Fungi of agricultural soils tend to only form single spores, though a few species form both. At the same time as mycorrhizas spread along and within the root system, hyphae elongate into the soil, either initiating colonisation of other roots or ramifying through the soil. In this way, the soil phase is expanded. The density of the hyphae in soil is highest just beneath the soil surface and declines down the profile, even though the density of colonisation within the root system down the soil profile is likely to be similar. This suggests that the fungi grow into soil in direct relation to the soil compaction and oxygen status.
Hyphae are at low densities in compacted or continually anoxic soil.
Spores are formed when adequate reserves of energy have been stored in the hyphae. Spore formation is also usually related to the amount of colonisation associated with the mycelium. The hyphae also form specific associations within soil fragments. Microscopic examination of microaggregates indicates that hyphae physically bind particles together. The exudates also function, at least temporarily, to glue fragments at this microscopic level.