Effects of mycorrhizal inoculum on the dynamics of heavy metals in the rhizoshere.

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To investigate the dynamics of heavy metals in the rhizosphere under the application of steriled and non-sterile arbuscular mycorrhizal inoculum, sunflower, plants were grown in a rhizobox system. When the non-sterile mycorrhizal inoculum was supplied in the central compartment of the rhizobox, nutrient contents of the shoots increased without reducing the plant growth. The analysis of the rhizosphere soils showed the increase in the amounts of water soluble Zn and Fe in addition to the P, and in the activity of phosphomonoesterase activities. However, neither the excretion of low-molecular-weight organic acids (LMOAs) specific to the treatment nor the increase in the amounts of LMOAs was observed. These results indicated that the dissolution of insoluble phosphates was caused by the enzymes originated from arbuscular mycorrhiza and/or mycorrhizal roots and that the Zn and Fe sorbed by the insoluble P were released together with the P.It was supposed that appropriate application of mycorrhizal inoculum would be effective to utilize the nutrients accumulated in the soil.On the other hand, propagation of ectomycorrbizal fungi from the mycorrhizal tree to the non-mycorrhizal seedlings was examined at Forest Research Station Niah, Sarawak State, Malaysia. The effects of planting density and distance from the mycorrhizal tree on the infection rate, growth, and nutrient contents of the seedlings were evaluated. In this experiments, the dynamics of heavy metals in the rhizosphere could not be clarified due to the poor nutrient condition of the soil. However, the p content of the roots with high infection rates was higher than those with low infection rates, which suggested that the mycorrhizal tree was effective in supplying the nutrients to the seedlings even when the available nutrients in the soil are restricted. Further experiments will be needed, especially under the soil conditions which ectomycorrhizal fungi do not act parasitically towards the seedlings.