Comparative analysis of diversity and environmental niches of soil bacterial, archaeal, fungal and protist communities reveal niche divergences along environmental gradients in the Alps

Although widely used in ecology, comparative analyses of diversity and niche properties are still lacking for microorganisms, especially concerning niche variations. In this study, we identified important topoclimatic, edaphic, spatial and biotic drivers of the alpha and beta diversity of bacterial, archaeal, fungal and protist communities. Then, we calculated the niche breadth and position of each taxon along environmental gradients within all taxonomic groups, to determine how these vary within and between groups. Quantifying the niches of microbial taxa is necessary to then forecast how taxa and the communities they compose might respond to environmental changes. We found that edaphic properties were the most important drivers of both community diversity and composition for all microbial groups. Protists presented the largest niche breadths, followed by bacteria and archaea, with fungi displaying the smallest. Niche breadth generally decreased towards environmental extremes, especially along edaphic gradients, suggesting increased specialisation of microbial taxa in highly selective environments. Overall, we showed that microorganisms have well defined niches, as do macro-organisms, likely driving part of the observed spatial patterns of community variations. Assessing niche variation more widely in microbial ecology should open new perspectives, especially to tackle global change effects on microbes.

Edaphic properties as key drivers for woody species distributions in tropical savannic and forest habitats

Edaphic gradients can explain plant species distribution at a local scale in the neotropics and elsewhere, but few studies have evaluated the individual responses of species to such gradients. We collected data on species and soils in open savannic and forest formations (totalling five habitats in each formation), aiming to evaluate the importance of edaphic factors on the distribution of woody plant species in tropical habitats. Logistic regression was used to test the influence of predictor variables (soil texture and fertility) on plant occurrence (presence or absence). Most species (73%) responded to the edaphic gradients. However, the edaphic gradients did not explain the distribution of the remaining 27% of species, which implies the existence of other factors determining their occurrence. Soil fertility (nutritional status) was the major factor in forest habitats (65% of the species which showed significant response), while soil texture was the most explanatory factor for species occurrence in open habitats (55% of the species that showed a significant response). Thus, nutrient status was less limiting and soil texture was more limiting in savannic formations, whereas the opposite was observed for forest formations. Most species showing a relationship with edaphic gradients had a unimodal response, which is in accordance with the literature. Our study showed that soil properties largely regulate the distribution of plant species in tropical habitats, despite other factors not investigated here also having an effect on several of the studied species. Models of species distribution that take into account environmental heterogeneity are key for the elaboration of strategies for the conservation and restoration of ecosystems.

Estructura y composición de la vegetación de la barra costera El Mogote, Baja California Sur, México

Located in the southern region of the east coast of the state of Baja California Sur, the large sand bar, called El Mogote, is covered in 15.5 km2 of surface by vegetation whose features are particular of the merging of sandy coastal environments, the arid-tropical Cape Region, and the Sonoran Desert. We analyzed the vegetation by classification and ordination techniques to establish relationships between vegetation and edaphic gradients, identifying nine plant associations in three environments: dunes, salt flats, and mangrove. The vegetation gradient in the dunes is explained by salinity and size of soil particles. Some ecological variations account for species richness and diversity, which are higher in the protected surfaces containing more stable soil than in wind exposed areas. Vegetation in this area is threatened by a residential and touristic infrastructure and construction.