Some like it hot, some not – Tropical and arctic mushrooms

Highlights

• Characterisation of arctic and tropical rainforest biomes.

• Traits of arctic and tropical mushrooms.

• Stress responses.

• Morphological and physiological adaptations.

• Modes of dispersal.

• Pheno- and genotypic plasticity.

Abstract

Fungi are of pivotal importance for terrestrial ecosystems. They occur globally and show extremely high species diversities. In this review, we compiled information about the adaptability of pileate basidiomycetes by illustrating their habits in contrasting biomes, the arctic regions and tropical lowland rainforests. Mushrooms are faced with differing stress factors and levels in the two ecozones. They fight such challenges by using, by and large, similar physiological and morphological toolkits. They make them fit for extreme environmental conditions, by expressing traits according to biome characteristics. This way, fungal assemblages are formed and pheno- and genotypic plasticity is capitalised. Still, many questions remain open and need further clarification, such as trade-offs between thermal protection and predator defence, prevailing dispersal modes in the main ecozones, interactions with animals and the mechanisms that create genetic plasticity.

Introduction

Ectomycorrhizal and saprobic fungi occur in almost all climate belts and are essential drivers of ecosystem processes (Allen, 1991, Cooke and Rayner, 1984). Saprotrophic basidiomycetes are with more than 80,000 species (Hawksworth and Lücking, 2017) eminently important as decomposers and recyclers of organic material (Dighton and Boddy, 1989, Swift, 1982). The ectomycorrhizal guild as a symbiotic group relies with varying specificity on woody plants as hosts for carbon supply (photosynthate). Carbon is traded mainly for nitrogen and phosphorus extracted from soil-borne, predominantly organic sources in (mineral) nitrogen-limited habitats (Smith and Read, 2008). There are estimates that speak of 20,000 ectomycorrhizal species (van der Heijden et al., 2015), of which ca. 60 % are basidiomycetes, the rest mainly ascomycetes (Tedersoo et al., 2010). In this review, we focus on pileate basidiomycetes.

Like any other organismal group, mushrooms are first of all challenged by climate conditions, particularly thermal and hydrological extremes (Gostinčar et al., 2010). In addition, soil properties play a major role in the habitability of environments (Voroney, 2007). Mushrooms need to disperse and reproduce. To reach a suitable substrate or host, mushrooms not only use wind as dispersal agent, but a number of vectors (arthropods, molluscs, mammals and more), or transport by percolating water (Halbwachs and Bässler, 2015). Biome-related conditions may have significant impacts on dispersal and reproductive modes (Lawrey, 1980, Peay and Bruns, 2014). Moreover, disease and predation are likely to show different patterns in different biomes.

These circumstances raise questions about mushroom diversity, abundance and life strategies in distinct biomes. Biotic and abiotic differences imply adaptations and/or marked pheno- and genotypic plasticity, i.e. stress tolerance. To illustrate the complex factors implicated, we are going to look into two extremely contrasting ecozones, tropical lowland rainforests and alpine/boreal/(sub-)arctic tundras, in the following “arctic” for short (Fig. 1).

We will first compare general geographical and ecological characteristics of the two biomes, followed by a description of fungal responses to environmental stress. Finally, we identify knowledge gaps and suggest further lines of research.