What is the relationship between soil methane oxidation and other C compounds?

Interactions between Cyanobacteria and Methane Processing Microbes Mitigate Methane Emissions from Rice Soils

Cyanobacteria play a relevant role in rice soils due to their contribution to soil fertility through nitrogen (N2) fixation and as a promising strategy to mitigate methane (CH4) emissions from these systems. However, information is still limited regarding the mechanisms of cyanobacterial modulation of CH4 cycling in rice soils. Here, we focused on the response of methane cycling microbial communities to inoculation with cyanobacteria in rice soils. We performed a microcosm study comprising rice soil inoculated with either of two cyanobacterial isolates (Calothrix sp. and Nostoc sp.) obtained from a rice paddy. Our results demonstrate that cyanobacterial inoculation reduced CH4 emissions by 20 times. Yet, the effect on CH4 cycling microbes differed for the cyanobacterial strains. Type Ia methanotrophs were stimulated by Calothrix sp. in the surface layer, while Nostoc sp. had the opposite effect. The overall pmoA transcripts of Type Ib methanotrophs were stimulated by Nostoc. Methanogens were not affected in the surface layer, while their abundance was reduced in the sub surface layer by the presence of Nostoc sp. Our results indicate that mitigation of methane emission from rice soils based on cyanobacterial inoculants depends on the proper pairing of cyanobacteria-methanotrophs and their respective traits.

A new approach to suppress methane emissions from rice cropping systems using ethephon

Rice is the main staple food for more than half of the world's population. Yet, rice cultivation is subjected to criticism because of its important role in methane (CH₄) emissions. Although several agronomic practices such as controlled irrigation and conservation tillage have been widely adopted to mitigate CH₄ emissions from rice cultivation, the benefits gained by these practices are highly dependent on site-specific soil and climate conditions, and often offset by yield reduction. The use of plant growth regulating compounds having the potential to increase the crop yield and mitigate CH₄ emissions may be an innovative approach to sustainable agriculture. Ethylene (C₂H₄), a plant growth regulator is known to have a strong inhibitory effect on methanogenesis. However, due to gaseous form and low water solubility, C₂H₄ has not been used to suppress methanogenesis in paddy fields. To develop C₂H₄ as a prospective soil amendment for reducing methane (CH₄) emissions, ethephon (2-Chloroethylphosphonic acid), a precursor of C₂H₄ was tested. We found that ethephon reduced CH₄ formation by 43%, similar to other well known methanogenic inhibitors (2-Bromoethanesulfonate, 2-Chlomoethanesulfonate, 2-Mercaptoethanesulfonate). However, ethephon rapidly hydrolyzed to C₂H₄ and methanogenic activity recuperated completely after C₂H₄ removal. To slow down the release of C₂H₄, ethephon was mixed with bio-degradable polymers such as cellulose acetate and applied to paddy soils. We found that compared with the control, the C₂H₄ release of ethephon slowed down to 90 days, and the CH₄ emissions were reduced by 90%. The application of ethephon at lower concentrations did not significantly alter bacterial communities, their relative abundance, and the abundance of methanotrophs, but it significantly reduced archaeal communities and the relative abundance and expression level of methanogens in paddy soils. Results suggest that cellulose acetate-mixed ethephon has great promise to suppress CH₄ emissions in rice paddies while ensuring sustainable yields.

How Can Litter Modify the Fluxes of CO2 and CH4 from Forest Soils? A Mini-Review

Forests contribute strongly to global carbon (C) sequestration and the exchange of greenhouse gases (GHG) between the soil and the atmosphere. Whilst the microbial activity of forest soils is a major determinant of net GHG exchange, this may be modified by the presence of litter through a range of mechanisms. Litter may act as a physical barrier modifying gas exchange, water movement/retention and temperature/irradiance fluctuations; provide a source of nutrients for microbes; enhance any priming effects, and facilitate macro-aggregate formation. Moreover, any effects are influenced by litter quality and regulated by tree species, climatic conditions (rainfall, temperature), and forest management (clear-cutting, fertilization, extensive deforestation). Based on climate change projections, the importance of the litter layer is likely to increase due to an litter increase and changes in quality. Future studies will therefore have to take into account the effects of litter on soil CO2 and CH4 fluxes for various types of forests globally, including the impact of climate change, insect infestation, and shifts in tree species composition, as well as a better understanding of its role in monoterpene production, which requires the integration of microbiological studies conducted on soils in different climatic zones.

Effects of changes in throughfall on soil GHG fluxes under a mature temperate forest, northeastern China

Climate change scenarios predict a change in the rainfall regimes for this current century, which has different impacts on soil greenhouse gas (GHG) fluxes. However, how changes in annual rainfall affect annual GHG fluxes of forest soils remain unknown. A six-year field experiment with -25% and -50% throughfall (TF) and +25% TF manipulation was performed to explore the mechanisms involving GHG fluxes under a mature temperate forest, northeastern China and to work out whether the TF effect sizes on annual soil GHG fluxes vary with dry and wet years. The results showed that both -25% TF and -50% TF treatments depressed annual soil nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions but increased annual soil methane (CH₄) uptake. A contrary pattern of annual soil GHG fluxes was observed in the +25% TF treatment. When annual TF input was decreased by 100 mm, annual soil N₂O and CO₂ emissions were decreased by 18.1 ± 3.1 mg N m^-2 and by 39.4 ± 6.1 g C m^-2 during the growing season, respectively, and annual soil CH₄ uptake was increased by 11.5 ± 3.4 mg C m^-2. Both -25% TF and -50% TF treatments reduced annual soil dissolved organic C (DOC) leaching by 29.3% and 45.6% and dissolved total N (DN) leaching by 30.8% and 39.6%, respectively. Contrary to annual soil N₂O and CO₂ emissions, annual soil CH₄ uptake during the growing season significantly decreased with an increase in the annual leaching fluxes of soil DOC, inorganic N, and DN. Besides soil moisture and temperature and pH, soil GHG fluxes under manipulating TF condition were regulated by soil labile C and N status. Our findings indicated that the TF effect sizes on both annual GHG fluxes and net annual GHG balance (GWP) of forest soils varied with dry and wet years in northeastern China. The results highlight the importance of altered annual rainfall in regulating annual soil GHG fluxes and the GWP in temperate forests under global climate change.

Asymmetric response of soil methane uptake rate to land degradation and restoration: Data synthesis

Land degradation and restoration profoundly affect soil CH₄ uptake capacity in terrestrial ecosystems. However, a comprehensive assessment of the response of soil CH₄ uptake to land degradation and restoration at global scale is not available. Here, we present a global meta-analysis with a database of 228 observations from 83 studies to investigate the effects of land degradation and restoration on the capacity of soil CH₄ uptake. We found that land degradation significantly decreased the capacity of soil CH₄ uptake, except the conversion of pasture to cropland where the soil CH₄ uptake rate showed no response. In contrast, all types of land restoration significantly increased the capacity of soil CH₄ uptake. Interestingly, the response of soil CH₄ uptake rate to land degradation and restoration was asymmetric: the increased soil CH₄ uptake rate in response to the land restoration was smaller compared to the decrease in CH₄ uptake rate induced by the land degradation. The effect of land degradation on soil CH₄ uptake rate was not dependent on the time since land use change, but the CH₄ sink strength increased with the time since land restoration. The response of soil CH₄ uptake rate to both land degradation and restoration was predominantly regulated by changes in the soil water-filled pore space, soil bulk density, and pH, whereas alterations in the substrate quantity and quality had negligible effect. Additionally, the effects of land degradation and restoration on soil CH₄ uptake were strongly related to the mean annual precipitation and soil texture. Overall, our results provide novel insights for understanding of how land degradation and restoration can affect the CH₄ sink strength of upland soils, and more importantly, our findings are beneficial to take measures to enhance the potential of soil CH₄ uptake in response to global land use change.

Facultative methanotrophs - diversity, genetics, molecular ecology and biotechnological potential: a mini-review

Methane-oxidizing bacteria (methanotrophs) play a vital role in reducing atmospheric methane emissions, and hence mitigating their potent global warming effects. A significant proportion of the methane released is thermogenic natural gas, containing associated short-chain alkanes as well as methane. It was one hundred years following the description of methanotrophs that facultative strains were discovered and validly described. These can use some multi-carbon compounds in addition to methane, often small organic acids, such as acetate, or ethanol, although Methylocella strains can also use short-chain alkanes, presumably deriving a competitive advantage from this metabolic versatility. Here, we review the diversity and molecular ecology of facultative methanotrophs. We discuss the genetic potential of the known strains and outline the consequent benefits they may obtain. Finally, we review the biotechnological promise of these fascinating microbes.