Effects of environmental and temporal factors on Glomeromycotina spores in sand dunes along the Gulf of Valencia (Spain)

Hawaiian Island endemic and indigenous plant species have higher mycorrhizal incidence than the global average

PREMISE

Prior efforts have shown that continents harbor a greater proportion of mycorrhizal hosts than on islands. However, in the Hawaiian Islands, estimates of the proportion of mycorrhizal plant species are higher than on continents (>90%), but there are few studies to support this claim. Concurrently, Hawaii's flora faces some of the greatest global risks of extinction, and significant efforts are aimed at restoring native vegetation. Arbuscular mycorrhizal (AM) fungi have been shown to improve plant restoration success, but little work has been done in Hawaii to understand the extent of mycorrhizal associations among native plant populations.

METHODS

We surveyed 35 native Hawaiian plant species in the wild, focusing on plant species that are reared for reintroduction. Roots from wild individuals were collected from 10 sites on Oahu to determine degree of mycorrhizal fungal colonization and how this varies across host populations.

RESULTS

Of the species surveyed, 97% had evidence of mycorrhizal colonization, including 25 endemic and nine indigenous species from 23 families. The mycorrhizal status of 22 of the species surveyed was unknown before this study. For four species, the degree of colonization by AM fungi differed among sites, and these differences corresponded with variations in precipitation and temperature.

CONCLUSIONS

The high incidence of mycorrhizal colonization provides evidence that island flora can actually harbor more mycorrhizal hosts than species on mainlands and that future reintroduction projects should consider the potentially important roles of AM fungi for success of these hosts in the wild.

Arbuscular Mycorrhizal Fungal Community Structure in the Rhizosphere of Three Plant Species of Crystalline and Sedimentary Areas in the Brazilian Dry Forest

The Brazilian dry forest (Caatinga) is located in one of the world's largest tropical semiarid regions, and it occurs on two large geological environments named the crystalline and sedimentary basins. In order to determine the structure and the main drivers of the composition of communities of arbuscular mycorrhizal fungi (AMF) in the Caatinga, we collected soil samples from the rhizosphere of Jatropha mollissima, J. mutabilis, and Mimosa tenuiflora, species that occur in crystalline and sedimentary areas. Ninety-six AMF taxa were identified from soils collected directly in the field and trap cultures. Acaulospora, Glomus, and Rhizoglomus represented almost 49% of the taxon richness. The composition of the AMF communities differed between the crystalline and sedimentary areas and between the rhizospheres of the three plant species. Coarse sand, total sand, natural clay, calcium, soil particles density, flocculation, pH, and base saturation were the principal edaphic variables related to the distribution of these organisms. We registered nine and 17 AMF species classified as indicators, for the geological environments and plant species, respectively. Glomerospores of Glomerales predominated in crystalline basins, whereas glomerospores of Gigasporales prevailed in sedimentary areas; among the plant species, lower number of glomerospores of Archaeosporales and Glomerales was recorded in the rhizosphere of J. mollissima. The results show that the AMF community composition is shaped by geological environments and plant hosts. In addition, soil characteristics, mainly physical attributes, significantly influence the structure of Glomeromycota communities occurring in areas of the Brazilian semiarid.

Preparation of Samples for Characterization of Arbuscular Mycorrhizal Fungi

Arbuscular mycorrhizal fungi (AMF) are an important element of the plant microbiome as they establish an endosymbiotic relationship with the roots of most plant species. This association enhances access to nutrients and water for plants, and provides the fungus with plant-derived organic carbon. In this chapter, I describe a range of methods to work with AMF including: soil sampling; isolation of AMF propagules (spores, sporocarps, roots, and mycelium) by a wet sieving and centrifugation in a sucrose solution; trap (from field soil with AMF spores) and one-species pot cultures (from AMF spores divided into morphotypes); staining of mycorrhizae in plant roots; and production of diagnostic slides. These methods are widely used in taxonomic and ecological studies to characterize the morphology of AMF.

Glomus ibericum, Septoglomus mediterraneum, and Funneliformis pilosus, three new species of arbuscular mycorrhizal fungi

Three new arbuscular mycorrhizal fungal species-Glomus ibericum, Septoglomus mediterraneum, and Funneliformis pilosus-are described and illustrated. In the field, the three species were associated with roots of Ammophila arenaria (Poaceae), Elymus farctus (Poaceae), Otanthus maritimus (Asteraceae), and Echinophora spinosa (Apiaceae) colonizing maritime dunes located along the Mediterranean coast in eastern Spain. The novelty of these species is supported by morphological, molecular, and phylogenetic analyses. Single-species cultures of S. mediterraneum and F. pilosus were obtained using Trifolium repens as a host plant, both forming arbuscular mycorrhizae, whereas single-species cultures from G. ibericum could not be obtained. Spores of G. ibericum usually occur in sporocarps, rarely singly in soil or inside roots. In contrast, S. mediterraneum only forms single spores in soil and F. pilosus occurs in sporocarps and singly in soil or inside roots. The respective small subunit, internal transcribed spacer, and large subunit (SSU-ITS1-5.8S-ITS2-LSU) nrDNA sequences placed the new species in the genera Glomus, Septoglomus, and Funneliformis, all of them separated from previously described species.

Seasonal shifts of arbuscular mycorrhizal fungi in Cocos nucifera roots in Yucatan, Mexico

The diversity and community structure of arbuscular mycorrhizal fungi (AMF) associated with coconut (Cocos nucifera) roots was evaluated by next generation sequencing (NGS) using partial sequences of the 18S rDNA gene and by spore isolation and morphological identification from rhizosphere soil. Root samples from six different Green Dwarf coconut plantations and from one organic plantation surrounded by tropical dry forest along the coastal sand dunes in Yucatan, Mexico, were collected during the rainy and dry seasons. In total, 14 root samples were sequenced with the Illumina MiSeq platform. Additionally, soil samples from the dry season were collected to identify AMF glomerospores. Based on a 95-97% similarity, a total of 36 virtual taxa (VT) belonging to nine genera were identified including one new genus-like clade. Glomus was the most abundant genus, both in number of VT and sequences. The comparison of dry and rainy season samples revealed differences in the richness and composition of AMF communities colonizing coconut roots. Our study shows that the main AMF genera associated with coconut tree roots in all samples were Glomus, Sclerocystis, Rhizophagus, Redeckera, and Diversispora. Based on glomerospore morphology, 22 morphospecies were recorded among which 14 were identified to species. Sclerocystis sinuosa, Sclerocystis rubiformis, Glomus microaggregatum, and Acaulospora scrobiculata were dominant in field rhizosphere samples. This is the first assessment of the composition of AMF communities colonizing coconut roots in rainy and dry seasons. It is of importance for selection of AMF species to investigate for their potential application in sustainable agriculture of coconut.