Nitrification is a central process of the aquatic nitrogen cycle that controls the supply of nitrate used in other key processes, such as phytoplankton growth and denitrification. Through time series observation and modeling of a seasonally stratified, eutrophic coastal basin, we demonstrate that physical dilution of nitrifying microorganisms by water column mixing can delay and decouple nitrification. The findings are based on a 4-y, weekly time series in the subsurface water of Bedford Basin, Nova Scotia, Canada, that included measurement of functional (amoA) and phylogenetic (16S rRNA) marker genes. In years with colder winters, more intense winter mixing resulted in strong dilution of resident nitrifiers in subsurface water, delaying nitrification for weeks to months despite availability of ammonium and oxygen. Delayed regrowth of nitrifiers also led to transient accumulation of nitrite (3 to 8 μmol · kg_sw⁻¹) due to decoupling of ammonia and nitrite oxidation. Nitrite accumulation was enhanced by ammonia-oxidizing bacteria (Nitrosomonadaceae) with fast enzyme kinetics, which temporarily outcompeted the ammonia-oxidizing archaea (Nitrosopumilus) that dominated under more stable conditions. The study reveals how physical mixing can drive seasonal and interannual variations in nitrification through control of microbial biomass and diversity. Variable, mixing-induced effects on functionally specialized microbial communities are likely relevant to biogeochemical transformation rates in other seasonally stratified water columns. The detailed study reveals a complex mechanism through which weather and climate variability impacts nitrogen speciation, with implications for coastal ecosystem productivity. It also emphasizes the value of high-frequency, multiparameter time series for identifying complex controls of biogeochemical processes in aquatic systems. Significance Changes in both quantity and speciation of nitrogen in coastal waters impact phytoplankton communities, contributing to eutrophication and harmful algal blooms. Multidisciplinary oceanographic time series of high resolution are rare but crucial for identifying complex mechanisms that underlie such anthropogenic impacts. Analysis and modeling of such a time series from a seasonally stratified fjord showed that dilution of nitrifier biomass by variable winter mixing altered the timing and rates of nitrification, which converts ammonia to nitrite and nitrate. This reveals a link among climate-sensitive physical dynamics, nitrifier abundance, and diversity, with controls on phytoplankton ecology. The findings imply that explicit measurement and modeling of microbial communities will be required to project impacts of climate change on coastal ecosystems.

Microbial observatories can track phytoplankton at frequencies that resolve monthly, seasonal, and multiyear trends in environmental change from short-lived events. Using 4-years of weekly flow cytometry along with chloroplast and cyanobacterial 16S rRNA gene sequence data from a time-series station in the coastal Northwest Atlantic (Bedford Basin, Nova Scotia, Canada), we analyzed temporal observations for globally-relevant genera (e.g., Bolidomonas, Teleaulax, Minidiscus, Chaetoceros, Synechococcus, and Phaeocystis) in an oceanic region that has been recognized as a likely hotspot for phytoplankton diversity. Contemporaneous Scotian Shelf data also collected during our study established that the major phytoplankton within the Bedford Basin were important in the Scotian Shelf during spring and fall, therefore pointing to their broader significance within the coastal Northwest Atlantic (NWA). Temporal trends revealed a subset of indicator taxa along with their DNA signatures (e.g., Eutreptiella and Synechococcus), whose distribution patterns make them essential for timely detection of environmentally-driven shifts in the NWA. High-resolution sampling was key to identifying important community shifts towards smaller phytoplankton under anomalous environmental conditions, while further providing a detailed molecular view of community compositions underpinning general phytoplankton succession within the coastal NWA. Our study demonstrates the importance of accessible coastal time-series sites where high-frequency DNA sampling allows for the detection of shifting baselines in phytoplankton communities.

The high diversity and global distribution of heterotrophic bacterial diazotrophs (HBDs) in the ocean has recently become apparent. However, understanding the role these largely uncultured microorganisms play in marine N ₂ fixation poses a challenge due to their undefined growth requirements and the complex regulation of the nitrogenase enzyme. We isolated and characterized Candidatus Thalassolituus haligoni, a member of a widely distributed clade of HBD belonging to the Oceanospirillales. Analysis of its nifH gene via amplicon sequencing revealed the extensive distribution of Cand. T. haligoni across the Pacific, Atlantic, and Arctic Oceans. Pangenome analysis indicates that the isolate shares >99% identity with an uncultured metagenome-assembled genome called Arc-Gamma-03, recently recovered from the Arctic Ocean. Through combined genomic, proteomic, and physiological approaches, we confirmed that the isolate fixes N ₂ gas. However, the mechanisms governing nitrogenase regulation in Cand. T. haligoni remain unclear. We propose Cand. T. haligoni as a globally distributed, cultured HBD model species within this understudied clade of Oceanospirillales.

Novel species of fungi described in this study include those from various countries as follows: Australia, Agaricus albofoetidus, Agaricus aureoelephanti and Agaricus parviumbrus on soil, Fusarium ramsdenii from stem cankers of Araucaria cunninghamii, Keissleriella sporoboli from stem of Sporobolus natalensis, Leptosphaerulina queenslandica and Pestalotiopsis chiaroscuro from leaves of Sporobolus natalensis, Serendipita petricolae as endophyte from roots of Eriochilus petricola, Stagonospora tauntonensis from stem of Sporobolus natalensis, Teratosphaeria carnegiei from leaves of Eucalyptus grandis × E. camaldulensis and Wongia ficherai from roots of Eragrostis curvula. Canada, Lulworthia fundyensis from intertidal wood and Newbrunswickomyces abietophilus (incl. Newbrunswickomyces gen. nov.) on buds of Abies balsamea. Czech Republic, Geosmithia funiculosa from a bark beetle gallery on Ulmus minor and Neoherpotrichiella juglandicola (incl. Neoherpotrichiella gen. nov.) from wood of Juglans regia. France, Aspergillus rouenensis and Neoacrodontium gallica (incl. Neoacrodontium gen. nov.) from bore dust of Xestobium rufovillosum feeding on Quercus wood, Endoradiciella communis (incl. Endoradiciella gen. nov.) endophytic in roots of Microthlaspi perfoliatum and Entoloma simulans on soil. India, Amanita konajensis on soil and Keithomyces indicus from soil. Israel, Microascus rothbergiorum from Stylophora pistillata. Italy, Calonarius ligusticus on soil. Netherlands, Appendopyricularia juncicola (incl. Appendopyricularia gen. nov.), Eriospora juncicola and Tetraploa juncicola on dead culms of Juncus effusus, Gonatophragmium physciae on Physcia caesia and Paracosmospora physciae (incl. Paracosmospora gen. nov.) on Physcia tenella, Myrmecridium phragmitigenum on dead culm of Phragmites australis, Neochalara lolae on stems of Pteridium aquilinum, Niesslia nieuwwulvenica on dead culm of undetermined Poaceae, Nothodevriesia narthecii (incl. Nothodevriesia gen. nov.) on dead leaves of Narthecium ossifragum and Parastenospora pini (incl. Parastenospora gen. nov.) on dead twigs of Pinus sylvestris. Norway, Verticillium bjoernoeyanum from sand grains attached to a piece of driftwood on a sandy beach. Portugal, Collybiopsis cimrmanii on the base of living Quercus ilex and amongst dead leaves of Laurus and herbs. South Africa, Paraproliferophorum hyphaenes (incl. Paraproliferophorum gen. nov.) on living leaves of Hyphaene sp. and Saccothecium widdringtoniae on twigs of Widdringtonia wallichii. Spain, Cortinarius dryosalor on soil, Cyphellophora endoradicis endophytic in roots of Microthlaspi perfoliatum, Geoglossum lauri-silvae on soil, Leptographium gemmatum from fluvial sediments, Physalacria auricularioides from a dead twig of Castanea sativa, Terfezia bertae and Tuber davidlopezii in soil. Sweden, Alpova larskersii, Inocybe alpestris and Inocybe boreogodeyi on soil. Thailand, Russula banwatchanensis, Russula purpureoviridis and Russula lilacina on soil. Ukraine, Nectriella adonidis on overwintered stems of Adonis vernalis. USA, Microcyclus jacquiniae from living leaves of Jacquinia keyensis and Penicillium neoherquei from a minute mushroom sporocarp. Morphological and culture characteristics are supported by DNA barcodes. Citation: Crous PW, Boers J, Holdom D, et al. 2022. Fungal Planet description sheets: 1383-1435. Persoonia 48: 261-371. https://doi.org/10.3767/persoonia.2022.48.08.

UCYN-A is a globally important nitrogen-fixing symbiotic microbe often found in colder regions and coastal areas where nitrogen fixation has been overlooked. We present a 3-year coastal Northwest Atlantic time series of UCYN-A by integrating oceanographic data with weekly nifH and16 S rRNA gene sequencing and quantitative PCR assays for UCYN-A ecotypes. High UCYN-A relative abundances dominated by A1 to A4 ecotypes reoccurred annually in the coastal Northwest Atlantic. Although UCYN-A was detected every summer/fall, the ability to observe separate ecotypes may be highly dependent on sampling time given intense interannual and weekly variability of ecotype-specific occurrences. Additionally, much of UCYN-A’s rarer diversity was populated by short-lived neutral mutational variants, therefore providing insight into UCYN-A’s microevolutionary patterns. For instance, rare ASVs exhibited community composition restructuring annually, while also sharing a common connection to a dominant ASV within each ecotype. Our study provides additional perspectives for interpreting UCYN-A intraspecific diversity and underscores the need for high-resolution datasets when deciphering spatiotemporal ecologies within UCYN-A.

We describe diazotrophs present during a 2015 GEOTRACES expedition through the Canadian Arctic Gateway (CAG) using nifH metabarcoding. In the less studied Labrador Sea, Bradyrhizobium sp. and Vitreoscilla sp. nifH variants were dominant, while in Baffin Bay, a Stutzerimonas stutzeri variant was dominant. In comparison, the Canadian Arctic Archipelago (CAA) was characterized by a broader set of dominant variants belonging to Desulfobulbaceae, Desulfuromonadales, Arcobacter sp., Vibrio spp., and Sulfuriferula sp. Although dominant diazotrophs fell within known nifH clusters I and III, only a few of these variants were frequently recovered in a 5-year weekly nifH times series in the coastal NW Atlantic presented herein, notably S. stutzeri and variants belonging to Desulfobacterales and Desulfuromonadales. In addition, the majority of dominant Arctic nifH variants shared low similarity (< 92% nucleotide identities) to sequences in a global noncyanobacterial diazotroph catalog recently compiled by others. We further detected UCYN-A throughout the CAG at low-levels using quantitative-PCR assays. Temperature, depth, salinity, oxygen, and nitrate were most strongly correlated to the Arctic diazotroph diversity observed, and we found a stark division between diazotroph communities of the Labrador Sea versus Baffin Bay and the CAA, hence establishing that a previously unknown biogeographic community division can occur for diazotrophs in the CAG.