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Climate change and human activities may alter the structure and function of boreal peatlands by warming waters and changing their hydrology. Diatoms can be used to assess or track these changes. However, effective biomonitoring requires consistent, reliable identification. To address this need, this study developed a diatom voucher flora of species found across a boreal fen gradient (e.g., vegetation) in interior Alaskan peatlands. Composite diatom samples were collected bi-weekly from three peatland complexes over the 2017 summer. The morphological range of each taxon was imaged. The fens contained 184 taxa across 38 genera. Eunotia (45), Gomphonema (23), and Pinnularia (20) commonly occurred in each peatland. Tabellaria was common in the rich and moderate fen but sparse in the poor fen. Eunotia showed the opposite trend. Approximately 11% of species are potentially novel and 25% percent matched those at risk or declining in status on the diatom Red List (developed in Germany), highlighting the conservation value of boreal wetlands. This voucher flora expands knowledge of regional diatom biodiversity and provides updated, verifiable taxonomic information for inland Alaskan diatoms, building on Foged’s 1981 treatment. This flora strengthens the potential to effectively track changes in boreal waterways sensitive to climate change and anthropogenic stressors. 

Mitochondria carry the remnant of an ancestral bacterial chromosome and express those genes with a system separate and distinct from the nucleus. Mitochondrial genes are transcribed as poly-cistronic primary transcripts which are post-transcriptionally processed to create individual translationally competent mRNAs. Algae post-transcriptional processing has only been explored in Chlamydomonas reinhardtii (Class: Chlorophyceae) and the mature mRNAs are different than higher plants, having no 5′ UnTranslated Regions (UTRs), much shorter and more variable 3′ UTRs and polycytidylated mature mRNAs. In this study, we analyzed transcript termini using circular RT-PCR and PacBio Iso-Seq to survey the 3′ and 5′ UTRs and termini for two green algae, Pediastrum duplex (Class: Chlorophyceae) and Chara vulgaris (Class: Charophyceae). This enabled the comparison of processing in the chlorophyte and charophyte clades of green algae to determine if the differences in mitochondrial mRNA processing pre-date the invasion of land by embryophytes. We report that the 5′ mRNA termini and non-template 3′ termini additions in P. duplex resemble those of C. reinhardtii, suggesting a conservation of mRNA processing among the chlorophyceae. We also report that C. vulgaris mRNA UTRs are much longer than chlorophytic examples, lack polycytidylation, and are polyadenylated similar to embryophytes. This demonstrates that some mitochondrial mRNA processing events diverged with the split between chlorophytic and streptophytic algae. 

Filamentous representatives of Cladophorales (Chlorophyta) are major contributors to algal biomass of littoral communities. In the present study, community analysis of a reported bloom in the Ogeechee River in Georgia provided an opportunity to combine morphological and genetic analyses with ecological information related to an understudied nuisance alga. A polyphasic approach of incorporating genotypic and phenotypic methods led to the identification of the algal community as Pithophora roettleri (Roth) Wittrock. Morphological analysis showed a monospecific community based on the average length and diameter of the heterosporous intercalary and terminal akinetes, along with the diameter of the principal filaments. Single-gene and concatenated-gene phylogenetic analyses of the LSU (28S rRNA) and SSU (18S rRNA) markers further confirmed this species identification. In this study, we conducted a morphological treatment of P. roettleri, produced 17 novel gene sequences, and produced a new, schematic diagram illustrating the four steps of the asexual reproduction of an intercalary akinete. Morphological characteristics, like the position and shape of akinetes documented here, and the availability of genetic sequences can improve identification and further ecological understanding of filamentous green algae. Flowing mats of P. roettleri, like those observed in this study, can lower light availability for other biota and structurally alter the habitat. 

Examination of algal assemblages from aerial environments around the globe, especially those from pseudoaerial habitats found on moistened rocks underneath waterfalls or around springs and seeps, reveals the presence of unique diatom floras. Yet, diatom assemblages from northern regions like Iceland remain understudied, especially those from the volcanic rock outcrops and boulders that create euaerial habitats where biota receive moisture from the atmosphere or the rock itself. During the summers of 2013 and 2015, we examined the biodiversity of mostly euaerial, but also pseudoaerial, diatom assemblages collected from volcanic rock outcrops or large boulders on the landscape from southwestern Iceland. We used light and scanning electron microscopy to document the biodiversity of common, smaller, new, or interesting specimens, such as Humidophila and Eunotia. We describe one new Humidophila species, H. eldfjallii sp. nov., with triundulate valve margins and include information on another unidentified taxon, Humidophila sp. 1, naviculoid in shape with tapering to rounded ends, continuous striae through the length of the valve, and a circular central area. We formally transfer Diadesmis contenta var. biceps to Humidophila biceps. To correct the nomenclature, we recognized Humidophila parallela at the species level. Relative abundance estimates of diatom populations provided further characterization of the assemblages on these habitats. Humidophila taxa, especially H. gallica dominated the diverse diatom flora. We discuss adaptations for survival with access to mostly atmospheric water. The diatom flora described here adds to the flora for this region, highlights the diversity of diatom assemblages that can inhabit euaerial environments, and provides evidence of adaptive success of diatoms in extreme habitats with limited moisture and nutrients. 

The large population sizes and high dispersal potential of microbes suggests that a given microbial species should be found in all suitable habitats worldwide. Consequently, microbes should not exhibit the kinds of biogeographic patterns seen in macroorganisms. This paradigm is challenged by a growing list of exotic microbes with biogeographic disjunctions that instead promotes microbial dispersal as inherently limited. We sampled water bodies in the United States and compiled records from the literature and public databases to characterize the distribution of the freshwater planktonic diatom, Discostella asterocostata (Xie, Lin, and Cai) Houk and Klee. Discostella asterocostata was thought to be restricted to the Far East, but we report its presence in ecologically similar water bodies across the eastern United States. Populations from the U.S. and China are indistinguishable morphometrically, suggesting they may be recently separated—a hypothesis supported by paleolimnological data, which support an introduction of D. asterocostata into the U.S. as recently as the mid-1980s. The overlapping distributions of D. asterocostata and invasive carp species, in both their native and nonnative ranges, highlighted Asian carp as a possible vector for introduction of the diatom in the U.S. The existence of exotic diatoms underscores natural constraints on microbial dispersal, resulting in biogeographic distributions that can be upended through human activity.