Fungal root symbionts of high-altitude vascular plants in the Himalayas

Abstract

Arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) form symbiotic relationships with plants influencing their productivity, diversity and ecosystem functions. Only a few studies on these fungi, however, have been conducted in extreme elevations and none over 5500 m a.s.l., although vascular plants occur up to 6150 m a.s.l. in the Himalayas. We quantified AMF and DSE in roots of 62 plant species from contrasting habitats along an elevational gradient (3400–6150 m) in the Himalayas using a combination of optical microscopy and next generation sequencing. We linked AMF and DSE communities with host plant evolutionary history, ecological preferences (elevation and habitat type) and functional traits. We detected AMF in elevations up to 5800 m, indicating it is more constrained by extreme conditions than the host plants, which ascend up to 6150 m. In contrast, DSE were found across the entire gradient up to 6150 m. AMF diversity was unimodally related to elevation and positively related to the intensity of AMF colonization. Mid-elevation steppe and alpine plants hosted more diverse AMF communities than plants from deserts and the subnival zone. Our results bring novel insights to the abiotic and biotic filters structuring AMF and DSE communities in the Himalayas.

Patterns of root colonization by arbuscular mycorrhizal fungi and dark septate endophytes across a mostly-unvegetated, high-elevation landscape

“…Here we focus on high-elevation alpine environments because alpine plants are vulnerable to climate change due to an often greater magnitude of change (Pepin and Lundquist, 2008) and susceptibility to habitat loss (Engler et al, 2011;Elsen and Tingley, 2015) compared to lower-elevation plants. Previous work suggests that AMF colonization increases at lower elevations (Schmidt et al, 2008;Kotilínek et al, 2017) as well as lower P, N (Johnson et al, 2015), and moisture levels (Aug e, 2004;Smith and Read, 2008;Camenzind et al, 2014). Mechanisms discussed in this literature to explain these trends include both the temperature and moisture optima of the fungus, the amount of fungal spores, and the amount of photosynthate the plant devotes to the fungus.…”

Functional roles of microbial symbionts in plant cold tolerance

“…As identified here, these symbionts may also be less effective at acquiring nutrient‐limiting nutrients from soil, possibly because of the effects of low temperatures on the growth of their hyphae in the rhizosphere or the formation of symbiotic interfaces in roots, which compromise their abilities to forage for nutrients and transfer them to the host (Liu et al 2004). Instead, in cold habitats, the arbuscular mycorrhizal fungi tend to be replaced by another group of root‐inhabiting fungi, the dark septate endophytes (Haselwandter & Read 1980; Read & Haselwandter 1981; Stoyke & Currah 1991; Väre et al 1992; Upson et al 2008; Casanova‐Katny et al 2011; Kotilínek et al 2017). In contrast to the arbuscular mycorrhizal fungi, dark septate endophytes have been shown to secrete extracellular proteolytic and peptidolytic enzymes that degrade proteins and peptides (Caldwell et al 2000; Nissinen et al 2012; Suryanarayanan et al 2012), which, owing to restricted organic matter decomposition, are abundant in permanently cold soils (Swift et al 1979; Roberts et al 2009).…”

Non‐random association patterns in a plant–mycorrhizal fungal network reveal host–symbiont specificity

“…Such associations ("partial" or "ecological" specificity) are likely to represent a relatively recent stage in the evolution of the AM symbiosis (Smith, Grace, & Smith, 2009). At a finer taxonomic scale, the composition of AM fungal communities in the roots of plant individuals appears to depend on plant functional traits (Kotilínek et al, 2017). Furthermore, there is some evidence that plant adaptation to certain environmental conditions is related to the ability to selectively form functional symbiosis with AM fungi (Osborne et al, 2018).…”