The Role of Endomycorrhizas in Mineral Nutrient Uptake by Crop Plants.

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The dry matter production, seed yield and phosphorus accumulation of soybean greatly increased irrespective of phosphate fertilization when a mixture of spores of vesicular-arbuscular mycorrhizal fungi, Glomus mosseae and G. etunicatus was inoculated in irradiated Aso soil (andosol) which had high total phosphate content but low available phosphate content. The growth stimulation also occurred in the unsterilized soil with added phosphate.Mycorrhizal and nonmycorrhizal soybean shoot had a similar specific radioactivity of phosphorus accumulated from <^(32)P> -labelled soil phosphate. Absorption of <^(32)P> by mycorrhizal soybean from Fe <^(32)P> <O_4> or Al <^(32)P> <O_4> added in water-culture solution was almost identical with that by nonmycorrhizal soybean. Changes in Al-phosphate content of Aso soil inoculated with G. mosseae did not always explain the increased accumulation of phosphorus in mycorrhizal soybean shoot. These results show that endomycorrhizas largely contribute the phosphate absorption of crop plants in andosol having large phosphate fixing capacity due to the extension of a network of mycorrhizal hyphae beyond the root-hair zone.The addition of powdered bamboo charcoal efficiently increased the rate and density of infection with G. mosseae and G. etunicatus in well-fertilized Aso and Sadohara soil (andosol). However, vesicular-arbuscular mycorrhizas did not stimulate the absorption of less mobile nutrients, zinc and copper from the soils.Inoculation with better endomycorrhizal fungi will increase phosphate absorption by crop plants from soil and may in turn save phosphate fertilizer to be applied.