Current Knowledge on Mycorrhizal Symbiosis and Endophytes in Northwest Patagonia, Argentina

FONTENLA SONIA; PUNTIERI JAVIER; FERNÁNDEZ NATALIA; MESTRE MARÍA CECILIA

Mycorrhizal Fungi in South America. Biodiversity, Conservation, and Sustainable Food Production

Springer International Publishing

Año: 2022; p. 256 - 279

The northwest Patagonian region is characterized by a pronounced precipitation gradient setting an interesting scene for the study of mycorrhizal associations. In this chapter we summarize the current knowledge on mycorrhizal associations in Andean and Extra-Andean northwest Patagonian subregions, including High-Andean environments, forest, steppes and meadows, derived from studies performed in the last two decades. In the NW Patagonian High-Andean environments, 76% of plants are associated with mycorrhiza, DSE co-occur with arbuscular mycorrhizal (AM) and non-host (NH) species. The extreme conditions characteristic of these environments seem not to have modified most of the mycorrhizal parameters, although low AM colonization values have been registered in the most extreme site respect the Patagonian steppe; the prevalence of the Acaulosporaceae family, not usually found in this kind of environment, is worth noticing. Nothofagus forests are distributed widely throughout the Andean region, Nothofagus spp. being some of the few Patagonian native species with ectomycorrhizal symbiosis. These Nothofagus forests have numerous and abundant AM understory plants, generating a mixed mycorrhizal state that possibly upgrades the benefits of both types of symbiosis. Arbuscular mycorrhiza are prevalent (in terms of number of plant species, dominance and abundance of them) in Patagonian vegetation, including plants of almost all environments of the Andean subregion ? High-Andean plants, native conifers and other dominant forest trees (except Nothofagus spp.) and their understory species (including those under Nothofagus forests) ⎯; AM are also abundant in Extra-Andean steppe plants. The central zones of meadows are an exception, due to the abundance and dominance of NH plants. Mycorrhizal status (number of plant species with the simbiosis) decreases from the forests to the meadows. The number of soil AM spores and infective propagules shows an opposite trend to the mycorrhizal status. These contrasting trends suggest that forests, together with steppes and meadow borders behave as AM-generating communities. However, the centers of almost all meadows (where NH plants are plentiful) behave as accumulative AM-spores communities, with a high infective capacity predominantly through spores. Mycorrhizal colonization decreases along the plant-habit gradient: trees > shrubs > perennial herbs > annual herbs > pteridophytes. Few studies have been carried out on Patagonian bryophytes, thus limiting their inclusion in this sequence. In general, along the precipitation gradient, and in both Patagonian subregions, mixed mycorrhizal infections are rarely seen, and a relatively low frequency of other mycorrhizal types has been observed. Ericoid mycorrhiza (ErM) are present in a small number of plant species, some of which are highly abundant in the forest understory. A recent taxonomic study of ericoid mycorrhiza in NW Patagonia produced the first record of Rhizoscyphus ericae in the Southern Hemisphere, identified from High-Andean Gaultheria spp. In the other environments ErM is formed predominantly by Sebacinales (Basiodiomycota) in NW Patagonian forests; or by Oidiodendron maius, Rhizoscyphus sp., Cadophora finlandia and Meliniomyces cf. variabilis isolated from Vaccinium plants from a local blueberry´s production situated into a native forest area. Microscopic observation also suggests the presence of other Basidiomycota fungi (no Sebacinales) which have not been identified, and ought to be studied with more detail for robust conclusions. The occurrence and prevalence of ErM mycobionts vary between environments, suggesting site and also plant species dependence. Cadophora finlandia and Meliniomyces variabilis were identified from Gaultheria (probable ErM forming) and also from Nothofagus ectomorphotypes (possible EcM?). This raises the question of whether some Helotiales recorded in these works could form both mycorrhizal types in different hosts. Dark septate endophytes (DSE) coexist with mycorrhiza; they occurred in almost all species/individuals analyzed, regardless of mycorrhizal status or environmental characteristics, e.g. extreme conditions. Two fungi typical of DSE ? Leptodontidium orchidicola and Phialocephala cf. fortinii ? were identified on Gaultheria spp. and on Nothofagus ectomorphotypes; maybe these endophytes can be shared between these hosts and contribute to some kind of interaction, like nutrient exchange. We encourage further research on these communities so as to expand our knowledge and deepen our understanding of global diversity patterns and their determining factors.