The benefits of the arbuscular mycorrhizal (AM) symbiosis between plants and fungi are modulated by the functional characteristics of both partners. However, it is unknown to what extent functionally distinct groups of plants naturally associate with different AM fungi.We reanalysed 14 high-throughput sequencing data sets describing AM fungal communities associating with plant individuals (2427) belonging to 297 species. We examined how root-associating AM fungal communities varied between plants with different growth forms, photosynthetic pathways, CSR (competitor, stress-tolerator, ruderal) strategies, mycorrhizal statuses and N-fixing statuses.AM fungal community composition differed in relation to all studied plant functional groups. Grasses, C 4 and nonruderal plants were characterised by high AM fungal alpha diversity, while C 4 , ruderal and obligately mycorrhizal plants were characterised by high beta diversity. The phylogenetic diversity of AM fungi, a potential surrogate for functional diversity, was higher among forbs than other plant growth forms. Putatively ruderal (previously cultured) AM fungi were disproportionately associated with forbs and ruderal plants. There was phylogenetic correlation among AM fungi in the degree of association with different plant growth forms and photosynthetic pathways.Associated AM fungal communities constitute an important component of plant ecological strategies. Functionally different plants associate with distinct AM fungal communities, linking mycorrhizal associations with functional diversity in ecosystems.

Drought stress is an alarming constraint to plant growth, development, and productivity worldwide. However, plant-associated bacteria, fungi, and viruses can enhance stress resistance and cope with the negative impacts of drought through the induction of various mechanisms, which involve plant biochemical and physiological changes. These mechanisms include osmotic adjustment, antioxidant enzyme enhancement, modification in phytohormonal levels, biofilm production, increased water and nutrient uptake as well as increased gas exchange and water use efficiency. Production of microbial volatile organic compounds (mVOCs) and induction of stress-responsive genes by microbes also play a crucial role in the acquisition of drought tolerance. This review offers a unique exploration of the role of plant-associated microorganisms—plant growth promoting rhizobacteria and mycorrhizae, viruses, and their interactions—in the plant microbiome (or phytobiome) as a whole and their modes of action that mitigate plant drought stress.

Aim Organisms on our planet form spatially congruent and functionally distinct communities, which at large geographical scales are called “biomes”. Understanding their pattern and function is vital for sustainable use and protection of biodiversity. Current global terrestrial biome classifications are based primarily on climate characteristics and functional aspects of plant community assembly. These and other existing biome schemes do not take account of soil organisms, including highly diverse and functionally important microbial groups. We aimed to define large‐scale structure in the diversity of soil microbes (soil microbiomes), pinpoint the environmental drivers shaping it and identify resemblance and mismatch with existing terrestrial biome schemes. Location Global. Time period Current. Major taxa studied Soil eukaryotes and prokaryotes. Methods We collected soil samples from natural environments world‐wide, incorporating most known terrestrial biomes. We used high‐throughput sequencing to characterize soil biotic communities and k‐means clustering to define soil microbiomes describing the diversity of microbial eukaryotic and prokaryotic groups. We used climatic data and soil variables measured in the field to identify the environmental variables shaping soil microbiome structure. Results We recorded strong correlations among fungal, bacterial, archaeal, plant and animal communities, defined a system of global soil microbiomes (producing seven biome types for microbial eukaryotes and six biome types for prokaryotes) and showed that these are typically structured by pH alongside temperature. None of the soil microbiomes are directly paralleled by any current terrestrial biome scheme, with mismatch most substantial for prokaryotes and for microbial eukaryotes in cold climates; nor do they consistently distinguish grassland and forest ecosystems. Main conclusions Existing terrestrial biome classifications represent a limited surrogate for the large‐scale diversity patterns of microbial soil organisms. We show that empirically defined soil microbiomes are attainable using metabarcoding and statistical clustering approaches and suggest that they can have wide application in theoretical and applied biodiversity research.

Towards a consistent benchmark for plant mycorrhizal association databasesA reply to Soudzilovskaia et al. (2020) 'FungalRoot: global online database of plant mycorrhizal associations'Mycorrhizal symbiosis, comprising functionally distinctive plant-fungus associations, mediates key plant population and community processes, and ultimately the functioning of terrestrial ecosystems (Tedersoo et al., 2020). It is estimated that c. 90% of the world's vascular flora forms mycorrhizal symbioses with soil fungi (Smith & Read, 2008;Brundrett & Tedersoo, 2018). Although this general estimate is probably adequate, there is a severe shortage of empirical information about mycorrhizal associations at the plant species level, with only c. 5% of the world's flora explored (Moora, 2014;Bueno et al., 2019b). Several database developments have emerged since the seminal work of Harley & Harley (1987; HH); extending both the number and the geography of plant species covered (Wang & Qiu, 2006, WQ; Akhmetzhanova et al., 2012, MID), and defining and describing some key mycorrhizal traits of plant species -'mycorrhizal type' and 'mycorrhizal status ' (Hempel et al., 2013, MF;Moora, 2014). Nonetheless, this expansion poses new challenges connected with the compilation of global data based on heterogeneous sources with different practical and conceptual frameworks (Bueno et al., 2019b;Kattge et al., 2020). Careful work developing consistent definitions and standardizing field and laboratory protocols is essential for harmonizing database content and avoiding critical inconsistencies (P erez- Harguindeguy et al., 2013;Schneider et al., 2019).Recently, Soudzilovskaia et al. (2020) presented the largest compilation to date of empirical information about mycorrhizal associations in plants based on scientific literature (FungalRoot). Although this is a valuable and unique effort, we note three critical aspects that seriously hamper consistent data harmonization and should be addressed before the FungalRoot database can be considered as a standard reference in the field. Namely: (1) conceptual inconsistency in the designation of plant mycorrhizal associations; (2) incoherent application of plant mycorrhizal trait concepts; and (3) limited transparency in the incorporation of expert opinion. As we explain below, these issues appear particularly problematic in the cases of arbuscular mycorrhizal (AM) and nonmycorrhizal (NM) plants, and perhaps of lesser concern in the cases of other mycorrhizal types. However, given the high share of AM and NM plant species in the previous largest mycorrhizal database (73.1% and 18.0%, respectively, in WQ) and in the FungalRoot database (76.6% for AM, 15.5% for NM), these are critical issues to be resolved.

Deserts cover a significant proportion of the Earth’s surface and continue to expand as a consequence of climate change. Mutualistic arbuscular mycorrhizal (AM) fungi are functionally important plant root symbionts, and may be particularly important in drought stressed systems such as deserts. Here we provide a first molecular characterization of the AM fungi occurring in several desert ecosystems worldwide. We sequenced AM fungal DNA from soil samples collected from deserts in six different regions of the globe using the primer pair WANDA-AML2 with Illumina MiSeq. We recorded altogether 50 AM fungal phylotypes. Glomeraceae was the most common family, while Claroideoglomeraceae, Diversisporaceae and Acaulosporaceae were represented with lower frequency and abundance. The most diverse site, with 35 virtual taxa (VT), was in the Israeli Negev desert. Sites representing harsh conditions yielded relatively few reads and low richness estimates, for example, a Saudi Arabian desert site where only three Diversispora VT were recorded. The AM fungal taxa recorded in the desert soils are mostly geographically and ecologically widespread. However, in four sites out of six, communities comprised more desert-affiliated taxa (according to the MaarjAM database) than expected at random. AM fungal VT present in samples were phylogenetically clustered compared with the global taxon pool, suggesting that nonrandom assembly processes, notably habitat filtering, may have shaped desert fungal assemblages.