Increased CH4 Emissions Research Articles

The characteristics and driving factors of household CO2 and non-CO2 emissions in China

Approximately 60% of global greenhouse gas (GHG) emissions are attributable to household consumption. This presents a great opportunity to reduce them. However, most research has focused only on CO2 emissions and paid limited attention to non-CO2 emissions which account for a quarter of household emissions. This study investigates key characteristics and driving factors associated with Chinese household emissions, which include CO2, CH4, N2O, and F-gases. Our work also combines detailed household survey data, GHG inventory, and input-output tables. The empirical results suggest that household GHG emissions per capita in 2015 were 2.74 tCO2eq, of which non-CO2 gases accounted for 27%, mainly from food (48%) and dwelling-related consumption (18%). Urban households emit 4.02 tCO2eq per capita—nearly twice that of rural households—and have a higher rate of non-CO2 emissions. Consumption expenditure is the primary driver of emissions differences between rural and urban households, while consumption structure only plays a minor role. The reduction in CO2 emissions resulting from urban homes switching from coal to natural gas has been offset by an increase in CH4 emissions from gas production and supply. These findings highlight the significance of non-CO2 emissions in policy-making, as well as the important potential of adjusting households' consumption structure.

Atmospheric data support a multi-decadal shift in the global methane budget towards natural tropical emissions

Abstract. We use the GEOS-Chem global 3-D model and two inverse methods (the maximum a posteriori and ensemble Kalman filter) to infer regional methane (CH4) emissions and the corresponding stable-carbon-isotope source signatures from 2004–2020 across the globe using in situ and satellite remote sensing data. We use the Siegel estimator to determine linear trends from the in situ data. Over our 17-year study period, we estimate a linear increase of 3.6 Tg yr−1 yr−1 in CH4 emissions from tropical continental regions, including North Africa, southern Africa, tropical South America, and tropical Asia. The second-largest increase in CH4 emissions over this period (1.6 Tg yr−1 yr−1) is from China. For boreal regions we estimate a negative emissions trend of −0.2 Tg yr−1 yr−1, and for northern and southern temperate regions we estimate trends of 0.03 Tg yr−1 yr−1 and 0.2 Tg yr−1 yr−1, respectively. These increases in CH4 emissions are accompanied by a progressively isotopically lighter atmospheric δ13C signature over the tropics, particularly since 2012, which is consistent with an increased biogenic emissions source and/or a decrease in a thermogenic/pyrogenic emissions source with a heavier isotopic signature. Previous studies have linked increased tropical biogenic emissions to increased rainfall. Over China, we find a weaker trend towards isotopically lighter δ13C sources, suggesting that heavier isotopic source signatures make a larger contribution to this region. Satellite remote sensing data provide additional evidence of emissions hotspots of CH4 that are consistent with the location and seasonal timing of wetland emissions. The collective evidence suggests that increases in tropical CH4 emissions are from biogenic sources, with a significant fraction from wetlands. To understand the influence of our results on changes in the hydroxyl radical (OH), we also report regional CH4 emissions estimates using an alternative scenario of a 0.5 % yr−1 decrease in OH since 2004, followed by a larger 1.5 % drop in 2020 during the first COVID-19 lockdown. We find that our main findings are broadly insensitive to those idealised year-to-year changes in OH, although the corresponding change in atmospheric CH4 in 2020 is inconsistent with independent global-scale constraints for the estimated annual-mean atmospheric growth rate.

Impact of Haemonchus contortus infection on feed intake, digestion, liveweight gain, and enteric methane emission from Red Maasai and Dorper sheep

A study was conducted with Red Maasai and Dorper lambs to evaluate the effects of infection with the gastrointestinal nematode (GIN) Haemonchus contortus on feed intake, liveweight gain (LWG), feed energy and nitrogen partitioning, and enteric methane (CH4) emissions. Six- to seven-month-old Red Maasai (n=12) and Dorper (n=12) lambs were randomly allocated to three treatments (n=8, four lambs per breed) in a 2×3 factorial cross-over study over two periods (P1 and P2) of 36 days each. The treatments consisted of three combinations of GIN infection and feeding level: Infected + ad libitum feeding (I-adlib), uninfected + ad libitum feeding (Un-adlib), and uninfected + restricted feeding (Un-restd), across the two breeds. Lambs in the I-adlib group were trickle-infected daily with 1,000 L3 stage larvae of H. contortus for four consecutive days (Days 1–4), whereas lambs in the other experimental treatments were kept GIN free. The feed intake was measured daily. Liveweight (LW), faecal egg counts (FEC), and packed cell volume (PCV) were measured on Day 1 and weekly thereafter. On Days 29–33 total faecal and urine outputs were determined in metabolic crates. The lambs were then housed in respiration chambers for three consecutive days (Days 34–36). There was a washout period of 21 days before P2 started. Uninfected lambs (Un-adlib and Un-restd) had undetectable FEC throughout the study. On Day 36, FEC did not differ between the breeds (P>0.05). Infected lambs (I-adlib) had lower PCV than uninfected (Un-adlib and Un-restd) lambs on day 36. Neither breed nor infection influenced feed and nutrient intake, but as expected, restricted-fed lambs had a lower intake (P<0.05). The LWG of Un-adlib lambs was significantly higher than that of I-adlib and Un-restd lambs (P<0.05), whereas there was no breed difference (P>0.05). Neither breed nor infection affected feed digestibility, nitrogen retention or energy metabolisability (P>0.05). However, feed restriction decreased feed intake, LWG and N retention, whereas feed digestibility and energy metabolisability were unaffected. Neither daily CH4 emissions nor yield (per unit of feed intake) were affected by experimental infection, but Un-restd lambs had lower CH4 emissions per day. Red Maasai lambs had consistently lower daily CH4 emissions and yields than Dorper (P<0.01). This study confirmed the relative resistance of indigenous sheep (Red Maasai) to H. contortus infection, but the increased CH4 emission and yield due to GIN observed in other studies was not confirmed. Further investigations are needed to test whether in environments with multiple stress factors, local or indigenous breeds or their crossbreeds with exotic breeds may be better equipped to sustain production and simultaneously have a reduced carbon footprint than purebred exotic breeds.

Sheepfolds induce significant increase of seasonal CO2, CH4 and N2O emissions in temperate steppes of Inner Mongolia

IntroductionThe changes in grassland management and grassland types are strongly linked with dynamics in soil physico-chemical properties and vegetation attributes, with important implications for carbon/nitrogen cycling and greenhouse gas (GHG) fluxes. However, the seasonal variations of GHG emissions from sheepfolds, and the underlying biotic and abiotic drivers affecting GHG exchanges across different steppe and management types remain largely unclear.MethodsTaking the Inner Mongolian grassland as a model system, we measured the fluxes of CO2, CH4 and N2O, as well as soil and vegetation variables, in three contrasting grassland management areas (grazing, sheepfold, enclosure) and in three representative (wet typical, dry typical, desert) grassland ecosystems in July, September and November 2016.ResultsOur results showed that: (1) GHG fluxes were mostly higher in the plant growing season (July and September) than in the nongrowing season (November); sheepfold area had significantly higher GHG emissions (in July and mean over the season) than enclosed and grazing areas, with the effects being most pronounced in dry typical steppe. (2) The high GHG emissions in dry typical steppe were closely associated with the interactions among favorable soil temperature and moisture, high total organic carbon (TOC) content, and high aboveground biomass. The important predictors for CO2 emission were soil TOC and pH, whereas that for CH4 and N2O emissions were soil temperature and moisture content, in sheepfold areas. (3) Three GHG emissions were negatively affected by species richness across all steppe and management types, which might be a consequence of indirect effects through the changes in soil TOC and total nitrogen (TN).DiscussionThese results indicate that sheepfold areas are intensive hotspot sources of GHGs in the steppes, and it is of great importance to help to account GHG emissions and develop mitigation strategies for sheepfold areas for sustainable grassland management in the natural steppe based pastoral production ecosystems.

Frequent export of pig slurry for outside storage reduced methane but not ammonia emissions in cold and warm seasons

Manure management is a significant source of methane (CH4) and ammonia (NH3), and there is an urgent need for strategies to reduce these emissions. More frequent export of manure for outside storage can lower gaseous emissions from housing facilities, but the longer residence time may then increase emissions during outside storage. This study examined CH4 and NH3 emissions from liquid pig manure (pig slurry) removed from the in-house slurry collection pits at three different frequencies, i.e., three times per week (T2.3), once per week (T7), or once after 40 days (T40, reference). The slurry from treatments T2.3 and T7 was transferred for outside storage weekly over four weeks, and slurry from treatment T40 once after 40 days, in connection with summer and winter production cycles with growing-finishing pigs. The slurry was stored in pilot-scale storage tanks with solid cover and continuous ventilation. Compared to T40, the treatments T2.3 and T7 increased CH4 emissions during outside storage, but in-house emissions were reduced even more, and the net effects on total CH4 emissions from manure management (housing unit and outside storage) were reductions of 18–41% in summer and 53–83% in winter. The frequent slurry export for outside storage led to more NH3 emissions, except for the treatment T2.3, which has slurry funnel inserts beneath the slatted floor. Measurements of in-vitro CH4 production rates suggested that shorter residence time for slurry in pig houses delayed the development of active methanogenic populations, and that this contributed to the reduction of CH4 emissions.

Spatial distribution of CH4 emissions from livestock farming in Poland: a comparison of 2010 and 2020

ABSTRACT Among greenhouse gases (GHGs), methane (CH4) is a major contributor to global warming. Agriculture accounts for about 40% of CH4 emissions, with livestock being a crucial source. CH4 emissions from livestock primarily arise during enteric fermentation and manure management in livestock. This study aims to estimate Poland’s CH4 emissions from enteric fermentation and manure management in 2010 and 2020 at the municipal level (LAU-2). Data from the National Agricultural Census (NAC) and the UNFCCC National Inventory Report (NIR) for 2010 and 2020 were used for the analysis. The results reveal a slight overall increase in total CH4 emissions from livestock farming in Poland over the decade. The highest emissions were observed in regions where livestock farming was predominant, while significant changes in emissions occurred in regions experiencing considerable livestock production growth. Conversely, the lowest emissions were found in areas where the decrease in livestock population was most prominent. Understanding the spatial distribution of CH4 emissions from livestock farming at the municipal level is essential for effective climate change mitigation efforts. This study highlights the importance of continuous monitoring and analysis of livestock farming in Poland to assess its impact on GHG emissions and facilitate informed policy-making for sustainable agricultural practices.

Rewetting of Disused Drained Peatlands and Reduction of Greenhouse Gas Emissions

Drained peatlands are a significant source of greenhouse gas emissions to the atmosphere. When abandoned, they become the most likely sites of peat fires. An effective way to reduce greenhouse gas emissions and prevent peatland fires in disused drained peatlands is through rewetting and wetland restoration. These can make significant contributions to the implementation of the Paris Climate Agreement within the Land Use, Land-Use Change and Forestry sector and, ultimately, to climate change mitigation. An approach for estimating greenhouse gas emission reductions following rewetting, applicable to national and regional accounting, as well as to specific rewetting projects, is presented. It includes a methodology for determining effectively rewetted areas that can be considered wetlands, the application of IPCC greenhouse gas emission factors to said sites, and an uncertainty assessment. Starting from 2020 the Russian Federation National Report of anthropogenic emissions by sources and removals by sinks of greenhouse gasses not controlled by the Montreal Protocol utilised this approach in its inclusion of rewetted peatlands. An assessment of greenhouse gas emission reductions is presented using the example of a 1500 ha section of a peatland within the Fire Hazardous Peatland Rewetting Programme in Moscow Oblast (2010–2013). CO2 emission reductions were cumulatively 33.4 thous. t by 2022 (taking into account nitrous oxide fluxes, dissolved organic carbon removal and increased CH4 emissions—20 thous. t CO2-eq.) and are projected to reach almost 113 (68) thous. t by 2050. Greenhouse gas emission reductions not yet included as well as possible ways of accounting for them in the future are also noted.

Methane and nitrous oxide emissions from rice grown on organic soils in the temperate zone

Organic soils are important carbon stocks. The conventional (dry) cultivation of these soils turns them into strong sources of greenhouse gas (GHG) emissions. For situations where restoration of natural land cover is not possible, solutions to this problem include the wet cultivation of these soils, reducing CO2 and N2O emissions. One option, paddy rice cultivation, has begun in the Swiss Central Plateau, which hitherto did not provide a suitable climate for wet rice. Wet rice is however associated with high CH4 emissions. These need to be quantified for this region, as the increased CH4 fluxes might negate the expected reductions in CO2 and N2O. Here, we quantify CH4 and N2O emissions from wet rice on organic soil with chamber measurements, in an outdoor mesocosm experiment in the Swiss Central Plateau, located in the cool temperate moist zone. We apply two water treatments (a high water table (WT) treatment, − 6 cm with mid-season drainage, and two medium WT treatments, − 11 and − 17 cm without mid-season drainage) and additionally test the use of a mineral cover layer to reduce N2O emissions. Additionally, a deeply-drained grassland treatment is used as a reference treatment. Annual CH4 emissions from rice cultivation are 6.2 g CH4.m-2.a-1 for the higher WT treatment, 6.4 g CH4.m-2.a-1 for the medium WT treatment and 2.4 g CH4.m-2.a-1 for the medium WT treatment with mineral cover. The corresponding N2O emissions are 203, 190 and 56 mg N2O-N.m-2.a-1, respectively. These results show that adding a mineral cover layer reduces annual emissions from both GHGs substantially. In total, the maximum increase in CH4 and N2O emissions resulting from rice cultivation, compared to the drained grassland treatment, is 2.3 t CO2-eq.ha-1.a-1. Expected CO2 emissions savings (derived from a literature-based model) due to a higher WT are a factor of 5–9 greater than this. We thus conclude that the cultivation of these organic soils in this region with wet rice could reduce their induced warming compared to their cultivation with (deeply drained) grassland.

Optimizing fertilizer management mitigated net greenhouse gas emissions in a paddy rice-upland wheat rotation system: A ten-year in situ observation of the Yangtze River Delta, China

Optimizing the type and rate of nitrogen (N) fertilizer is an effective approach for achieving food security and minimizing environmental impacts. In this study, a ten-year in situ field experiment was conducted to evaluate the interannual responses of crop yields and greenhouse gas (GHG) emissions to the continuous application of chemical fertilizer (CF) and partial manure application (30 %, CFM) in a paddy rice-upland wheat rotation system. The results indicated that the trends of crop yields and GHG emissions were stable over ten years, and an appropriate N rate (200/150 kg N ha-1 for rice/wheat) in the rice-wheat system had greater potential for maintaining crop yields (9.25/3.32 t ha-1 for rice/wheat) and reducing their net GHG emissions by 20.8–38.7 % in contrast to the high rate (300/225 kg N ha-1 for rice/wheat). Among CF treatments, CH4 emissions had a negative correlation with the N rate, while N2O emissions were positively correlated. The CFM treatments significantly increased CH4 emissions (37.5–112.2 %) compared to the CF treatments during the rice season, but mitigated N2O emissions during both the rice (55.7–58.2 %) and wheat season (32.0–48.2 %). In a comprehensive assessment of the CH4 and N2O emissions in rice-wheat system, 81 % of the net GHG emissions was occurred in the rice season, and there was no significant difference between the CF and CFM at rate of 200/150 kg N ha-1. The study suggests that partial manure application at an optimum rate can effectively mitigate GHG emissions and be beneficial for the sustainability of rice and wheat production in a paddy rice-upland wheat rotation system.

Optimizing the Incorporated Amount of Chinese Milk Vetch (Astragalus sinicus L.) to Improve Rice Productivity without Increasing CH4 and N2O Emissions

Chinese milk vetch (CMV) is a leguminous green manure that is commonly cultivated in paddy fields and can partially substitute synthetic nitrogen fertilizer. However, the impacts of incorporating CMV on CH4 and N2O emissions are still a subject of controversy. Therefore, we conducted a field experiment over three years to investigate emissions under different substitution ratios: urea only (CF); incorporating a traditional amount of CMV (MV); and with incorporation ratios of 1/3 (MV1/3), 2/3 (MV2/3), and 4/3 (MV4/3) of MV for partial urea substitution. Compared with CF, MV2/3, MV, and MV 4/3 resulted in increased yields. MV and MV4/3 reduced N2O emissions but increased CH4 emissions by 28.61% and 85.60% (2019), 32.38% and 103.19% (2020), and 28.86% and 102.98% (2021), respectively, resulting in an overall increase in total global warming potential (except for MV in 2021). MV2/3 exhibited a low greenhouse gas intensity value ranging from 0.46 to 0.47. Partial least-squares-path model results showed that CH4 and N2O emissions were influenced by substitution ratios, which indirectly regulated the gene abundances of mcrA and nosZ. Overall, the impact of CMV on CH4 and N2O emissions was determined by substitution ratios. MV2/3, which involved partial substitution of synthetic N fertilizer with 15.0 t ha−1 of CMV, resulted in improved rice productivity without increasing CH4 and N2O emissions, making it a recommended approach in the study area.

Assessing the efficacy of water management and wheat straw addition in mitigating methane emissions from rice paddy fields

AbstractTo improve the quality of soil, agriculture typically uses organic additions like wheat straw (WS). Water management (WM) methods such as alternative wetness and dryness irrigation (AWDI) in paddy rice farming can increase water use efficiency and reduce greenhouse gas (GHG) emissions. In this study, a randomized complete block design (RCBD) pot greenhouse experiment was conducted to assess the effects of WM (CFI (continued flooding irrigation) and AWDI), WS (15.0 and 30.0 ton ha−1), and their interaction (WS*WM) on CH4 emissions and rice yield in a paddy calcareous soil cultivated with rice. The largest CH4 emission occurred 30 and 70 days following rice planting. Single applications of WS at 15.0 and 30.0 ton ha−1 significantly increased CH4 emissions by 19.60% and 68.70% (P < 0.01), respectively, compared to the Control. Compared to CFI, the AWDI reduced CH4 emissions by 31.20% (P < 0.01). The correlations between AWDI and CH4 emissions in days after rice planting were significantly negative at the 0.01 level based on Pearson correlation. Adding WS in the AWDI significantly decreased CH4 emissions by 27.70 and 25.64% in 15.0 and 30.0 ton ha−1 added WS (P < 0.05), respectively, compared to sole WS. Both rates of WS resulted in a considerable increase in biomass and rice grain compared to the Control, while the AWDI had no significant effect on biomass and grain yield. Our data showed significant interaction between AWDI and WS on biomass. Our study shows that the AWDI saved 18.50% water compared to the CFI.

The Importance of Spatial Resolution in the Modeling of Methane Emissions from Natural Wetlands

An important uncertainty in the modeling of methane (CH4) emissions from natural wetlands is the wetland area. It is difficult to model wetlands’ CH4 emissions because of several factors, including its spatial heterogeneity on a large range of scales. In this study, we investigate the impact of model resolution on the simulated wetland methane emission for the Fennoscandinavian Peninsula. This is carried out using a high-resolution wetland map (100 × 100 m2) and soil carbon map (250 × 250 m2) in combination with a highly simplified CH4 emission model that is coarsened in five steps from 0.005° to 1°. We find a strong relation between wetland emissions and resolution, which is sensitive, however, to the sub-grid treatment of the wetland fraction. In our setup, soil carbon and soil moisture are positively correlated at a high resolution, with the wetland location leading to increasing CH4 emissions with increasing resolution. Keeping track of the wetland fraction reduces the impact of resolution. However, uncertainties in CH4 emissions remain high because of the large uncertainty in the representation of wetland the area, as demonstrated using the output of the WetChimp intercomparison over our study domain. Because of wetland mapping uncertainties, existing models are unlikely to realistically represent the correlation between soil moisture and soil carbon availability. The correlation is positive in our simplified model but may be different in more complex models depending on their method of representing substrate availability. Therefore, depending on the correlation, CH4 emissions may be over- or underestimated. As increasing the model resolution is an effective approach to mitigate the problem of accounting for the correlation between soil moisture and soil carbon and to improve the accuracy of models, the main message of this study is that increasing the resolution of global wetland models, and especially the input datasets that are used, should receive high priority.

Integrating low levels of organic fertilizer improves soil fertility and rice yields in paddy fields by influencing microbial communities without increasing CH4 emissions

Although organic fertilizer is usually recommended for improving soil quality and crop yields, it inevitably enhances methane (CH4) emissions. Effective measures to mitigate CH4 emissions while ensuring crop yields are urgently needed. A two-year experiment was performed to examine the effects of organic-inorganic fertilizer combinations on CH4 emissions, the CH4-related microbial community, soil biochemical characteristics, and rice yields during dual rice growing seasons in 2020–2021 at two locations (i.e., Nanning and Yulin City, Southern, China). The treatments were as follows: no N fertilizer (Neg-CF), 100 % chemical fertilizer (CF) (Pos-CF), 60 % cattle manure (CM) + 40 % CF (High-CM), 30 % CM + 70 % CF (Low-CM), 60 % poultry manure (PM) + 40 % CF (High-PM), and 30 % PM + 70 % CF (Low-PM). CH4 fluxes and related functional microorganism abundances were investigated using the closed chamber method and molecular procedures, respectively. The addition of organic manure significantly improved rice grain yields and soil properties, including total nitrogen (TN), soil organic carbon (SOC), and pH compared to the Pos-CF. Similarly, integrating organic and inorganic fertilizers led to significant increases in seasonal CH4 emissions, global warming potential (GWP), and the abundance of CH4-related soil microbes. Average increases in SOC, TN, CH4 emissions, and GWP in the High-PM treatment relative to the Pos-CF were 44.7, 36.4, 20.6, and 24.4 %, respectively, in Nanning; and 28.9, 33.3, 23.4, and 20.8 % in Yulin City, averaged across the years. Moreover, co-fertilization resulted in the highest increase in methanogenic diversity and abundance relative to Pos-CF only. Applying high proportions of manure improved the abundance of methanogenic soil archaea related to CH4 production compared with the plots with low proportions of manure. Interestingly, lower manure amendments produced the highest rice grain yields and lowest CH4 emissions while maintaining high soil qualities. In addition, regression analysis exhibited that SOC was highly positively associated with CH4 emissions. Above all, controlling the proportions of organic manure and CF may be a feasible approach for enhancing rice yields and soil quality while mitigating CH4 emissions. Of the treatments tested, the combination of 30 % organic manure (i.e., CM or PM) with 70 % CF (urea) performed the best. This study showed that combining manure and CF at a 30:70 ratio was the most effective approach for improving soil health and rice yields while ensuring environmental sustainability.

Biochar return in the rice season and straw mulching in the oilseed rape season achieve high nitrogen fertilizer use efficiency and low greenhouse gas emissions in paddy-upland rotations

Straw return can enhance crop yields and nitrogen fertilizer use efficiency (NFUE) in paddy-upland rotation systems. However, straw return in wetland rice systems can significantly increase CH4 emissions, which could be alleviated if the straw is converted to biochar before incorporation. This study investigated the effect of different crop residue management strategies on NFUE and greenhouse gas (GHG) emissions in a paddy-upland rotation over a four-year field experiment. We compared two treatments where all crop residues were removed (no N fertilizer (PK), recommended N fertilizer (NPK)) with three different methods of straw return. This included (i) direct straw return (NPK+S/S), where all crop residues were directly applied to the field after harvest; (ii) straw return as biochar (NPK+B/B), where all crop residues were converted into biochar before incorporation; (iii) straw return as biochar in the rice season and direct straw return in the oilseed rape season (NPK+B/S). Four-year crop yields, NFUE, two-year ammonia (NH3) volatilization, and GHG emissions were determined. The results showed that compared with the NPK treatment, straw and biochar return increased rice and oilseed rape yields by 0.41–0.80 t ha−1 and 0.24–0.33 t ha−1, respectively, and the annual NFUE by 4.3–6.9%. Direct straw return (NPK+S/S) did not significantly affect annual NH3 volatilization, but significantly increased cumulative N2O emissions (by 27.3%), CH4 (by 132.4%), global warming potential (GWP, by 75.2%) and greenhouse gas emissions intensity (GHGI, by 61.1%), respectively. In contrast, converting crop residues into biochar before incorporation significantly reduced annual NH3 volatilization and N2O and CH4 emissions. Compared with the NPK+S/S treatment, the NPK+B/B and NPK+B/S treatments reduced cumulative N2O by 20.5–26.7% and CH4 emissions by 56.5–65.9% with the corresponding reduction in GWP value (42.3–50.4%) and GHGI value (44.3–52.6%). Considering biochar production cost, we recommended straw return as biochar in the rice season and straw mulching in the upland season as a measure to increase crop yields and NFUE while reducing GHG emissions in the paddy-upland rotation.

Potential functional differentiation from microbial perspective under dryland-paddy conversion in black soils

Improving soil carbon sequestration and reducing greenhouse gas emissions in farmland require understanding how the microbial communities that control the agroecosystem function. Here, we surveyed the soil microbial communities in neighboring pairs of dryland and paddy fields in the black soils of northeastern China. Soil moisture, mean weight diameter of aggregates, fluorescence index and biological index of dissolvable organic matter, total anion concentration, and prokaryotic community α-diversity were higher in paddy soils than in dryland soils, while soil saturated hydraulic conductivity (SHC), dissolvable total nitrogen, and fungal community α-diversity were lower in paddy soils than in dryland soils. Moreover, soil moisture (P < 0.01) and SHC (P < 0.05) had significantly positive correlations with the α-diversity of prokaryotic and fungal communities, respectively. The co-occurrence network complexity of microbial communities was lower in paddy fields than in dryland fields, while the co-occurrence network tightness and cooperation of microbial communities were higher in paddy fields than in dryland fields, which may help paddy microbiome resist environmental disturbances. Taken together, both dryland and paddy fields had their own advantages in evaluating soil biological health from microbial community diversity and network stability. Additionally, the differential groups of CH4 production, S cycle, and Fe cycle (e.g., Bathyarchaeota, Bacteroidetes, and Geobacter) increased, while those of environmental remediation and biological control (e.g., Blastococcus and Roseiflexus) decreased after the change from dryland to paddy fields. Further combined with metagenomic analysis, the functions of CH4 production, CO2 fixation, N fixation, and sulfur reduction were enhanced in paddy soils, while those of CH4 oxidation, nitrification, and N2O production were reduced. In conclusion, the ecological functioning of the differential groups may lead to the increase of CH4 emission and CO2 fixation, and the decrease of N2O emission in paddy fields of black soil, even in non-flooding period.

Contrasting response strategies of microbial functional traits to polycyclic aromatic hydrocarbons contamination under aerobic and anaerobic conditions

PAHs (Polycyclic aromatic hydrocarbons) are widely distributed in soil ecosystems, but our knowledge regarding the impacts of PAHs effects on soil microbial functional traits is limited. In this study, we evaluated the response and regulating strategies of microbial functional traits that are associated with the typical C, N, P, S cycling processes in a pristine soil under aerobic and anaerobic conditions after the addition of PAHs. Results revealed that indigenous microorganisms had strong degradation potential and adaptability to PAHs especially under aerobic conditions, while anaerobic conditions favored the degradation of high molecular weight PAHs. PAHs exhibited contrasting effects on soil microbial functional traits under different aeration conditions. It would probably change microbial carbon source utilization preference, stimulate inorganic P solubilization and strengthen the functional interactions between soil microorganisms under aerobic conditions, while might cause the increase of H2S and CH4 emissions under anaerobic conditions. This research provides an effective theoretical support for the ecological risk assessment of soil PAHs pollution.

Methane emission, intake, digestibility, performance and blood metabolites in sheep supplemented with cupuassu and tucuma cake in the eastern Amazon.

The use of co-products as a feed supplement for ruminants makes livestock sustainable and optimizes the use of available areas and animal performance. Furthermore, when cakes are used, the residual fat composition can influence ruminal metabolism and methane (CH4) production. This study aimed to assess the effects of a diet containing cupuassu (CUP; Theobroma grandiflorum) and tucuma (TUC; Astrocaryum vulgare Mart.) cakes on intake, digestibility, serum metabolites, performance, and CH4 emissions in confined sheep in the Amazon. Approximately 28 animals, Dorper-Santa Inês, castrated, with an average initial live weight (ILW) of 35 ± 2.3 kg, were distributed in metabolic cages, in a completely randomized design, with four treatments and seven replications: (1) Control (C40), without the addition of Amazonian cake and with 40 g of ether extract (EE)/kg of dietary dry matter (DM); (2) CUP, the inclusion of the CUP cake and 70 g of EE/kg; (3) TUC, the inclusion of the TUC cake and 70 g of EE/kg; and (4) Control (C80), without the addition of Amazonian cake and with 80 g of EE/kg of dietary DM, with roughage to concentrate ratio of 40:60. The use of the TUC cake as a feed supplement reduced the intake of DM, crude protein (CP), and EE compared to the inclusion of the CUP cake (p < 0.05); however, it increased the intake of neutral detergent fiber (NDF) by 32% (p < 0.01). The highest averages of DM (732 g/kg) and CP (743 g/kg) digestibility were presented in C40, while the highest digestibility of NDF was presented in TUC (590 g/kg). Albumin levels stayed above and protein levels were below the reference values, and the C40 diet also obtained below results for cholesterol, triglycerides and High Density Lipoprotein (HDL) (P < 0.05). Sheep fed CUP (91 g) and TUC (45 g) had lower daily weight gains (DWGs) than those fed with diets without the inclusion of cakes (C40 = 119 g; C80 = 148 g), and feed efficiency (FE) was also lower in CUP (84) and TUC (60) diets than in C40 (119) and C80 (137) diets. CH4 emissions were lower in animals fed TUC (26 L/day) and higher in C40 (35 L/day); however, TUC resulted in higher CH4 emissions in grams/body live weight (BW) gain/day (353 g/BW/day) vs. 183 g/BW/day (C40), 157 g/BW/day (C80), and 221 g/BW/day (CUP). The supplementation with cakes did not improve intake, digestibility and performance, did not compromise blood metabolites and did not reduce the enteric CH4 emission in confined sheep in the Amazon; however, the use of CUP cake showed similar results to the control treatments and did not increase CH4 emissions, as occurred with the inclusion of TUC cake.

The unexpected long period of elevated CH4 emissions from an inundated fen meadow ended only with the occurrence of cattail (Typha latifolia).

Drainage and agricultural use transform natural peatlands from a net carbon (C) sink to a net C source. Rewetting of peatlands, despite of high methane (CH4 ) emissions, holds the potential to mitigate climate change by greatly reducing CO2 emissions. However, the time span for this transition is unknown because most studies are limited to a few years. Especially, nonpermanent open water areas often created after rewetting, are highly productive. Here, we present 14 consecutive years of CH4 flux measurements following rewetting of a formerly long-term drained peatland in the Peene valley. Measurements were made at two rewetted sites (non-inundated vs. inundated) using manual chambers. During the study period, significant differences in measured CH4 emissions occurred. In general, these differences overlapped with stages of ecosystem transition from a cultivated grassland to a polytrophic lake dominated by emergent helophytes, but could also be additionally explained by other variables. This transition started with a rapid vegetation shift from dying cultivated grasses to open water floating and submerged hydrophytes and significantly increased CH4 emissions. Since 2008, helophytes have gradually spread from the shoreline into the open water area, especially in drier years. This process was periodically delayed by exceptional inundation and eventually resulted in the inundated site being covered by emergent helophytes. While the period between 2009 and 2015 showed exceptionally high CH4 emissions, these decreased significantly after cattail and other emergent helophytes became dominant at the inundated site. Therefore, CH4 emissions declined only after 10 years of transition following rewetting, potentially reaching a new steady state. Overall, this study highlights the importance of an integrative approach to understand the shallow lakes CH4 biogeochemistry, encompassing the entire area with its mosaic of different vegetation forms. This should be ideally done through a study design including proper measurement site allocation as well as long-term measurements.

Rice husk and husk biochar soil amendments store soil carbon while water management controls dissolved organic matter chemistry in well-weathered soil

Rice agriculture feeds over half the world's population, and paddy soils impact the carbon cycle through soil organic carbon (SOC) preservation and production of carbon dioxide (CO2) and methane (CH4), which are greenhouse gases (GHG). Rice husk is a nutrient-rich, underutilized byproduct of rice milling that is sometimes pyrolyzed or combusted. It is unresolved how the incorporation of these residues affects C dynamics in paddy soil. In this study, we sought to determine how untreated (Husk), low-temperature pyrolyzed (Biochar), and combusted (CharSil) husk amendments affect SOC levels, GHG emissions, and dissolved organic matter (DOM) chemistry. We amended Ultisol paddy mesocosms and collected SOC and GHG data for three years of rice grown under alternate wetting and drying (AWD) conditions. We also performed a greenhouse pot study that included water management treatments of nonflooded, AWD, and flooded. Husk, Biochar, and CharSil amendments and flooding generally increased SOC storage and CH4 emissions, while nonflooded conditions increased N2O emissions and nonflooded and CharSil treatments increased CO2 emissions. All amendments stored ∼0.15 kg C m−2 y−1 more SOC than CH4 emissions (as CO2 equivalents), but the combustion of husk to produce CharSil resulted in the net release of CO2 which negates any SOC storage. UV–visible absorption/fluorescence spectroscopy from the pot study suggests that nonflooded treatment decreased DOM aromaticity and molecular size. Our data show that flooding and amendment of Husk and Biochar maximized C storage in the highly weathered rice paddy soil under study despite Husk increasing CH4 emissions. Water management affected dissolved organic matter chemistry more strongly than amendments, but this requires further investigation. Return of rice husk that is untreated or pyrolyzed at low temperature shows promise to close nutrient loops and preserve SOC in rice paddy soils.

Exploring the effects of extreme weather events on methane emissions from croplands: A study combining site and global modeling

Croplands, especially rice paddies, are important anthropogenic sources of methane (CH4) emission. Currently, the effects of extreme weather events, which are occurring more frequently with climate warming, on CH4 emissions from croplands still remain uncertain. In this study, we calibrated the CLM5BGCCrop model and implemented it to nine cropland sites and global simulations, in order to a) analyze the spatial and temporal variations of CH4 emissions from different crop and climate types, b) identify corresponding environmental controlling factors, and c) investigate the effects of extreme weather events on CH4 emissions. The results show that parameterized CLM5BGCCrop could simulate CH4 emissions from croplands well at both site and global scales. The simulated CH4 emissions from rice paddies (44.35 Tg CH4 yr−1) are 1–2 orders of magnitude higher than those from corn (0.38 Tg CH4 yr−1) and wheat (2.57 Tg CH4 yr−1) fields. Soil water content is the key factor affecting global CH4 emissions from croplands under present and future climate. Extreme high-temperature events occurring during the rice booting-flowering stage could reduce the CH4 emissions by 28%, while the CH4 emissions could be increased by 12–16% when extreme high-temperature events occurred during the rice milky-maturity stage. Extreme precipitation events increased CH4 emissions by 7% at the rice paddy site. At the global scale, extreme high temperature increased CH4 emissions from rice paddies by 8% at middle latitudes, in contrast, extreme high temperature reduced corresponding emissions by 12% at low latitudes, but the decrease in CH4 emissions from rice paddies at low latitudes will be reversed to a 9% increase in 2081–2100. Overall, the increasing frequency and intensity of extreme weather events in future may lead to increased global CH4 emissions from croplands.