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1. Climate drivers alter nitrogen availability in surface peat and decouple N₂ fixation from CH₄ oxidation in the Sphagnum moss microbiome

   https://doi.org/10.1111/gcb.16651  

   Petro, Caitlin; Carrell, Alyssa A.; Wilson, Rachel M.; Duchesneau, Katherine; Noble‐Kuchera, Sekou; Song, Tianze; Iversen, Colleen M.; Childs, Joanne; Schwaner, Geoff; Chanton, Jeffrey P.; et al (March 2023, Global Change Biology)

   Abstract Peat mosses (Sphagnumspp.) are keystone species in boreal peatlands, where they dominate net primary productivity and facilitate the accumulation of carbon in thick peat deposits.Sphagnummosses harbor a diverse assemblage of microbial partners, including N₂‐fixing (diazotrophic) and CH₄‐oxidizing (methanotrophic) taxa that support ecosystem function by regulating transformations of carbon and nitrogen. Here, we investigate the response of theSphagnumphytobiome (plant + constituent microbiome + environment) to a gradient of experimental warming (+0°C to +9°C) and elevated CO₂(+500 ppm) in an ombrotrophic peatland in northern Minnesota (USA). By tracking changes in carbon (CH₄, CO₂) and nitrogen (NH₄‐N) cycling from the belowground environment up toSphagnumand its associated microbiome, we identified a series of cascading impacts to theSphagnumphytobiome triggered by warming and elevated CO₂. Under ambient CO₂, warming increased plant‐available NH₄‐N in surface peat, excess N accumulated inSphagnumtissue, and N₂fixation activity decreased. Elevated CO₂offset the effects of warming, disrupting the accumulation of N in peat andSphagnumtissue. Methane concentrations in porewater increased with warming irrespective of CO₂treatment, resulting in a ~10× rise in methanotrophic activity withinSphagnumfrom the +9°C enclosures. Warming's divergent impacts on diazotrophy and methanotrophy caused these processes to become decoupled at warmer temperatures, as evidenced by declining rates of methane‐induced N₂fixation and significant losses of keystone microbial taxa. In addition to changes in theSphagnummicrobiome, we observed ~94% mortality ofSphagnumbetween the +0°C and +9°C treatments, possibly due to the interactive effects of warming on N‐availability and competition from vascular plant species. Collectively, these results highlight the vulnerability of theSphagnumphytobiome to rising temperatures and atmospheric CO₂concentrations, with significant implications for carbon and nitrogen cycling in boreal peatlands. 

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2. Clonality, local population structure and gametophyte sex ratios in cryptic species of the Sphagnum magellanicum complex

   https://doi.org/10.1093/aob/mcad077  

   Shaw, A. Jonathan; Duffy, Aaron M.; Nieto-Lugilde, Marta; Aguero, Blanka; Schuette, Scott; Robinson, Sean; Loveland, James; Hicks, Karen A.; Weston, David; Piatkowski, Bryan; et al (July 2023, Annals of Botany)

   Abstract Background and AimsSphagnum (peatmoss) comprises a moss (Bryophyta) clade with ~300–500 species. The genus has unparalleled ecological importance because Sphagnum-dominated peatlands store almost a third of the terrestrial carbon pool and peatmosses engineer the formation and microtopography of peatlands. Genomic resources for Sphagnum are being actively expanded, but many aspects of their biology are still poorly known. Among these are the degree to which Sphagnum species reproduce asexually, and the relative frequencies of male and female gametophytes in these haploid-dominant plants. We assess clonality and gametophyte sex ratios and test hypotheses about the local-scale distribution of clones and sexes in four North American species of the S. magellanicum complex. These four species are difficult to distinguish morphologically and are very closely related. We also assess microbial communities associated with Sphagnum host plant clones and sexes at two sites. MethodsFour hundred and five samples of the four species, representing 57 populations, were subjected to restriction site-associated DNA sequencing (RADseq). Analyses of population structure and clonality based on the molecular data utilized both phylogenetic and phenetic approaches. Multi-locus genotypes (genets) were identified using the RADseq data. Sexes of sampled ramets were determined using a molecular approach that utilized coverage of loci on the sex chromosomes after the method was validated using a sample of plants that expressed sex phenotypically. Sex ratios were estimated for each species, and populations within species. Difference in fitness between genets was estimated as the numbers of ramets each genet comprised. Degrees of clonality [numbers of genets/numbers of ramets (samples)] within species, among sites, and between gametophyte sexes were estimated. Sex ratios were estimated for each species, and populations within species. Sphagnum-associated microbial communities were assessed at two sites in relation to Sphagnum clonality and sex. Key ResultsAll four species appear to engage in a mixture of sexual and asexual (clonal) reproduction. A single ramet represents most genets but two to eight ramets were dsumbers ansd text etected for some genets. Only one genet is represented by ramets in multiple populations; all other genets are restricted to a single population. Within populations ramets of individual genets are spatially clustered, suggesting limited dispersal even within peatlands. Sex ratios are male-biased in S. diabolicum but female-biased in the other three species, although significantly so only in S. divinum. Neither species nor males/females differ in levels of clonal propagation. At St Regis Lake (NY) and Franklin Bog (VT), microbial community composition is strongly differentiated between the sites, but differences between species, genets and sexes were not detected. Within S. divinum, however, female gametophytes harboured two to three times the number of microbial taxa as males. ConclusionsThese four Sphagnum species all exhibit similar reproductive patterns that result from a mixture of sexual and asexual reproduction. The spatial patterns of clonally replicated ramets of genets suggest that these species fall between the so-called phalanx patterns, where genets abut one another but do not extensively mix because of limited ramet fragmentation, and the guerrilla patterns, where extensive genet fragmentation and dispersal result in greater mixing of different genets. Although sex ratios in bryophytes are most often female-biased, both male and female biases occur in this complex of closely related species. The association of far greater microbial diversity for female gametophytes in S. divinum, which has a female-biased sex ratio, suggests additional research to determine if levels of microbial diversity are consistently correlated with differing patterns of sex ratio biases. 

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3. Functional trait evolution in Sphagnum peat mosses and its relationship to niche construction

   https://doi.org/10.1111/nph.15825  

   Piatkowski, Bryan T.; Shaw, A. Jonathan (April 2019, New Phytologist)

   Summary Species in the genusSphagnumcreate, maintain, and dominate boreal peatlands through ‘extended phenotypes’ that allow these organisms to engineer peatland ecosystems and thereby impact global biogeochemical cycles. One such phenotype is the production of peat, or incompletely decomposed biomass, that accumulates when rates of growth exceed decomposition. Interspecific variation in peat production is thought to be responsible for the establishment and maintenance of ecological gradients such as the microtopographic hummock‐hollow gradient, along which sympatric species sort within communities.This study investigated the mode and tempo of functional trait evolution across 15 species ofSphagnumusing data from the most extensive studies ofSphagnumfunctional traits to date and phylogenetic comparative methods.We found evidence for phylogenetic conservatism of the niche descriptor height‐above‐water‐table and of traits related to growth, decay and litter quality. However, we failed to detect the influence of phylogeny on interspecific variation in other traits such as shoot density and suggest that environmental context can obscure phylogenetic signal. Trait correlations indicate possible adaptive syndromes that may relate to niche and its construction.This study is the first to formally test the extent to which functional trait variation amongSphagnumspecies is a result of shared evolutionary history. 

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4. Sex‐biased gene content is associated with sex chromosome turnover in Danaini butterflies

   https://doi.org/10.1111/mec.17256  

   Mora, Pablo; Hospodářská, Monika; Voleníková, Anna Chung; Koutecký, Petr; Štundlová, Jana; Dalíková, Martina; Walters, James R.; Nguyen, Petr (January 2024, Molecular Ecology)

   Abstract Sex chromosomes play an outsized role in adaptation and speciation, and thus deserve particular attention in evolutionary genomics. In particular, fusions between sex chromosomes and autosomes can produce neo‐sex chromosomes, which offer important insights into the evolutionary dynamics of sex chromosomes. Here, we investigate the evolutionary origin of the previously reportedDanausneo‐sex chromosome within the tribe Danaini. We assembled and annotated genomes ofTirumala septentrionis(subtribe Danaina),Ideopsis similis(Amaurina),Idea leuconoe(Euploeina) andLycorea halia(Itunina) and identified their Z‐linked scaffolds. We found that theDanausneo‐sex chromosome resulting from the fusion between a Z chromosome and an autosome corresponding to theMelitaea cinxiachromosome (McChr) 21 arose in a common ancestor of Danaina, Amaurina and Euploina. We also identified two additional fusions as the W chromosome further fused with the synteny block McChr31 inI. similisand independent fusion occurred between ancestral Z chromosome and McChr12 inL. halia. We further tested a possible role of sexually antagonistic selection in sex chromosome turnover by analysing the genomic distribution of sex‐biased genes inI. leuconoeandL. halia. The autosomes corresponding to McChr21 and McChr31 involved in the fusions are significantly enriched in female‐ and male‐biased genes, respectively, which could have hypothetically facilitated fixation of the neo‐sex chromosomes. This suggests a role of sexual antagonism in sex chromosome turnover in Lepidoptera. The neo‐Z chromosomes of bothI. leuconoeandL. haliaappear fully compensated in somatic tissues, but the extent of dosage compensation for the ancestral Z varies across tissues and species. 

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5. Fresh Air for the Mire-Breathing Hypothesis: Sphagnum Moss and Peat Structure Regulate the Response of CO2 Exchange to Altered Hydrology in a Northern Peatland Ecosystem

   https://doi.org/10.3390/w14203239  

   O’Neill, Ally; Tucker, Colin; Kane, Evan S. (October 2022, Water)

   Sphagnum-dominated peatlands store more carbon than all of Earth’s forests, playing a large role in the balance of carbon dioxide. However, these carbon sinks face an uncertain future as the changing climate is likely to cause water stress, potentially reducing Sphagnum productivity and transitioning peatlands to carbon sources. A mesocosm experiment was performed on thirty-two peat cores collected from two peatland landforms: elevated mounds (hummocks) and lower, flat areas of the peatland (hollows). Both rainfall treatments and water tables were manipulated, and CO2 fluxes were measured. Other studies have observed peat subsiding and tracking the water table downward when experiencing water stress, thought to be a self-preservation technique termed ‘Mire-breathing’. However, we found that hummocks tended to compress inwards, rather than subsiding towards the lowered water table as significantly as hollows. Lower peat height was linearly associated with reduced gross primary production (GPP) in response to lowered water tables, indicating that peat subsidence did not significantly enhance the resistance of GPP to drought. Conversely, Sphagnum peat compression was found to stabilize GPP, indicating that this mechanism of resilience to drought may transmit across the landscape depending on which Sphagnum landform types are dominant. This study draws direct connections between Sphagnum traits and peatland hydrology and carbon cycling. 

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