Ectomycorrhizal fungal community assembly on seedlings of a Neotropical monodominant tree

New species of Thelephora (Thelephorales, Basidiomycota) associated with Dicymbe and Aldina in Guyana

Species of Thelephora Ehrh. ex Willd. (Thelephorales, Basidiomycota) are known from all continents where ectomycorrhizal (ECM) host plants occur. Although often poorly represented in sporocarp surveys due to the cryptic basidiomata of the resupinate species, belowground sequencing studies in both temperate and tropical systems have shown that thelephoroid fungi are often the dominant ECM group. In the South American lowland tropics, thelephoroid fungi remain poorly known, and very few species have been described from the region. Long-term surveys in Guyana have revealed a wide diversity of ECM fungal species in association with the ECM trees Dicymbe corymbosa (Fabaceae subfam. Detarioideae) and Aldina insignis (Benth.) Endl. (Fabaceae subfam. Papilionoideae). Thelephoroid species form a prominent component of this ECM fungal assemblage, as evidenced by their dominance in both adult tree and seedling root tip surveys and frequent occurrence as fertile basidiomata on a variety of substrata. Here we describe four new thelephoroid species from Guyana that are among the most frequently collected as basidiomata: Thelephora ascendens, Thelephora compacta, Thelephora singularis, and Thelephora ventricobasidia. Three of these species have resupinate basidiomata and would have formerly been assigned to the genus Tomentella Pers. ex Pat. Morphological descriptions, habit, habitat, and known distribution are provided for each new species. Sequence data for the barcode internal transcribed spacer (ITS) locus is provided for types and most other collections of the new species, and a molecular phylogenetic analysis across the Thelephoraceae corroborates their status as novel taxa.

Ectomycorrhizal fungal community varies across broadleaf species and developmental stages

Ectomycorrhizal fungi (EMF) play pivotal roles in determining temperate forest ecosystem processes. We tracked root EMF community succession across saplings, juveniles, and adults of three temperate broadleaf trees (Acer mono, Betula platyphylla, and Quercus mongolica) in Northeast China. Adult stages showed higher alpha diversity but lower community dissimilarity compared to earlier stages. In particular, the EMF alpha diversity of Quercus mongolica marginally increased along with host developmental stages and ranked as sapling < juvenile < adult. Unlike those of Acer mono and Quercus mongolica, the EMF community composition of Betula platyphylla showed greater variation between the sapling and juvenile stages than between the sapling and adult stages. Cooccurrence networks revealed increasing interconnectivity with host maturity, dominated by positive correlations (> 99%). LEfSe was employed to identify stage- and/or host-specific EMF indicators. This study highlighted the assembly of EMF community during the development of broadleaf trees in temperate forests, thereby advancing understanding of the succession and coevolution of symbiotic relationships.

Leaf-cutter ants - mycorrhizal fungi: observations and research questions from an unexpected mutualism

Leaf-cutter ants (LCAs) are widely distributed and alter the physical and biotic architecture above and below ground. In neotropical rainforests, they create aboveground and belowground disturbance gaps that facilitate oxygen and carbon dioxide exchange. Within the hyperdiverse neotropical rainforests, arbuscular mycorrhizal (AM) fungi occupy nearly all of the forest floor. Nearly every cubic centimeter of soil contains a network of hyphae of Glomeromycotina, fungi that form arbuscular mycorrhizae. Our broad question is as follows: how can alternative mycorrhizae, which are-especially ectomycorrhizae-essential for the survival of some plant species, become established? Specifically, is there an ant-mycorrhizal fungus interaction that facilitates their establishment in these hyperdiverse ecosystems? In one lowland Costa Rican rainforest, nests of the LCA Atta cephalotes cover approximately 1.2% of the land surface that is broadly scattered throughout the forest. On sequencing the DNA from soil organisms, we found the inocula of many AM fungi in their nests, but the nests also contained the inocula of ectomycorrhizal, orchid mycorrhizal, and ericoid mycorrhizal fungi, including Scleroderma sinnamariense, a fungus critical to Gnetum leyboldii, an obligate ectomycorrhizal plant. When the nests were abandoned, new root growth into the nest offered opportunities for new mycorrhizal associations to develop. Thus, the patches created by LCAs appear to be crucial sites for the establishment and survival of shifting mycorrhizal plant-fungal associations, in turn facilitating the high diversity of these communities. A better understanding of the interactions of organisms, including cross-kingdom and ant-mycorrhizal fungal interactions, would improve our understanding of how these ecosystems might tolerate environmental change.