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Methane emissions from wetlands contribute to the currently rising levels of methane in the atmosphere. Nonetheless, the assessments of methane-producing Archaea (methanogens) and their environmental controls are still rare particularly in soils from estuarine tidal marshes. In estuarine tidal marshes, the salinity gradient is commonly observed, and its effects on the methanogenic community are hardly known. In this study, in the Min River estuary, southeast China, we analyzed two freshwater and two brackish (oligohaline) marshes in a subtropical estuary, where we assessed methanogenic community structure and abundance by molecular cloning, sequencing, and quantitative PCR methods, as well as by means of soil physicochemical characteristics and concentration of methane dissolved in pore water. The common and dominant genera of these methanogens include Methanoregula , Methanobacterium , Methanosarcina , and Methanolinea in the four marshes. Phylotypes of the methanogens using H 2 /CO 2 (Methanomicrobiales) or acetate (Methanosarcinales) were identified in the mcrA gene clone libraries and by restriction fragment length polymorphism (RFLP) analyses. The abundance levels of methanogens in the two freshwater marshes were significantly higher than those in the two brackish marshes. The value of the Shannon Index ( H ′) of diversity and Simpson index ( D ) of evenness of methanogen mcrA clone libraries decreased along the salinity gradient from freshwater to brackish water. Methanogen community structure varied with soil depth in the four wetlands. The concentrations of methane in pore water also decreased from the freshwater sites to the brackish sites; this pattern is consistent with a change in the abundance of methanogens. Our results showed that in a low-level salinity gradient of a subtropical estuary, salinity is still a major factor controlling the overall community structure and abundance of methanogens. [ABSTRACT FROM AUTHOR]

Assessing the diverse communities of methanogenic Archaea and sulfate-reducing bacteria (SRB) is important to understand methane (CH 4 ) production in wetland ecosystems. However, the vertical distribution of composition and diversity, and the effects of environmental factors on the methanogen and SRB communities in the sediments of subtropical estuarine brackish marshes have been poorly characterized. To assess the effects of variable environmental conditions on methanogenic and SRB communities in marshes, we studied three brackish marsh zones dominated by Phragmites australis , Cyperus malaccensis and Spartina alterniflora , respectively, in the Min River estuary, southeastern China. Methanogens of the Methanomicrobiales order was the dominant group at sediment depths of 0–30 cm, which indicated that the main pathway of methane production was H 2 /CO 2 in this zone. In general, methanogens of the genus Methanoregula were dominant in the three marsh zones. For SRB, Desulfobacterales was the dominant group, and Desulfobacterium and Desulfosarcina were the predominant genera at the depth of 0–30 cm. The community composition of methanogens and SRB changed with vegetation type and soil depth. Compared with SRB, vegetation type demonstrated a stronger influence on the community composition of methanogens. Canonical correspondence analysis (CCA) analysis further revealed that the main factors affecting the methanogens community composition were EC (electric conductivity) and pH, and the main factors affecting SRB community composition were pH, SOC and TN, suggesting that pH is a common factor influencing the community compositions of both methanogen and SRB in the sediments of brackish marshes. [ABSTRACT FROM AUTHOR]

This article is composed of three independent commentaries about the state of Integrated, Coordinated, Open, Networked (ICON) principles in the American Geophysical Union Biogeosciences section, and discussion on the opportunities and challenges of adopting them. Each commentary focuses on a different topic: (a) Global collaboration, technology transfer, and application (Section 2), (b) Community engagement, community science, education, and stakeholder involvement (Section 3), and (c) Field, experimental, remote sensing, and real‐time data research and application (Section 4). We discuss needs and strategies for implementing ICON and outline short‐ and long‐term goals. The inclusion of global data and international community engagement are key to tackling grand challenges in biogeosciences. Although recent technological advances and growing open‐access information across the world have enabled global collaborations to some extent, several barriers, ranging from technical to organizational to cultural, have remained in advancing interoperability and tangible scientific progress in biogeosciences. Overcoming these hurdles is necessary to address pressing large‐scale research questions and applications in the biogeosciences, where ICON principles are essential. Here, we list several opportunities for ICON, including coordinated experimentation and field observations across global sites, that are ripe for implementation in biogeosciences as a means to scientific advancements and social progress. Plain Language Summary: Biogeosciences is an interdisciplinary field that requires multiscale global data and concerted international community efforts to tackle grand challenges. However, several technical, institutional, and cultural hurdles have remained as major roadblocks toward scientific progress, hindering seamless global data acquisition and international community engagement. To bring a paradigm shift in biogeosciences, there is a need to implement integrated, coordinated, open, and networked efforts, collectively known as the Integrated, Coordinated, Open, Networked (ICON) principles. In this article, we present three related commentaries about the state of ICON, discuss needs to reduce geographical bias in data for enhancing scientific progress, and identify action items. Action items are primarily people‐centric and include but are not limited to: longer‐term funding priorities to institutionalize capacity and reduce entry costs, engagement of local stakeholders across the globe, incentivization of collaborations, and development of training and workshops for capacity building. Key Points: Biogeosciences needs Integrated, Coordinated, Open, Networked (ICON) principles to address multiscale global problems and reduce geographical bias in scientific progressMuch potential exists for emphasizing people‐centric capacity building, involving relevant stakeholders within an ICON frameworkGlobally coordinated experimental and field data provide challenges and opportunities for scientific advancement in biogeosciences [ABSTRACT FROM AUTHOR]

• Rare eddy covariance flux measurements of CO 2 and CH 4 in a palm swamp peatland in the Peruvian Amazon. • The peatland was a large CO 2 sink and a CH 4 source. • Photosynthetic activity was inhibited and respiration enhanced during warm-dry conditions. • Carbon cycling in Amazonian palm swamp forests are sensitive to hydrometeorological forcings. • Longer-term measurements are needed to assess their potential vulnerability to climate change. Tropical peatlands are a major, but understudied, biophysical feedback factor on the atmospheric greenhouse effect. The largest expanses of tropical peatlands are located in lowland areas of Southeast Asia and the Amazon basin. The Loreto Region of Amazonian Peru contains ~63,000 km2 of peatlands. However, little is known about the biogeochemistry of these peatlands, and in particular, the cycling of carbon dioxide (CO 2) and methane (CH 4), and their responses to hydrometeorological forcings. To address these knowledge gaps, we established an eddy covariance (EC) flux tower in a natural palm (Mauritia flexuosa L.f.) swamp peatland near Iquitos, Peru. Here, we report ecosystem-scale CO 2 and CH 4 flux observations for this Amazonian palm swamp peatland over a two-year period in relation to hydrometeorological forcings. Seasonal and short-term variations in hydrometeorological forcing had a strong effect on CO 2 and CH 4 fluxes. High air temperature and vapor pressure deficit (VPD) exerted an important limitation on photosynthesis during the dry season, while latent heat flux appeared to be insensitive to these climate drivers. Evidence from light-response analyses and flux partitioning support that photosynthetic activity was downregulated during dry conditions, while ecosystem respiration (RE) was either inhibited or enhanced depending on water table position. The cumulative net ecosystem CO 2 exchange indicated that the peatland was a significant CO 2 sink ranging from −465 (−279 to −651) g C m−2 y−1 in 2018 to −462 (−277 to −647) g C m−2 y−1 in 2019. The forest was a CH 4 source of 22 (20 to 24) g C m−2 y−1, similar in magnitude to other tropical peatlands and larger than boreal and arctic peatlands. Thus, the annual carbon budget of this Amazonian palm swamp peatland appears to be a major carbon sink under current hydrometeorological conditions. [ABSTRACT FROM AUTHOR]