Chromium resistance of dandelion (Taraxacum platypecidum Diels.) and bermudagrass (Cynodon dactylon [Linn.] Pers.) is enhanced by arbuscular mycorrhiza in Cr(VI)‐contaminated soils

Abstract

In a greenhouse pot experiment, dandelion (Taraxacum platypecidum Diels.) and bermudagrass (Cynodon dactylon[Linn.] Pers.), inoculated with and without arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis, were grown in chromium (Cr)-amended soils (0 mg/kg, 5 mg/kg, 10 mg/kg, and 20 mg/kg Cr[VI]) to test whether arbuscular mycorrhizal (AM) symbiosis can improve Cr tolerance in different plant species. The experimental results indicated that the dry weights of both plant species were dramatically increased by AM symbiosis. Mycorrhizal colonization increased plant P concentrations and decreased Cr concentrations and Cr translocation from roots to shoots for dandelion; in contrast, mycorrhizal colonization decreased plant Cr concentrations without improvement of P nutrition in bermudagrass. Chromium speciation analysis revealed that AM symbiosis potentially altered Cr species and bioavailability in the rhizosphere. The study confirmed the protective effects of AMF on host plants under Cr contaminations.

Chromium immobilization by extra- and intraradical fungal structures of arbuscular mycorrhizal symbioses

“…This is confirmed by our previous study showing a higher P concentration in mycorrhizal dandelion compared with nonmycorrhizal dandelion under Cr(VI) contamination [14]. Another explanation is the direct immobilization of Cr by AM structures such as spores, extraradical mycelium (ERM), intraradical mycelium, arbuscules, etc.…”

Chromium immobilization by extraradical mycelium of arbuscular mycorrhiza contributes to plant chromium tolerance

“…AMF is well known for its positive effects on plant P nutrition especially under stressful conditions. For example, AM symbiosis substantially increased P uptake efficiency of dandelion plants under Cr(VI) contaminations (Wu et al, 2014). However, we do not know if this is the main way AM fungi enhance plant Cr(VI) tolerance, and if AM function can be replaced by exogenous P addition.…”

“…Additionally, AMF can relieve plant drought stress (Li et al, 2014), protect host plants from pathogens (Singh et al, 2013b), improve soil structure (Rillig and Steinberg, 2002), and even play an important role in maintaining plant biodiversity and ecosystem stability (van der Heijden et al, 1998). Various studies have demonstrated that AM symbiosis take an active part in plant resistance to heavy metal contamination including As, Cd, Cu and Cr etc (Chen et al, 2007a(Chen et al, ,b, 2005Davies et al, 2001;Wu et al, 2014). For example, Davies et al (2001) found that AMF could enhance Cr tolerance of sunflower (Helianthus annuus) under Cr stress.…”

Transformation and Immobilization of Chromium by Arbuscular Mycorrhizal Fungi as Revealed by SEM–EDS, TEM–EDS, and XAFS

“…Our recent work has shown that AM symbiosis can greatly enhance plant Cr tolerance, especially at high levels of Cr(VI) contamination. 22 However, to date, the underlying mechanisms of the enhanced plant Cr(VI) tolerance by AM symbiosis are largely unknown. One potential mechanism is that AM symbiosis can improve plant growth via improving plant mineral nutrition (e.g., phosphorus, nitrogen, etc.…”

“…For example, in our recent study, AM symbiosis dramatically increased the dry weight of dandelion plants in Cr(VI)-contaminated soils by increasing plant P uptake. 22 The larger plant biomass may dilute Cr in the plants, thus minimizing the Cr phytotoxicity, resulting in the so-called "growth dilution effect". 23 Another possible mechanism is that the extraradical mycelium (ERM) of mycorrhizal roots may directly reduce Cr(VI) to Cr(III), immobilize Cr(III), and restrict Cr(III) transfer to plants, similar to Cd 24 and U.…”