Auditing data resolves systemic errors in databases and confirms mycorrhizal trait consistency for most genera and families of flowering plants.

Nearly 150 years of research has accumulated large amounts of data on mycorrhizal association types in plants. However, this important resource includes unreliable allocated traits for some species. An audit of six commonly used data sources revealed a high degree of consistency in the mycorrhizal status of most species, genera and families of vascular plants, but there were some records that contradict the majority of other data (~ 10% of data overall). Careful analysis of contradictory records using rigorous definitions of association types revealed that the majority were diagnosis errors, which often stem from references predating modern knowledge of mycorrhiza types. Other errors are linked to inadequate microscopic examinations of roots or plants with complex root anatomy, such as phi thickenings or beaded roots. Errors consistently occurred at much lower frequencies than correct records but have accumulated in uncorrected databases. This results in less accurate knowledge about dominant plants in some ecosystems because they were sampled more often. Errors have also propagated from one database to another over decades when data were amalgamated without checking their suitability. Due to these errors, it is often incorrect to designate plants reported to have inconsistent mycorrhizas as "facultatively mycorrhizal". Updated protocols for resolving conflicting mycorrhizal data are provided here. These are based on standard morphological definitions of association types, which are the foundations of mycorrhizal science. This analysis also identifies the need for adequate training and mentoring of researchers to maintain the quality of mycorrhizal research.

FungalRoot: global online database of plant mycorrhizal associations.

Testing of ecological, biogeographical and phylogenetic hypotheses of mycorrhizal traits requires a comprehensive reference dataset about plant mycorrhizal associations. Here we present a database, FungalRoot, which summarizes publicly available data about vascular plant mycorrhizal type and intensity of root colonization by mycorrhizal fungi, accompanied with rich metadata. We compiled and digitized data about plant mycorrhizal colonization in nine widespread languages. The present version of the FungalRoot database contains 36 303 species-by-site observations for 14 870 plant species, tripling the previously available compiled information about plant mycorrhizal associations. Based on these data, we provide a recommended list of genus-level plant mycorrhizal associations, based on the majority of data for species and careful analysis of conflicting data. The majority of ectomycorrhizal and ericoid mycorrhizal plants are trees (92%) and shrubs (85%), respectively. The majority of arbuscular and nonmycorrhizal plant species are herbaceous (50% and 70%, respectively). Our publicly available database is a powerful resource for mycorrhizal scientists and ecologists. It features possibilities for dynamic updating and addition of data about plant mycorrhizal associations. The new database will promote research on plant and fungal biogeography and evolution, and on links between above- and belowground biodiversity and ecosystem functioning.

Global mycorrhizal plant distribution linked to terrestrial carbon stocks.

Vegetation impacts on ecosystem functioning are mediated by mycorrhizas, plant-fungal associations formed by most plant species. Ecosystems dominated by distinct mycorrhizal types differ strongly in their biogeochemistry. Quantitative analyses of mycorrhizal impacts on ecosystem functioning are hindered by the scarcity of information on mycorrhizal distributions. Here we present global, high-resolution maps of vegetation biomass distribution by dominant mycorrhizal associations. Arbuscular, ectomycorrhizal, and ericoid mycorrhizal vegetation store, respectively, 241 ± 15, 100 ± 17, and 7 ± 1.8 GT carbon in aboveground biomass, whereas non-mycorrhizal vegetation stores 29 ± 5.5 GT carbon. Soil carbon stocks in both topsoil and subsoil are positively related to the community-level biomass fraction of ectomycorrhizal plants, though the strength of this relationship varies across biomes. We show that human-induced transformations of Earth's ecosystems have reduced ectomycorrhizal vegetation, with potential ramifications to terrestrial carbon stocks. Our work provides a benchmark for spatially explicit and globally quantitative assessments of mycorrhizal impacts on ecosystem functioning and biogeochemical cycling.

Evolutionary history of mycorrhizal symbioses and global host plant diversity.

Contents Summary 1108 I. Introduction 1108 II. Mycorrhizal plant diversity at global and local scales 1108 III. Mycorrhizal evolution in plants: a brief update 1111 IV. Conclusions and perspectives 1114 References 1114 SUMMARY: The majority of vascular plants are mycorrhizal: 72% are arbuscular mycorrhizal (AM), 2.0% are ectomycorrhizal (EcM), 1.5% are ericoid mycorrhizal and 10% are orchid mycorrhizal. Just 8% are completely nonmycorrhizal (NM), whereas 7% have inconsistent NM-AM associations. Most NM and NM-AM plants are nutritional specialists (e.g. carnivores and parasites) or habitat specialists (e.g. hydrophytes and epiphytes). Mycorrhizal associations are consistent in most families, but there are exceptions with complex roots (e.g. both EcM and AM). We recognize three waves of mycorrhizal evolution, starting with AM in early land plants, continuing in the Cretaceous with multiple new NM or EcM linages, ericoid and orchid mycorrhizas. The third wave, which is recent and ongoing, has resulted in root complexity linked to rapid plant diversification in biodiversity hotspots.

Limited carbon and mineral nutrient gain from mycorrhizal fungi by adult Australian orchids.

PREMISE OF THE STUDY: In addition to autotrophic and fully mycoheterotrophic representatives, the orchid family comprises species that at maturity obtain C and N partially from fungal sources. These partial mycoheterotrophs are often associated with fungi that simultaneously form ectomycorrhizas with trees. This study investigates mycorrhizal nutrition for orchids from the southwestern Australian biodiversity hotspot. METHODS: The mycorrhizal fungi of 35 green and one achlorophyllous orchid species were analyzed using molecular methods. Nutritional mode was identified for 27 species by C and N isotope abundance analysis in comparison to non-orchids from the same habitat. As a complementary approach, (13)CO(2) pulse labeling was applied to a subset of six orchid species to measure photosynthetic capacity. KEY RESULTS: Almost all orchids associated with rhizoctonia-forming fungi. Due to much higher than expected variation within the co-occurring nonorchid reference plants, the stable isotope approach proved challenging for assigning most orchids to a specialized nutritional mode; therefore, these orchids were classified as autotrophic at maturity. The (13)CO(2) pulse labeling confirmed full autotrophy for six selected species. Nonetheless, at least three orchid species (Gastrodia lacista, Prasophyllum elatum, Corybas recurvus) were identified as nutritionally distinctive from autotrophic orchids and reference plants. CONCLUSIONS: Despite the orchid-rich flora in southwestern Australia, partial mycoheterotrophy among these orchids is less common than in other parts of the world, most likely because most associate with saprotrophic fungi rather than ectomycorrhizal fungi.

Carbon and nitrogen supply to the underground orchid, Rhizanthella gardneri.

*Rhizanthella gardneri is a rare and fully subterranean orchid that is presumably obligately mycoheterotrophic. R. gardneri is thought to be linked via a common mycorrhizal fungus to co-occurring autotrophic shrubs, but there is no experimental evidence to support this supposition. *We used compartmentalized microcosms to investigate the R. gardneri tripartite relationship. (13)CO(2) was applied to foliage of Melaleuca scalena plants and [(13)C-(15)N]glycine was fed to the common mycorrhizal fungus, and both sources traced to R. gardneri plants. *In our microcosm trial, up to 5% of carbon (C) fed as (13)CO(2) to the autotrophic shrub was transferred to R. gardneri. R. gardneri also readily acquired soil C and nitrogen (N), where up to 6.2% of C and 22.5% of N fed as labelled glycine to soil was transferred via the fungus to R. gardneri after 240 h. *Our study confirms that R. gardneri is mycoheterotrophic and acquires nutrients via mycorrhizal fungus connections from an ectomycorrhizal autotrophic shrub and directly from the soil via the same fungus. This connection with a specific fungus is key to explaining why R. gardneri occurs exclusively under certain Melaleuca species at a very limited number of sites in Western Australia.

Development of in situ and ex situ seed baiting techniques to detect mycorrhizal fungi from terrestrial orchid habitats.

An innovative ex situ fungal baiting method using soil collected from field sites which allows the simultaneous detection of mycorrhizal fungi for multiple terrestrial orchids is presented. This method demonstrated that coarse organic matter (> 2 mm) in the litter and topsoil was the most important reservoir of inoculum of these fungi. A new in situ seed baiting method using multi-chambered packets to simultaneously assess germination for different orchid species within soil is also introduced. These in situ and ex situ methods are compared using seed of orchids in the genera Monadenia, Microtis, Caladenia, Pterostylis and Diuris, using urban Banksia woodland sites with high or low weed cover. Both these seed baiting methods detected compatible fungi for these orchids, but common orchids germinated more frequently than those which were uncommon at the field sites. Germination rates were not significantly affected by weed cover even though adult orchids were rare in areas with high weed cover. The two new seed baiting methods vary in efficiency and applicability depending on the situation where they are used. However, the ex situ method allowed the time-course of germination to be observed, resulting in the production of more protocorms and facilitation of the isolation of mycorrhizal fungi. These techniques provide valuable new tools for detection of compatible mycorrhizal fungi to assist orchid research and conservation.

Coevolution of roots and mycorrhizas of land plants.

Here, the coevolution of mycorrhizal fungi and roots is assessed in the light of evidence now available, from palaeobotanical and morphological studies and the analysis of DNA-based phylogenies. The first bryophyte-like land plants, in the early Devonian (400 million years ago), had endophytic associations resembling vesicular-arbuscular mycorrhizas (VAM) even before roots evolved. Mycorrhizal evolution would have progressed from endophytic hyphae towards balanced associations where partners were interdependent due to the exchange of limiting energy and nutrient resources. Most mycorrhizas are mutualistic, but in some cases the trend for increasing plant control of fungi culminates in the exploitative mycorrhizas of achlorophyllous, mycoheterotrophic plants. Ectomycorrhizal, ericoid and orchid mycorrhizas, as well as nonmycorrhizal roots, evolved during the period of rapid angiosperm radiation in the Cretaceous. It is hypothesised that roots gradually evolved from rhizomes to provide more suitable habitats for mycorrhizal fungi and provide plants with complex branching and leaves with water and nutrients. Selection pressures have caused the morphological divergence of roots with different types of mycorrizas. Root cortex thickness and exodermis suberization are greatest in obllgately mycorrhizal plants, while nonmycorrhizal plants tend to have fine roots, with more roots hairs and relatively advanced chemical defences. Major coevolutionary trends and the relative success of plants with different root types are discussed. Contents Summary 275 I. Introduction 276 II. Mycorrhizal Fungi 276 III. The Dawn of Mycorrhizas 279 IV. Mycorrhizal Associations of Living and Extinct Plants 282 V. Evolution of Roots 288 VI. The Root as a Habitat for Fungi 290 VII. Mycorrhizal Evolution Trends 295 Acknowledgements 298 References 298.

Mycorrhizal fungus propagules in the jarrah forest: II. Spatial variability in inoculum levels.

Spatial variations in the capacity of propagules of arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi to form associations in their natural habitats were investigated using bioassays with bait plants grown in intact cores of forest soil. These cores were collected from a sclerophyllous forest community dominated by Eucalyptus marginata Donn ex Smith (jarrah) and E. calophylla Lindley (marri) trees with a diverse shrub understorey in the mediterranean (winter rainfall) climatic zone of Western Australia. Small-scale (adjacent core) variations in the capacity of AM fungi to form associations were found to be as substantial as differences between locations 1 5 m apart. Comparisons of AM fungus colonization patterns within the roots of seedlings growing in the same core indicated that there was considerable spatial heterogeneity in the inoculums potential of 'individual' fungi within these 1 1 volumes of soil. A second experiment included bait plants to measure ECM formation as welt as AM formation and also considered the impact of soil disturbance. The disruption of hyphal networks reduced mycorrhizal formation somewhat, but it still remained highly variable. Some of this spatial heterogeneity could be attributed to differences in the organic matter content, length of fungal hyphae, or length of old mycorrhizal roots, measured within soil cores. In jarrah forest soil, mycelial systems of AM and ECM fungi apparently were localized in separate domains, and there were also zones where non-mycorrhizal roots (mostly cluster roots produced by members of the Proteaceae) predominated. More research is required to determine the size of domains of mycorrhizal mycelial systems in soils, how these spatial patterns change with time, and if they are associated with zones of resource utilization by different 'functional groups' of roots.