Arbuscular mycorrhizal and septate endophyte fungal associations in lycophytes and ferns of south India

Mycorrhizal association and its relation with pteridophytes

Mycorrhizal association is one of the earliest and diversely distributed symbiotic associations on the Earth. This association helped early terrestrial plants to colonize the land by improved supply of nutrients like phosphate, nitrogen and zinc. It also helped plants to tolerate unfavorable soil conditions with increased water retention capacity, resistance to drought and pathogens. In return, fungi benefitted with carbon as their food source from the plants. More than 80% of terrestrial plants including pteridophytes, gymnosperms and angiosperms are reported to form arbuscular mycorrhizal (AM) association. Plants with root systems appeared on land during the Devonian period and many of them like pteridophytes still exist today. Various molecular and fossil studies confirm that the plants belonging to Ordovician-Devonian are associated with fungi, which are very similar to genus Glomus. AM association is very common in pteridophytes and the growth of its sporophyte and gametophyte is directly affected in the presence of AM association. Pteridophytes as early land plants with root systems have a very significant place in the plant kingdom. They have evolved and adapted to fill various habitats and facilitated early terrestrialization of other land plants by providing suitable niche with the help of AM fungi. In spite of pteridophytes being a very important plant group in the land system, very few reports are available on fungal-pteridophyte association. The present review is an effort to gather information about AM association in pteridophytes that might help in unraveling the evolution and significance of plant and fungi association.

Endorhizal fungal symbiosis in lycophytes and metal(loid)-accumulating ferns growing naturally in mine wastes in Mexico

Ferns and lycophytes are pioneer plants that can be useful for revegetation. Their natural distribution and interaction with soil fungal endophytes can increase plant fitness but have received little attention. This study aimed to identify these plant species in mine wastes, and determine colonization by arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE). The pseudo-total and diethylenetriamine pentaacetic acid (DTPA)-extractable rhizosphere concentrations of As, Cu, Cd, Pb, and Zn, bioavailability index (BI), and bioconcentration factor (BCF) were analyzed. Six ferns and one lycophyte were identified. Arsenic and metal concentrations were high, which were plant and site-dependent. All species showed hyperaccumulation of As in fronds, especially Argyrochosma formosa (2,883) and Notholaena affinis (2,160) had the highest concentrations (mg kg^-1). All plants were colonized by AMF (3%-24%) and DSE (2%-33%). Astrolepis sinuata and Myriopteris notholaenoides had the maximum colonization by AMF and A. formosa by DSE. This study identifies for the first time five ferns and one lycophyte species on mine wastes, their As hyperaccumulation capacity and the simultaneous fungal colonization by AMF and DSE. These are relevant plant traits for phytoremediation. However, fungal identification and the role colonization by AMF and DSE requires full analysis.

Taxonomic, phylogenetic and functional diversity of root-associated fungi in bromeliads: effects of host identity, life forms and nutritional modes

Bromeliads represent a major component of neotropical forests and encompass a considerable diversity of life forms and nutritional modes. Bromeliads explore highly stressful habitats and root-associated fungi may play a crucial role in this, but the driving factors and variations in root-associated fungi remain largely unknown. We explored root-associated fungal communities in 17 bromeliad species and their variations linked to host identity, life forms and nutritional modes by using ITS1 gene-based high-throughput sequencing and by characterizing fungal functional guilds. We found a dual association of mycorrhizal and nonmycorrhizal fungi. The different species, life forms and nutritional modes among bromeliad hosts had fungal communities that differ in their taxonomic and functional composition. Specifically, roots of epiphytic bromeliads had more endophytic fungi and dark septate endophytes and fewer mycorrhizal fungi than terrestrial bromeliads and lithophytes. Our results contribute to a fundamental knowledge base on different fungal groups in previously undescribed Bromeliaceae. The diverse root-associated fungal communities in bromeliads may enhance plant fitness in both stressful and nutrient-poor environments and may give more flexibility to the plants to adapt to changing environmental conditions.

Biotic and abiotic factors shape arbuscular mycorrhizal fungal communities associated with the roots of the widespread fern Botrychium lunaria (Ophioglossaceae)

Arbuscular mycorrhizal fungi (AMF) play central roles in terrestrial ecosystems by interacting with both above and belowground communities as well as by influencing edaphic properties. The AMF communities associated with the roots of the fern Botrychium lunaria (Ophioglossaceae) were sampled in four transects at 2400 m a.s.l. in the Swiss Alps and analyzed using metabarcoding. Members of five Glomeromycota genera were identified across the 71 samples. Our analyses revealed the existence of a core microbiome composed of four abundant Glomus operational taxonomic units (OTUs), as well as a low OTU turnover between samples. The AMF communities were not spatially structured, which contrasts with most studies on AMF associated with angiosperms. pH, microbial connectivity and humus cover significantly shaped AMF beta diversity but only explained a minor fraction of variation in beta diversity. AMF OTUs associations were found to be significant by both cohesion and co-occurrence analyses, suggesting a role for fungus-fungus interactions in AMF community assembly. In particular, OTU co-occurrences were more frequent between different genera than among the same genus, rising the hypothesis of functional complementarity among the AMF associated to B. lunaria. Altogether, our results provide new insights into the ecology of fern symbionts in alpine grasslands.

Arbuscular mycorrhizal colonization in field-collected terrestrial cordate gametophytes of pre-polypod leptosporangiate ferns (Osmundaceae, Gleicheniaceae, Plagiogyriaceae, Cyatheaceae)

To determine the mycorrhizal status of pteridophyte gametophytes in diverse taxa, the mycorrhizal colonization of wild gametophytes was investigated in terrestrial cordate gametophytes of pre-polypod leptosporangiate ferns, i.e., one species of Osmundaceae (Osmunda banksiifolia), two species of Gleicheniaceae (Diplopterygium glaucum, Dicranopteris linearis), and four species of Cyatheales including tree ferns (Plagiogyriaceae: Plagiogyria japonica, Plagiogyria euphlebia; Cyatheaceae: Cyathea podophylla, Cyathea lepifera). Microscopic observations revealed that 58 to 97% of gametophytes in all species were colonized with arbuscular mycorrhizal (AM) fungi. Fungal colonization was limited to the multilayered midrib (cushion) tissue in all gametophytes examined. Molecular identification using fungal SSU rDNA sequences indicated that the AM fungi in gametophytes primarily belonged to the Glomeraceae, but also included the Claroideoglomeraceae, Gigasporaceae, Acaulosporaceae, and Archaeosporales. This study provides the first evidence for AM fungal colonization of wild gametophytes in the Plagiogyriaceae and Cyatheaceae. Taxonomically divergent photosynthetic gametophytes are similarly colonized by AM fungi, suggesting that mycorrhizal associations with AM fungi could widely occur in terrestrial pteridophyte gametophytes.

Differences in Arbuscular Mycorrhizal Fungal Community Composition in Soils of Three Land Use Types in Subtropical Hilly Area of Southern China

Land use type is key factor in restoring the degraded soils due to its impact on soil chemical properties and microbial community. In this study, the influences of land use type on arbuscular mycorrhizal fungal (AMF) community and soil chemical properties were assessed in a long-run experimental station in subtropical hilly area of southern China. Soil samples were collected from forest land, orchard and vegetable field. Soil chemical properties were analyzed, and PCR-DGGE was performed to explore the AMF community structure. Cloning and sequencing of DGGE bands were conducted to monitor AMF community composition. Results indicate that the contents of total P, available P and available K were the highest while the contents of soil organic matter, total N, total K and available N were the lowest in vegetable field soils, with forest land soils vice versa. According to DGGE profiling, AMF community in forest soils was more closely related to that in orchard soils than that in vegetable field soils. Sequencing indicated that 45 out of 53 excised bands were AMF and 64.4% of AMF belonged to Glomeraceae, including some “generalists” present in all soils and some “specialists” present only in soils of particular land use. Category principle component analysis demonstrated that total N, soil organic matter and available P were the most important factors affecting AMF community, and some AMF phylotypes were closely associated with particular soil chemical properties. Our data suggest that AMF communities are different with different land use types.

The diversity of endophytic fungi in the above-ground tissue of two Lycopodium species in Poland

Endophytes are a large and diverse group of fungi that colonize healthy plant tissues without causing any symptoms. The majority of studies have focused on angiosperm and conifer hosts and few have examined the endophytes of lycophytes. In the present study, we characterized culturable endophytic fungi in two closely related Lycopodium species (L. annotinum and L. clavatum) from pine, beech, oak and spruce forests across Poland. More than 400 strains were isolated but only 18 Ascomycete species were identified. Members of the Dothideomycetes dominated the fungal endophyte communities in Lycopodium. The most abundant taxa cultured were Phoma brasiliensis (from L. clavatum) and Paraconiothyrium lycopodinum (from L. annotinum). Five taxa were isolated exclusively from L. annotinum, but only two of them (Paraconiothyrium lycopodinum and Mycosphaerella sp.) were relatively abundant. Two taxa were only found in L. clavatum, namely: Stagonospora pseudovitensis and an unidentified Dothideomycete. The taxon assigned as Ascomycota 2 (SH219457.06FU) was isolated only from strobili of both host species. Direct PCR and cloning from L. annotinum shoots revealed a substantially greater endophyte richness compared with the results from culturing.