Effect of the actinomycetes and arbuscular mycorrhizae isolated from heavy metal polluted sites on tolerance of peanut plants grown in soil spiked with manganese, zinc and iron

Abstract

In the present study, isolation and enumeration of different microorganisms were carried out. The isolates were obtained from soil and Zea mays plant roots irrigated with water effluents from two locations contaminated with heavy metals. The most heavy metals tolerant microorganisms were selected by inoculation on their specified media, supplemented with the mixture of ion solutions of the common heavy metals (Zn, Mn and Fe) in the collected soil samples. Out of these surveys, one isolate of actinomycetes identified as Streptomyces catenulae selected as the most resistant to these heavy metals. Isolation and identification of arbuscular mycorrhizal (AM) spores that collected from the soil samples were carried out and six isolates were obtained.

A pot experiment studies were conducted using the most resistant microorganisms (S. catenulae and AM fungi)to study the heavy metal tolerance mechanisms in peanut plants grown on sand culture fed with the common heavy metals at concentration 250 ppm. The obtained results could be summarized as follows: • Heavy metals application slightly increased the total dry weight of peanut plants, compared with untreated controls. However, the addition of AM fungi singly or in combination with S. catenulae appeared significant increase in the total dry weight of the plants at all treatments. • The root surface area of the plants was increased by the addition of Zn, Mn or Fe to the soil. The soil treatment with S. catenulae and AM fungi showed significant increase. • The yield components of peanut plants grew in heavy metals was increased significantly when S. catenulae and AM fungi were used together. • Nodules number were increased by the addition of Mn, and decreased with Zn or Fe. However, the dry weight of nodules was decreased by Zn and increased by Mn or Fe. • The activity of nitrogenase enzyme in peanut plants was increased by the addition of the investigated heavy metals. However, the application of AM fungi together with S. catenulae appeared significant increase in all nodulation status under all conditions. • The combination of AM fungi and S. catenulae increased the metal tolerance index in peanut plants treated with heavy metals compared to control plants (plants treated with Bradyrhizobium sp. only). • N, P and K contents in leaves and seeds of peanut plants appeared slight variations in presence of the heavy metals. However, the values obtained for AM plants remained greater than those of non-mycorrhizal ones, especially when S. catenulae was applied. • The translocation of heavy metals into leaves and seeds of peanut plants was decreased by AM fungi and S. catenulae separately. However, the combination of the two microorganisms showed the best results. • The metabolites content were increased in the plants especially when AM fungi and S. catenulae were present. • The total photosynthetic pigments were increased by the addition of Zn, Mn or Fe to the soil. The values obtained for AM plants were significantly greater than those of non-mycorrhizal ones, especially when S. catenulae also applied. • Addition of heavy metals to the soil showed negative effect on the rate of mycorrhizal colonization in peanut roots, especially the plants treated with Fe. However, the treatment with S. catenulae and AM fungi recorded the highest significant values of colonization. • The spore number of AM fungi was increased in the soil of peanut plants spiked with Zn, Mn or Fe especially when S. catenulae was applied.