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FIG. 5. The growth of ectomycorrhizal rhizomorphs in the surface soil at the James Reserve, in the mixed conifer forest on Mount San Jacinto. The nearest tree is a ponderosa pine, whose roots probably extend to the groundwater, several meters below the soil surface. These images were taken during the dry season; surface soil moisture sensors (where these images were taken) stopped recording in July, when the soil moisture declined below the detectable levels. We estimated that the soil water potential was between –4 and –5 MPa, below what should be necessary for hyphal growth unless there is another source at the distal end of the rhizomorph. We postulate that this source is hydraulically lifted water. Similar phenomena were observed for individual hyphal networks of arbuscular mycorrhizae fungi (Allen and Stozle, unpublished observations, 2005).
