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We describe the metagenome composition, community functional annotation, and prokaryote diversity in calcareous stromatolites from a dry stream bed of the San Felipe Creek in the Anza Borrego Desert. Analyses show a community capable of nitrogen fixation, assimilatory nitrate reduction, biofilm formation, quorum sensing, and potential thick-walled akinete formation for desiccation resistance.
LeRoy, Carri J.; Claeson, Shannon M.; Garthwaite, Iris J.; Thompson, Madeline A.; Thompson, Lauren J.; Kamakawiwo’ole, Brandy K.; Froedin-Morgensen, Angie M.; McConathy, Victoria; Ramstack Hobbs, Joy M.; Stancheva, Rosalina; et al(
, Aquatic Sciences)
Abstract Determining how streams develop naturally, particularly the ecological role of newly developed riparian canopy cover, is essential to understanding the factors that structure new stream communities and provides valuable information for restoring highly disturbed ecosystems. However, attempts to understand primary succession in riverine ecosystems have been hindered by a lack of data owing to the infrequent formation of new rivers on the landscape. In the present study, we used five streams formed following the 1980 eruption of Mount St. Helens (WA, USA) to examine the influence of canopy cover development on algal and benthic macroinvertebrate assemblages, biomass, and organic matter processing. Newly established closed canopy reaches had less available light, but no significant differences in algal biomass or macroinvertebrate assemblages compared to open canopy reaches. Instead, algal and macroinvertebrate communities were structured mainly by hydrologic differences among watersheds. In contrast, organic matter processing rates were sensitive to canopy cover development, and rates were faster under closed canopies, especially in late summer or after terrestrial preconditioning. After 40 years of stream and riparian primary successional development, canopy cover strongly influences ecosystem function, but aquatic organism assembly was more influenced by physio-chemical and hydrologic variation. Our findings provide insight into the development of in-stream assemblages and ecosystem functions, which is also relevant to efforts to address major disturbances to stream channels, such as volcanic eruptions, floods, forest fires, and clear-cut logging.
Schvarcz, Christopher R.; Wilson, Samuel T.; Caffin, Mathieu; Stancheva, Rosalina; Li, Qian; Turk-Kubo, Kendra A.; White, Angelicque E.; Karl, David M.; Zehr, Jonathan P.; Steward, Grieg F.(
, Nature Communications)
Abstract
Persistent nitrogen depletion in sunlit open ocean waters provides a favorable ecological niche for nitrogen-fixing (diazotrophic) cyanobacteria, some of which associate symbiotically with eukaryotic algae. All known marine examples of these symbioses have involved either centric diatom or haptophyte hosts. We report here the discovery and characterization of two distinct marine pennate diatom-diazotroph symbioses, which until now had only been observed in freshwater environments. Rhopalodiaceae diatomsEpithemia pelagicasp. nov. andEpithemia catenatasp. nov. were isolated repeatedly from the subtropical North Pacific Ocean, and analysis of sequence libraries reveals a global distribution. These symbioses likely escaped attention because the endosymbionts lack fluorescent photopigments, havenifHgene sequences similar to those of free-living unicellular cyanobacteria, and are lost in nitrogen-replete medium. Marine Rhopalodiaceae-diazotroph symbioses are a previously overlooked but widespread source of bioavailable nitrogen in marine habitats and provide new, easily cultured model organisms for the study of organelle evolution.
Here, we report the discovery of a novel Sediminibacterium sequenced from laboratory cultures of freshwater stream cyanobacteria from sites in Southern California, grown in BG11 medium. Our genome-wide analyses reveal a highly contiguous and complete genome (97% BUSCO) that is placed within sediminibacterial clades in phylogenomic analyses. Functional annotation indicates the presence of genes that could be involved in mutualistic/commensal relationship with associated cyanobacterial hosts.
Although most lotic ecosystems experience frequent and sometimes large disturbances, opportunities are uncommon to study primary succession in streams. Exceptions include new stream channels arising from events such as glacial retreat, volcanism, and catastrophic landslides. In 1980, the eruption and massive landslide at Mount St. Helens (WA, U.S.A.) created an entire landscape with five new catchments undergoing primary succession. We asked if riparian and lotic assemblages at early successional stages (36 years after the eruption) showed predictable change along longitudinal gradients within catchments, and whether assemblages were similar among five replicate catchments.
In July 2016, we collected environmental data and characterised riparian, algal, and benthic macroinvertebrate assemblages at 21 stream reaches distributed within and among five neighbouring catchments. We evaluated patterns of richness, abundance, biomass, multivariate taxonomic community structure, and functional traits both longitudinally and among catchments.
We found minimal evidence that longitudinal gradients had developed within catchments at 36 years post‐eruption. Increases in diatom and macroinvertebrate richness with downstream distance were the only biological responses with longitudinal trends. Conversely, we documented substantial variation in community structure of riparian plants, soft‐bodied algae, diatoms, and macroinvertebrates at the among‐catchment scale. Among‐catchment differences consistently separated two eastern catchments from three western catchments, and these two groups also differed in stream water chemistry, water temperature, and geomorphology.
Overall, we documented greater diversity in the young catchments than predicted by ecologists in the years immediately following the eruption, yet functional traits indicate that these catchments are still in relatively early stages of succession. Variation at the among‐catchment scale is likely to be driven in part by hydrological source variation, with the two eastern catchments showing environmental signatures associated with glacial ice‐melt and the three western catchments probably fed primarily by springs from groundwater aquifers. Contemporary flow disturbance regimes also varied among catchments and successional trajectories were probably reset repeatedly in streams experiencing more frequent disturbance.
Similar to new stream channels formed following glacial retreat, our results support a tolerance model of succession in streams. However, contrasting abiotic templates among Mount St. Helens catchments appear to be driving different successional trajectories of riparian plant, algal, and macroinvertebrate assemblages among neighbouring small catchments sharing the same catastrophic disturbance history.
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