Dark Septate Endophytes (DSE) in Polluted Areas 131symbiosis with nearly 75% of all families of vascular plants from natural
ecosystems, (Brundrett, 2009) as well as in degraded and contaminated areas
(Jeffries et al., 2003). These associations improve nutrition, tolerance and
accumulation of heavy metals in the plants (Tonin et al., 2001). In case of
ECM, estimated point towards only 4.5% of plants with this type of
association (Brundrett, 2009). Despite its great importance in plants with
agroforestry interest^ (Marx & Cordell, 1989). ECM fungi are able to mobilize
soil nutrients by secreting low molecular weight organic compounds (oxalates,
siderophores or citrates), and are involved in several biogeochemical cycles
such as the carbon (C) and nitrogen (N).
Nonetheless, other fungi that can be found abundantly and with worldwide
distribution in these stressful environmental conditions (Cevnik et al., 2000;
Vrålstad et al., 2002a; Wilberforce et al., 2003; Li et al., 2012; Fernández-
Miranda, 2014) are dark septate endophytes (DSE). Jumpponen (2001) defined
them as conidial or sterile ascomycetes fungi mostly belonging to the order
Helotiales with darkly pigmented and septate hyphae that colonise living plant
roots without causing apparent negative effect. Colonization by DSE produces
typical intracellular structures called microsclerotia (Figure 1) inside root cells.
Figure 1. Intracellular microsclerotia formed by Cadophora finlandica inside of root of
Salix atrocinerea.
The role of these fungi on host plant is controversial because while some
authors observe his influence as a promoter of plant hormones (Schulz, 2006)
and positive effects, as would a mycorrhizal fungus (Jumpponen, 2001;
Newsham, 2011) others observe negative effects (Wilcox & Wang, 1987;
Tellenbach et al., 2011). The predominance of DSE as endophytes in heavy