Soil mediated effects of phosphorus supply on the formation of mycorrhizas byScutellispora calospora(Nicol. & Gerd.) Walker & Sanders on subterranean clover

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Abstract
Summary: A split‐root technique was used to separate plant and soil mediated effects of phosphorus (P) supply on the formation of mycorrhizas byScutellispora calospora(Nicol. & Gerd.) Walker & Sanders on subterranean clover (Trifolium subterraneumL.). There were 10 split‐root treatments, incorporating four concentrations of P (0, 18, 105 and 280 μg P g−1soil) ranging from severely deficient for plant growth to luxurious. Increasing the supply of P to plants decreased the percentage of root length infected and the total length of roots infected byS. calospora.Applications of 18 and 105 μg P g−1soil to half of the root system of plants reduced the percentage of root length infected in that half of the root system and in the other half of the root system to the same extent. The effects of severely deficient and moderately deficient rates of P on infection byS. calosporawere therefore mediated through the plant. These effects could be related directly to effects of P supply in decreasing the concentrations of soluble carbohydrates in roots because carbohydrate concentrations in roots did not differ between each half of the root system. In contrast to the concentrations of soluble carbohydrates in roots, the length of roots and the concentrations of P in roots were generally greater in the half of the root system that received the highest application of P. Applications of 280 μg p g−1soil to half of the root system of plants also reduced the percentage of root length infected byS. calosporain both halves of the root system but to a greater extent in the half that received 280 μg P g−1soil. This effect was associated with greater length of roots, higher concentrations of P in roots and higher concentrations of P in the soil in the half of the root system that received 280 μg P g−1soil. We concluded that the effects of luxury amounts of P on infection byS. calosporacould be mediated through the soil.