Biogeochemistry of Heavy Metals in the Rhizosphere of Alfalfa

• Main Authors: Moshiri,Farhad, Rejali ,Farhad, Besharati,H, Khademi,Z, Esmaeili,M, Esmail-Zadeh.L, Mansouri.F, Esmailizad.A, Shamshiripour.M, Radmehr. S
• Format: Publication
• Language: Persian
• Published: Karaj (Iran) Soil and Water Research Institute 2013
• Subjects: HEAVY METALS; MEDICAGO SATIVA; METAL LOURD; METALES PESADOS; RHIZOSPHERE; RIZOSFERA

Industry and Agriculture today's activities include the use of industrial and municipal wastewater in agricultural production has led to increased levels of heavy metals in soils. In addition, due to limited arable land, the use of marginal land, such as lands around mines and melting factories has provoked the expansion of this problem. Thus, is seems necessary to study about soil pollution with heavy metals and production of healthy crops from these soils. In this study, the state of biogeochemical changes of heavy metals in the rhizosphere as one of the defense mechanisms of plants against soil contamination has been adressed and the role of arbuscular mycorrhizal fungi in these changes has been investigated. In this experiment, the Rhizobox system with ability to study the rhizospheric changes at different distances from roots was used. Two soils, Kalsinasion and Angouran, in Zanjan province with different degrees of contamination of Zn and Pb were selected. A control (non-inoculated) and inoculation with mycorrhizal fungi in soil was used in both soils as treatments. Alfalfa root and shoot dry weight, concentration and uptake of Zn and Pb, changes in chemical fractions of Zn and Pb in the rhizosphere were investigated. In addition, the rate of root colonization with fungi and fungal spores in the rhizosphere were determined. The results showed that the levels of contamination did not affect alfalfa growth so that the difference in mean dry weight of shoots and roots of alfalfa was not observed in both soils. In both soils, shoot and root dry weight of alfalfa was incresed with inoculation of mycorrhizal fungi by 31.5 and 39.3 percent, respectively. Positive effect of mycorrhiza inoculation on root dry weight was higher in Kalsinasion soil with lower contamination level than Angouran. In terms of heavy metal contamination in soil, 70 to 90% of the zinc and lead uptaken by alfalfa had been gathered in roots. Root colonization increased with inoculation of both soils with mycorrhizal fungi.This coexistence has the highest rate of 66%. Inoculation with mycorrhizal fungi increased the organic, carbonatic and available Zn in rhizosphere. Effect of mycorrhizal inoculation was significant only on oxidic and available chemical forms of Pb. The effect of mycorrhiza on chemical changes of Zn and Pb was related to heavy metal contamination level in soil. Organic and available chemical forms of Zn were more near the roots, otherwise least amount of exchangable form of Zn was observed near the roots. Chnages in chamical forms of Pb in different distance from roots was not considrable. In overall, results showed that alfalfa through lack of transfer of Zn and Pb from roots to shoots shows resistance against pollution conditions. Mycorrhizal fungies in heavy metal contamination condition were also active and are effective on the growth of alfalfa and chemical changes of zinc and lead in the rhizosphere. Probably, the resistance of alfalfa to pollution of Zn and Pb is also attributed to its ability to transform chemical elements in the rhizosphere. Key words: Alfalfa, Rhizosphere, Heavy metals, Zinc, Lead, Mycorrhiza