132 Elena Fernández-Miranda Cagigal
metal contaminated areas can relate to their melanised cell walls, which can
sequester heavy metals and therefore confer protective effects to the plant.
However, despite this evidence, a limited number of studies have focused on
DSE function.
DISTRIBUTION
DSE fungi were previously thought to be restricted to infertile boreal or
cold-stressed habitats (Jumpponen & Trappe, 1998), where AM fungi, the
typical mutualists of herbaceous plant roots at lower latitudes and altitudes,
cannot persist or occur only sporadically (Upson et al., 2007; Newsham et al.,
2011). However, in recent years there have been reports of more than 600
plant species spanning 100 plant families worldwide (Barrow & Aaltonen,
2001; Addy et al., 2005). They appear in diverse habitats such as arid, arctic,
boreal, alpine, temperate forest, or tropical ecosystems (Jumpponen & Trappe,
1998; Mandyam & Jumpponen, 2005). Moreover, latest studies have shown
that DSE are the dominant fungi in metal contaminated sites (Cevnik et al.,
2000; Vrålstad et al., 2002a; Wilberforce et al., 2003; Li et al., 2012;
Fernández-Miranda, 2014). They colonize both herbaceous and ligneous
plants, and particularly roots of metal hyperaccumulators, halophytes, orchids,
or marine macrophytes (Mandyam & Jumpponen, 2005). And recent studies
demonstrated that DSE reported that DSE are the dominant fungi from healthy
fine roots of Erica herbacea (Cevnik et al., 2000) Betula pubescens, Populus
tremula, Picea abies, Pinus sylvestris, Calluna vulgaris, Vaccinium myrtillus,
V. vitis-idaea, Deschampsia flexuosa (Vrålstad et al., 2002a) Arabis hirsuta,
Acacia decurrens, Symplocos paniculata, Rabbosia eriocalyx, Arenaria
serpyllifolia, Rosa longicuspis (Li et al., 2012) B. celtiberica and Salix
atrocinerea (Fernández-Miranda, 2014) in polluted soils in around the world.
With all these data, Mandyam & Jumpponen (2005) analyzed the reports
of present of DSE in alpine, arctic, antarctic, boreal, temperate and tropical
habitats and conclude that DSE may be as abundant as mycorrhizal fungi, are
ubiquitous in occurrence, co-occur with different types of mycorrhizae c) are
most prevalent in stressed environments. So what is the function of these fungi
in a natural ecosystem?