CH4 Emission Flux Research Articles

Greenhouse Gas Emission Characteristics and Influencing Factors from Vegetable Fields with Different Organic Planting Years

To clarify the characteristics of greenhouse gas emissions （CO2, CH4, and N2O） and the comprehensive greenhouse effect from vegetable fields with different organic planting years, the differences in greenhouse gas emission flux, emission intensity （GHGI）, and global warming potential （GWP） and their influencing factors among vegetable fields with different organic planting years in Songhuaba, including 10 years, 6 years, 3 years, and conventional planting, were analyzed. The results showed that the CO2 emissions from organic planting treatments were higher than those from conventional planting, whereas the N2O and CH4 emissions were the opposite. Compared to those from conventional planting, the CO2 emission fluxes and cumulative emissions from organic cultivation for 10, 6, and 3 years increased by 121.28% and 40.44%, 144.61% and 51.39%, and 130.10% and 41.77% （P < 0.05）, respectively, and the N2O emission fluxes and cumulative emissions decreased by 26.08% and 186.03%, 9.6% and 3.55%, and 35.9% and 151.78%, respectively. The CH4 emission flux was shown as follows： conventional planting > organic planting for 10 years > organic planting for 6 years > organic cultivation for 3 years, and the CH4 emissions from cultivational planting and organic planting for 10 years were shown as "source," while the CH4 emissions from organic planting for 6 years and 3 years were shown as "sink." Compared with those from conventional planting, the GWP and GHGI from organic planting for 10 years and 3 years were reduced by 40.57% and 61.43%, 43.83% and 57.98% （P < 0.05）, respectively. Organic planting slightly reduced the vegetable yield but significantly reduced GWP and GHGI （P < 0.05）. Soil temperature and humidity, SOC, and inorganic nitrogen were the key factors affecting the difference in greenhouse gas emissions between treatments. Organic planting significantly reduced greenhouse gas emissions from vegetable fields, and the differences in greenhouse gas emissions among different years of organic planting were closely related to soil organic carbon and inorganic nitrogen. The research results can provide a scientific basis for carbon sequestration, emission reduction, and the green development of organic vegetable production systems.

Effects of Different Rice Varieties and Water Management Practices on Greenhouse Gas (CH4 and N2O) Emissions in the Ratoon Rice System in the Upper Yangtze River Region, China

Ratoon rice can improve rice yield by increasing the multiple cropping index in China. However, the greenhouse gas (CH4 and N2O) emission characteristics from ratoon rice fields and the cultivation methods to reduce CH4 and N2O emissions are rarely reported. This study first conducted the analysis of genotype differences in greenhouse gas emission fluxes using five strong ratoon ability rice varieties in 2020. Second, water management methods, including alternating the wet–dry irrigation (AWD) pattern and conventional flooding irrigation (CF) during the main season, were carried out in 2021. CH4 and N2O emission flux, agronomic traits, and rice yield during both main and ratoon seasons were investigated. The results showed that the CH4 emission flux during the main and ratoon seasons was 157.05–470.73 kg·ha–1 and 31.03–84.38 kg·ha–1, respectively, and the total N2O emission flux was 0.13–0.94 kg·ha–1 in the ratoon rice system over the two seasons (RRSTS). Compared with the main season, the CH4 emission flux during the ratoon season was significantly reduced, thus decreasing the greenhouse gas global warming potential (GWP) and greenhouse gas emission intensity (GHGI) in the ratoon rice system. Cliangyouhuazhan (CLYHZ) showed a high yield, and the lowest GWP and GHGI values among the five rice varieties in RRSTS. Compared with CF, the AWD pattern reduced the CH4 emission flux during the main and ratoon seasons by 67.4–95.3 kg·ha–1 and 1.7–5.1 kg·ha–1, respectively, but increased the N2O emission flux by 0.1–0.6 kg·ha–1 during the RRSTS. Further, compared with CF, the AWD pattern had a declined GWP by 14.3–19.4% and GHGI by 30.3–34.3% during the RRSTS, which was attributed to the significant reduction in GWP and GHGI during the main season. The AWD pattern significantly increased rice yield by 21.9–22.9% during the RRSTS, especially for YX203. Correlation analysis showed that CH4, GWP, and GHGI exhibited significant negative correlations with spikelet number per m2 and the harvest index during the main and ratoon seasons. Collectively, selecting the high-yield, low-emission variety CLYHZ could significantly reduce greenhouse gas emissions from ratoon rice while maintaining a high yield. The AWD pattern could reduce total CH4 emission during the main season, reducing the GWP and GHGI while increasing the ratoon rice system yield. It could be concluded that a variety of CLYHZ and AWD patterns are worthy of promotion and application to decrease greenhouse gas emissions in the ratoon rice area in the upper reaches of Yangtze River, China.

Effects of Rice Root Development and Rhizosphere Soil on Methane Emission in Paddy Fields.

Paddy fields are important anthropogenic emission sources of methane (CH4). However, it is not clear how rice root development and rhizosphere soil properties affect CH4 emissions. Therefore, we selected rice varieties with similar growth periods but different root traits in the local area. We measured CH4 emission fluxes, cumulative CH4 emissions, root dry weight, root length, and the dissolved organic carbon (DOC), microbial biomass carbon (MBC), redox potential (Eh), ammonium nitrogen (NH4+-N), and nitrate nitrogen (NO3--N) contents in rhizosphere soil. Methanogens and methanotrophs are crucial factors influencing CH4 emissions; thus, their abundance and community composition were also assessed. The result showed that CH4 fluxes of each rice variety reached the peak at tillering stage and jointing-booting stage. The CH4 emissions in tillering stage were the largest in each growth period. CH4 emissions had negative correlations with root length, root dry weight, Eh NO3--N, methanotroph abundance, and the pmoA/mcrA ratio, and positive correlations with NH4+-N, MBC, DOC, and methanogen abundance. Path analysis confirmed methanogens and methanotrophs as direct influences on CH4 emissions. Root development and rhizosphere soil properties affect CH4 emissions indirectly through these microbes. This study suggests that choosing rice varieties with good root systems and managing the rhizosphere soil can effectively reduce CH4 emissions.

Response of grassland greenhouse gas emissions to different human disturbances – A global Meta-analysis

Human disturbances have increased greenhouse gas (GHG) emissions from grassland, worsening global warming. However, the response of grassland GHG (CO2, N2O, and CH4) to human disturbances across various climatic zones requires further elucidation, as does the intricate relationship between GHG emissions and temperature and precipitation. A Meta-analysis of the effects of human disturbances on GHG in grassland over the past 40 years revealed that grazing, fertilization, mowing, and burning significantly influenced the total emissions of N2O, CH4, CO2, and GHG from grassland. However, the light and moderate grazing exerted no substantial impact on CO2 emission flux. In frigid zone grassland, the N2O emission flux was most significantly affected by grazing, the CH4 emission flux affected by fertilization was higher than grazing, and the CO2 emission flux was more sensitive to heavy grazing than severe fertilization. In temperate grassland and savanna, GHG emission flux was most sensitive to fertilization, with CO2 emission flux in savanna being particularly responsive to burning. The effect of increased temperature and precipitation on CO2e in fertilized grassland was approximately double that of grazed grassland and quadruple that of mowed grassland. This study emphasizes the increased effect of human disturbances on GHG emissions in the grassland, especially with the most significant impact of fertilization disturbances on GHG emissions in most grassland areas. Lowering the level of fertilization during grassland management could serve as a crucial step in mitigating GHG emissions from grassland. In summary, rigorous control of disturbance intensity represented an effective strategy for mitigating greenhouse gas emissions, albeit potentially impacting grassland productivity. Future endeavors should focus on determining the optimal disturbance intensity to strike a balance amidst these complex effects.

Impact of iron-modified fillers on enhancing water purification performance and mitigating greenhouse effect in constructed wetlands

ABSTRACT Iron is gradually being introduced into constructed wetlands (CWs) to enhance the removal of pollutants due to its active chemical properties and ability to participate in various reactions, but its effectiveness in greenhouse effect control needs to be studied. In this study, three CWs were established to evaluate the effect of iron scraps and iron-carbon as substrates on pollutants removal and greenhouse gas (GHG) emissions, and the corresponding mechanisms were explored through analysis of microbial characteristics. The results showed that iron scraps and iron – carbon are effective in enhancing the effluent quality of CWs. Iron-carbon exhibited notable efficacy in removing nitrate nitrogen (NO3 --N) and chemical oxygen demand (COD), achieving stable removal rates of 98.46% and 84.89%, respectively. Iron scraps had advantages in promoting the removal of ammonia nitrogen (NH4 +-N) and total nitrogen (TN), with removal rates of 43.73% and 71.56%, respectively. The emission fluxes of nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) had temporal variability, always peaking in the early phases of operation. While iron scraps and iron-carbon effectively reduced the average emission flux of N2O and CO2, they simultaneously increased the average emission flux of CH4 (from 0.2349–2.2698 and 1.1956mg/m2/h, respectively). From the perspective of reducing global warming potential (GWP), iron – carbon had superior performance (from 146.2548–86.7447 mg/m2/h). In addition, the greenhouse gas emission flux was closely related to the microbial community structure in CWs, particularly with a more pronounced response observed in N2O emissions.

Straw type and nitrogen-water management balance rice yield and methane emissions by regulating rhizosphere microenvironment

Context or problemStraw incorporation improves soil fertility but also poses environmental challenges due to increasing methane (CH4) emissions in paddy fields. Whether nitrogen (N) and water management can balance rice yield and CH4 emissions under different crop straw incorporation is still not well-documented. ObjectiveA three-year field experiment was conducted to probe the comprehensive effects of N application ratios and irrigation regimes on rice yield, rhizosphere soil properties, and CH4 emissions, along with the underlying mechanisms of CH4 emission variations among different straw types. MethodsA two-factor randomized block design was used with two Japonica rice cultivars as materials in 2020 and 2021. The straw incorporation treatment included no straw incorporation (NS), wheat straw incorporation (WS), and rape straw incorporation (RS). The N fertilizer application treatments included local farmers' fertilizer practice (LFP) and increasing basal fertilizer rate (IBF). Two irrigation practices, continuously-flooded irrigation (CF) and alternate wetting and drying irrigation (AWD), were designed under the WS and RS treatments in 2022. Results1) WS-IBF and RS-IBF enhanced yield by 6.70∼9.03 % and 8.13∼9.50 % compared to WS-LFP and RS-LFP, respectively. AWD further increased yield by 6.28∼7.76 % compared to CF. 2) WS-IBF and RS-IBF enhanced dissolved organic carbon (DOC) content, synchronously boosted the methanogens (mcrA) and methanotrophs (pmoA) abundances, but decreased the pmoA/mcrA ratio, which significantly promoted CH4 emission flux in early growth stage. This resulted in a 5.04∼8.01 % and 4.60∼7.88 % increase in CH4 emissions compared to WS-LFP and RS-LFP, respectively, but a decrease in yield-scaled CH4 emissions. AWD reduced DOC content, facilitated the conversion of ammonium N to nitrate N, increased dissolved oxygen content, and hence decreased CH4 emissions by 23.41∼24.38 % compared to CF. 3) RS significantly increased microbial biomass C, N, and related metabolites, leading to a 1.29∼2.73 % increase in yield compared to WS. Meanwhile, RS promoted Nitrospira abundance as well as pterin and flavonoid metabolites associated with mcrA inhibition, while decreasing Anaeromyxobacter abundance, ammonium N, and DOC content, resulting in an increase in the pmoA/mcrA ratio and a noticeable drop in CH4 emissions compared to WS. ConclusionsRS combined with IBF and AWD is a more sustainable integrated practice in light of the synergistic improvement in rice production and environmental benefits. ImplicationsThe results reveal that optimizing N and water management can synergize high-yield and low-carbon by regulating rhizosphere microenvironment in rice production under crop straw incorporation.

Overlooked drivers of the greenhouse effect: The nutrient-methane nexus mediated by submerged macrophytes

Submerged macrophytes remediation is a commonly used technique for improving water quality and restoring habitat in aquatic ecosystems. However, the drivers of success in the submerged macrophytes assembly process and their specific impacts on methane emissions are poorly understood. Thus, we conducted a mesocosm experiment to test the growth plasticity and carbon fixation of widespread submerged macrophytes (Vallisneria natans) under different nutrient conditions. A refined dynamic chamber method was utilized to concurrently collect and quantify methane emission fluxes arising from ebullition and diffusion processes. Significant correlations were found between methane flux and variations in the physiological activities of V. nantas by the fluorescence imaging system. Our results show that exceeding tolerance thresholds of ammonia in the water significantly interfered with the photosynthetic systems in submerged leaves and the radial oxygen loss in adventitious roots. The recovery process of V. natans accelerated the consumption of dissolved oxygen, leading to increase in the populations of methanogen (153.3 % increase of mcrA genes) and subsequently elevating CH4 emission fluxes (23.7 %) under high nutrient concentrations. Conversely, V. natans increased the available organic carbon under low nutrient conditions by radial oxygen loss, further increasing CH4 emission fluxes (94.7 %). Quantitative genetic and modeling analyses revealed that plant restoration processes drive ecological niche differentiation of methanogenic and methane oxidation microorganisms, affecting methane release fluxes within the restored area. The speciation process of V. natans is incapable of simultaneously meeting improved water purification and reduced methane emissions goals.

Effects of filter-feeding fish faeces on microbial driving mechanism of lake sediment carbon transformation

Silver carp (Hypophthalmichthys molitrix) can filter the carbon in the food taken up by phytoplankton and plays an important role in carbon fixation. In this study, the faeces of silver carp, the dominant fish species in Qiandao Lake, China, were collected and subjected to a closed incubation and transformation experiment for three months. The physical and chemical indices of water and sediment mixture, carbon metabolic enzyme activity, and microbial sequences were analyzed to identify the key microbial strains that affect carbon transformation as well as the main factors influencing carbon transformation. The results showed maximum CO2 and CH4 emission fluxes on day 15 of fish faeces and sediment interaction. In the faeces addition group, the contents of soluble organic carbon, soluble inorganic carbon, SO42−, and PO43− were significantly increased, while the dissolved oxygen content was significantly decreased. Furthermore, the pH, total carbon content, volatile suspended solids content, and activities of four carbon-metabolizing enzymes were significantly increased in the faeces addition group. The 16sRNA analysis of methanogenic and methane-oxidizing bacteria showed that Euryarchaea and Pseudomonas accounted for the highest proportion respectively. The most significant differences expression were found for Methylbacterium in the methanogenic bacteria and Methylobacter in the methane oxidizing bacteria. Structural variance model showed that interaction of fish faeces and sediments mainly caused changes in sulfate content, leading to variations in methanogens and methanotrophs and promotion of CH4 emission. The results of this study can provide a theoretical reference for the mechanism of carbon reduction and emission reduction of lake filter-feeding fish.

Research Progress on Production and Emission of CH4 and N2O from Urban Rivers

Methane （CH4） and nitrous oxide （N2O） are concerning greenhouse gases. Urban rivers have been important emission sources of CH4 and N2O in recent years. It is meaningful for city greenhouse gas reduction to provide a systematic analysis of spatiotemporal characteristics, mechanisms, and influencing factors of the production and emission of CH4 and N2O from urban rivers. This study combed measured data of urban river CH4 and N2O dissolution concentrations and emission fluxes from related literature published in the past 20 years and also concluded the spatiotemporal characteristics of urban river CH4 and N2O emissions. This study estimated that CH4 and N2O emissions （expressed by CO2-eq） from urban rivers in Beijing were 234.63 and 59.53 Gg CO2-eq in 2018, whereas CH4 and N2O emissions （expressed by CO2-eq） from urban rivers in Shanghai were 159.86 and 260.24 Gg CO2-eq in 2018, respectively. These results demonstrated that urban rivers have become important CH4 and N2O emission sources. This study summarized the production/consumption processes and import/export pathways of CH4 and N2O in urban rivers. What is more, this study discussed the main influencing factors of urban river CH4 and N2O production and emissions from the perspectives of river environmental conditions and urbanization effects. At last, the present work prospected the future research trends of urban river CH4 and N2O emissions and provides urban rivers with scientific support for greenhouse gas reduction.

New insights for simultaneous nitrogen removal and greenhouse gas reduction by biological-electrolysis constructed wetland in the treatment of aquaculture wastewater under varied C/N

Aiming to address the challenges of poor nitrogen (N) removal and greenhouse gas (GHG) emissions in aquaculture wastewater treatment, biological-electrolysis constructed wetland (BECW) and constructed wetland (CW) were established to comparatively evaluate the N removal efficiency, the greenhouse gas (GHG) emissions, and specific microbial gene abundances under various influent C/N ratios. Increasing influent C/N ratio markedly enhanced the removal rates of COD, NH4+-N, NO3−-N, and TN, while markedly reduced N2O fluxes in CW and BECW. The integration of an electric field with CW (BECW) significantly compensated for the shortcomings of the poor NO3−-N removal efficiency and high N2O emissions when C/N < 6. However, this compensating effect gradually weakened with the continue increase of C/N. BECW simultaneously achieved the high COD (89.26 ± 6.08 %), NO3−N (97.03 ± 1.22 %), and TN (83.17 ± 3.19 %) removal rates, and low GHG emissions (486.00 ± 36.61 mg/m2/h) at C/N = 6. The BECW significantly decreased the abundance of mcrA and pmoA genes while increased the abundance of nirK, nirS, and nosZ genes, and the ratios of pmoA/mcrA and nosZ/(nirS + nirK) across all C/N condition. The emission flux of CH4 in BECW was positively correlated with C/N and the mcrA abundance but significantly negatively correlated with pmoA abundance and pmoA/mcrA. The emission flux of N2O was positively correlated with nirS and nirK abundance but significantly negatively correlated with C/N, NO3−-N removal rates, nosZ abundance, and the index of nosZ/(nirS + nirK). This research offers an innovative approach to get both low GHG emissions and high NO3−-N removal rate in aquaculture wastewater treatment.

Greenhouse gas emissions and carbon and water footprints during processing of Lei bamboo shoots

Lei bamboo shoots are extensively used in the food processing industry, producing solid waste such as bamboo shoot shells and liquid wastewater. This study analyzed several sewage indicators, revealing that the majority exceed the national standards of China for direct water discharge. A field experiment was conducted over a period of 4 months to evaluate the effects of different treatments during the natural decomposition of bamboo shoot shells.The treatment groups consisted of the boiled experimental group (EG) and the control group (CG). Results showed that in EG, the methane emission increased by 8.6% (P < 0.05), the carbon dioxide emission increased significantly by 19.7% (P < 0.01), and the nitrous oxide emission decreased by 37.9% (P < 0.01) relative to those in CG. Regression analysis was employed to establish a relationship model between CH4, CO2, and N2O emission fluxes and temperature and humidity in the EG and CG groups. A specific functional relationship was identified between CH4 and CO2 emission fluxes and temperature and humidity, but N2O emission was present. No significant correlation was found between flux and ambient temperature and humidity (R2 < 0.3). We also estimated that the carbon dioxide emissions and water consumption of producing 1 kg of canned bamboo shoots were 2.8669 kg and 86.8 L, covering the processes in the life cycle of bamboo shoot products. This study identifies the potential water pollution problems and provides insights into resource utilization and recycling in bamboo shoot food processing, facilitating the realization of clean production processes. It also sheds light on the water footprint of bamboo shoot products throughout their life cycle, and the carbon footprint research provides valuable references.

Evaluating annual soil carbon emissions under biochar-added farmland subjecting from freeze-thaw cycle

Straw biochar is a commonly recognized agricultural amendment that can improve soil quality and reduce carbon emissions while sequestering soil carbon. However, the mechanisms underlying biochar's effects on annual soil carbon emissions in seasonally frozen soil areas and intrinsic drivers have not been clarified. Here, a 2-y field experiment was conducted to investigate the effects of different biochar dosages (0, 15, and 30, t ha−1; B0 (CK), B15, and B30, respectively) on carbon emissions (CO2 and CH4) microbial colony count, and soil-environment factors. The study period was the full annual cycle, including the freeze-thaw period (FTP) and the crop growth period (CP). Structural equation modeling (SEM) was developed to reveal the key drivers and potential mechanisms of biochar on carbon emissions. Biochar application reduced soil carbon emissions, with the reduction rate positively related to the biochar application rate (B30 best). During FTP, the reduction rate was 11.5% for CO2 and 48.2% for CH4. During CP, the reduction rate was 17.9% for CO2 and 34.5% for CH4. Overall, compared with CK, B30 treatment had a significant effect on reducing total soil carbon emissions (P < 0.05), with an average decrease of 16.7% during the two-year test period. The study also showed that for soils with continuous annual cycles (FTP and CP), carbon emissions were best observed from 10:00–13:00. After two years of freeze-thaw cycling, biochar continued to improve soil physical and chemical properties, thereby increasing soil microbial colony count. Compared with B0, the B30 treatment significantly increased the total colony count by 74.3% and 263.8% during FTP and CP (P < 0.05). Structural equation modeling (SEM) indicated that, with or without biochar application, the soil physicochemical properties directly or indirectly affected soil CO2 and CH4 emission fluxes through microbial colony count. The total effects of biochar application on CO2 emission fluxes were 0.50 (P < 0.05) and 0.64 (P < 0.01), respectively, but there was no significant effect on CH4 emission fluxes (P > 0.05). Among them, soil water content (SWC), soil temperature (ST) and soil organic carbon (SOC) were the main environmental determinants of CO2 emission fluxes during the FTP and CP. The total effects were 0.57, 0.65, and 0.53, respectively. For CH4, SWC, soil salinity (SS) and actinomycete colony count were the main environmental factors affecting its emission. The total effects were 0.50, 0.45, 0.44, respectively. For freeze-thaw alternating soils, the application of biochar is a feasible option for addressing climate change through soil carbon sequestration and greenhouse gas emissions mitigation. Soil water-heat-salt-fertilization and microbial communities are important for soil carbon emissions as the reaction matrix and main participants of soil carbon and nitrogen biochemical transformation.

External resistance as a potential tool for bioelectricity and methane emission control from rice plants in hydroponic microbial fuel cell

Recently, hydroponic plant microbial fuel cell (H-PMFC) was incorporated into cultivation medium to decrease methane (CH4) production while generating bioelectricity. However, no information is available about the effect of the external/internal resistance (Rext/Rint) ratio on the performance of H-PMFCs. To study the possibility of controlling biomass production, bioelectricity generation, and CH4 emissions from hydroponic rice plants (Oryza sativa L.) under different Rext/Rint ratios. In this study three H-PMFCs were operated as follows: H-PMFC-A had external resistance (Rext) lower than internal resistance (Rint); H-PMFC-B had Rext equal to Rint, and H-PMFC-C had Rext higher than Rint. Results showed that H-PMFC-B (Rext = Rint) has the highest biomass yield. H-PMFC-C (Rext > Rint) displayed the highest average power density (PDmax), which was 4.77 and 1.23 times higher than H-PMFC-A and H-PMFC-B over 131 days of operation. The PDmax was obtained from H-PMFC-C of 536.79 mW/m3 when Rext/Rint = 150 %. The highest current with the lowest CH4 was produced by H-PMFC-A (0.14 mA and 453.52 ± 0.28 g/m2/h). The CH4 emission exhibits an inverse trend with current production, which decreasing with the Rext/Rint decreased from 50 % to 5 %. The total CH4 emission flux in H-PMFC-A was 1.42 and 2.07 times lower than H-PMFC-B and H-PMFC-C, respectively. Furthermore, the COD removal rate in H-PMFCs negatively correlates with Rext/Rint, and the Rext does not affect the COD removal rate when 50 % ≤ Rext/Rint ≤ 150 %. The above results indicated that the performance of H-PMFCs can be controlled by changing the Rext/Rint ratio of H-PMFC according to actual needs. If the goal is to achieve higher biomass production, then Rext = Rint; to obtain the highest PDmax, then Rext > Rint; to obtain the highest current and lowest CH4 generation, then Rext < Rint.

Effect and Mechanism of Root Characteristics of Different Rice Varieties on Methane Emissions

Methane (CH4), which is an important component of the greenhouse gases from paddy ecosystems, is a major contributor to climate change. CH4 emissions from paddy ecosystems are closely related to the rice root system; however, how the rice root system affects CH4 emissions remains unclear. We conducted a field experiment in 2023 at the Heping Irrigation District Rice Irrigation Experiment Station in Qing’an County, Heilongjiang Province. The field experiment used five local rice varieties with similar fertility periods to observe rice root morphology and physiology indexes, CH4 emission fluxes, and cumulative CH4 emissions. A structural equation model (SEM) was established to investigate the effects of root characteristics on the CH4 emissions from rice and understand the potential mechanisms of these effects. The results showed that the seasonal patterns of CH4 emission fluxes were similar in different rice varieties, and that, during the tillering to heading–flowering stages, the cumulative CH4 emissions accounted for 89.8–92.6% of the total cumulative CH4 emissions of rice. Significant negative correlations were observed between CH4 emission fluxes and root volume, root dry weight, root oxidation activity (ROA), and root radial oxygen loss (ROL) (r = −0.839, −0.885, −0.401 and −0.934, p &lt; 0.05), while there were significant positive correlations between root diameter; malic acid, citric acid, and succinic acid contents; and CH4 emission fluxes (r = 0.407, 0.753, 0.797, and 0.685, p &lt; 0.05). The SEM showed that CH4 emission fluxes were directly influenced by ROL and organic acid contents, while the other root indicators had indirect effects by modulating ROL and organic acid contents. ROL and root volume had the largest total effect, indicating that ROL and root volume were the most significant root physiological and morphological indicators affecting CH4 emission fluxes. This study provides theoretical support and reference data for achieving sustainable agricultural development in the black soil region of Northeast China.

Soil Gaseous Carbon Emissions from Lettuce Fields as Influenced by Different Irrigation Lower Limits and Methods

Lettuce is a water-sensitive stem-used plant, and its rapid growth process causes significant disturbances to the soil. Few studies have focused on the gaseous carbon emissions from lettuce fields under different irrigation methods. Therefore, this study investigated the effect of different drip-irrigation lower limits and methods (drip and furrow irrigation) on greenhouse gas (CO2, CH4) emissions from lettuce fields. Thus, drip irrigation (DI) was implemented using three different lower limits of irrigation corresponding to 75%, 65%, and 55% of the field capacity, and named DR1, DR2, and DR3, respectively. Furrow irrigation (FI) was used as a control treatment. The CO2 and CH4 emission fluxes, soil temperature, and soil enzyme activities were detected. The results showed that the cumulative CO2 emission was highest under DR3 and relatively lower under DR1. For the FI treatment, the cumulative CO2 emission (382.7 g C m−2) was higher than that under DR1 but 20.2% lower than that under DR2. The cumulative CH4 emissions under FI (0.012 g C m−2) were the greatest in the whole lettuce growth period, while DR2 and DR3 treatments emitted lower amounts of CH4. The irrigation method considerably enhanced the activity of urease and catalase, meanwhile promoting CO2 emission. The low irrigation amount each time combined with high irrigation frequency reduced soil CO2 emission while increasing CH4 emission. From the perspective of the total reduction of gaseous carbon, DR1 is the optimal drip irrigation method among all the irrigation lower limits and methods.

Effect of tire wear particle accumulation on nitrogen removal and greenhouse gases abatement in bioretention systems: Soil characteristics, microbial community, and functional genes

Tire wear particles (TWPs), as predominant microplastics (MPs) in road runoff, can be captured and retained by bioretention systems (BRS). This study aimed to investigate the effect of TWPs accumulation on nitrogen processes, focusing on soil characteristics, microbial community, and functional genes. Two groups of lab-scale bioretention columns containing TWPs (0 and 100 mg g−1) were established. The removal efficiencies of NH4+-N and TN in BRS significantly decreased by 7.60%–24.79% and 1.98%–11.09%, respectively, during the 101 days of TWPs exposure. Interestingly, the emission fluxes of N2O and CO2 were significantly decreased, while the emission flux of CH4 was substantially increased. Furthermore, prolonged TWPs exposure significantly influenced the contents of soil organic matter (increased by 27.07%) and NH4+-N (decreased by 42.15%) in the planting layer. TWPs exposure also significantly increased dehydrogenase activity and substrate-induced respiration rate, thereby promoting microbial metabolism. Microbial sequencing results revealed that TWPs decreased the relative abundance of nitrifying bacteria (Nitrospira and Nitrosomonas) and denitrifying bacteria (Dechloromonas and Thauera), reducing the nitrification rate by 42.24%. PICRUSt2 analysis further indicated that TWPs changed the relative abundance of functional genes related to nitrogen and enzyme-coding genes.

Methane emissions sources and impact mechanisms altered by the shift from rice-wheat to rice-crayfish rotation

Methane (CH4) emissions from rice paddies constitute a significant source of greenhouse gases in the agricultural sector. However, the impact and mechanisms of changing traditional paddy-upland systems to rice-crayfish symbiotic systems on CH4 sources are not well understood. This study involved a two-year field experiment to investigate the sources and determinants of CH4 emissions in rice‒wheat rotation (RW) and rice-crayfish rotation (RC) by collecting CH4 emission fluxes from paddy fields, non-rhizosphere soil, and rice plants in conjunction with environmental and soil indicators. Our study shows that due to the increase in the amount and activity of carbon sources brought by crayfish farming, the activity of mcrA in RC increased by 156.17% before rice planting. The peak CH4 emissions from RC paddy fields occurred earlier and were higher, and the total emissions were 19.51%–37.17% higher than RW in the rice growing season. Moreover, the regreening and tillering stages were the peak periods of CH4 emissions, during which the CH4 emissions from non-rhizosphere soil in RW accounted for 44.86%–60.28%, and after conversion to RC, the contribution rate increased from 45.15% to 83.28%. However, the total CH4 emissions from rice plants were consistent in both RW and RC, with contributions between 46.09% and 64.06%. Rice roots were more conducive to CH4 production in the early stage and more conducive to CH4 oxidation in the late stage. Environmental indicators at a depth of 10–20 cm were more reflective of CH4 emission flux in RW, with moisture being the most important factor. After conversion to RC, the depth increased to 20–30 cm, and the most important environmental indicator became dissolved organic carbon (DOC) in surface water. These findings help to clarify the role of human activity management, including field water and carbon sources, on CH4 production under two rotation systems and provide a basis for mitigating the greenhouse effect.

Efficient rural sewage treatment with manganese sand-pyrite soil infiltration systems: Performance, mechanisms, and emissions reduction

The application of soil infiltration systems (SISs) in rural domestic sewage (RDS) is limited due to suboptimal denitrification resulting from factors such as low C/N (<5). This study introduced filler-enhanced SISs and investigated parameter impacts on pollutant removal efficiency and greenhouse gas (GHG) emission reduction. The results showed that Mn sand-pyrite SISs, with hydraulic load ratios of 0.003 m3/m2·h and dry-wet ratios of 3:1, achieved excellent removal efficiency of COD (92.7 %), NH4+-N (95.8 %), and TN (76.4 %). Moreover, N2O and CH4 emission flux were 0.046 and 0.019 mg/m2·d, respectively. X-ray photoelectron spectroscopy showed that the relative concentrations of Mn(Ⅱ) in Mn sand and Fe(Ⅲ) and SO42- in pyrite increased after the experiment. High-throughput sequencing indicated that denitrification was mainly performed by Thiobacillus. This study demonstrated that RDS treatment using the enhanced SIS resulted in efficient denitrification and GHG reduction.

Isotopic composition and emission characteristics of CO2 and CH4 in glacial lakes of the Tibetan Plateau

Carbon dioxide (CO2) and methane (CH4) emissions from freshwater ecosystems are predicted to increase under climate warming. However, freshwater ecosystems in glacierized regions differ critically from those in non-glacierized regions. The potential emissions of CO2 and CH4 from glacierized environments in the Tibetan Plateau (TP) were only recently recognized. Here, the first direct measurement of CO2 and CH4 emission fluxes and isotopic composition during the spring of 2022 in 13 glacial lakes of the TP revealed that glacial lakes were the previously overlooked CO2 sinks due to chemical weathering in glacierized regions. The daily average CO2 flux was −5.1 ± 4.4 mmol m−2 d−1, and the CO2 consumption could reach 38.9 Gg C-CO2 yr−1 by all glacial lakes in the TP. This consumption might be larger during summer when glaciers experience intensive melting, highlighting the importance of CO2 uptake by glacial lakes on the global carbon cycle. However, the studied glacial lakes were CH4 sources with total emission flux ranging from 4.4 ± 3.3 to 4082.5 ± 795.6 μmol m−2 d−1. The large CH4 range was attributed to ebullition found in three of the glacial lakes. Low dissolved organic carbon concentrations and CH4 oxidation might be responsible for the low CH4 diffusive fluxes of glacial lakes without ebullition. In addition, groundwater input could alter CO2 and CH4 emissions from glacial lakes. CH4 in glacial lakes probably had a thermogenic source; whereas CO2 was influenced mainly by atmospheric input, as well as organic matter remineralization and CH4 oxidation. Overall, glacial lakes in the TP play an important role in the global carbon cycle and budget, and more detailed isotopic and microbial studies are needed to constrain the contributions of different pathways to CO2 and CH4 production, consumption and emissions.

Estimates of the CO2 and CH4 Emission and Uptake Flux Imbalances in the Barents and Kara Seas in the Summers of 2016 and 2017

Estimates of the CO2 and CH4 Emission and Uptake Flux Imbalances in the Barents and Kara Seas in the Summers of 2016 and 2017