Abstract
The effect of mycorrhizal symbiosis on metal accumulation and plant tolerance are not commonly studied in medicinal plants under metal stress. The objective of this study was to assess the impact of mycorrhiza on alfalfa plants with the increase of Zn and Cd toxicity. The experiment was conducted under controlled laboratory conditions. Zinc (Zn) and cadmium (Cd) uptake, some biochemical and physiological parameters were studied in eight-week-old alfalfa plants in response to inoculation or not with arbuscular mycorrhizal fungi (AMF) and with the increase of Zn (0, 100, 300, 900 mg·kg-1) and Cd concentrations (0, 100, 300, 600 mg·kg-1) in soil. The results showed that mycorrhizal (M) plants exhibited tolerance to Zn and Cd up to 300 mg·kg-1 in comparison to non-mycorrhizal (NM) plants which exhibited a significant growth reduction at the same soil Zn and Cd level. M inoculation reduced the Zn and Cd accumulation in shoot and showed higher Zn and Cd contents in roots which showed a different Zn and Cd distribution in AMF associated or non-associated plants. Mycorrhizal plants increased phosphorus (P) contents at all Zn and Cd concentrations except the highest (600 and 900 mg·kg-1) leading significant alterations in biochemical contents such as proline, antioxidant enzymes in leaves and also in nutrients (N, P, K, Cu, Ni, Fe, Mn). Zn and cadmium toxicity cause to increase the proline content in shoot of NM plants, however, proline contents are lower in M plants. Results confirmed that AMF protected alfalfa plants against Zn and Cd toxicity. Mycorrhizal colonization was able to form an efficient symbiosis with alfalfa plants in moderately contaminated Zn and Cd soils (300 mg·kg-1) and play an important role in food quality and safety.
Highlights
Soil pollution by heavy metals due to anthropogenic activities is the most important problem nowadays because metals are noxious, persistent and non-biodegradable
The results showed arbuscular mycorrhizal fungi (AMF) colonization was not found in non-inoculated plants, while all the inoculated plants showed high colonization rates
The results of the present study indicated increased alfalfa growth and biomass in the presence of arbuscular mycorrhizal (AM) fungi under Zn and Cd toxicity
Summary
Soil pollution by heavy metals due to anthropogenic activities is the most important problem nowadays because metals are noxious, persistent and non-biodegradable. They tend to accumulate readily in soils and organisms, mainly where effects of human activities are severe. Zn toxicity may occur in soils polluted by human activities such as mining, smelting and application of sewage sludge in agricultural soils [3]. The most important factors which affects metal uptake in plants are: pH, redox potential, texture, organic matter, mineral composition, temperature and water regime [4]
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