Wetlands

Anaerolineae, particularly uncultured representatives, are one of the most abundant microbial groups in coastal salt marshes, dominating the belowground rhizosphere, where over half of plant biomass production occurs. However, this class generally remains poorly understood, particularly in a salt marsh context. Here, novel Anaerolineae metagenome-assembled genomes (MAGs) were generated from the salt marsh rhizosphere representing Anaerolineales, Promineifilales, JAAYZQ01, B4-G1, JAFGEY01, UCB3, and Caldilineales orders. Metagenome and metatranscriptome reads were mapped to annotated MAGs, revealing nearly all Anaerolineae encoded and transcribed genes required for oxidation of carbon compounds ranging from simple sugars to complex polysaccharides, fermentation, and carbon fixation. Furthermore, the majority of Anaerolineae expressed genes involved in anaerobic and aerobic respiration and secondary metabolite production. The data revealed that the belowground salt marsh Anaerolineae in the rhizosphere are important players in carbon cycling, including degradation of simple carbon compounds and more recalcitrant plant material, such as cellulose, using a diversity of electron acceptors and represent an unexplored reservoir of novel secondary metabolites.IMPORTANCEGiven that coastal salt marshes are recognized as biogeochemical hotspots, it is fundamentally important to understand the functional role of the microbiome in this ecosystem. In particular, Anaerolineae are abundant members of the salt marsh rhizosphere and have been identified as core microbes, suggesting they play an important functional role. Yet, little is known about the metabolic pathways encoded and expressed in this abundant salt marsh clade. Using an 'omics-based approach, we determined that Anaerolineae are capable of oxidizing a range of carbon compounds, including simple sugars to complex carbon compounds, while also encoding fermentation and carbon fixation. Surprisingly, Anaerolineae encoded and transcribed genes involved in aerobic respiration, which was unexpected given the reduced nature of the salt marsh rhizosphere. Finally, the majority of Anaerolineae appear to be involved in secondary metabolite production, suggesting that this group represents an unexplored reservoir of novel and important secondary metabolites.

The rising atmospheric concentration of CO2 is a major concern to society due to its global warming potential. In soils, CO2-fixing microorganisms are preventing some of the CO2 from entering the atmosphere. Yet, the controls of dark CO2 fixation are rarely studied in situ. Here, we examined the gene and transcript abundance of key genes involved in microbial CO2 fixation along major environmental gradients within estuarine wetlands. A combined multi-omics approach incorporating metabarcoding, deep metagenomic, and metatranscriptomic analyses confirmed that wetland microbiota harbor four out of seven known CO2 fixation pathways, namely, the Calvin cycle, reverse tricarboxylic acid cycle, Wood-Ljungdahl pathway, and reverse glycine pathway. These pathways are transcribed at high frequencies along several environmental gradients, albeit at different levels depending on the environmental niche. Notably, the transcription of the key genes for the reverse tricarboxylic acid cycle was associated with high nitrate concentration, while the transcription of key genes for the Wood-Ljungdahl pathway was favored by reducing, O2-poor conditions. The transcript abundance of the Calvin cycle was favored by niches high in organic matter. Taxonomic assignment of transcripts implied that dark CO2 fixation was mainly linked to a few bacterial phyla, namely, Desulfobacterota, Methylomirabilota, Nitrospirota, Chloroflexota, and Pseudomonadota.ImportanceThe increasing concentration of atmospheric CO2 has been identified as the primary driver of climate change and poses a major threat to human society. This work explores the mostly overlooked potential of light-independent CO2 fixation by soil microbes (a.k.a. dark CO2 fixation) in climate change mitigation efforts. Applying a combination of molecular microbial tools, our research provides new insights into the ecological niches where CO2-fixing pathways are most active. By identifying how environmental factors, like oxygen, salinity and organic matter availability, influence these pathways in an estuarine wetland environment, potential strategies for enhancing natural carbon sinks can be developed. The importance of our research is in advancing the understanding of microbial CO2 fixation and its potential role in the global climate system.

Peatlands store more carbon (C) than any other terrestrial ecosystem and as a C sink they are vital to mitigating climate change. The keystone of many peatland ecosystems is Sphagnum, a bryophyte genus of c. 350 species found on every continent except Antarctica. With climate change, many peatlands face increasing frequency and severity of drought. How Sphagnum responds to and recovers from drought will be key to sustaining peatlands over the coming decades. Here, we synthesise the latest evidence for how interactions of drought with Sphagnum affect peatland functioning. We discuss how Sphagnum traits, from the cellular to the community, control its ecohydrology and what changes occur during drought. We detail the effects of drought on Sphagnum C cycling and biochemistry, including photosynthesis, growth, respiration and methane (CH4) fluxes. We also highlight drought resilience and tipping points for Sphagnum physiology and at the ecosystem level. The implications of Sphagnum drought responses for peatland hydrology, restoration and wildfires are also outlined. Finally, we identify knowledge gaps and propose some urgent questions which should be addressed in future research.

Area of habitat (AOH) maps provide a high-resolution representation of the habitat available in a species' range and can support conservation policy and planning processes. However, until recently, there was insufficient knowledge on the distribution of inland wetlands and freshwater biodiversity to develop AOH mapping methods specifically tailored to inland wetlands. We used a combined empirical and thematic approach to translate inland wetland habitat classes in the International Union for Conservation of Nature (IUCN) Habitats Classification Scheme into spatially explicit wetland-cover types derived from the Global Lakes and Wetlands Database 2 and the World Karst Aquifer Map. The AOH was subsequently estimated as the area in the mapped range that corresponded to each species' habitat and elevation associations. We developed and tested the method with IUCN Red List assessment data, range maps, and point locality data for fishes, odonates, decapod crustaceans, and mollusks (22,876 species). The method performed well in comparison with similar methods already developed for terrestrial mammals, birds, amphibians, and reptiles. The mean map prevalence (proportion of area in a species' range that was AOH) was 18-32% for each taxonomic group. Based on data on known localities of occurrence, 78-100% of species per taxonomic group had a higher classification accuracy than expected if AOH were distributed in the range at random. This represents an increased accuracy in the distribution of wetland species. Our study represents the first attempt to distinguish between inland wetland habitat subclasses and to include subterranean habitats in an AOH mapping method. Our method will facilitate the inclusion of previously underrepresented taxa in key conservation tools and analyses and is expected to increase the accuracy of AOH mapping for any species associated with inland wetlands.