Single and mixed arbuscular mycorrhizal fungal species inocula have a different effect on the growth and oxidative stress defense in Lolium perenne exposed to phenol and polynuclear aromatic hydrocarbons

Arbuscular mycorrhizal fungi (AMF) are ubiquitous mutualistic plant
symbionts which promote plant growth and protect them from abiotic
stresses. Studies on AMF-assisted phytoremediation have shown that AMF can
increase plant tolerance to the presence of hydrocarbon contaminants by
improving plant nutrition status and mitigating oxidative stress. This
work aimed to evaluate the impact of single-species or mixed-species AMF
inocula, obtained from the contaminated environment (Funneliformis
caledonium, Diversispora varaderana, Claroideoglomus walkeri), on a
growth, oxidative stress (DNA oxidation and lipid peroxidation) and
activity of antioxidative enzymes (superoxide dismutase, catalase,
peroxidase) in Lolium perenne cultured in a substrate contaminated with
0/0 - 30/120 mg phenol/polynuclear aromatic hydrocarbons (PAHs) kg-1. The
assessment of AMF resistance to the presence of contaminants was based on
mycorrhizal root colonization, spore production, the level of oxidative
stress and antioxidative activity in AMF spores. In contrast to the
mixed-species AMF inoculum, single AMF species significantly enhanced the
growth of host plants cultured in the contaminated substrate. Their effect
on the level of oxidative stress and the activity of antioxidative enzymes
in plant tissues differed between the AMF species. Changes in the level of
oxidative stress and the activity of antioxidative enzymes in AMF spores
in response to contamination also depended on AMF species. Although, the
concentration of phenol and PAHs had a negative effect on the production
of AMF spores, low (5/20 mg phenol/PAHs kg-1) and substrate (15/60 mg
phenol/PAHs kg-1) contamination stimulated the mycorrhizal colonization of
roots. Among the studied AMF species, F. caledonium was the most resistant
to phenol and PAHs and showed the highest potential in plant growth
promotion. Adverse effects of mixed AMF inoculum on L. perenne growth
might result from the competitive associations between the AMF species and
excessive development of C. walkeri. Presented results might contribute to
the development of functionally customized strategies of AMF-assisted
phytoremediation with indigenous AMF inocula, adapted to form mycorrhizal
associations in the presence of contaminants, which might enhance
phytoremediation more effective than commercial AMF inocula.