Soil yeasts represent a poorly known fraction of the soil microbiome due to limited ecological surveys. Here, we provide the first comprehensive inventory of cultivable soil yeasts in a Mediterranean ecosystem, which is the leading biodiversity hotspot for vascular plants and vertebrates in Europe. We isolated and identified soil yeasts from forested sites of Serra da Arrábida Natural Park (Portugal), representing the Mediterranean forests, woodlands and scrub biome. Both cultivation experiments and the subsequent species richness estimations suggest the highest species richness values reported to date, resulting in a total of 57 and 80 yeast taxa, respectively. These values far exceed those reported for other forest soils in Europe. Furthermore, we assessed the response of yeast diversity to microclimatic environmental factors in biotopes composed of the same plant species but showing a gradual change from humid broadleaf forests to dry maquis. We observed that forest properties constrained by precipitation level had strong impact on yeast diversity and on community structure and lower precipitation resulted in an increased number of rare species and decreased evenness values. In conclusion, the structure of soil yeast communities mirrors the environmental factors that affect aboveground phytocenoses, aboveground biomass and plant projective cover.

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The diversity of yeasts has grown rapidly as the discovery of new species has benefited from intensified sampling and largely improved identification techniques. An environmental study typically reports the isolation of yeast species, some of which are new to science. Rare species represented by a few isolates often do not result in a taxonomic description. Nucleic acid sequences from these undescribed yeasts remain in public sequence databases, often without a proper taxonomic placement. This study presents a constrained phylogenetic analysis for many rare yeasts from unpublished but publicly available DNA sequences and from studies previously conducted by the authors of this work. We demonstrate that single isolates are an important source of taxonomic findings such as including new genera and species. Independent surveys performed during the last 20 years on a large geographic scale yielded a number of single strains, which were proved to be conspecific in the phylogenetic analyses presented here. The following new species were resolved and described: Vustinia terrea

Freshwater and soil are not strictly isolated habitats. In particular, floods may facilitate the exchange of organisms and nutrients. Flooding can have both a stimulating and a harmful effect on the organisms of the respective habitats. The effects of short-term flooding on microeukaryotic communities in the aquatic and terrestrial habitat have so far been scarcely studied. Here, we investigated the effect of a 24 h artificial inundation on the microeukaryotic community composition in AquaFlow mesocosm systems. We investigated the shift of community composition based on molecular amplicon diversity both on soil and water during flooding and for a period of 12 d after flooding. Community composition was, as expected, strongly different between soil and water. Flooding had a significant effect on the freshwater community, whereas the soil community was hardly affected. In particular, we observed a transfer of nutrients from the terrestrial habitat into the aquatic habitat and identified ~50 taxa that were transferred by the flooding event. This effect of flooding was, however, overlaid by shifts of the communities with time, presumably reflecting an acclimatization to the conditions in the AquaFlow systems.