Effects of functional microorganisms and environmental factors on CO2 and CH4 emissions in a typical floodplain lake system.

Rational utilization of leguminous green manure to mitigate methane emissions by influencing methanogenic and methanotrophic communities

Long-term agricultural drainage stimulates CH4 emissions from ditches through increased substrate availability in a boreal peatland

This study provides an opportunity to quantify the biogenic component of the carbon balance, its dynamics and relationship with environmental factors. This study is the first to evaluate the functioning of microbial communities in floodplain lakes in the middle reaches of the Ob River from the perspective of studying their metabolic activity in the context of seasonal and spatial environmental changes. The purpose of this work was to assess seasonal changes in the metabolic spectra of bacterial communities in water bodies of the Middle Ob floodplain. During the summer low water period (September 2023), winter low water period (snow period, March 2024) and spring flood (May 2024), functional diversity and quantitative microbiological characteristics of heterotrophic microbial communities in the surface and bottom layers of the water column of three floodplain lakes located in the vicinity of the TSU research station “Kaibasovo” (N 57.24569342272839, E 84.18459154598635), as well as the water of the Ob River itself, were studied. Functional diversity was determined using the multisubstrate testing method on 96-well Biolog Ecoplate test systems (USA) with calculation of the AWCD (average well-covered development) index. The TMC (total microbial count), obtained by direct counting of bacterial cells in a fluorescent-stained sample, was used as a quantitative characteristic. According to the nonparametric analysis of variance (Kruskal-Wallis ANOVA test, Median test), AWCD and TMC did not differ between lakes (p>0.05). Seasonal changes were revealed for AWCD and TMC (see Fig. 1). AWCD correlated (Spearman rank correlations were used, p < 0.05) with the consumption of amino acids (0.52), carbohydrates (0.54), amines (0.50) and oxycar-boxylic acids (0.62), TMC correlated with the consumption of carbohydrates (0.45) and polymers (0.63). The dynamics of AWCD were similar for the surface layer of all lakes, and did not show obvious patterns in the bottom layer. Throughout the year, higher TMC values were observed in the bottom layer, although this pattern was not observed for AWCD (see Fig. 1). This is due to the effect of ultraviolet radiation from the sun and the influence of allochthonous microflora on the current AWCD values. TMC in floodplain lakes increased during winter low water and had minimum values during the flood period. During the winter low water period, the AWCD and the consumption of most substrate groups are higher in the bottom layer. Seasonal differences in consumption of carboxylic acid phosphates (Kruskal-Wallis test: H (2, N = 18) = 10.36; p = 0.01; Median test: Chi-Square = 12.00; df = 2; p = 0.00) and polymers (Kruskal-Wallis test: H (2, N = 18) =7.18; p = 0.03; Median test: Chi-Square = 9.33; df = 2; p = 0.01) have been identified (see Fig. 2). A large number of correlations between the consumption of different groups of substrates, including within the surface and bottom layers, indicate the cosmopolitan nature and functional interchangeability of representatives of microbial communities. Moreover, during low water, when conditions are most favorable for the growth of microflora, the number of correlations was maximum (9 out of 15); during the freeze-up period it decreased significantly (4 out of 15), which may indicate a targeted growth of more specialized microflora. In May, the number of correlations increased again (5 out of 15). Seasonal changes in the functional and quantitative characteristics of microbial communities did not correspond to each other - the increase in the number of microorganisms did not cause an increase in functional diversity. The microflora suppression during flooding characterizes the demi-seasonal succession of the microbial community. Based on the data obtained, one can judge the functional cosmopolitanism and functional interchangeability of representatives of microbial communities of floodplain water bodies. The article contains 2 Figures, 12 References. To the team of the USI "System of Experimental Bases Located Along the Latitudinal Gradient" for assistance in organizing and conducting field work. The Authors declare no conflict of interest.

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.

The composition of bacterial communities in freshwater ecosystems is influenced by numerous factors including environmental conditions and biological interactions. In grassland inland closed lakes, factors affecting lake ecosystems are either exogenous or endogenous, contributing to the formation of distinct habitats in the surface and bottom waters of the bacterial communities. However, the extent to which environmental factors selectively shape the bacterial communities in aquatic systems remains unclear. Therefore, we sampled the surface, middle, and bottom waters at 13 sampling points in each layer. High-throughput sequencing techniques were employed to examine the spatial heterogeneity of the bacterial community structure during summer in Hulun Lake, the largest grassland-type lake in Inner Mongolia, China, to determine the microbial community dynamics and symbiosis patterns under different habitat conditions. Our results revealed a decrease in the diversity and heterogeneity of the bacterioplankton community, influenced by changes in the environment from exogenous inputs to endogenous releases. Furthermore, this alteration in community structure was concomitant with enhanced co-occurrences among microorganisms in the bottom water layers. This finding suggests that endogenous release promotes heightened symbiotic interactions, thereby facilitating the development of more complex modular structures. Symbiotic networks in different layers were differentiated by key species, with the ecological clustering modules of these species demonstrating dissimilar environmental preferences. The microbial communities were highly habitat-specific, mimicking responses to total nitrogen (TN) in the surface layer, pH in the middle layer, and chemical oxygen demand (COD) in the bottom layer. Bacterioplankton functions were assessed using Tax4Fun, indicating exogenous inputs and endogenous release increased the relative abundance of genes with nitrogen-fixing and nitrification potential nitrogen metabolism functions in surface and bottom waters, respectively. With Planctomycetota and Proteobacteria phyla as potential key groups for regulating nitrogen metabolic processes, Proteobacteria may facilitate the depletion of nitrate in surface and bottom waters, while the close contact of surface waters with the atmosphere accelerated Planctomycetota-dominated nitrogen fixation into the lake. Our findings contribute to the understanding of vertical microbial diversity and its network patterns in grassland type lakes, underscoring the potential role of environmental factors (exogenous inputs and endogenous releases) in bacterioplankton community formation.

Acidification of livestock manure can reduce emission of the greenhouse gases methane (CH) and nitrous oxide (NO), as well as ammonia (NH). We examined the relation between emission of these gases and transformation of organic matter as affected by acidification. Liquid cattle manure was acidified with sulfuric acid to pH 5.5 at a pilot scale (100 L), and we measured effects on CH, NO, CO and NH emissions and on transformation of pH buffer components and organic matter. Acidification reduced NH emissions by 62% (47 d) and emission of CH by 68% (57 d). Emissions of NO were negligible, probably due to the absence of a surface crust. Reductions in NH and CH emission were highest at the start but declined over time concomitantly with a gradual increase in the stored liquid manure pH. Acidification did not significantly affect CO emissions. Emission of CO was high, five- to ten-fold of CH emissions, until Day 16 of storage, after which the CO emission rate declined to around twice the CH emission rate; consequently, the majority of C loss during the early stages of storage was CO. Cumulative emission of C in CO and CH closely matched depletion of dissolved organic carbon (DOC), suggesting that DOC may be a predictor for CH emission from dilute slurries. volatile fatty acid and total ammoniacal nitrogen concentrations in surface layers were substantially higher than at the center of stored liquid manure, perhaps resulting from microbial activity at the surface. This pattern deserves attention when predicting NH emission from stored slurry.

Water samples were collected from the Yellow and Bohai seas during November 2013 and the chromophoric dissolved organic matter (CDOM) and nutrients concentrations were investigated, including their composition, source and distribution characteristics. CDOM was analyzed by excitation-emission matrix spectroscopy (EEMS) in combination with a parallel factor analysis (PARAFAC). Three terrestrial humic-like substances (C1, C2, and C3) and one protein-like (C4) substances were identified. The three terrestrial humic-like components had a similar horizontal distribution, decreasing from inshore to offshore. The protein-like component, showed higher values for both inshore and offshore areas in the Yellow Sea at the surface layer and the middle layer of the Bohai Sea, while in other layers it had a similar distribution pattern as the terrestrial humic-like components. In the Bohai Sea, the dissolved inorganic nitrogen (DIN) concentration showed a decreasing trend from inshore to offshore areas and the concentration of dissolved inorganic phosphorus (DIP) gradually decreased from the Caofeidian coastal and central areas to other adjacent areas. The dissolved organic nitrogen (DON) showed an increasing from inshore to the central area of the Bohai Sea. DIN and DON were higher in surface layer than in the bottom layer and for DIP this was the opposite in the Bohai Sea. In the Yellow Sea, DON concentrations showed a decreasing trend from inshore to offshore areas. DIN and DIP had higher concentrations at inshore areas in the surface and middle layers, while in the bottom layer they had higher concentrations in offshore areas. The vertical distribution of the DIN and DIP showed higher values in the bottom layer than surface layers and for DON this was the opposite. These results also showed that the concentrations of DIN, DON, and DIP in the Bohai sea were overall higher than the Yellow Sea. A discriminant analysis was performed through redundancy analysis (RAD) of these water quality parameters, including the four fluorescent components, an absorption coefficient (a355), chlorophyll a concentration, conductivity, dissolved oxygen (DO), dissolved organic carbon (DOC), DIN, DON, and DIP. The RDA indicated that the four fluorescent components are mainly affected by terrestrial inputs. DOC was affected by both terrestrial and marine sources but terrestrial inputs were the major contributor. It was also indicated that the DIN concentration was affected by terrestrial inputs in the Bohai Sea area and by both terrestrial and marine sources in the Yellow Sea. DON concentrations were mainly affected by marine sources in the Bohai Sea and terrestrial inputs in the Yellow Sea. DIP concentrations were affected by both terrestrial and marine sources in the studied areas.

Applying investigation data about Pb in Jiaozhou Bay in August, 1992 and according to horizontal matter content change model and the vertical matter content change model proposed by the authors, the horizontal loss amount, vertical diluted amount and vertical sediment amount of Pb content in the surface and bottom layers from southeast bay to southwest bay are calculated. What’s more, the model diagram of vertical change and horizontal change of Pb content is designed. The calculation results show that in August in 1992, the absolutely loss amount of Pb content in the bottom layer was 11.03μg/L, and the relative loss amount of Pb content in the bottom layer was 58.42%. Meanwhile, the absolutely increase amount of Pb content in the surface layer was 4.60μg/L, and the relatively increase amount of Pb content in the surface layer was 28.93%. In the southeast bay, the relatively vertical sediment amount of Pb content in the surface and bottom layers was 40.14%, and the absolutely vertical sediment amount of Pb content in the surface and bottom layers was 7.58μg/L. Similarly, in the southwest bay, Pb content in the surface layer and bottom layer had an absolutely vertical diluted amount of 8.05μg/L with a relatively vertical diluted amount of 50.62%. In August, the main sea current carried Pb content through the surface nearshore waters around the bay where many sources of Pb content existed. The law of horizontal loss amount shows that: when Pb content migrated horizontally in the surface layer, Pb content did not lose but increased. However, when Pb content migrated horizontally in the bottom layer, a lot of Pb content was lost due to a long distance. Moreover, the law of the vertical loss amount revealed that Pb content was transported by the main sea current and was relatively high in its vertical migration process. As a result, the vertical sediment amount 40.14% of Pb content in surface and bottom layers was changed to the vertical diluted amount 50.62% of Pb content in the surface and bottom layers when the main sea current flowed from southeast bay waters to southwest bay waters.

The biological decomposition and chemical changes of leaf litter ofGinkgo bilobaboth at the surface and bottom layers were studied for 1 year. The changes in components such as the yields of 80% ethanol and water extractives, neutral sugars, uronic acids, Klason residues, acid-soluble phenolics, ash, nitrogen, and carbon were investigated. There were great drops of the yields of 80% ethanol extractives and water extractives in both surface and bottom mulch layers. Klason residues and sugars were the major components of the solid residues. The Klason residues lost 2.2% and 30.5% of their initial mass at the surface and bottom layers, respectively, during mulching. The total losses of the neutral sugars were 71.6% at the surface layer and 89.3% at the bottom layer. These results implied that the Klason residues were the most important inner component restraining the decomposition of the leaf litter ofG. bilobaand all analyzed cell wall components at the bottom layer had faster decomposition rates than those at the surface layer. Nitrogen content increased during one year of mulching, while changes in carbon contents were less than 1% throughout experiment.

The application of biochar in conjunction with fertilizer in agricultural production is one of the most promising types of management to improve soil quality. However, the effects on the soil microbial community and methane (CH4) emissions from the interactive mechanisms of biochar combined with fertilizer are unclear. In this study, soil column trial was conducted to monitor the surface water nitrogen, dissolved organic carbon (DOC) and CH4 emission dynamics during the process of leaching. Additionally, bacterial and archaeal communities of the soil (0-10 cm) amended with biochar derived from different pyrolysis temperatures (300°C, 500°C, and 700°C) were also analyzed. High-throughput sequencing revealed that the soil archaeal and bacterial community diversities increased under the biochar amendments. The CH4 emission flux of all the treatments in the whole leaching period ranged from 0.0001 to 2.04 μg m-2 h-1, and the DOC ranged from 1.86 to 24.4 mg L-1. Our results showed that biochar amendments significantly increase the soil pH, total nitrogen (TN), and DOC contents, while inhibiting the loss of NO3− N during leaching. In addition, biochar addition increased the paddy soil CH4 emissions, which ascribed to the increasing ratio of the abundances of methanogens to methanotrophs. Consequently, the higher CH4 emissions were probably caused by the stimulation of methanogenic archaea under the biochar amendments. Thus, the results obtained in this study can be applied to guide the application of biochar on greenhouse gas emissions in paddy soil.

长期施肥对双季稻田甲烷排放和关键功能微生物的影响

不同施肥处理对土壤活性有机碳和甲烷排放的影响

Abstract. Uncertainties in the magnitude and seasonality of various gas emission modes, particularly among different lake types, limit our ability to estimate methane (CH4) and carbon dioxide (CO2) emissions from northern lakes. Here we assessed the relationship between CH4 and CO2 emission modes in 40 lakes along a latitudinal transect in Alaska to lakes' physicochemical properties and geographic characteristics, including permafrost soil type surrounding lakes. Emission modes included direct ebullition, diffusion, storage flux, and a newly identified ice-bubble storage (IBS) flux. We found that all lakes were net sources of atmospheric CH4 and CO2, but the climate warming impact of lake CH4 emissions was 2 times higher than that of CO2. Ebullition and diffusion were the dominant modes of CH4 and CO2 emissions, respectively. IBS, ~10% of total annual CH4 emissions, is the release to the atmosphere of seasonally ice-trapped bubbles when lake ice confining bubbles begins to melt in spring. IBS, which has not been explicitly accounted for in regional studies, increased the estimate of springtime emissions from our study lakes by 320%. Geographically, CH4 emissions from stratified, mixotrophic interior Alaska thermokarst (thaw) lakes formed in icy, organic-rich yedoma permafrost soils were 6-fold higher than from non-yedoma lakes throughout the rest of Alaska. The relationship between CO2 emissions and geographic parameters was weak, suggesting high variability among sources and sinks that regulate CO2 emissions (e.g., catchment waters, pH equilibrium). Total CH4 emission was correlated with concentrations of soluble reactive phosphorus and total nitrogen in lake water, Secchi depth, and lake area, with yedoma lakes having higher nutrient concentrations, shallower Secchi depth, and smaller lake areas. Our findings suggest that permafrost type plays important roles in determining CH4 emissions from lakes by both supplying organic matter to methanogenesis directly from thawing permafrost and by enhancing nutrient availability to primary production, which can also fuel decomposition and methanogenesis.

Methane production is influenced by the abundance of methanogens and the availability of substrates. Sulfate-reducing bacteria (SRB) also play an important role in the anaerobic decomposition of organic matter. However, the relationships between methane production and abundance of methanogen and pore water substrates in estuarine brackish marshes are poorly characterized, and even to our knowledge, no published research has explored the relationship between methane production rate and pore water dimethyl sulfide (DMS) concentration. We investigated methane production rate, abundances of methanogens and SRB, sediment organic carbon contents, and concentrations of pore water substrates (acetate and DMS) and terminal electron acceptors (SO4 2−, NO3 −, and Fe3+) at a brackish marsh landscape dominated by Phragmites australis marsh, Cyperus malaccensis marsh, and Spartina alterniflora marsh in the Min River estuary, southeast China. The average rates of methane production over the entire 30 cm of the sediment profile (5 cm sampling interval) in the three marshes were 0.142, 0.058, and 0.067 μg g−1 day−1, respectively. The abundance of both methanogens and SRB in the sediment of the P. australis marsh with the highest sediment organic carbon content was higher than in the C. malaccensis and S. alterniflora marshes. Mean pore water DMS concentrations over the entire 30 cm of the sediment profile under the S. alterniflora marsh were higher than those in the C. malaccensis marsh and P. australis marsh. Methane production rate correlated weakly with the abundance of methanogens across the three marsh zones together, but did not correlate with the concentrations of pore water acetate and DMS. Our results suggest that the abundance of methanogens is controlled by sediment organic carbon supply, and further, methane production is affected by the abundance of methanogens in the subtropical estuarine brackish marshes.

Mercury and methylmercury in the Gulf of Trieste (northern Adriatic Sea)