Μg CH4 Research Articles

Landfill intermediate cover soil microbiomes and their potential for mitigating greenhouse gas emissions revealed through metagenomics

Landfills are a major source of anthropogenic methane emissions and have been found to produce nitrous oxide, an even more potent greenhouse gas than methane. Intermediate cover soil (ICS) plays a key role in reducing methane emissions but may also result in nitrous oxide production. To assess the potential for microbial methane oxidation and nitrous oxide production, long sequencing reads were generated from ICS microbiome DNA and reads were functionally annotated for 24 samples across ICS at a large landfill in New York. Further, incubation experiments were performed to assess methane consumption and nitrous oxide production with varying amounts of ammonia supplemented. Methane was readily consumed by microbes in the composite ICS and all incubations with methane produced small amounts of nitrous oxide even when ammonia was not supplemented. Incubations without methane produced significantly less nitrous oxide than those incubated with methane. In incubations with methane added, the observed specific rate of methane consumption was 0.776 +/− 0.055 μg CH4 g dry weight (DW) soil−1 h−1 and the specific rate of nitrous oxide production was 3.64 × 10−5 +/− 1.30 × 10−5 μg N2O g DW soil−1 h−1. The methanotrophs Methylobacter and an unclassified genus within the family Methlyococcaceae were present in the original ICS samples and the incubation samples, and their abundance increased during incubations with methane. Genes encoding particulate methane monooxygenase/ ammonia monooxygenase (pMMO) were much more abundant than genes encoding soluble methane monooxygenase (sMMO) across the landfill ICS. Genes encoding proteins that convert hydroxylamine to nitrous oxide were not highly abundant in the ICS or incubation metagenomes. In total, these results suggest that although ammonia oxidation via methanotrophs may result in low levels of nitrous oxide production, ICS microbial communities have the potential to greatly reduce the overall global warming potential of landfill emissions.

Temporal Variability in Soil Greenhouse Gas Fluxes and Influencing Factors of a Primary Forest on the Eastern Qinghai-Tibetan Plateau

Soil greenhouse gas (GHG) fluxes relate to soil carbon and nitrogen budgets and have a significant impact on climate change. Nevertheless, the temporal variation and magnitude of the fluxes of all three major GHGs (CO2, CH4 and N2O) and their influencing factors have not been elucidated clearly in primary forests on the eastern Qinghai-Tibetan Plateau. Herein, field chamber GHG fluxes from May to November, soil microbial community and enzyme activity were analyzed in a fir-dominated (Abies fargesii var. faxoniana) primary forest. The emission rates of CO2 and N2O ranged between 64.69–243.22 mg CO2 m−2 h−1 and 1.69–5.46 ug N2O m−2 h−1, exhibiting a temporally unimodal pattern with a peak in July. The soil acted as a CH4 sink, and the uptake rate varied between 52.96 and 84.67 μg CH4 m−2 h−1 with the higher uptake rates in June and November. The temporal variation in the CO2 flux was significantly correlated with the geometric mean of enzyme activities, suggesting that the soil CO2 flux was determined by microbial activity rather than soil microbial biomass. The soil N2O flux was positively related to nitrate concentration with marginal significance, probably because N2O was a byproduct of nitrification and denitrification processes. The soil CH4 uptake was closely associated with methanotrophic biomass (18:1ω7c). The results highlight divergent temporal dynamics of GHG fluxes owing to different driving mechanisms and an important CH4 sink in the primary forest soil, helping to evaluate the carbon and nitrogen budgets of primary forests on the eastern Qinghai-Tibetan Plateau.

Differences in Methanogenic Pathways and Communities in Paddy Soils Under Three Typical Cropping Modes

AbstractThe methane (CH4) production process in paddy fields varies depending on different cropping modes. However, there is limited knowledge on the changes in anaerobically produced CH4 isotopic ratios (δ13CH4), the methanogenic pathways, and the dominant communities of methanogens in paddy soils under different modes. To address this, we conducted experiments using anaerobic incubation methods, stable carbon isotope fractionation through inhibition studies with fluoromethane, and high‐throughput sequencing. These methods allowed us to measure the CH4 production potential (MPP), the relative contribution of acetoclastic methanogenesis to CH4 production (fac), and the composition of the methanogen community in paddy soils under three typical cropping modes: Rice‐Wheat (RW), Rice‐Fallow (RF), and Double‐Rice (DR) in China. The results showed that MPP was 30.7 μg CH4 g−1 d−1 in DR soil, around 57% and 66% higher than that in RW and RF soils, respectively, possibly due to the lower pH, clay content, and higher abundance of the mcrA gene. Moreover, RF soil had the highest value of produced δ13CH4 (−43.9‰) but the lowest value of produced δ13CO2 (−26.3‰). Based on the carbon isotope fractionation associated with methanogenesis via H2/CO2 reduction (1.049–1.062), the values of fac estimated in the RF soil (80%–98%) were much higher than that in the RW (39%–60%) and DR soils (52%–75%). This could be supported by the finding showing that Methanosarcina, the acetoclastic methanogens, were dominant in RF soil, while Methanosarcina and Methanobacterium (the hydrogenotrophic methanogens) dominated in RW and DR soils. Redundancy analysis revealed that the community structure of methanogens was significantly affected by soil pH. The findings suggest that differences in the abundance and composition of methanogens, possibly driven by soil pH, play a key role in regulating methanogenesis in the paddy soils, and further provide valuable insights into the process of CH4 production in different cropping modes.

Conversion of natural coastal wetlands to mariculture ponds dramatically decreased methane production by reducing substrate availability

Coastal wetlands are increasingly being converted into aquaculture ponds to meet growing global demand for fish protein. Coastal wetlands conversion has been predicted to result in significant carbon (C) emissions; however, a mechanistic understanding of the effects of coastal wetland conversion on soil’s capacity to produce greenhouse gases remains lacking. Here, integrated biogeochemical investigations on methanogenic substrates, community structures, and activities were conducted in a coastal Spartina alterniflora saltmarsh and three saltmarsh-converted mariculture ponds aged 6, 13, and 20 years. Saltmarsh conversion into mariculture ponds decreased CH4 production potential from 353 to 16.3–78.3 µg CH4 kg−1 d−1. The concentrations of dissolved organic C and non-competitive methanogenic substrate, trimethylamine, were reduced by 84.8% and 79.7%, respectively, whereas methanogens abundance decreased by 43.7%, probably due to the decreased C input following conversion. Among the ponds, CH4 production potential, methanogenic substrates (acetate and trimethylamine), and methanogen abundance decreased with conversion chronosequence. However, the dominant methanogen group did not shift after land conversion, and the potential methylamine-utilizing Methanosarcinaceae accounted for 86.5% and 85.3–89.7% of the total populations in the S. alterniflora saltmarsh and mariculture ponds, respectively, implying that methylotrophic methanogenesis was the predominant pathway of CH4 production in both ecosystems. The results indicated that the conversion of natural coastal saltmarsh to mariculture ponds decreased CH4 production by reducing substrate availability and methanogen abundance, and CH4 production potential in mariculture ponds was more efficiently suppressed with conversion chronosequence.

How climate warming and plant diversity affect carbon greenhouse gas emissions from boreal peatlands: Evidence from a mesocosm study

Understanding synchronous vegetation changes are crucial to assess the impact of carbon cycle on climate warming in peatlands. We established a mesocosm system to monitor ecosystem respiration (Re) and methane (CH4) fluxes in the growing season from 2020 to 2021 under different scenarios, including warming and manipulations of species diversity. Overall, the mean Re and CH4 fluxes varied in the ranges of 1.38 ± 0.18 to 46.25 ± 6.62 mg CO2–C m−2 h−1 and 2.72 ± 2.36 to 319.55 ± 96.22 μg CH4–C m−2 h−1, respectively, with the highest values appearing in the middle of growing season. The Re and CH4 fluxes in L-III and L-IV mesocosms showed significant increases of 38.86% and 54.28%, and 56.38% and 107.54%, respectively, compared to the monoculture treatment. The primary controls for this phenomenon were the plant biomass and the concentrations of dissolved organic carbon and phenolics. Warming significantly increased the emissions of CO2 by ∼40% during the study period, but it reduced the fluxes of CH4 in 2021. Sustained warming and soil water loss may destroy the original anaerobic environment, which plays a role in inhibiting the generation and emission of CH4 in the long term. Interestingly, although warming has reduced CH4 emissions, a mixture of three and four species seems to buffer more than 50% of this impact, further demonstrating the positive contribution of species diversity. Our results indicate that an increase in species diversity, specifically manifested in the expansion of vascular plants as a community process adapting to warming, can strongly affect carbon fluxes in peatlands and create potential feedback on future climate environments.

Effect of Compost Derived from Urban Waste on Chard (Beta vulgaris L., var cycla) Yield and Soil GHG Fluxes in a Mediterranean Agricultural System

The use of recycled materials as soil amendments and fertilizers is an important priority in the agronomic sector to valorize waste from a circular economic perspective and reduce waste disposal, reduce dependence on external inputs, and provide better climate change mitigation options. In this study, we evaluated the agroecological performance of compost derived from recycled organic matrices of urban waste (mixed composted amendment, MCA) of the metropolitan area of Rome. MCA is available in big quantities and might represent an interesting option to substitute conventional mineral nitrogen fertilizer (CF). The effect of MCA, CF, and a combination of both (MIX 1:1) was tested on crop yield and greenhouse gas emissions in a field trial on a common Mediterranean crop (Swiss chart, one season, two crop cycles). The MCA effect on crop yield was positive and comparable to CF and MIX treatments, while MCA treatment showed the lower soil mineral nitrogen (N) content. GHG emissions in the MCA treatment were comparable to those observed in CF and MIX, being overall quite low. The soil acted as a weak net CH4 sink in all treatments (−12.6 ± 6.1 μg CH4 m−2 h−1); no differences in CO2 emissions between MCA and CF or MIX treatments were observed (range 0.1−0.2 g m−2 h−1). The N2O emission intensity of MCA was slightly lower than MIX and CF treatments (0.09, 0.011, and 0.011 g N2O kg−1 crop dry weight, respectively). Overall, MCA seemed a valid alternative to CF for the tested agro-environmental indicators in the spring/summer Mediterranean conditions.

Methane Production Linked to Organic Matter Molecule and Methanogenic Community in Estuarine Benthic Sediments

AbstractThe importance of dissolved organic matter (DOM) and methanogenic community to methane (CH4) production in estuarine benthic sediments remains poorly understood. Here, we determined CH4 production rate, DOM molecule, and methanogenic community in benthic sediments of Min River Estuary. CH4 production rates in freshwater and saline sediments varied between 0.28 and 0.56 μg CH4 m−2 h−1, and between 0.17 and 0.27 μg CH4 m−2 h−1, respectively. CH4 production rates in freshwater sediments were increased by 36%–66% under saline incubation, compared to freshwater incubation, indicating that elevated salinity can stimulate CH4 production. The δ13C‐CH4 decreased and fractionation factor between δ13C‐CO2 and δ13C‐CH4 increased from high‐ to low‐OM sediments, suggesting a shift of CH4 production from acetoclastic to hydrogenotrophic pathways. A decrease in labile fractions and an increase in recalcitrance fractions of DOM were accompanied by the decrease in CH4 production. The Methanoregula, Methanocellales, Methanosarcina, and Methanosaeta were the predominant methanogenic communities in mediating CH4 production. The differences in DOM molecules and methanogenic archaea taxa could drive the distinct CH4 production rates in estuarine benthic sediments. These results suggest that DOM quantity and molecules and methanogenic archaea can substantially affect CH4 production, which have broader implications for global CH4 estimates under the ongoing eutrophication in estuarine and coastal ecosystems.

Tidal restoration to reduce greenhouse gas emissions from freshwater impounded coastal wetlands

Freshwater impounded wetlands are created by artificially restricting coastal wetlands connection to tides. The decrease in salinity and altered hydrology can significantly increase greenhouse gas (GHG) emissions, specifically methane (CH4). Restoration of freshwater impounded wetlands through tidal reintroduction can potentially reduce GHG emissions; however, studies in tropical regions are scare. This study investigates the potential for tidal restoration of impounded freshwater coastal wetlands by comparing their GHG emissions with tidally connected mangrove and saltmarshes in the Burdekin catchment in Queensland, Australia. We found that freshwater impounded wetlands had significantly higher CH4 emissions (3,633 ± 812 μg CH4 m−2 hour−1) than mangroves (27 ± 8 μg CH4 m−2 hour−1) and saltmarsh (13 ± 8 μg CH4 m−2 hour−1). Soil redox, moisture, carbon, nitrogen, and bulk density were all significantly correlated to methane emissions. Conversely, freshwater impounded wetlands had significantly lower nitrous oxide (N2O) emissions (−0.72 ± 0.18 μg N2O m−2 hour−1) than mangroves and saltmarsh (0.35 ± 0.29 and 1.32 ± 0.52 μg N2O m−2 hour−1 respectively). Nevertheless, when converting to CO2 equivalents (CO2‐eq), freshwater impounded wetlands emitted 91 ± 20 g CO2‐eq m−2 hour−1, compared to the much lower 0.8 ± 0.2 and 0.7 ± 0.2 g CO2‐eq m−2 hour−1 emission rates for mangroves and saltmarsh. In conclusion, restoration of freshwater impounded wetlands through tidal restoration is likely to result in reduced GHG emissions.

Reduced nitrogen fertilization under flooded conditions cut down soil N2O and CO2 efflux: An incubation experiment

Unreasonable water (W) and inorganic nitrogen (N) fertilization cause an intensification of soil greenhouse gas (GHGs) emissions. W–N interactions (W × N) patterns can maximise the regulation of soil GHGs efflux through the rational matching of W and N fertilization factors. However, the effects of W × N patterns on soil GHGs efflux and the underlying mechanism remain unclear. In this study, urea fertilizers were applied to paddy soils in a gradient of 100 (N100), 80 (N80), and 60 mg kg−1 (N60) concentrations. Flooding (W1) and 60% field holding capacity (W2) was set for each N fertilizer application to observe the effects of W × N patterns on soil properties and GHGs efflux through incubation experiments. The results showed that W significantly affected soil electrical conductivity and different N forms (i.e., alkali hydrolyzed N, ammonium N, nitrate N and microbial biomass N) contents. Soil organic carbon (C) content was reduced by 14.40% in W1N60 relative to W1N100, whereas microbial biomass C content was increased by 26.87%. Moreover, soil methane (CH4) fluxes were low in all treatments, with a range of 1.60–1.65 μg CH4 kg−1. Soil nitrous oxide (N2O) and carbon dioxide (CO2) fluxes were significantly influenced by W, N and W × N. Global warming potential was maintained at the lowest level in W1N60 treatment at 0.67 g CO2-eq kg−1, suggesting W1N60 as the preferred W × N pattern with high environmental impact. Our findings demonstrate that reduced N fertilization contributes to the effective mitigation of soil N2O and CO2 efflux by lowering the soil total N and organic C contents and regulating soil microbial biomass C and N.

Switches of methane production pathways and emissions with human activity intensity in subtropical estuaries

• CH 4 fluxes increased significantly from minimally to highly impacted estuaries. • Water δ 13 C-CH 4 values increased from minimally to highly impacted estuaries. • Human activity drove CH 4 production from hydrogenotrophic to acetoclastic pathways. Nutrient loading caused by human activities can drive changes in methane (CH 4 ) production pathways, yet the mechanisms and magnitudes of estuary CH 4 emissions remain poorly understood. Here we investigated CH 4 fluxes and δ 13 C-CH 4 values in wet and dry seasons from five subtropical estuaries with varying human activity intensity and hydrologic conditions. Water dissolved CH 4 concentrations varied from 0.19 to 0.51 µmol CH 4 L –1 in these studied estuaries, resulting in coincident water–air CH 4 fluxes ranging from 5.46 to 29.6 µg CH 4 m –2 h −1 . Water CH 4 concentrations and fluxes were significantly lower in the wet than dry season, and were higher in the high human-impacted estuaries, indicating that large discharge and water flow could slow down areal CH 4 emissions. The ratios of C-CH 4 to organic carbon (OC) were much higher and showed a positive response to increasing nitrogen concentrations in high human-impacted estuaries, suggesting that eutrophic estuaries trigger high CH 4 emissions. In addition, an increase in δ 13 C-CH 4 and a declining in fractionation factor ( α app ) from the low to high human-impacted estuaries were accompanied by a switch of CH 4 production from hydrogenotrophic to acetoclastic pathways. These results suggest that human activity intensity can drive the alterations in the pathways and magnitudes of CH 4 production and that hydrologic conditions can modify CH 4 emissions, which have important implications for estimates of CH 4 emissions from global estuaries under increasing human activity intensity.

Excess soil moisture and fresh carbon input are prerequisites for methane production in podzolic soil

Abstract. Boreal upland forests are generally considered methane (CH4) sinks due to the predominance of CH4 oxidizing bacteria over the methanogenic archaea. However, boreal upland forests can temporarily act as CH4 sources during wet seasons or years. From a landscape perspective and in annual terms, this source can be significant as weather conditions may cause flooding, which can last a considerable proportion of the active season and because often, the forest coverage within a typical boreal catchment is much higher than that of wetlands. Processes and conditions which change mineral soils from acting as a weak sink to a strong source are not well understood. We measured soil CH4 fluxes from 20 different points from regularly irrigated and control plots during two growing seasons. We also estimated potential CH4 production and oxidation rates in different soil layers and performed a laboratory experiment, where soil microcosms were subjected to different moisture levels and glucose addition simulating the fresh labile carbon (C) source from root exudates. The aim was to find the key controlling factors and conditions for boreal upland soil CH4 production. Probably due to long dry periods in both summers, we did not find occasions of CH4 production following the excess irrigation, with one exception in July 2019 with emission of 18 200 µg CH4 m−2 h−1. Otherwise, the soil was always a CH4 sink (median CH4 uptake rate of 260–290 and 150–170 µg CH4 m−2 h−1, in control and irrigated plots, respectively). The median soil CH4 uptake rates at the irrigated plot were 88 % and 50 % lower than at the control plot in 2018 and 2019, respectively. Potential CH4 production rates were highest in the organic layer (0.2–0.6 nmol CH4 g−1 d−1), but some production was also observed in the leaching layer, whereas in other soil layers, the rates were negligible. Potential CH4 oxidation rates varied mainly within 10–40 nmol CH4 g−1 d−1, except in deep soil and the organic layer in 2019, where potential oxidation rates were almost zero. The laboratory experiment revealed that high soil moisture alone does not turn upland forest soil into a CH4 source. However, a simple C source, e.g., substrates coming from root exudates with high moisture, switched the soil into a CH4 source. Our unique study provides new insights into the processes and controlling factors on CH4 production and oxidation, and the resulting net efflux that should be incorporated in process models describing global CH4 cycling.

Use of methanotrophically activated biochar in novel biogeochemical cover system for carbon sequestration: Microbial characterization

Biochar-amended soils have been explored to enhance microbial methane (CH4) oxidation in landfill cover systems. Recently, research priorities have expanded to include the mitigation of other components of landfill gas such as carbon dioxide (CO2) and hydrogen sulfide (H2S) along with CH4. In this study, column tests were performed to simulate the newly proposed biogeochemical cover systems, which incorporate biochar-amended soil for CH4 oxidation and basic oxygen furnace (BOF) slag for CO2 and H2S mitigation, to evaluate the effect of cover configuration on microbial CH4 oxidation and community composition. Biogeochemical covers included a biochar-amended soil (10% w/w), and methanotroph-enriched activated biochar amended soil (5% or 10% w/w) as a biocover layer or CH4 oxidation layer. The primary outcome measures of interest were CH4 oxidation rates and the structure and abundance of methane-oxidation bacteria in the covers. All column reactors were active in CH4 oxidation, but columns containing activated biochar-amended soils had higher CH4 oxidation rates (133 to 143 μg CH4 g−1 day−1) than those containing non-activated biochar-amended soil (50 μg CH4 g−1 day−1) and no-biochar soil or control soil (43 μg CH4 g−1 day−1). All treatments showed significant increases in the relative abundance of methanotrophs from an average relative abundance of 5.6% before incubation to a maximum of 45% following incubation. In activated biochar, the abundance of Type II methanotrophs, primarily Methylocystis and Methylosinus, was greater than that of Type I methanotrophs (Methylobacter) due to which activated biochar-amended soils also showed higher abundance of Type II methanotrophs. Overall, biogeochemical cover profiles showed promising potential for CH4 oxidation without any adverse effect on microbial community composition and methane oxidation. Biochar activation led to an alteration of the dominant methanotrophic communities and increased CH4 oxidation.

Methane Emissions From Nordic Seagrass Meadow Sediments

Shallow coastal soft bottoms are important carbon sinks. Submerged vegetation has been shown to sequester carbon, increase sedimentary organic carbon (Corg) and thus suppress greenhouse gas (GHG) emissions. The ongoing regression of seagrass cover in many areas of the world can therefore lead to accelerated emission of GHGs. In Nordic waters, seagrass meadows have a high capacity for carbon storage, with some areas being recognized as blue carbon hotspots. To what extent these carbon stocks lead to emission of methane (CH4) is not yet known. We investigated benthic CH4 emission (i.e., net release from the sediment) in relation to seagrass (i.e. Zostera marina) cover and sedimentary Corg content (%) during the warm summer period (when emissions are likely to be highest). Methane exchange was measured in situ with benthic chambers at nine sites distributed in three regions along a salinity gradient from ∼6 in the Baltic Sea (Finland) to ∼20 in Kattegat (Denmark) and ∼26 in Skagerrak (Sweden). The net release of CH4 from seagrass sediments and adjacent unvegetated areas was generally low compared to other coastal habitats in the region (such as mussel banks and wetlands) and to other seagrass areas worldwide. The lowest net release was found in Finland. We found a positive relationship between CH4 net release and sedimentary Corg content in both seagrass meadows and unvegetated areas, whereas no clear relationship between seagrass cover and CH4 net release was observed. Overall, the data suggest that Nordic Zostera marina meadows release average levels of CH4 ranging from 0.3 to 3.0 μg CH4 m–2 h–1, which is at least 12–78 times lower (CO2 equivalents) than their carbon accumulation rates previously estimated from seagrass meadows in the region, thereby not hampering their role as carbon sinks. Thus, the relatively weak CH4 emissions from Nordic Z. marina meadows will not outweigh their importance as carbon sinks under present environmental conditions.

Soil CO2 and CH4 emissions and their carbon isotopic signatures linked to saturated and drained states of the Three Gorges Reservoir of China

Human activities such as dams disturb the structure and function of wetlands, triggering large soil CO2 and CH4 emissions. However, controls over field CO2 and CH4 emissions and their carbon isotopic signatures in reservoir wetlands are not yet fully understood. We investigated in situ CO2 and CH4 emissions, the δ13C values of CO2 and CH4, and associated environments in the saturated and drained states under four elevations (i.e., the water column, <147 m, permanent inundation area without plants; the low, 145–160 m, frequently flooded area with revegetation; the high, 160–175 m, rarely flooded area with revegetation; and the upland area as the control, >175 m, nonflooded area with original plants) in the Three Gorges Reservoir area. The CO2 emissions was significantly higher in high elevation, and they also significantly differed between the saturated and drained states. In contrast, the CH4 emissions on average (41.97 μg CH4 m−2 h−1) were higher at high elevations than at low elevations (22.73 μg CH4 m−2 h−1) during the whole observation period. CH4 emissions decreased by 90% at low elevations and increased by 153% at high elevations from the saturated to drained states. The δ13C of CH4 was more enriched at high elevations than in the low and upland areas, with a more depleted level under the saturated state than under the drained state. We found that soil CO2 and CH4 emissions were closely related to soil substrate quality (e.g., C: N ratio) and enzyme activities, whereas the δ13C values of CO2 and CH4 were primarily associated with root respiration and methanogenic bacteria, respectively. Specifically, the effects of the saturated and drained states on soil CO2 and CH4 emissions were stronger than the effect of reservoir elevation, thereby providing an important basis for assessing carbon neutrality in response to anthropogenic activities.

Assessing soil carbon dioxide and methane fluxes from a Scots pine raised bog-edge-woodland

Scots pine bog edge woodland is a type of habitat typical on raised bogs where trees cohabitate with bog vegetation to form a low-density stand. Even though nowadays this habitat does not cover large areas, in a future scenario it is possible that this environment will expand, either naturally (drier climate) or anthropogenically, as the result of the application of new restoration strategies that could increase net landscape carbon benefits from both peatland and woodland environments. This study is the first reported investigation in Scotland exploring carbon flux dynamics from sparse woodlands on raised bogs. We examined how Scots pine trees directly or indirectly affected soil temperature and moisture, ground vegetation, and consequently carbon dioxide (CO2) and methane (CH4) soil fluxes. Soil CO2 and CH4 were measured at different distance from the tree and thereafter assessed for both spatial and temporal variability. Our results showed that these low-density trees were able to modify the ground vegetation composition, had no effect on soil temperature, but did affect the soil moisture, with soils close to tree roots significantly drier (0.25 ± 0.01 m3 m-3) than those on open bog (0.39 ± 0.02 m3 m-3). Soil CO2 fluxes were significantly higher in the vicinity of trees (34.13 ± 3.97 μg CO2 m−2 s−1) compared to the open bog (24.34 ± 2.86 μg CO2 m−2 s−1). On the opposite, CH4 effluxes were significantly larger in the open bog (0.07 ± 0.01 μg CH4 m−2 s−1) than close to the tree (0.01 ± 0.00 μg CH4 m−2 s−1). This suggests that Scots pine trees on bog edge woodland may affect soil C fluxes in their proximity primarily due to the contribution of root respiration, but also as a result of their effects on soil moisture, enhancing soil CO2 emissions, while reducing the CH4 fluxes. There is, however, still uncertainty about the complete greenhouse gas assessment, and further research would be needed in order to include the quantification of soil nitrous oxide (N2O) dynamics together with the analysis of complete gas exchanges at the tree-atmosphere level.

Fourier transform infrared spectroscopy and interference of volatile organic compounds on measurements of methane (CH4) fluxes at tree stems – a general phenomenon for plant systems?

Fourier transform infrared spectroscopy and interference of volatile organic compounds on measurements of methane (CH₄) fluxes at tree stems – a general phenomenon for plant systems?

Watershed scale patterns and controlling factors of ecosystem respiration and methane fluxes in a Tibetan alpine grassland

Ecosystem respiration (Re) and methane (CH4) fluxes are two important soil-atmosphere carbon exchange processes that have been well documented at the local scale. However, the spatial patterns and controlling factors of these processes remain unclear in the Tibetan alpine permafrost region at the watershed scale. We conducted a two-year field monitoring study of Re and CH4 fluxes at three altitudinal positions on shady and sunny slopes in a Tibetan alpine grassland to determine the spatial variability in the two processes and to identify their underlying mechanisms. The microbial factor had a controlling effect on Re spatial variability in alpine grassland watersheds. The lower soil temperature and soil organic matter content at the upper slope positions on the shady slopes inhibited Re because they reduced the soil microbial activity. We found that the alpine grassland to be a net sink of atmospheric CH4, and the average CH4 flux rates exhibited large spatial variance ranging from −1.60 to −10.48 µg CH4 m−2 h−1 within the watersheds. The spatial variability in soil volumetric water content explained 76% of the variation in CH4 fluxes within the watersheds. We suggest that the influence of permafrost on hydrologic conditions may increase the spatial variability of soil moisture (measured as soil volumetric water content and water-filled pore space) in alpine grassland watersheds, and generally form poorly drained landscape at the lower slope position where Re and CH4 uptake are inhibited. Our results highlight the indirect effects of terrain and permafrost on Re and CH4 fluxes through their effects on biophysiochemical factors. We recommend that the spatial variability in Re and CH4 fluxes at the watershed scale of Tibetan alpine grassland should be given more attention in earth system models, especially the variability of CH4 fluxes with altitudinal position.

Field-scale performance of biochar-amended soil covers for landfill methane oxidation

A field validation of three biochar-amended soil covers (2%, 10%, and 100% biochar-amended soils) along with a soil control cover was conducted within the intermediate cover of an active municipal solid waste (MSW) landfill in conjunction with laboratory studies evaluating the effect of biochar in enhancing methane (CH4) oxidation in cover soils. Baseline CH4 emissions and pre-existing site conditions were characterized prior to installation of test plots simulating three cover designs evaluated in related laboratory studies. Static chamber measurements of surface CH4 fluxes and sampling of soil pore gas at different depths were conducted across the 8-month monitoring period to assess cover performance. Surface fluxes from the test plots exhibited wide spatial variability, with one location emitting fluxes > 1100 g CH4 m−2 day−1 in one survey. Potential rates of CH4 oxidation were determined in batch assays of exhumed soil core subsamples following termination of the field trial and ranged from ~1 to 350 μg CH4 g−1 day−1. The heterogeneity of the waste led to nonuniform CH4 loads in the test plots. The soil control test plot was exposed to higher CH4 loads and biochar-amended test plots were exposed to significantly lower CH4 loads. As a result, the soil control test plot showed higher CH4 oxidation rates (257–289 μg CH4 g−1 day−1) than the biochar-amended test plots. Similarly, the soil control plot also showed higher relative abundance of methanotrophs which was positively correlated with the CH4 oxidation rates. The test plot with 10% biochar-amended soil experienced CH4 loads nearly 25% of that in soil control and still showed CH4 oxidation rates (260 μg CH4 g−1 day−1) comparable to that of soil control which showed the efficacy of biochar amendment in enhancing CH4 oxidation rates. The environmental and CH4 exposure conditions affected the microbial community composition in the test plots and showed the dominance of type I methanotrophic genus such as Methylomonas and Crenothrix spp. Overall, the waste heterogeneity led to nonuniform CH4 exposure conditions at each test plot making it hard to distinctly quantify the effect of biochar amendment on CH4 oxidation rates.

Disproportionate CH4 Sink Strength from an Endemic, Sub-Alpine Australian Soil Microbial Community.

Soil-to-atmosphere methane (CH4) fluxes are dependent on opposing microbial processes of production and consumption. Here we use a soil–vegetation gradient in an Australian sub-alpine ecosystem to examine links between composition of soil microbial communities, and the fluxes of greenhouse gases they regulate. For each soil/vegetation type (forest, grassland, and bog), we measured carbon dioxide (CO2) and CH4 fluxes and their production/consumption at 5 cm intervals to a depth of 30 cm. All soils were sources of CO2, ranging from 49 to 93 mg CO2 m−2 h−1. Forest soils were strong net sinks for CH4, at rates of up to −413 µg CH4 m−2 h−1. Grassland soils varied, with some soils acting as sources and some as sinks, but overall averaged −97 µg CH4 m−2 h−1. Bog soils were net sources of CH4 (+340 µg CH4 m−2 h−1). Methanotrophs were dominated by USCα in forest and grassland soils, and Candidatus Methylomirabilis in the bog soils. Methylocystis were also detected at relatively low abundance in all soils. Our study suggests that there is a disproportionately large contribution of these ecosystems to the global soil CH4 sink, which highlights our dependence on soil ecosystem services in remote locations driven by unique populations of soil microbes. It is paramount to explore and understand these remote, hard-to-reach ecosystems to better understand biogeochemical cycles that underpin global sustainability.

CH4 and N2O fluxes from planted forests and native Cerrado ecosystems in Brazil

Forest soils are N2O sources and commonly act as CH4 sinks. This study evaluated the dynamics of the CH4 and N2O fluxes of soils under Eucalyptus plantations and native Cerrado vegetation, as well as possible interactions between environmental factors and fluxes. The study was carried out in the Distrito Federal, Brazil, during 26 months, in three areas: in two stands of the hybrid Eucalyptus urophylla × Eucalyptus grandis, planted in 2011 (E1), and in 2009 (E2) and native Cerrado vegetation (CE). Measurements to determine the fluxes in a closed static chamber were carried out from Oct 2013 to Nov 2015. Soil and climate factors were monitored. During the study period, the mean CH4 fluxes were –22.48, –8.38 and –1.31 μg CH4 m–2 h–1 and the mean N2O fluxes 5.45, 4.85 and 3.85 μg N2O m–2 h–1 from E1, E2 and CE, respectively. Seasonality affected plantations in the studied sites. Cumulative CH4 influxes were calculated (year-1: –1.86 to -0.63 kg ha–1 yr–1; year-2: –1.85 to –1.34 kg ha–1 yr–1). Cumulative N2O fluxes in the three sites were ≤ 0.85 kg ha–1 yr–1. The change in land use from Cerrado to Eucalyptus plantations did not significantly changed regarding greenhouse gases (GHG), compared to the native vegetation. Flux rates of both gases (N2O and CH4) were low. Temporal variations in GHG fluxes and different ages of the stands did not cause significant differences in cumulative annual fluxes.