. [Google Scholar] [CrossRef]
  7. Cong, J.X.; Gao, C.Y.; Han, D.X.; Li, Y.H.; Wang, G.P. Stability of the permafrost peatlands carbon pool under climate change and wildfires during the last 150 years in the northern Great Khingan Mountains, China. Sci. Total Environ. 2020, 712, 136476. [Google Scholar] [CrossRef]
  8. Groenevelt, P.H.; Grant, C.D. Heave and Heaving Pressure in Freezing Soils: A Unifying Theory. Vadose Zone J. 2013, 12, 11. [Google Scholar] [CrossRef]
  9. Xia, H.; Peng, Y.; Yan, W.; Ning, W. Effect of Snow Depth and Snow Duration on Soil N Dynamics and Microbial Activity in the Alpine Areas of the Eastern Tibetan Plateau. Russ. J. Ecol. 2014, 45, 263–268. [Google Scholar] [CrossRef]
  10. Feng, X.; Xia, X.; Chen, S.T.; Lin, Q.M.; Zhang, X.H.; Cheng, K.; Liu, X.Y.; Bian, R.J.; Zheng, J.F.; Li, L.Q.; et al. Amendment of crop residue in different forms shifted micro-pore system structure and potential functionality of macroaggregates while changed their mass proportion and carbon storage of paddy topsoil. Geoderma 2022, 409, 13. [Google Scholar] [CrossRef]
  11. Zhou, W.J.; Wang, Q.Z.; Fang, J.H.; Wang, K.J.; Zhao, X.Q. Study of the Mechanical and Microscopic Properties of Modified Silty Clay under Freeze-Thaw Cycles. Geofluids 2022, 2022, 9613176. [Google Scholar] [CrossRef]
  12. Matzner, E.; Borken, W. Do freeze-thaw events enhance C and N losses from soils of different ecosystems? A review. Eur. J. Soil Sci. 2008, 59, 274–284. [Google Scholar] [CrossRef]
  13. Wu, X.; Brüggemann, N.; Gasche, R.; Shen, Z.Y.; Wolf, B.; Butterbach-Bahl, K. Environmental controls over soil-atmosphere exchange of N2O, NO, and CO2 in a temperate Norway spruce forest. Glob. Biogeochem. Cycle 2010, 24, 16. [Google Scholar] [CrossRef]
  14. Brooks, P.D.; Schmidt, S.K.; Williams, M.W. Winter production of CO2 and N2O from Alpine tundra: Environmental controls and relationship to inter-system C and N fluxes. Oecologia 1997, 110, 403–413. [Google Scholar] [CrossRef]
  15. Elberling, B.; Brandt, K.K. Uncoupling of microbial CO2 production and release in frozen soil and its implications for field studies of arctic C cycling. Soil Biol. Biochem. 2003, 35, 263–272. [Google Scholar] [CrossRef]
  16. Wu, X.; Brüggemann, N.; Butterbach-Bahl, K.; Fu, B.J.; Liu, G.H. Snow cover and soil moisture controls of freeze-thaw-related soil gas fluxes from a typical semi-arid grassland soil: A laboratory experiment. Biol. Fertil. Soils 2014, 50, 295–306. [Google Scholar] [CrossRef]
  17. Panikov, N.S.; Dedysh, S.N. Cold season CH4 and CO2 emission from boreal peat bogs (West Siberia): Winter fluxes and thaw activation dynamics. Glob. Biogeochem. Cycle 2000, 14, 1071–1080. [Google Scholar] [CrossRef]
  18. Herrmann, A.; Witter, E. Sources of C and N contributing to the flush in mineralization upon freeze-thaw cycles in soils. Soil Biol. Biochem. 2002, 34, 1495–1505. [Google Scholar] [CrossRef]
  19. Groffman, P.M.; Driscoll, C.T.; Fahey, T.J.; Hardy, J.P.; Fitzhugh, R.D.; Tierney, G.L. Effects of mild winter freezing on soil nitrogen and carbon dynamics in a northern hardwood forest. Biogeochemistry 2001, 56, 191–213. [Google Scholar] [CrossRef]
  20. Hanson, R.S.; Hanson, T.E. Methanotrophic bacteria. Microbiol. Rev. 1996, 60, 439–471. [Google Scholar] [CrossRef]
  21. Thauer, R.K. Biochemistry of methanogenesis: A tribute to Marjory!Stephenson. Microbiology 1998, 144, 2377–2406. [Google Scholar] [CrossRef]
  22. Müller, C.; Martin, M.; Stevens, R.J.; Laughlin, R.J.; Kammann, C.; Ottow, J.C.G.; Jäger, H.J. Processes leading to N2O emissions in grassland soil during freezing and thawing. Soil Biol. Biochem. 2002, 34, 1325–1331. [Google Scholar] [CrossRef]
  23. Costello, E.K.; Schmidt, S.K. Microbial diversity in alpine tundra wet meadow soil: Novel Chloroflexi from a cold, water-saturated environment. Environ. Microbiol. 2006, 8, 1471–1486. [Google Scholar] [CrossRef] [PubMed]
  24. Xu, S.Q.; Wang, M.; Zhou, J.H.; Huang, Y.J.; Zhang, J.; Wang, S.Z. Soil bacteria, archaea, and enzymatic activity of natural and rewetted peatlands display varying patterns in response to water levels. Catena 2023, 228, 10. [Google Scholar] [CrossRef]
  25. Liu, Y.; Zhang, J.; Yang, W.Q.; Wu, F.Z.; Xu, Z.F.; Tan, B.; Zhang, L.; He, X.H.; Guo, L. Canopy gaps accelerate soil organic carbon retention by soil microbial biomass in the organic horizon in a subalpine fir forest. Appl. Soil Ecol. 2018, 125, 169–176. [Google Scholar] [CrossRef]
  26. Chang, X.L.; Jin, H.J.; Zhang, Y.L.; He, R.X.; Luo, D.L.; Wang, Y.P.; Lü, L.Z.; Zhang, Q.L. Thermal impacts of boreal forest vegetation on active layer and permafrost soils in northern Da Xing’anling (Hinggan) Mountains, Northeast China. Arct. Antarct. Alp. Res. 2015, 47, 267–279. [Google Scholar] [CrossRef]
  27. Wang, X.; Bai, X.Y.; Ma, L.; He, C.G.; Jiang, H.B.; Sheng, L.X.; Luo, W.B. Snow depths’ impact on soil microbial activities and carbon dioxide fluxes from a temperate wetland in Northeast China. Sci. Rep. 2020, 10, 11962. [Google Scholar] [CrossRef]
  28. Lang, M.; Cai, Z.C.; Chang, S.X. Effects of land use type and incubation temperature on greenhouse gas emissions from Chinese and Canadian soils. J. Soils Sediments 2011, 11, 15–24. [Google Scholar] [CrossRef]
  29. Butterbach-Bahl, K.; Stange, F.; Papen, H.; Li, C.S. Regional inventory of nitric oxide and nitrous oxide emissions for forest soils of southeast Germany using the biogeochemical model PnET-N-DNDC. J. Geophys. Res.-Atmos. 2001, 106, 34155–34166. [Google Scholar] [CrossRef]
  30. Vinther, F.P.; Eiland, F.; Lind, A.M.; Elsgaard, L. Microbial biomass and numbers of denitrifiers related to macropore channels in agricultural and forest soils. Soil Biol. Biochem. 1999, 31, 603–611. [Google Scholar] [CrossRef]
  31. Kværno, S.H.; Oygarden, L. The influence of freeze-thaw cycles and soil moisture on aggregate stability of three soils in Norway. Catena 2006, 67, 175–182. [Google Scholar] [CrossRef]
  32. Lovett, G.M.; Mitchell, M.J. Sugar maple and nitrogen cycling in the forests of eastern North America. Front. Ecol. Environ. 2004, 2, 81–88. [Google Scholar] [CrossRef]
  33. Christopher, S.F.; Shibata, H.; Ozawa, M.; Nakagawa, Y.; Mitchell, M.J. The effect of soil freezing on N cycling: Comparison of two headwater subcatchments with different vegetation and snowpack conditions in the northern Hokkaido Island of Japan. Biogeochemistry 2008, 88, 15–30. [Google Scholar] [CrossRef]
  34. Deluca, T.H.; Keeney, D.R.; McCarty, G.W. Effect of freeze-thaw events on mineralization of soil nitrogen. Biol. Fertil. Soils 1992, 14, 116–120. [Google Scholar] [CrossRef]
  35. Zhang, X.; Bai, W.; Gilliam, F.S.; Wang, Q.; Han, X.; Li, L. Effects of in situ freezing on soil net nitrogen mineralization and net nitrification in fertilized grassland of northern China. Grass Forage Sci. 2011, 66, 391–401. [Google Scholar] [CrossRef]
  36. Song, Y.Z.; Song, T.J.; An, Y.; Shan, L.P.; Su, X.S.; Yu, S.D. Soil ecoenzyme activities coupled with soil properties and plant biomass strongly influence the variation in soil organic carbon components in semi-arid degraded wetlands. Sci. Total Environ. 2024, 922, 11. [Google Scholar] [CrossRef] [PubMed]
  37. Mikan, C.J.; Schimel, J.P.; Doyle, A.P. Temperature controls of microbial respiration in arctic tundra soils above and below freezing. Soil Biol. Biochem. 2002, 34, 1785–1795. [Google Scholar] [CrossRef]
  38. Allaire, S.E.; Roulier, S.; Cessna, A.J. Quantifying preferential flow in soils: A review of different techniques. J. Hydrol. 2009, 378, 179–204. [Google Scholar] [CrossRef]
  39. Blanco-Canqui, H.; Lal, R. Mechanisms of carbon sequestration in soil aggregates. Crit. Rev. Plant Sci. 2004, 23, 481–504. [Google Scholar] [CrossRef]
  40. Chen, Q.; Zhao, Q.; Li, J.; Jian, S.G.; Ren, H. Mangrove succession enriches the sediment microbial community in South China. Sci. Rep. 2016, 6, 9. [Google Scholar] [CrossRef] [PubMed]
  41. Holtan-Hartwig, L.; Dörsch, P.; Bakken, L.R. Low temperature control of soil denitrifying communities: Kinetics of N2O production and reduction. Soil Biol. Biochem. 2002, 34, 1797–1806. [Google Scholar] [CrossRef]
  42. Goldberg, S.D.; Borken, W.; Gebauer, G. N2O emission in a Norway spruce forest due to soil frost: Concentration and isotope profiles shed a new light on an old story. Biogeochemistry 2010, 97, 21–30. [Google Scholar] [CrossRef]
  43. Kariyapperuma, K.A.; Furon, A.; Wagner-Riddle, C. Non-growing season nitrous oxide fluxes from an agricultural soil as affected by application of liquid and composted swine manure. Can. J. Soil Sci. 2012, 92, 315–327. [Google Scholar] [CrossRef]
  44. Hobbie, S.E.; Nadelhoffer, K.J.; Högberg, P. A synthesis: The role of nutrients as constraints on carbon balances in boreal and arctic regions. Plant Soil 2002, 242, 163–170. [Google Scholar] [CrossRef]
  45. Conant, R.T.; Steinweg, J.M.; Haddix, M.L.; Paul, E.A.; Plante, A.F.; Six, J. Experimental warming shows that decomposition temperature sensitivity increases with soil organic matter recalcitrance. Ecology 2008, 89, 2384–2391. [Google Scholar] [CrossRef]
  46. Robroek, B.J.M.; Heijboer, A.; Jassey, V.E.J.; Hefting, M.M.; Rouwenhorst, T.G.; Buttler, A.; Bragazza, L. Snow cover manipulation effects on microbial community structure and soil chemistry in a mountain bog. Plant Soil 2013, 369, 151–164. [Google Scholar] [CrossRef]
  47. Tokida, T.; Mizoguchi, M.; Miyazaki, T.; Kagemoto, A.; Nagata, O.; Hatano, R. Episodic release of methane bubbles from peatland during spring thaw. Chemosphere 2007, 70, 165–171. [Google Scholar] [CrossRef]
  48. Dutaur, L.; Verchot, L.V. A global inventory of the soil CH4 sink. Glob. Biogeochem. Cycle 2007, 21, 7949–7950. [Google Scholar] [CrossRef]
  49. Campbell, J.L.; Socci, A.M.; Templer, P.H. Increased nitrogen leaching following soil freezing is due to decreased root uptake in a northern hardwood forest. Glob. Change Biol. 2014, 20, 2663–2673. [Google Scholar] [CrossRef]
  50. Smith, J.; Wagner-Riddle, C.; Dunfield, K. Season and management related changes in the diversity of nitrifying and denitrifying bacteria over winter and spring. Appl. Soil Ecol. 2010, 44, 138–146. [Google Scholar] [CrossRef]
Figure 1. The variation characteristics of TN in peatland soil under seasonal freeze–thaw conditions (A,B). The variation characteristics of total SOC in peat soil under seasonal freeze–thaw conditions (C,D). Different lowercase letters indicate significant differences among groups (p < 0.05).
Figure 1. The variation characteristics of TN in peatland soil under seasonal freeze–thaw conditions (A,B). The variation characteristics of total SOC in peat soil under seasonal freeze–thaw conditions (C,D). Different lowercase letters indicate significant differences among groups (p < 0.05).
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Figure 2. The variation characteristics of DOC (A,B) and DON (C,D) in peat soil under seasonal freeze–thaw conditions. Different lowercase letters indicate significant differences among groups (p < 0.05).
Figure 2. The variation characteristics of DOC (A,B) and DON (C,D) in peat soil under seasonal freeze–thaw conditions. Different lowercase letters indicate significant differences among groups (p < 0.05).
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Figure 3. The variation in CO2 emission rate in peat soil under seasonal freeze–thaw conditions (A,B): Permanent permafrost and seasonal permafrost control group; (C,D): Permanent permafrost and active permafrost autumn freeze-thaw experiment group; (E,F): Permanent permafrost and active permafrost spring freeze-thaw experiment group. Different lowercase letters indicate significant differences among groups (p < 0.05).
Figure 3. The variation in CO2 emission rate in peat soil under seasonal freeze–thaw conditions (A,B): Permanent permafrost and seasonal permafrost control group; (C,D): Permanent permafrost and active permafrost autumn freeze-thaw experiment group; (E,F): Permanent permafrost and active permafrost spring freeze-thaw experiment group. Different lowercase letters indicate significant differences among groups (p < 0.05).
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Figure 4. The variation in CO2 (A,B), CH4 (C,D) and N2O (E,F) emission fluxes in peat soil under seasonal freeze–thaw cycles.
Figure 4. The variation in CO2 (A,B), CH4 (C,D) and N2O (E,F) emission fluxes in peat soil under seasonal freeze–thaw cycles.
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Figure 5. The cumulative emission fluxes of CO2 (A), CH4 (B), and N2O (C) and the global warming potential (D) of greenhouse gases.
Figure 5. The cumulative emission fluxes of CO2 (A), CH4 (B), and N2O (C) and the global warming potential (D) of greenhouse gases.
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Figure 6. Relationship diagram between bacterial community structure Circos samples and species under the number of freeze–thaw cycles (A). Analysis of the regulatory effects of freeze–thaw processes on bacterial communities and greenhouse gas emissions in peat soil (B).
Figure 6. Relationship diagram between bacterial community structure Circos samples and species under the number of freeze–thaw cycles (A). Analysis of the regulatory effects of freeze–thaw processes on bacterial communities and greenhouse gas emissions in peat soil (B).
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Figure 7. Relative abundance distribution of functional genes associated with greenhouse gas emissions in peat soil under different freeze–thaw conditions (A). Relative abundance of microbial functional genes in peat soil under freeze–thaw conditions (B).
Figure 7. Relative abundance distribution of functional genes associated with greenhouse gas emissions in peat soil under different freeze–thaw conditions (A). Relative abundance of microbial functional genes in peat soil under freeze–thaw conditions (B).
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Gong, Y.; Yang, T.; Yan, J.; Yu, X. The Influence of Seasonal Freeze–Thaw in Northeast China on Greenhouse Gas Emissions and Microbial Community Structure in Peat Soil. Water 2025, 17, 2395. https://doi.org/10.3390/w17162395

AMA Style

Gong Y, Yang T, Yan J, Yu X. The Influence of Seasonal Freeze–Thaw in Northeast China on Greenhouse Gas Emissions and Microbial Community Structure in Peat Soil. Water. 2025; 17(16):2395. https://doi.org/10.3390/w17162395

Chicago/Turabian Style

Gong, Yanru, Tao Yang, Jiawen Yan, and Xiaofei Yu. 2025. "The Influence of Seasonal Freeze–Thaw in Northeast China on Greenhouse Gas Emissions and Microbial Community Structure in Peat Soil" Water 17, no. 16: 2395. https://doi.org/10.3390/w17162395

APA Style

Gong, Y., Yang, T., Yan, J., & Yu, X. (2025). The Influence of Seasonal Freeze–Thaw in Northeast China on Greenhouse Gas Emissions and Microbial Community Structure in Peat Soil. Water, 17(16), 2395. https://doi.org/10.3390/w17162395

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