不同干扰因素对森林和湿地温室气体通量影响的研究进展

Spartina alterniflora invasions impact CH4 and N2O fluxes from a salt marsh in eastern China

Currently, there is a lack of knowledge about GHG emissions, specifically N2O and CH4, in subtropical coastal freshwater wetland and mangroves in the southern hemisphere. In this study, we quantified the gas fluxes and substrate availability in a subtropical coastal wetland off the coast of southeast Queensland, Australia over a complete wet-dry seasonal cycle. Sites were selected along a salinity gradient ranging from marine (34 psu) in a mangrove forest to freshwater (0.05 psu) wetland, encompassing the range of tidal influence. Fluxes were quantified for CH4 (range −0.4–483 mg C–CH4 h−1 m−2) and N2O (−5.5–126.4 μg N–N2O h−1 m−2), with the system acting as an overall source for CH4 and N2O (mean N2O and CH4 fluxes: 52.8 μg N–N2O h−1 m−2 and 48.7 mg C–CH4 h−1 m−2, respectively). Significantly higher N2O fluxes were measured during the summer months (summer mean 64.2 ± 22.2 μg N–N2O h−1 m−2; winter mean 33.1 ± 24.4 µg N–N2O h–1 m−2) but not CH4 fluxes (summer mean 30.2 ± 81.1 mg C–CH4 h−1 m−2; winter mean 37.4 ± 79.6 mg C–CH4 h−1 m−2). The changes with season are primarily driven by temperature and precipitation controls on the dissolved inorganic nitrogen (DIN) concentration. A significant spatial pattern was observed based on location within the study site, with highest fluxes observed in the freshwater tidal wetland and decreasing through the mangrove forest. The dissolved organic carbon (DOC) varied throughout the landscape and was correlated with higher CH4 fluxes, but this was a nonlinear trend. DIN availability was dominated by N–NH4 and correlated to changes in N2O fluxes throughout the landscape. Overall, we did not observe linear relationships between CH4 and N2O fluxes and salinity, oxygen or substrate availability along the fresh-marine continuum, suggesting that this ecosystem is a mosaic of processes and responses to environmental changes.

The main purpose of this study was to explore the dynamic changes of greenhouse gas (GHG) from grasslands under different degradation levels during the growing seasons of Inner Mongolia, China. Grassland degradation is associated with the dynamics of GHG fluxes, e.g., CO2, CH4 and N2O fluxes. As one of the global ecological environmental problems, grassland degradation has changed the vegetation productivity as well as the accumulation and decomposition rates of soil organic matter and thus will influence the carbon and nitrogen cycles of ecosystems, which will affect the GHG fluxes between grassland ecosystems and the atmosphere. Therefore, it is necessary to explore how the exchanges of CO2, CH4 and N2O fluxes between soil and atmosphere are influenced by the grassland degradation. We measured the fluxes of CO2, CH4 and N2O in lightly degraded, moderately degraded and severely degraded grasslands in Inner Mongolia of China during the growing seasons from July to September in 2013 and 2014. The typical semi-arid grassland of Inner Mongolia plays a role as the source of atmospheric CO2 and N2O and the sink for CH4. Compared with CO2 fluxes, N2O and CH4 fluxes were relatively low. The exchange of CO2, N2O and CH4 fluxes between the grassland soil and the atmosphere may exclusively depend on the net exchange rate of CO2 in semi-arid grasslands. The greenhouse gases showed a clear seasonal pattern, with the CO2 fluxes of –33.63 –386.36 mg/(m•h), CH4 uptake fluxes of 0.113–0.023 mg/(m•h) and N2O fluxes of –1.68 –19.90 μg/(m•h). Grassland degradation significantly influenced CH4 uptake but had no significant influence on CO2 and N2O emissions. Soil moisture and temperature were positively correlated with CO2 emissions but had no significant effect on N2O fluxes. Soil moisture may be the primary driving factor for CH4 uptake. The research results can be in help to better understand the impact of grassland degradation on the ecological environment.

Nitrous oxide and methane emissions from the restored mangrove ecosystem of the Ciénaga Grande de Santa Marta, Colombia

火干扰在湿地生态系统中起着重要的作用,尽管湿地占全球陆地生态系统很小一部分,却是陆地生态系统一个重要的碳汇。然而关于火干扰对我国小兴安岭森林沼泽生态系统土壤碳库影响的研究鲜有报道。因此选取两种森林沼泽典型地段进行土壤取样,研究火干扰对小兴安岭白桦(<em>Betula platyphylla</em>)沼泽和落叶松(<em>Larix gmelinii</em>)-苔草(<em>Carex schmidtii</em>)沼泽地表凋落物和土壤碳储量(0-50 cm)的影响。研究结果表明:①重度火烧使得白桦沼泽地表凋落物量和碳储量降低了36.36% (0.50 kg/m²)和35.52% (0.23 kg C/m²),而轻度火烧无显著影响;轻度火烧和重度火烧落叶松-苔草沼泽地表凋落物量和碳储量分别减少了45.32% (0.99 kg/m²)和44.66% (0.42 kg C/m²)、50.42% (1.10 kg/m²)和49.71% (0.47 kg C/m²);②白桦沼泽和落叶松-苔草沼泽两者对照样地、轻度火烧样地、重度火烧样地的土壤碳储量(0-50 cm)分别为(23.55±6.34) kg C/m²、(18.50±8.16) kg C/m²、(32.50±7.22) kg C/m²和(20.89±2.59) kg C/m²、(23.52±16.03) kg C/m²、(21.75±6.60) kg C/m²,然而火干扰对两种森林沼泽土壤碳储量(0-50 cm)影响不显著。研究结果可为我国东北开展森林湿地计划火烧和碳管理提供理论依据。;Fire disturbance plays an important role in wetland ecosystems. Although wetlands account for a small percentage of the earth's land surface, they are an important global terrestrial carbon sink. A large amount of carbon stored in wetland soils could be released as carbon dioxide into the atmosphere after fire and this could have a significant impact on global warming. It is for these reasons that soil carbon storage in wetlands after fire disturbance has attracted much research attention in recent years. Previous studies on the influence of fire disturbance on forested swamp ecosystems in the Xiaoxing'an Mountains of Northeast China have lacked adequate reports. Therefore, the objective of this study was to describe both the litter mass and soil carbon storage changes after fire disturbance in two different forested swamp ecosystems to provide a theoretical basis for restoration of forested swamp ecosystems and sustainable wetland management. Soil samples from<em> Betula platyphylla</em> and<em> Larix gmelinii-Carex schmidtii </em>forested swamps in the Xiaoxing'an Mountains of Northeast China were collected from plots disturbed by different intensities of fire and control plots to comprehensively investigate the effects of fire disturbance on litter mass and soil carbon storage (within 0-50 cm depth) of the ecosystems. The results showed the following: 1) The surface litter mass of the control plots, the low intensity fire plots and the high intensity fire plots were 1.37 kg/m² (0.65 kg C/m²), 1.36 kg/m² (0.62 kg C/m²), and 0.87 kg/m² (0.42 kg C/m²), respectively, in the<em> B. platyphylla</em> swamps and 2.19 kg/m² (0.94 kg C/m²), 1.20 kg/m² (0.52 kg C/m²), and 1.09 kg/m² (0.47 kg C/m²), respectively, in the<em> L. gmelinii-C. schmidtii </em>swamps. The surface litter mass and carbon storage in the <em>B. platyphyll</em> swamp decreased by 36.36% (0.50 kg/m²) and 35.52% (0.23 kg C/m²), respectively, after high intensity fire disturbance but no significant changes were detected after low intensity fire disturbance. The surface litter mass and carbon storage of the <em>L. gmelinii-C. schmidtii </em>swamps decreased by 45.32% (0.99 kg/m²) and 44.66% (0.42 kg C/m²), respectively, after low intensity fire disturbance and 50.42% (1.10 kg/m²) and 49.71% (0.47 kg C/m²), respectively, after high intensity fire disturbance. 2) The soil carbon storage of the control plots, low intensity fire plots and high intensity fire plots was (23.55±6.34) kg C/m², (18.50±8.16) kg C/m², and (32.50±7.22) kg C/m², respectively, in the <em>B. platyphylla</em> swamps and (20.89±2.59) kg C/m², (23.52±16.03) kg C/m², and (21.75±6.60) kg C/m², respectively, in the <em>L. gmelinii-C. schmidtii</em> swamps. There was no significant difference between different sampling plots at 0-50 cm depth. However the soil carbon storage of the high intensity fire plots at 0-10 cm in the<em> L. gmelinii-C. schmidtii </em>swamps was decreased by 62.58% (4.61 kg C/m²) and 60.51% (4.22 kg C/m²) compared with the control plots and low intensity fire plots, respectively, at the same depth. There were significant (<em>P<</em>0.01) differences between the high intensity fire plot and the control plot and between the high intensity fire plot and low intensity fire plot (<em>P</em><0.01). This study aimed to provide useful information for the carbon management and prescribed fire disturbance in the development of the forested wetland ecosystems in Northeast China.

Simulated NH4+-N Deposition Inhibits CH4 Uptake and Promotes N2O Emission in the Meadow Steppe of Inner Mongolia, China

Using high-frequency soil oxygen sensors to predict greenhouse gas emissions from wetlands

Measuring and modeling the effects of drainage water management on soil greenhouse gas fluxes from corn and soybean fields

Methane (CH4) and nitrous oxide (N2O) substantially contribute to global greenhouse gas (GHG) emissions together with carbon dioxide (CO2). To understand their impact on future climate change, prioritizing the study of CH4 and N2O fluxes becomes critical. Forest ecosystems, primarily investigated for CO2 exchange, are less explored concerning their exchange of CH4 and N2O. Forests are known to be sinks for CH4, while their role in N2O fluxes varies, acting as either sources or sinks. However, comprehensive studies that concurrently examine CH4 and N2O fluxes in forests, particularly over extended periods and at high elevation, remain scarce. At high altitudes, measuring GHG fluxes with chambers during snowy periods is challenging, leading to a lack of winter flux data which are crucial for understanding flux dynamics related to freeze-thaw cycles and snow patterns. This study addresses this gap by investigating long-term CH4 and N2O fluxes in a subalpine Norway spruce forest (Davos, CH-Dav, ICOS Class 1 Ecosystem station, Switzerland), encompassing both soil and canopy interactions with the atmosphere.Over five years (2017, 2020-2023 for CH4; 2017, 2020 for N2O), we employed automatic chambers to measure forest-floor fluxes, complemented by below-canopy eddy covariance CH4 flux measurements starting from May 2023, as well as static chamber measurements in 2023. Our research objectives were to 1) characterize the magnitude and seasonal dynamics of CH4 and N2O forest-floor fluxes, and 2) compare CH4 fluxes using chamber and eddy covariance techniques to better understand the interaction of soil and vegetation with the atmosphere.We hypothesized that the forest floor primarily acts as a net sink for CH4, with soil temperature and snow dynamics being important drivers due to their impact on microbial activity and diffusion rates between soil and atmosphere. Given the low nitrogen availability at the study site, we anticipated very low N2O emissions. Additionally, we hypothesized that comparing CH4 fluxes from chambers and eddy covariance would reveal small differences in their magnitudes, attributable to the distinct measurement scales and scopes of these two techniques. Our results confirmed the forest floor as a consistent CH4 sink, exhibiting substantial short-term fluctuations driven predominantly by air temperature and snow cover. N2O fluxes were negligible over the two-year observation period. Our study contributes to a deeper understanding of how environmental drivers and seasonal dynamics influence CH4 and N2O fluxes in high-elevation forests.

Context Conversion of grasslands to croplands can usually result in the degradation of soils and increased greenhouse gas (GHG) emissions such as carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). However, little is known about the impacts of grassland conversion to recently tilled croplands on soils and GHG fluxes. Aims A field experiment was established in 2016 to evaluate the impacts of grassland conversion to tilled cropland under different landscape positions (upslope, backslope, and footslope) on select soil properties and soil GHG fluxes. Key results The findings showed that the grassland conversion significantly increased soil bulk density and electrical conductivity but reduced pH and total nitrogen (TN). The conversion impacted soil biome community grassland and tilled croplands. The landscape position significantly impacted soil pH (footslope &lt; upslope) and TN (footslope &gt; upslope). The grassland conversion significantly decreased soil CO2 fluxes, but increased soil CH4 and N2O fluxes. The landscape position significantly impacted soil CO2 (footslope &gt; upslope and backslope) and CH4 (upslope &gt; footslope and backslope) fluxes for some periods. Soil CO2 and N2O fluxes generally followed upward and downward trends over time, respectively. Conclusions These results indicate that grassland conversion was able to lose soil N, increase soil compaction, acidity, salts, and soil N2O and CH4 fluxes, and decrease the diversity of abundant genera and CO2 fluxes. Footslope increased TN, soil acidity, CO2, and CH4 fluxes, compared with upslope and backslope. CO2 fluxes under grassland and tilled cropland significantly increased over time, whereas N2O fluxes under grassland significantly reduced. Implications Conversion of grassland to tilled cropland significantly impacted on sol quality. It caused a loss in soil N and increased soil compaction, acidity and salts. Grassland conversion also decreased the abundance and diversity soil microbiome.

Plants have been suggested to have significant effects on methane (CH4) and nitrous oxide (N2O) fluxes from littoral wetlands, but it remains unclear in subtropical lakes. We conducted in situ measurement of CH4 and N2O fluxes for two years. To distinguish between the effects of shoots and roots, three treatments (i.e., intact plants as control, shoot clipping, and root exclusion) were used. Effects of plant biomass, temperature, and soil moisture on CH4 and N2O fluxes were analyzed. The mean ecosystem CH4 emission rate was 36 μg CH4 m−2 h−1 for drying periods, but 8219 μg CH4 m−2 h−1 for drying-wetting transition periods. CH4 fluxes were positively correlated with below-ground and total biomass, but not with above-ground biomass. Clipping did not significantly alter CH4 flux rate, but root exclusion decreased the CH4 flux by 116 % as compared to the control. N2O emissions were similar for both the drying and drying-wetting transition periods, with a mean rate of 20 μg N2O m−2 h−1. Both clipping and root exclusion significantly increased N2O fluxes as compared to the control. There was no significant correlation between CH4 and N2O fluxes. Roots dominated plant-mediated enhancement in CH4 fluxes, but played almost an equal role as shoots in plant-regulated suppression on N2O fluxes in this Carex meadow during drawdown periods.

Fluxes of nitrous oxide and methane in different coastal Suaeda salsa marshes of the Yellow River estuary, China

IntroductionFarmlands are key sources of greenhouse gas (GHG) emissions, which are susceptible to changes in precipitation regimes. The soils of seasonal fallow contribute approximately half of annual GHG emissions from farmlands, but the effect of precipitation frequency on soil GHG emissions from seasonal fallow croplands remains virtually unknown.Materials and MethodsWe conducted a microcosm study to evaluate the response of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes from typical paddy and upland soils to the changes in watering frequency simulating precipitation scenarios of subtropical regions during seasonal fallow. We also analyzed changes of soil properties and biotic characteristics associated with GHG emissions, including abundances of soil denitrifiers (nirK, nirS, nosZI and nosZII genes), methanotrophs (pmoA gene) and methanogens (mcrA gene) to altered watering frequency.ResultsIncreased watering frequency led to overall increases in soil N2O and CO2 fluxes compared with low frequency. Compared with low frequency, high watering frequency decreased CH4 flux from the paddy soil by 3.5 times, while enhanced CH4 flux from the upland soil by 60%. Furthermore, the increased watering frequency had positive effects on cumulative N2O and CO2 fluxes from the upland soil, whereas no similar trend was observed for the paddy soil. Hierarchical partitioning analyses showed that N2O fluxes from the paddy soil were mostly related to nitrogen availability, and mcrA gene abundance had more than 90% of relative independent effects on CH4 and CO2 fluxes from the paddy soil. For the upland soil, nosZ (60.34%), pmoA (53.18%) and nir (47.07%) gene abundances were important predictors of N2O, CH4 and CO2 fluxes, respectively.ConclusionOur results demonstrate that increased watering frequency facilitates GHG emissions by changing soil properties and functional gene abundances. These findings provide new insights into GHG fluxes from seasonal fallow croplands in response to altered precipitation patterns.

Quantifying and predicting spatio-temporal variability of soil CH4 and N2O fluxes from a seemingly homogeneous Australian agricultural field

Complete annual CO2, CH4, and N2O balance of a temperate riparian wetland 12 years after rewetting