Phosphate transport by communities of arbuscular mycorrhizal fungi in intact soil cores

Variation in phosphate uptake capacity is reported here for natural communities of arbuscular mycorrhizal fungi associated with annual pasture plants. Tests were made of methodology for quantifying phosphate uptake by hyphae associated with clover in soil cores from pastures containing different morphotypes of the fungi. This provided a direct measure of the phosphate uptake capacity of hyphae from P-32-labelled soil in a root-free mesh bag inserted into the centre of intact soil cores. Bicarbonate-extractable phosphorus in the soils ranged from very deficient to close to adequate for plant growth. Uptake of P-32 was related to an estimate of the length of hyphae formed in four of the five soils, but not to either the length or the proportion of roots colonized. In the fifth soil type, phosphate uptake by hyphae was negligible. Phosphate uptake by natural communities of arbuscular mycorrhizal fungi in intact soil cores can be assessed directly, and is shown to be highly variable. The experimental approach could be applied widely for field investigations of phosphate uptake by hyphal networks.