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In spite of the major advances in understanding the functioning of symbioses between plants and arbuscular mycorrhizal fungi, details of the ecology of mycorrhizal fungi are not well documented. The benefits of the association are related to the timing and extent of colonization of roots, and fungi differ in their contribution to plant growth and presumably to soil aggregation. Knowledge of the processes that lead to successful colonization of roots by beneficial fungi at appropriate times for the host plants will form the basis of guidelines for soil management to maximize the benefits from the symbiosis.Fungi differ in the manner and extent to which they colonize roots. They also differ in their capacity to form propagules. The importance of hyphae, spores and propagules within living or dead mycorrhizal roots also differs among species and for the same species in different habitats. The relationships between colonization of roots and propagule formation, and between propagule distribution and abundance and subsequent mycorrhiza formation, for different fungi in field environments, are not well understood.Methods for quantifying mycorrhizal fungi are not especially suitable for distinguishing among different fungi within roots. Consequently, the dynamics of colonization of roots by different fungi, within and between seasons, have been little studied. Research is required that focuses on the dynamics of fungi within roots as well as on changes in the abundance of propagules of different fungi within soil. Interactions between fungi during the colonization of roots, the colonization of soil by hyphae and sporulation are all poorly understood. Without knowledge of these processes, it will by difficult to predict the likely success of inoculation with introduced fungi. Such knowledge is also required for selecting soil management procedures to enhance growth and survival of key species within the population.The relative tolerance of various fungi to perturbations in their surroundings will provide a basis for identifying those fungi that are likely to persist in specific environments. The processes that influence mycorrhizal fungi in field soils can be identified in controlled studies. However, greater emphasis is required on studying these processes with mixed populations of fungi. The role played by diversity within populations of mycorrhizal fungi is virtually unexplored.

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 32P‐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 32P 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.