Contrasting biodiversity-ecosystem functioning relationships in phylogenetic and functional diversity.

It is well known that ecosystem functioning is positively influenced by biodiversity. Most biodiversity-ecosystem functioning experiments have measured biodiversity based on species richness or phylogenetic relationships. However, theoretical and empirical evidence suggests that ecosystem functioning should be more closely related to functional diversity than to species richness. We applied different metrics of biodiversity in an artificial biodiversity-ecosystem functioning experiment using 64 species of green microalgae in combinations of two to 16 species. We found that phylogenetic and functional diversity were positively correlated with biomass overyield, driven by their strong correlation with species richness. At low species richness, no significant correlation between overyield and functional and phylogenetic diversity was found. However, at high species richness (16 species), we found a positive relationship of overyield with functional diversity and a negative relationship with phylogenetic diversity. We show that negative phylogenetic diversity-ecosystem functioning relationships can result from interspecific growth inhibition. The opposing performances of facilitation (functional diversity) and inhibition (phylogenetic diversity) we observed at the 16 species level suggest that phylogenetic diversity is not always a good proxy for functional diversity and that results from experiments with low species numbers may underestimate negative species interactions.

Biodiversity of green algae covering artificial hard substrate surfaces in a suburban environment: a case study using molecular approaches.

In Middle European suburban environments green algae often cover open surfaces of artificial hard substrates. Microscopy reveals the Apatococcus/Desmococcus morphotype predominant over smaller coccoid forms. Adverse conditions such as limited water availability connected with high PAR and UV irradiance may narrow the algal diversity to a few specialists in these subaerial habitats. We used rRNA gene cloning/sequencing from both DNA extracts of the biofilms without culturing as well as cultures, for the unambiguous determination of the algal composition and to assess the algal diversity more comprehensively. The culture independent approach revealed mainly just two genera (Apatococcus, Trebouxia) for all study sites and five molecular operational taxonomic units (OTUs) for a particular study site, which based on microscopic observation was the one with the highest morphological diversity. The culture approach, however, revealed seven additional OTUs from five genera (Chloroidium, Coccomyxa, Coenochloris, Pabia, Klebsormidium) and an unidentified trebouxiophyte lineage for that same site; only two OTUs were shared by both approaches. Two OTUs or species were recovered for which references have been isolated only from Antarctica so far. However, the internal transcribed spacer (ITS) sequence differences among them supported they are representing distinct populations of the same species. Within Apatococcus five clearly distinct groups of ITS sequences, each putatively representing a distinct species, were recovered with three or four such ITS types co-occurring at the same study site. Except for the streptophyte Klebsormidium only members of Trebouxiophyceae were detected suggesting these algae may be particularly well-adapted to subaerial habitats.

Widespread green algae Chlorella and Stichococcus exhibit polar-temperate and tropical-temperate biogeography.

Chlorella and Stichococcus are morphologically simple airborne microalgae, omnipresent in terrestrial and aquatic habitats. The minute cell size and resistance against environmental stress facilitate their long-distance dispersal. However, the actual distribution of Chlorella- and Stichococcus-like species has so far been inferred only from ambiguous morphology-based evidence. Here we contribute a phylogenetic analysis of an expanded SSU and ITS2 rDNA sequence dataset representing Chlorella- and Stichococcus-like species from terrestrial habitats of polar, temperate and tropical regions. We aim to uncover biogeographical patterns at low taxonomic levels. We found that psychrotolerant strains of Chlorella and Stichococcus are closely related with strains originating from the temperate zone. Species closely related to Chlorella vulgaris and Muriella terrestris, and recovered from extreme terrestrial environments of polar regions and hot deserts, are particularly widespread. Stichococcus strains from the temperate zone, with their closest relatives in the tropics, differ from strains with the closest relatives being from the polar regions. Our data suggest that terrestrial Chlorella and Stichococcus might be capable of intercontinental dispersal; however, their actual distributions exhibit biogeographical patterns.

Taxonomic revision and species delimitation of coccoid green algae currently assigned to the genus Dictyochloropsis (Trebouxiophyceae, Chlorophyta).

Coccoid green algae traditionally classified in Dictyochloropsis have a complex, reticulate chloroplast, when mature, without a pyrenoid. They occupy remarkably diverse ecological niches as free-living organisms or in association with lichen-forming fungi and were recently shown to form two distinct lineages within Trebouxiophyceae. We used a polyphasic approach to revise the taxonomy of the genus. Based on phylogenetic analysis of the 18S rRNA gene, and detailed morphological investigation using comparative conventional light and confocal microscopy, we have assigned these lineages to two genera, Dictyochloropsis and Symbiochloris gen. nov. We have reconsidered the diagnostic generic features as follows: Dictyochloropsis comprises only free-living algae with a reticulate chloroplast, forming lobes in a parallel arrangement at some ontogenetic stages, and which reproduce only by means of autospores. This agrees with Geitler's original diagnosis of Dictyochloropsis, but not with the later emendation by Tschermak-Woess. Consequently, the species of Dictyochloropsis sensu Tschermak-Woess are assigned to Symbiochloris, with new combinations proposed. Symbiochloris encompasses free-living and/or lichenized algae with lobed chloroplasts and that reproduce by forming zoospores characterized by two subapical isokont flagella that emerge symmetrically near the flattened apex. In addition, using coalescent-based approaches, morphological characters and secondary structure of ITS transcripts, we inferred species boundaries and taxonomic relationships within the newly proposed genera. Two species of Dictyochloropsis and nine species of Symbiochloris are delimited, including the newly described species D. asterochloroides, S. handae, S. tropica, and S. tschermakiae. Our results further support the non-monophyly of autosporine taxa within Trebouxiophyceae.

Interannual variation in land-use intensity enhances grassland multidiversity.

Although temporal heterogeneity is a well-accepted driver of biodiversity, effects of interannual variation in land-use intensity (LUI) have not been addressed yet. Additionally, responses to land use can differ greatly among different organisms; therefore, overall effects of land-use on total local biodiversity are hardly known. To test for effects of LUI (quantified as the combined intensity of fertilization, grazing, and mowing) and interannual variation in LUI (SD in LUI across time), we introduce a unique measure of whole-ecosystem biodiversity, multidiversity. This synthesizes individual diversity measures across up to 49 taxonomic groups of plants, animals, fungi, and bacteria from 150 grasslands. Multidiversity declined with increasing LUI among grasslands, particularly for rarer species and aboveground organisms, whereas common species and belowground groups were less sensitive. However, a high level of interannual variation in LUI increased overall multidiversity at low LUI and was even more beneficial for rarer species because it slowed the rate at which the multidiversity of rare species declined with increasing LUI. In more intensively managed grasslands, the diversity of rarer species was, on average, 18% of the maximum diversity across all grasslands when LUI was static over time but increased to 31% of the maximum when LUI changed maximally over time. In addition to decreasing overall LUI, we suggest varying LUI across years as a complementary strategy to promote biodiversity conservation.

Molecular diversity of phototrophic biofilms on building stone.

Composition and diversity of aeroterrestrial phototrophic microbial communities are up to now poorly understood. Here, we present a comparative study addressing the composition of algal communities on sandstone substrata based upon the analysis of rRNA gene clone libraries from environmental samples and crude cultures. From a west-facing, shaded wall area of the mediaeval castle ruin Gleichen (Thuringia, Germany), sequences mainly related to the green algae Prasiococcus and Trebouxia (Trebouxiophyceae) were retrieved. A south-west-facing, sun-exposed wall area was mainly colonized by Apatococcus and a Phyllosiphon-related alga. Just a few species, in particular Stichococcus-related strains, were ubiquitous in both areas. Samples from a basement vault exposed to low irradiance exhibited Chlorophyceae like Chromochloris and Bracteacoccus. Thus, most green algae on the daylight-exposed walls were affiliated to Trebouxiophyceae, whereas Chlorophyceae were dominant in samples taken from the site kept under low irradiance. Accordingly, cyanobacterial communities were different: the sun-exposed area was dominated by Synechococcus-related organisms, while on the shaded wall area, cyanobacteria were almost absent. The filamentous Leptolyngbya dominated samples from the basement vault. Scanning electron microscopy revealed endolithic algal morphotypes (coccoid algae and diatoms) dominant in open pores between mineral particles. Here, the organisms may be also involved in biogenic weathering of stone.