Effects Of Arbuscular Mycorrhizal Fungi On The Growth Of Plants And Uptake And Distribution Of Zinc And Copper

Pot experiments were adopted in this paper to study the effect of two arbuscular mycorrhizal(AM) fungi, namely Glomus intraradices (G.i) and Glomus mosseae (Gm), on the growth and heavy metals (Cu and Zn) uptake into Mimosa pudica. The effect of G. i on the growth and the uptake of Cu in three plants-Mimosa pudica, white clover (Trifolium repens Linn.) and Sudangrass (Sorghum sudanense) in the intercropping system was also determined in this experiment.1. The soils contaminated by Zn and Cu at different levels were adopted in the comparision experiment for the effect of two AM fungi on the growth of Mimosa pudica. The sustained strong colonization of G.i on the roots of Mimosa pudica on Zn-contaminated soils has provided a firm evidence of a robust resistance of G. i to Zn; and the inoculation of G.i played a significant role in promoting the growth of Mimosa pudica while bettering its phosphate uptake but had no significant impact on the Zn contents in shoots and roots of Mimosa pudica. However, the infection triggered by G.m suffered a substantial deduction along with the rise of Zn level in soil, and the occurrence of this effect of G.m inoculation on growth promotion lagged much behind than that of G.i. The effect of G.m inoculation on growth and phosphate adsorption deduced with the rise of Zn level in soils and this inoculation had no or little positive role, if any, on Zn contents in shoots and roots of Mimosa pudica.The infections of G.i and G.m into the roots of Mimosa pudica were remarkably restrained on Cu-contaminated soil with that of G.i being less inhibited. The incoluation of G.i was able to enhance phosphate contents in shoots and roots of Mimosa pudica, while the Gm inoculation’s positive role existed in exclusively in control. The inoculation of G.i, when put under the exposure of Cu, could harbor a capacity raising the Mimosa pudica biomoss of shoots and roots, but no such capacity could be seen in Gm inoculation. Similar as the results from Zn-contaminated soil, the inoculation of G.m displayed a capability of growth promotion to Mimosa pudica much later than G.i. The inoculation of G.i and Gm, in the treatment with Cu, did reduce remarkably Cu contents in Mimosa pudica and enhance the total Cu uptake into shoots and roots of Mimosa pudica.These results indicated that the rise of resistance of Mimosa pudica by G.i to Zn was not reached by means of the decline of Zn contents in its shoots but possibly through the betterment of its phosphorous nutrition. As for the increase of resistance to Cu by G.i, possibly it was reached though the improvement of phosphorous nutrition and the decline of Cu contents in shoots. Meanwhile, Gm bore a relatively loose relation with this plant’s phosphorous nutrition.2. In the intercropping experiment (Mimosa pudica/Sudangrass and white clover/Sudangrass), the treatment with Cu at a concentration of400mg kg-1bore a significantly restraint to the infection of G.i into Mimosa pudica, Sudangrass, white clover in comparison to the one at a concentration of200mg kg-1. In the treatment with200mg kg-1Cu, Mimosa pudica and white clover could inhibit the infection of G.i into the roots of Sudangrass, in the meantime, Sudangrass merely had a inhibitive effect on the infection of G.i into the roots of Mimosa pudica having no impact on that into the roots of white clover. In the treatment with400mg kg-1Cu, two plants involved in the intercropping system had no influence on the infection of G.i into each other. The inoculation of G.i was helpful to raise the phosphate contents in shoots but was not to improve the growth of three plants under Cu stress, and it had no remarkable influence on the Cu contents in shoots of Mimosa pudica and white clover. But the inoculation of G i was apt to bring down the Cu contents in shoots of Sudangrass treated with Cu at a concentration of200mg kg-1. The intercropping system could significantly bring down the dry weight of shoots per plant of Mimosa pudica and white clover and remarkably enhance that of Sudangrass, but have an insignificant impact on phosphate contents in shoots. And the intercropping system was apt to raise Cu contents in shoots of Mimosa pudica and white clover and to lower that of Sudangrass. These results showed that, the variables of dry weight of shoots per plant, in different treatment, were not in line with the changes of phosphate contents. It manifested that, for plants, phosphorous nutrition was not the main element affecting their growth, probably, this phenomenon might bear some relation with the relatively high phosphate contents in tested soils.