Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such “monodominant” forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees ≥ 10 cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors.

Amazonian forests are extraordinarily diverse, but the estimated species richness is very much debated. Here, we apply an ensemble of parametric estimators and a novel technique that includes conspecific spatial aggregation to an extended database of forest plots with up-to-date taxonomy. We show that the species abundance distribution of Amazonia is best approximated by a logseries with aggregated individuals, where aggregation increases with rarity. By averaging several methods to estimate total richness, we confirm that over 15,000 tree species are expected to occur in Amazonia. We also show that using ten times the number of plots would result in an increase to just ~50% of those 15,000 estimated species. To get a more complete sample of all tree species, rigorous field campaigns may be needed but the number of trees in Amazonia will remain an estimate for years to come.

Nomenclatural type definitions are one of the most important concepts in biological nomenclature. Being physical objects that can be re-studied by other researchers, types permanently link taxonomy (an artificial agreement to classify biological diversity) with nomenclature (an artificial agreement to name biological diversity). Two proposals to amend the International Code of Nomenclature for algae, fungi, and plants (ICN), allowing DNA sequences alone (of any region and extent) to serve as types of taxon names for voucherless fungi (mainly putative taxa from environmental DNA sequences), have been submitted to be voted on at the 11th International Mycological Congress (Puerto Rico, July 2018). We consider various genetic processes affecting the distribution of alleles among taxa and find that alleles may not consistently and uniquely represent the species within which they are contained. Should the proposals be accepted, the meaning of nomenclatural types would change in a fundamental way from physical objects as sources of data to the data themselves. Such changes are conducive to irreproducible science, the potential typification on artefactual data, and massive creation of names with low information content, ultimately causing nomenclatural instability and unnecessary work for future researchers that would stall future explorations of fungal diversity. We conclude that the acceptance of DNA sequences alone as types of names of taxa, under the terms used in the current proposals, is unnecessary and would not solve the problem of naming putative taxa known only from DNA sequences in a scientifically defensible way. As an alternative, we highlight the use of formulas for naming putative taxa (candidate taxa) that do not require any modification of the ICN.

Visando ampliar o conhecimento sobre diversidade de fungos conidiais, 10 folhas mortas de três indivíduos de C. melchiorii e de C. nemorosa foram coletadas bimestralmente na Serra da Jibóia, Bahia, no período de outubro/2005 a junho/2006. As folhas foram lavadas em água corrente e mantidas em câmara-úmida durante 30 dias. As estruturas fúngicas foram retiradas para estudo morfológico. Foram identificados 79 táxons de Ascomycota na forma anamórfica. Destes, 78 são hifomicetos e um celomiceto. Do total, 87% ocorreram sobre C. melchiorii e 55% sobre C. nemorosa. A maioria dos fungos apresentou freqüência esporádica e constância acidental. As espécies mais freqüentes foram: Beltrania rhombica Penz., Chaetopsina fulva Rambelli, Dactylaria ficusicola Paulus, Gadek & Hyde, Verticillium theobromae (Turconi) Mason & Hughes e Volutella sp. 1 (sobre C. melchiorii) e Atroseptaphiale flagelliformis Matsush., Pseudobeltrania sp., Zygosporium gibbum (Sacc., Rousseau & Bommer) Hughes, Verticillium theobromae (Turconi) Mason & Hughes e Volutella sp. 1 (sobre C. nemorosa). A similaridade de fungos entre as duas espécies de Clusia atingiu 60% e 11 táxons foram constantes nos dois hospedeiros: Atrosetaphiale flagelliformis, Beltraniella portoricensis (Stevens) Piroz. & Patil, Chalara alabamensis Jones & Ingram., Cryptophiale kakombensis Piroz., Parasympodiella laxa (Subram. & Vittal), Speiropsis scopiformis Kuthub. & Nawawi, Thozetella cristata Piroz. & Hodges, Umbellidion radulans Sutton & Hodges, Verticillium theobromae, Volutella sp. 2 e Zygosporium gibbum. Os dados mostram que o folhedo produzido por C. melchiorii e C. nemorosa, na Serra da Jibóia, é rico em fungos conidiais. Esses fungos, como decompositores, são importantes para a dinâmica do ecossistema estudado.

No abstract

Tree diversity and composition in Amazonia are known to be strongly determined by the water supplied by precipitation. Nevertheless, within the same climatic regime, water availability is modulated by local topography and soil characteristics (hereafter referred to as local hydrological conditions), varying from saturated and poorly drained to well-drained and potentially dry areas. While these conditions may be expected to influence species distribution, the impacts of local hydrological conditions on tree diversity and composition remain poorly understood at the whole Amazon basin scale. Using a dataset of 443 1-ha non-flooded forest plots distributed across the basin, we investigate how local hydrological conditions influence 1) tree alpha diversity, 2) the community-weighted wood density mean (CWM-wd) -a proxy for hydraulic resistance and 3) tree species composition. We find that the effect of local hydrological conditions on tree diversity depends on climate, being more evident in wetter forests, where diversity increases towards locations with well-drained soils. CWM-wd increased towards better drained soils in Southern and Western Amazonia. Tree species composition changed along local soil hydrological gradients in Central-Eastern, Western and Southern Amazonia, and those changes were correlated with changes in the mean wood density of plots. Our results suggest that local hydrological gradients filter species, influencing the diversity and composition of Amazonian forests. Overall, this study shows that the effect of local hydrological conditions is pervasive, extending over wide Amazonian regions, and reinforces the importance of accounting for local topography and hydrology to better understand the likely response and resilience of forests to increased frequency of extreme climate events and rising temperatures.

Durante o levantamento de fungos anamórficos associados à folhas em decomposição de diferentes plantas na região semi-árida do Estado da Bahia, 23 espécies, pertencentes a 19 gêneros foram encontradas. Dessas, uma espécie constitui novo registro para a Bahia e três para o Brasil, respectivamente: Drechslera victoriae (F. Meehan & H.C. Murphy) Subram. & B.L. Jain, Ochroconis crassihumicola (Matsush.) de Hoog & Arx, Pyricularia caffera Matsush. e Tretopileus sphaerophorus (Berk & M.A. Curtis) Hughes & Deighton. Descrições, comentários e ilustrações são apresentados para essas espécies.

As a result of an investigation of microfungi in northeastern Brazil, the hyphomycete Thozetella submersa sp. nov. is described from submerged wood. Its diagnostic features are the smooth, elliptic-fusiform, obclavate to rarely obovoid to obclavate, slightly curved, sometimes corniculate at the ends, microawns. T. boonjiensis and T. gigantea are recorded for the first time for the American continent. A key to all described species is included. A synopsis of drawings of microawns (most based on original papers) is provided for all Thozetella species.