SummaryCyanobacteria typically colonize the surface of arid soils, building biological soil crust (biocrusts) that provide a variety of ecosystem benefits, ranging from fertilization to stabilization against erosion. We investigated how future scenarios in precipitation anticipated for the Northern Chihuahuan Desert affected abundance and composition of biocrust cyanobacteria in two grassland ecosystems. Scenarios included a decrease in precipitation and a delay of monsoon rainfall. After three years, both treatments negatively affected cyanobacteria, although the effects of monsoon delay were milder than those of decreased precipitation. Mature biocrusts in black grama grassland suffered severe losses in cyanobacterial biomass and diversity, but compositionally simpler biocrusts in blue grama-dominated grassland maintained biomass, only suffering diversity losses. This could be partially explained by the differential sensitivity of cyanobacterial taxa: nitrogen-fixing Scytonema spp. were the most sensitive, followed by phylotypes in the Microcoleus steenstrupii complex. Microcoleus vaginatus was the least affected in all cases, but is known to be very sensitive to warming. We predict that altered precipitation will tend to prevent biocrusts from reaching successional maturity, selecting for M. vaginatus over competing M. steenstrupii, among pioneer biocrust-formers. A shift towards heat-sensitive M. vaginatus could ultimately destabilize biocrusts when precipitation changes are combined with global warming.

A new Phormidium-like genus was found during an investigation of Oscillatoriales diversity in Brazil. Eight aerophytic populations from south and southeastern regions were isolated in monospecific cultures and submitted to polyphasic evaluation. The populations presented homogeneous morphology with straight trichomes, not attenuated, and apical cell with thickened cell wall. Phylogenetic analyses based on 16S rRNA gene sequences showed that these populations, plus the Brazilian strain Phomidium sp. B-Tom from GenBank, formed a highly supported and distinctive clade, which corresponds to the new genus Pycnacronema, comprising six new species: P. brasiliensis (type species), P. arboriculum, P. conicum, P. marmoreum, P. rubrum, and P. savannensis. These results were confirmed and supported by rpoC1 and rbcL genes evaluated independently and by the concatenated analysis of 16S rRNA, rpoC1 and rbcL genes (for all species but P. savannensis). Secondary structures of the D1-D1 0 , box-B, and V3 regions of the internal transcribed spacer were informative at specific level, being conserved in P. brasiliensis and variable among the other strains, also confirming the phylogenetic analyses. The generic name and specific epithets of the new taxa are proposed under the provisions of the International Code of Nomenclature of algae, fungi, and plants.

The last decade was marked by efforts to define and identify the main cyanobacterial players in biological crusts around the world. However, not much is known about biocrusts in Brazil's tropical savanna (cerrado), despite the existence of environments favorable to their development and ecological relevance. We examined the community composition of cyanobacteria in biocrusts from six sites distributed in the Southeast of the country using high throughput sequencing of 16S rRNA and phylogenetic placement in the wider context of biocrusts from deserts. Sequences ascribable to 22 genera of cyanobacteria were identified. Although a significant proportion of sequences did not match those of known cyanobacteria, several clades of Leptolyngbya and Porphyrosiphon were found to be the most abundant. We identified significant differences in dominance and overall composition among the cerrado sites, much larger than within-site variability. The composition of cerrado cyanobacterial communities was distinct from those known in biocrusts from North American deserts. Among several environmental drivers considered, the opposing trend of annual precipitation and mean annual temperature best explained the variability in community composition within Brazilian biocrusts. Their compositional uniqueness speaks of the need for dedicated efforts to study the ecophysiology of tropical savanna biocrust and their roles in ecosystem function for management and preservation.

The genus Wilmottia was described based on polyphasic studies of Phormidium murrayi populations that revealed them not closely related to other Phormidium species, despite their morphological similarity. The genus contained one species, W. murrayi, found exclusively in cold and temperate areas of the world. Other species morphologically similar to Phormidium were expected to pertain to Wilmottia, but the genus remained unispecific until now. During a survey of Cyanobacteria in Brazil, 11 strains morphologically similar to Wilmottia from southern and southeastern regions were isolated in unicyanobacterial cultures and submitted to polyphasic evaluation (morphological, ecological and molecular studies). The populations studied presented homogeneous morphology (trichomes cylindrical, straight and not attenuated) and were found inhabiting quite diverse environments (freshwater, wet soil and barks of trees). The molecular analyses based on 16S rRNA gene sequences placed the 11 studied strains in two distinct clusters inside the highly supported Wilmottia clade. The 16S-23S ITS marker was very variable and did not provide consistent information to improve the differentiation among the strains. The characteristics of the Brazilian populations, essentially the genetic ones, resulted in the recognition of a new cryptic species of Wilmottia (W. stricta) and indicated a wider distribution for W. murrayi. Such distribution would comprehend a wide climatic range (from polar to tropical) and occurrence in very distinct habitats (aquatic and aerophytic). The possible explanations to that scenario would be the low sensitivity of 16S rRNA gene as marker for distinguishing species inside of this complex of strains or W. murrayi actually represents a case of ubiquitous species. The addition of other genes or whole genome sequencing could be the way to reach a more confident answer. Wilmottia reveals a very intricate phylogeny according to the 16S rRNA gene and more studies are recommended to confirm its monophyly.

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