Soil CH4 Uptake Research Articles

Dissolved organic matter and inorganic N jointly regulate greenhouse gases fluxes from forest soils with different moistures during a freeze-thaw period

ABSTRACT Antecedent soil moisture before freezing can affect greenhouse gases (GHG) fluxes from soils during thaw, but their critical threshold values for GHG fluxes and the underlying mechanisms are still not clear. By using packed soil-core incubation experiments, we have studied nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) fluxes from a mature broadleaf and Korean pine-mixed forest soil and an adjacent white birch forest soil with nine levels of soil moisture ranging from 10 to 90% water-filled pore space (WFPS) during a 2-month freezing at −8°C and the following 10-day thaw at 10°C. The threshold values of soil moisture ranged from 50 to 70% WFPS for CH4 uptake and from 70 to 90% WFPS for N2O and CO2 emissions from the two soils during the freeze-thaw period. Under the optimum soil moisture condition, fulvic-like compounds with high bioavailability contributed more than 60% of dissolved organic matter (DOM) in the soil. Cumulative N2O emissions from forest soils during the freeze-thaw period were greatest when the concentration ratio of nitrate-N to dissolved organic carbon (DOC) was 0.04 g N g−1 C. Cumulative soil CO2 emissions and CH4 uptake during the freeze-thaw period were both regulated by the interaction between soil DOC and net N mineralization. The activities of β-1,4-glucosidase and β-1,4-N-acetyl-glucosaminidase, microbial biomass C and N, and the microbial biomass C-to-N ratios, were all significantly correlated to the soil N2O, CO2, and CH4 fluxes. Overall, upon a freeze-thaw period with different soil moistures, GHG fluxes from forest soils were jointly regulated by inorganic N and DOC concentrations, and related to the labile components of DOM released into the soil, which could be strictly controlled by the related microbial properties.

Effect of Woodchips Biochar on Sensitivity to Temperature of Soil Greenhouse Gases Emissions

Research Highlights: Biochar is the carbonaceous product of pyrolysis or the gasification of biomass that is used as soil amendment to improve soil fertility and increase soil carbon stock. Biochar has been shown to increase, decrease, or have no effect on the emissions of greenhouse gases (GHG) from soil, depending on the specific soil and biochar characteristics. However, the temperature sensitivity of these gas emissions in biochar-amended soils is still poorly investigated. Background and Objectives: A pot experiment was set up to investigate the impact of woodchips biochar on the temperature sensitivity of the main GHG (CO2, CH4, and N2O) emissions from soil. Materials and Methods: Nine pots (14 L volume) were filled with soil mixed with biochar at two application rates (0.021 kg of biochar/kg of soil and 0.042 kg of biochar/kg of soil) or with soil alone as the control (three pots per treatment). Pots were incubated in a growth chamber and the emissions of CO2, CH4, and N2O were monitored for two weeks with a cavity ring-down gas analyzer connected to three closed dynamic chambers. The temperature in the chamber increased from 10 °C to 30 °C during the first week and decreased back to 10 °C during the second week, with a daily change of 5 °C. Soil water content was kept at 20% (w/w). Results: Biochar application did not significantly affect the temperature sensitivity of CO2 and N2O emissions. However, the sensitivity of CH4 uptake from soil significantly decreased by the application of biochar, reducing the CH4 soil consumption compared to the un-amended soil, especially at high soil temperatures. Basal CO2 respiration at 10 °C was significantly higher in the highest biochar application rate compared to the control soil. Conclusions: These results confirmed that the magnitude and direction of the influence of biochar on temperature sensitivity of GHG emissions depend on the specific GHG considered. The biochar tested in this study did not affect soil N2O emission and only marginally affected CO2 emission in a wide range of soil temperatures. However, it showed a negative impact on soil CH4 uptake, particularly at a high temperature, having important implications in a future warmer climate scenario and at higher application rates.

Effects of artificial nitrogen addition and reduction in precipitation on soil CO2 and CH4 effluxes and composition of the microbial biomass in a temperate forest

AbstractTo understand the effects of artificially increased atmospheric nitrogen (N) and decreased precipitation on the soil microbial community and soil CO2 and CH4 efflux, a two‐factorial field experiment was carried out with the following treatments: (a) control, (b) N addition (+50 kg N ha−1 year−1), (c) decreased precipitation (−30% of throughfall) and (d) combined N addition and decreased precipitation (+50 kg N ha−1 year−1, −30% of throughfall). The N addition and decreased precipitation treatments had a positive effect on mean CO2 efflux (2.61 μmol CO2 m−2 s−1 for control, 4.26 μmol CO2 m−2 s−1 for N addition, 3.62 μmol CO2 m−2 s−1 for reduction in precipitation) and mean rates of CH4 uptake (0.00088 μmol CH4 m−2 s−1 for control, 0.00154 μmol CH4 m−2 s−1 for N addition, 0.00151 μmol m−2 s−1 for reduction in precipitation) during the growing season. The combined N addition and reduction in precipitation also led to increased soil CO2 efflux and CH4 uptake, but the combined response was weaker than the response to single variable treatments (3.10 μmol CO2 m−2 s−1 and 0.00130 μmol CH4 m−2 s−1 interaction), indicating antagonistic effects of the combined treatment. At the seasonal scale, changes in soil CO2 and CH4 efflux were complex, especially in the spring freezing and thawing period, during which pulses of CO2 efflux and CH4 uptake occurred. Decreased precipitation altered the composition of the bacterial community in the winter and growing seasons, and composition of the microbial community also showed a seasonal change. However, changes in microbial community structure under N addition, precipitation reduction and their interaction might be important factors leading to an increase or decrease in soil carbon efflux.Highlights How global changes (N addition and decreased precipitation) affect soil C flux. Seasonal effects of global changes on soil C flux were analysed quantitatively. Decreased precipitation and N‐addition increased soil CO2 flux and decreased soil CH4 flux. Global changes regulate soil C flux by altering soil water, microbial and nutrient status.

Moderate grazing increases the abundance of soil methane-oxidizing bacteria and CH4 uptake rate in a typical steppe of Inner Mongolia, China.

Microbial oxidation is the only biological sink of atmospheric methane (CH4). It is essential to understand the variation of CH4 fluxes among different grassland use types for developing low-emission management system. Here, we measured the CH4 flux and the soil methane-oxidizing bacteria abundance in a typical steppe under grazing, mowing and fencing management in central Inner Mongolia, with the aims to determine the effects of these grassland use types on CH4 flux, and to test the hypothesis that pmoA functional gene abundance regulates CH4 fluxes. The measurements were conducted on the experimental grassland that had experienced four grassland use treatments over five years. The treatments were whole growing season grazing from May to September (T1), spring and summer grazing (twice in May and July)(T2), autumn mowing (T3) and enclosure (T0). We measured CH4 flux using static chamber method, and quantified the abundance of pmoA functional genes using molecular techniques. Moreover, we measured plant biomass and soil physicochemical properties. The results showed that moderate grazing significantly enhanced CH4 uptake rate and the methane-oxidizing bacteria abundance (i.e., the pmoA gene copy number per gram of dry soil). The pmoA gene copy number ranged from 6.9×104 to 3.9×105 per gram of dry soil in growing season. The CH4 uptake rate was (68.21±3.01) μg·m-2·h-1 under T1, which was 22.1%, 37.5% and 30.9% higher than that under T2, T3 or T0 , respectively. The CH4 uptake rate was positively correlated with abundance of CH4 oxidizing bacteria and soil sand content, but negatively correlated with soil silt content, soil moisture, NH4+-N and NO3--N content, and plant biomass. These results suggested that the steppe ecosystem is a CH4 sink under all land-use types in central Inner Mongolia, and that moderate grazing would enhance methane-oxidizing bacteria abundance and CH4 uptake by improving soil sand content, reducing soil mineral nitrogen content and plant production in the typical steppe ecosystem. These results were of significance for the development of low-emission grassland management system.

Short-term responses of greenhouse gas emissions and ecosystem carbon fluxes to elevated ozone and N fertilization in a temperate grassland

Growing evidence suggests that tropospheric ozone has widespread effects on vegetation, which can contribute to alter ecosystem carbon (C) dynamics and belowground processes. In this study, we used intact soil mesocosms from a semi-improved grassland and investigated the effects of elevated ozone, alone and in combination with nitrogen (N) fertilization on soil-borne greenhouse gas emissions and ecosystem C fluxes. Ozone exposure under fully open-air field conditions was occurred during the growing season. Across a one-year period, soil methane (CH4) and nitrous oxide (N2O) emissions did not differ between treatments, but elevated ozone significantly depressed soil CH4 uptake by 14% during the growing season irrespective of N fertilization. Elevated ozone resulted in a 15% reduction of net ecosystem exchange of carbon dioxide, while N fertilization significantly increased ecosystem respiration during the growing season. Aboveground biomass was unaffected by elevated ozone during the growing season but significantly decreased by 17% during the non-growing season. At the end of the experiment, soil mineral N content, net N mineralization and extracellular enzyme activities (i.e., cellobiohydrolase and leucine aminopeptidase) were higher under elevated ozone than ambient ozone. The short-term effect of single application of N fertilizer was primarily responsible for the lack of the interaction between elevated ozone and N fertilization. Therefore, results of our short-term study suggest that ozone exposure may have negative impacts on soil CH4 uptake and C sequestration and contribute to accelerated rates of soil N-cycling.

Impact of 13-years of nitrogen addition on nitrous oxide and methane fluxes and ecosystem respiration in a temperate grassland

Nitrogen (N) fertilizer application and atmospheric N deposition will profoundly affect greenhouse gas (GHGs) emissions, especially nitrous oxide (N2O) and methane (CH4) fluxes and ecosystem respiration (Re, i.e. CO2 emissions). However, the impacts of long-term N inputs and the often associated N-induced soil acidification on GHG fluxes in arid and semi-arid ecosystems, especially temperate grasslands, are still uncertain. An in situ experiment was conducted to investigate the effect of long-term (13-years) N addition on N2O and CH4 fluxes and Re from a temperate grassland in Inner Mongolia, northeast China, from April 2017 to October 2018. Soil pH values in the 0–5 cm layer receiving 120 (N120) and 240 (N240) kg N ha−1 decreased from 7.12 to 4.37 and 4.18, respectively, after 13 years of N inputs. Soil CH4 uptake was significantly reduced, but N2O emission was enhanced significantly by N addition. However, N addition had no impact on Re. Structural Equation Modeling indicated that soil NH4+-N content was the dominant control of N2O emissions, but with less effect of the decreasing pH. In contrast, CH4 uptake was generally controlled by soil pH and NO3−-N content, and Re by forb biomass. The measured changes in N2O and CH4 fluxes and Re from temperate grassland will have a profoundly impact on climate change.

Characteristics of annual greenhouse gas flux and NO release from alpine meadow and forest on the eastern Tibetan Plateau

The importance of the world’s largest plateau (i.e., the Tibetan Plateau) as a source/sink for atmospheric greenhouse gases (GHGs) still remains uncertain as field observations covering entire years and contrasting ecosystems are scarce. Here we report on year-round measurements of methane (CH4), nitrous oxide (N2O) and nitric oxide (NO) fluxes from two representative ecosystems (cattle-grazed meadow and natural forest, >3300 m a.s.l) on the eastern Tibetan Plateau. In our study, the alpine soils generally functioned as sinks for atmospheric CH4. The pronounced seasonality of CH4 uptake, with higher uptake in the growing season and lower uptake in the non-growing season, was mainly regulated by the combined changes in soil moisture and temperature. Soil CH4 uptake was lower at the meadow site due to high soil moisture and grazing-induced soil compaction reducing gas diffusivity and hampering CH4 uptake. For the alpine meadow pulses of N-oxide fluxes were observed during the freeze-thaw period, while freeze-thaw related pulses did not occur at the forest site, where the seasonality of N-oxide fluxes was primarily regulated by changes in soil temperature (Q10 = 3.0). Annual cumulative fluxes for the meadow and forest ecosystems ranged between −1.15 and −2.24 kg CH4-C ha−1 yr−1, 0.13-0.65 kg N2O-N ha−1 yr−1 and 0.022-0.047 kg NO-N ha−1 yr−1. Non-growing season fluxes contributed 34–45% and 21–51% to the annual budgets of CH4 and N-oxides, respectively. Multiple regression analyses showed that soil N-oxide fluxes were significantly positively correlated to concentrations of soil dissolved organic C (DOC) and inorganic N, with DOC and inorganic N concentrations being higher at the forest site. Our study also shows that alpine forest is a stronger source for non-CO2 GHGs relative to alpine meadow (higher by 195 kg CO2-eq ha−1 yr−1). This difference in GHG fluxes significantly offsets the net climate benefits due to increased C-sequestration associated with afforestation/reforestation.

CH4 Uptake in Different Saline-alkaline Soils in Hetao Irrigation District, Inner Mongolia

Soil salinization poses a great threat to sustainable land use and the limitation of greenhouse gas emissions. In this study, three saline alkali soils, saline soil[electrical conductivity (EC) 4.80 dS·m-1], high saline-alkaline soil (EC 2.60 dS·m-1), and low saline-alkaline soil (EC 0.74 dS·m-1) in the Hetao Irrigation District of Inner Mongolia were selected as research plots. Field experiments were conducted to study the uptake of methane (CH4) in the crop-growing season (April-October) for three years (2014-2016) using the static box method. There were significant differences in the soil CH4 uptake among the soil types in 2014 (F=18.0, P<0.001), 2015 (F=23.6, P<0.001), and 2016 (F=28.4, P<0.001). The uptake of CH4 by the soil decreases with increasing soil salinity. The accumulated CH4 uptake was 150.0 mg·m-2, 119.6 mg·m-2, and 99.9 mg·m-2 in the low saline-alkaline, high saline-alkaline, and saline soil in 2014, respectively. The cumulative uptake of CH4 was 27%, 28%, and 19% lower in the high saline-alkaline soil and 35%, 35%, and 53% lower in the saline soil than in the low saline-alkaline soil in 2014, 2015, and 2016, respectively. Redundancy analysis shows that the projection of the CH4 uptake flux and EC of saline-alkaline soil are in the positive direction, and in the opposite direction to the first principal component axis. The higher the soil EC, the lower the CH4 uptake flux. Soil EC was found to be the key factor controlling the uptakes of CH4, with a correlation coefficient (r) of -0.8809 (P<0.01, n=9).

Unimodal Response of Soil Methane Consumption to Increasing Nitrogen Additions.

Nitrogen (N) status has a great impact on methane (CH4) consumption by soils. Modeling studies predicting soil CH4 consumption assume a linear relationship between CH4 uptake and N addition rate. Here, we present evidence that a nonlinear relationship may better characterize changes in soil CH4 uptake with increasing N additions. By conducting a field experiment with eight N-input levels in a Tibetan alpine steppe, we observed a unimodal relationship; CH4 uptake increased at low to medium N levels but declined at high N levels. Environmental and microbial properties jointly determined this response pattern. The generality of the unimodal trend was further validated by two independent analyses: (i) we examined soil CH4 uptake across at least five N-input levels in upland ecosystems across China. A unimodal CH4 uptake-N addition rate relationship was observed in 3 out of 4 cases; and (ii) we performed a meta-analysis to explore the N-induced changes in soil CH4 uptake with increasing N additions across global upland ecosystems. Results showed that the changes in CH4 uptake exhibited a quadratic correlation with N addition rate. Overall, we suggest that the unimodal relationship should be considered in biogeochemistry models for accurately predicting soil CH4 consumption under global N enrichment.

Responses of soil greenhouse gas emissions to different application rates of biochar in a subtropical Chinese chestnut plantation

Biochar application has been proposed as an effective measure to mitigate greenhouse gas (GHG) emissions from soil. However, the effects of different biochar application rates on soil GHG emissions and their linkages with biochar-induced changes in soil environmental factors remain unclear in managed plantations. This study examined the responses of soil GHG emissions to different application rates of bamboo leaf biochar in a Chinese chestnut plantation. A two-year field trial was conducted to determine the changes in soil GHG emissions and key soil properties over time in B0 (control), B2, B5 and B10 treatments, representing biochar application rates of 0, 2, 5 and 10 t ha−1, respectively. Biochar application significantly (P < 0.05) decreased soil N2O emissions (from 2.60 to 2.11 t ha−1 yr−1) and increased soil CH4 uptake (from 3.13 to 4.22 t ha−1 yr−1), but did not change soil CO2 emissions. The biochar inhibition effect on soil GHG emissions increased with increasing biochar application rates, with greater inhibition in the first year than in the second year. Biochar application also decreased the concentrations of soil NH4+-N, NO3–-N and water-soluble organic N (WSON), but increased the concentrations of water-soluble organic C (WSOC) and microbial biomass C (MBC). Regardless of the treatments, the soil GHG emissions were significantly (P < 0.01) correlated with soil temperature, but not with soil moisture content. Soil CO2 and N2O emissions, and soil CH4 uptake were positively (P < 0.05) correlated with WSOC concentration under the B0, B2 and B5 treatments only. A significant relationship (P < 0.05) was observed between soil MBC and soil CO2 emissions (only for the B0 and B2 treatments), and soil MBC and soil N2O emissions (only for the B0, B2 and B10 treatments). The results suggest that biochar application rates can alter the relationships between GHG emissions and soil WSOC and MBC concentrations. The soil N2O emissions were positively (P < 0.05) correlated with the NH4+-N, NO3−-N and WSON concentrations in all treatments. This study demonstrated that the management practice (i.e. biochar application to soil) decreased soil GHG emissions in a Chinese chestnut plantation via changes in key soil properties, with implications for the mitigation of soil GHG emissions in subtropical plantations.

Effects of global change on methane uptake in forest soils and its mechanisms: A revie

Elevated atmospheric CO2 concentration, altered precipitation regime, increased nitrogen deposition, and land cover change have not only changed the physical and chemical properties of forest soils, but also affected plant growth and microbial activity, with concequences on soil carbon and nitrogen cycles, including soil CH4 uptake. In this study, we summarized the important role of soil CH4 uptake in forests under global change scenarios. The differences of responses as well as the underlying mechanisms of soil CH4 uptake in forests to global change were reviewed. Elevated atmospheric CO2 concentration inhibits soil CH4 uptake. Reduced precipitation tends to promote soil CH4 uptake. Increased nitrogen input inhibits soil CH4 uptake in nitrogen-rich forests, but promotes or has no effects on soil CH4 uptake in nitrogen-poor forests. Conversion of forests to grassland, farmland, or plantations would reduce soil CH4 uptake, while afforestation increases soil CH4 uptake. The future research should explore the long-term and multiple effects of global changes on forest soil CH4 uptake. In addition, molecular biology methods should be developed to explore the microbial mechanism of soil CH4 uptake.

Afforestation and deforestation enhanced soil CH4 uptake in a subtropical agricultural landscape: Evidence from multi-year and multi-site field experiments

The impact of afforestation and deforestation on the carbon cycle and carbon sequestration in agricultural landscape has been well studied, while the direction and magnitude of the effects on soil CH4 fluxes remain uncertain in particular in the subtropical region. Thus, multi-site and multi-year field experiments were conducted to measure soil CH4 fluxes from an afforestation chronosequence (cropland [wheat-maize rotation], 15-year old forest, 20-year old forest and 30-year forest) and a deforestation chronosequence (secondary forest, grassland, cropland without fertilization and cropland with fertilization [wheat-maize rotation]) in a subtropical agricultural landscape from 2012 to 2017. The soil at all land uses functioned exclusively as a sink for atmospheric CH4 through the whole experimental years. Soil CH4 uptakes showed great seasonal and inter-annual variations along with those of temporal patterns of soil environmental variables. At the afforestation chronosequence, annual CH4 uptake rates averaged 1.37, 1.68, 1.80 and 2.97 kg C ha−1 yr−1 for cropland, 15-year old forest, 20-year old forest and 30-year old forest. Compared to cropland, afforestation increased annual CH4 uptake by 23 to 117%. Soil CH4 uptake decreased with increasing soil content, soil NH4+ content and soil NO3− content but increased with increasing soil DOC content at the afforestation chronosequence (P < 0.05). At the deforestation chronosequence, annual CH4 uptake rates were 1.37, 1.70, 1.77 and 2.01 kg C ha−1 yr−1 for secondary forest, grassland, cropland without fertilization and cropland with fertilization. Compared to secondary forest, deforestation increased annual CH4 uptake by 24 to 47%. Soil CH4 uptakes were negatively correlated with soil water content and positively correlated with soil NO3− content. We conclude that both afforestation and deforestation have the potential to increase the sink capacities of atmospheric CH4 in the subtropical agricultural landscape and consequently provide the negative feedbacks to climate system.

不同恢复方式下大兴安岭重度火烧迹地林地土壤温室气体通量

PDF HTML阅读 XML下载 导出引用 引用提醒 不同恢复方式下大兴安岭重度火烧迹地林地土壤温室气体通量 DOI: 10.5846/stxb201809111952 作者: 作者单位: 东北林业大学林学院,东北林业大学,东北林业大学林学院,东北林业大学林学院 作者简介: 通讯作者: 中图分类号: 基金项目: 重度退化生态系统恢复与重建关键技术研究与示范（2011BAD08B02） Greenhouse gas emissions from woodland soils in a severely burned area under different restoration methods in the Greater Khingan Mountains Author: Affiliation: College of Forestry,Northeast Forestry University,College of Forestry,Northeast Forestry University,College of Forestry,Northeast Forestry University,College of Forestry,Northeast Forestry University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为研究大兴安岭重度火烧迹地在不同恢复方式下林地土壤CO2、CH4和N2O排放特征及其影响因素，采用静态箱/气相色谱法，在2017年生长季（6月-9月）对3种恢复方式（人工更新、天然更新和人工促进天然更新）林地土壤温室气体CO2、CH4、N2O通量进行了原位观测。研究结果表明：（1）3种恢复方式林地土壤在生长季均为大气CO2、N2O的源，CH4的汇；生长季林地土壤CO2排放通量大小关系为人工促进天然更新（（634.40±246.52）mg m-2 h-1） > 人工更新（（603.63±213.22）mg m-2 h-1） > 天然更新（（575.81±244.12）mg m-2 h-1），3种恢复方式间无显著差异；人工更新林地土壤CH4吸收通量显著高于人工促进天然更新；天然更新林地土壤N2O排放通量显著高于其他两种恢复方式。（2）土壤温度是影响3种恢复方式林地土壤温室气体通量的关键因素；土壤水分仅对人工更新林地土壤N2O通量有极显著影响（P < 0.01）；3种恢复方式林地土壤CO2通量与大气湿度具有极显著的响应（P < 0.01）；土壤pH仅与天然更新林地土壤CO2通量显著相关（P < 0.05）；土壤全氮含量仅与人工促进天然更新林地土壤CH4通量显著相关（P < 0.05）。（3）基于100年尺度，由3种温室气体计算全球增温潜势得出，人工促进天然更新（1.83×104 kg CO2/hm2） > 人工更新（1.74×104 kg CO2/hm2） > 天然更新（1.67×104 kg CO2/hm2）。（4）阿木尔地区林地土壤年生长季CO2和N2O排放量为8.85×106 t和1.88×102 t，CH4吸收量为1.05×103 t。 Abstract:Global climate change is the focus of humanity's attention. Greenhouse gases (GHG) are a crucial element of this focus. Forests are important for contributing to the maintenance of ecological balance, and forest soils are an important source and sink of GHG to the atmosphere. The study of the GHG from forest soil and its influence factors could assist the deceleration of global warming is highly significant. The Greater Khingan Mountains are often affected by fire and the restoration of severely degraded ecosystems has always been a focus of experts' attention. In 1987, the forest resources were severely damaged in the Greater Khingan Mountains and owing to short growth seasons and cold weather, the local ecological environment had difficulty recovering. The restoration methods affected the soil properties and vegetation of these degraded ecosystems. In order to know the effects of different restoration methods on woodland soil GHG (CO2, CH4 and N2O) emissions, we used a gas static chamber-GC technique to observe the soil GHG in situ from June to September in 2017. The results showed that in the growing season, the forest soil of three restoration methods was the source of atmospheric CO2 and N2O, and the sink of CH4. In the growing season, the woodland soil CO2 emission flux of artificial promotion of natural regeneration ((634.40±246.52) mg m-2 h-1) was greater than artificial regeneration ((603.63±213.22) mg m-2 h-1) and natural regeneration ((575.81±244.12) mg m-2 h-1). There was no significant difference between the three recovery methods. The woodland soil CH4 uptake flux of the artificial regeneration was significantly higher than that of the artificial promotion of natural regeneration. The emissions of N2O from the woodland soil of natural regeneration were significantly higher than the other two restoration methods. During the growing season, the woodland soil greenhouse gas fluxes of the three vegetation recovery methods were markedly different. Soil temperature was the key factor affecting the woodland soil greenhouse gas fluxes of the three vegetation recovery methods. Soil moisture had a significant effect on N2O fluxes of artificially regenerated soils (P < 0.01). The CO2 flux of woodland soil had a very significant response to atmospheric humidity. The soil pH value was significantly correlated only with the CO2 flux from the naturally regenerated woodland soil (P < 0.05) and the total nitrogen content in the soil was only significantly related to the CH4 flux of woodland soil from the artificial promotion of natural regeneration (P < 0.05). Based on the centennial scale, we calculated the global warming potential (GWP) from three greenhouse gases in three recovery modes. The contribution potential of greenhouse effects in the artificial promotion of natural regeneration was 1.83×104 kg CO2/hm2, and in artificial and natural regeneration were 1.74×104 and 1.67×104 kg CO2/hm2, respectively. The CO2 and N2O emissions of forest soils in the Amuer region were 8.85×106 t and 1.88×102 t and the absorption of CH4 was 1.05×103 t in the annual growth season. These results provide a scientific basis for the restoration and reconstruction of degraded ecosystems in the Greater Khingan Mountains. 参考文献 相似文献 引证文献

模拟降水减少对中亚热带杉木人工林土壤甲烷吸收的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 模拟降水减少对中亚热带杉木人工林土壤甲烷吸收的影响 DOI: 10.5846/stxb201807091488 作者: 作者单位: 福建师范大学,福建师范大学,福建师范大学,福建师范大学,福建师范大学,福建师范大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重大科学研究项目（2014CB954003）；国家自然科学基金项目（31670623） Effects of precipitation exclusion on soil methane uptake under Cunninghamia lanceolate plantation in mid-subtropical China Author: Affiliation: Fujian Normal University,Fujian Normal University,Fujian Normal University,Fujian Normal University,Fujian Normal University,Fujian Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:森林土壤是大气中甲烷重要的汇，降水变化是影响森林土壤甲烷吸收速率（VCH4）的重要因子。以中亚热带地区不同降水减少程度的杉木林土壤为研究对象，采用静态箱-气相色谱法来测定不同模拟降水减少处理样地的土壤甲烷吸收速率。结果表明：模拟降水减少后显著改变了土壤中的含水量，降水减少60%、降水减少20%和对照样地的年均土壤含水量分别为18.87%、23.89%和28.33%。杉木人工林土壤甲烷吸收速率在月变化上存在较大幅度的波动，其中土壤甲烷吸收速率在8月份达到一年中的最大值（对照75 μg m-2 h-1），2月份达到一年中的最小值（对照10.93 μg m-2 h-1）。3种处理样地的土壤全年均为甲烷汇，与对照样地的甲烷年通量（2.48 kg hm-2 a-1）相比，降水减少60%和20%样地的甲烷年通量分别增加44%和19%。在对照样地中，土壤甲烷吸收速率与土壤含水量呈现负相关（P=0.001），与温度相关性不显著（P > 0.05）；而模拟降水减少后，土壤甲烷吸收速率与土壤温度呈正相关关系（P=0.006和P=0.034），与土壤含水量相关性不显著（P > 0.05）。总之，模拟降水减少后不仅提高了杉木人工林土壤甲烷吸收的能力，同时也可能改变影响土壤甲烷吸收的环境因子；在模拟降水减少前土壤甲烷吸收速率与土壤水分相关性更为密切，而模拟降水减少后土壤甲烷吸收速率可能主要受土壤温度的影响。 Abstract:Forest soil plays an important role in atmospheric methane uptake, the rate of which is affected by soil water content and precipitation change. In this study, we excluded precipitation by 20% and 60% in a Cunninghamia lanceolate plantation to analyze how precipitation reduction affects soil methane uptake in subtropical China. The results showed that soil water content changed significantly in precipitation exclusion treatments, with an annual mean value of 18.87%, 23.89%, and 28.33% in 60% precipitation exclusion, 20% precipitation exclusion, and control treatments, respectively. We also found VCH4 had strong and substantial fluctuations in the study year, with the highest rate hit in August (control 75 μg m-2 h-1) and the minimum in February (control 10.93 μg m-2 h-1). Annual flux of soil CH4 uptake was 2.48 kg hm-2 a-1 in the control treatment, and increased by 44% and 19% in the 60% and 20% precipitation exclusion treatments, respectively. Precipitation exclusion may also alter the relationship of VCH4 and environmental factors. We found a negative correlation between VCH4 and soil water content (P=0.001), and a weak relationship between VCH4 and soil temperature in the control treatment. However, the relationship between VCH4 and soil temperature became stronger after precipitation exclusion (P=0.006 at 60% precipitation exclusion and P=0.034 at 20% precipitation exclusion), and no significant correlation was found between VCH4 and soil water content in both precipitation exclusion treatments. Our results suggest that precipitation decline may not only increase soil methane uptake in subtropical forests with global climate change in the future, but it may also change the main determining environmental factor of soil methane uptake rate from soil water content to soil temperature. 参考文献 相似文献 引证文献

Methane emissions in grazing systems in grassland regions of China: A synthesis

The effects of grazing on methane (CH4) budgets are important for understanding the balance of greenhouse gas emissions and removals in grassland ecosystems. However, the CH4 budgets of grazing systems, that is simultaneously considering CH4 uptake by grassland soils and emissions from ruminant enteric fermentation, livestock folds and animal feces, are poorly investigated, particularly for Chinese grasslands, and thus, remained unclear currently. Here, a synthesis of 43 individual studies was carried out to assess the grazing season/annual CH4 budgets and their responses to grazing in grassland ecosystems of China. The results showed that heavy grazing (HG) significantly decreased, while light grazing (LG) and moderate grazing (MG) had no significant effects soil CH4 uptake, as compared to un-grazing sites. Grazing has shifted Chinese grasslands from a sink to source for atmospheric CH4, and the grazing season/annual CH4 budgets increased with increasing grazing intensity, while the offset of CH4 uptake by grassland soils to total CH4 emissions from sheep, sheepfolds and feces were exponentially decreased with increasing grazing intensity. Moreover, the herbage biomass (HBM), organic matter intake (OMI) and live weight gain (LWG) were decreased while CH4 emission intensities (i.e., CH4 emission per HBM, OMI, and LWG) were linearly increased with increasing grazing intensity. Our results demonstrate that mediating grazing intensity, e.g., from HG to LG, could yield the optimal balance between maintaining productive grasslands and meanwhile mitigating CH4 emissions. This study could help for building strategies with implications for grassland management in China with similar CH4 emission problems.

Heavy grazing reduces grassland soil greenhouse gas fluxes: A global meta-analysis

Grazing degrades worldwide grasslands and possibly suppresses soil greenhouse gas (GHG: CO2, CH4 and N2O) fluxes. However, the global patterns of these three gas fluxes in response to grazing and the general mechanisms remain poorly understood. Here, we performed a meta-analysis of 63 independent grazing studies that measured soil GHG fluxes across global grasslands. Our results revealed that light and moderate grazing had no significant effect on soil CH4 uptake, N2O and CO2 emission, but heavy grazing consistently reduced them. The magnitudes of their responses to grazing were regulated by grazing duration and precipitation. In comparison with CO2 emission, soil CH4 uptake and N2O emission were reduced much more under heavier grazing, longer grazing duration or less precipitation. The decrease in soil CO2 emission was possibly caused by grazing-induced reduction in root biomass and soil moisture, while the decline in soil CH4 uptake and N2O emission was due to decreased soil moisture and substrate availability. Overall, this study provides the first large-scale evaluation on three main soil GHG fluxes in response to grazing, highlighting grazing inhibition of GHG emission but at the cost of plant productivity and soil fertility. We call for future efforts to identify an appropriate grazing intensity that is optimal to balance these complicated impacts.

Upscaling soil-atmosphere CO2 and CH4 fluxes across a topographically complex forested landscape

Upscaling soil-atmosphere greenhouse gas (GHG) fluxes across complex landscapes is a major challenge for environmental scientists and land managers. This study employs a quantile-based digital soil mapping approach for estimating the spatially continuous distributions (2 m spatial resolution) and uncertainties of seasonal mean mid-day soil CO2 and CH4 fluxes. This framework was parameterized using manual chamber measurements collected over two years within a temperate forested headwater watershed. Model accuracy was highest for early (r2 = 0.61) and late summer (r2 = 0.64) for CO2 and CH4 fluxes. Model uncertainty was generally lower for predicted CO2 fluxes than CH4 fluxes. Within the study area, predicted seasonal mean CO2 fluxes ranged from 0.17 to 0.58 μmol m−2 s−1 in winter, and 1.4 to 5.1 μmol m−2 s−1 in early summer. Predicted CH4 fluxes across the study area ranged from −0.52 to 0.02 nmol m−2 s−1 in winter, and −2.1 to 0.61 nmol m−2 s−1 in early and late summer. The models estimated a per hectare net GHG potential ranging from 0.44 to 4.7 kg CO2 eq. hr−1 in winter and early summer, with an estimated 0.4 to 1.5% of emissions offset by CH4 uptake. Flux predictions fell within ranges reported in other temperate forest systems. Soil CO2 fluxes were more sensitive to seasonal temperature changes than CH4 fluxes, with significant temperature relationships for soil CO2 emissions and CH4 uptake in pixels with high slope angles. In contrast, soil CH4 fluxes from flat low-lying areas near the stream network within the watershed were significantly correlated to seasonal precipitation. This study identified key challenges for modeling high spatial resolution soil CO2 and CH4 fluxes, and suggests a larger spatial heterogeneity and complexity of underlying processes that govern CH4 fluxes.

Declines in methane uptake in forest soils

Forest soils are a sink for atmospheric methane (CH4) and play an important role in modulating the global CH4 budget. However, whether CH4 uptake by forest soils is affected by global environmental change is unknown. We measured soil to atmosphere net CH4 fluxes in temperate forests at two long-term ecological research sites in the northeastern United States from the late 1990s to the mid-2010s. We found that annual soil CH4 uptake decreased by 62% and 53% in urban and rural forests in Baltimore, Maryland and by 74% and 89% in calcium-fertilized and reference forests at Hubbard Brook, New Hampshire over this period. This decrease occurred despite marked declines in nitrogen deposition and increases in atmospheric CH4 concentration and temperature, which should lead to increases in CH4 uptake. This decrease in soil CH4 uptake appears to be driven by increases in precipitation and soil hydrological flux. Furthermore, an analysis of CH4 uptake around the globe showed that CH4 uptake in forest soils has decreased by an average of 77% from 1988 to 2015, particularly in forests located from 0 to 60 °N latitude where precipitation has been increasing. We conclude that the soil CH4 sink may be declining and overestimated in several regions across the globe.

Boreal forest soil CO2 and CH4 fluxes following fire and their responses to experimental warming and drying

Boreal forests store large amounts of organic carbon and are susceptible to climate changes, particularly rising temperature, changed soil water and increased fire frequency. The young post-fire ecosystems might occupy larger proportions of the boreal forests region with the expected increases in fire frequency in the future and change the carbon (C) balance of this region. However, it is unclear how soil C fluxes in the post-fire boreal forest response to the climate changes. Therefore, a two-year field experiment was conducted in a boreal forest to investigate the effects of fire on the soil C (CO2 and CH4) fluxes and the responses of these fluxes to simulated warmer and drier climate conditions. The results showed that the boreal forest recovered form wildfire 7–8 years had higher soil CO2 flux than the mature forest. Furthermore, the treatments of warming, drying and the combination of warming and drying increased growing season cumulative soil CO2 flux in the post-fire forest by 15.8%, 20.4% and 34.2%, respectively. However, the boreal forest soil changed from a weak CH4 source to a weak CH4 sink after fire disturbance. Although CH4 absorption increased by warming and drying treatments, the interaction of warming and drying led to a decrease in soil CH4 uptake. The results indicated that the post-fire soil showed CO2 and CH4 fluxes with a greater global warming potential than before burning and that the global warming potential of the soil gas fluxes further increased by warming and drying. The predictive power of models of C cycle-climate feedbacks could be increased by incorporating the distinct ecosystem following fire with permafrost degradation and climate change across the boreal zone.

Variation in Soil Methane Release or Uptake Responses to Biochar Amendment: A Separate Meta-analysis

Agricultural soils play an important role in the atmospheric methane (CH4) budget, where paddy soils can contribute significant CH4 to atmosphere whereas upland soils may act as a source or sink of atmospheric CH4, dependent on soil water conditions. Biochar amendments have effects on soil CH4 production or oxidation processes in individual experiments, but the causative mechanisms are yet to be fully elucidated. To synthesize the response of soil CH4 release or uptake to biochar amendment, we performed a meta-analysis using data from 61 peer-reviewed papers with 222 updated paired measurements. When averaged across all studies, biochar amendment significantly decreased CH4 release rates by 12% for paddy soils and 72% for upland soils, and CH4 uptake rates by 84% for upland soils. Neither soil CH4 release nor uptake responses to biochar amendment were significant in field soils. Nitrogen (N) fertilizer application would weaken the response of soil CH4 release or uptake to biochar amendment. Biochar-incurred decreases in soil CH4 release and uptake rates were the largest in medium-textured soils or neutral-pH soils. Soil CH4 release or uptake responses to biochar were also significantly altered by biochar characteristics, such as feedstock source, C/N ratio, pH, and pyrolysis temperature. The results of this synthesis suggest that the role of biochar in soil CH4 mitigation potential might have been exaggerated, particularly in fields when biochar is applied in combination with N fertilizer.