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Mycorrhizal Fungi: Highways for Water and Nutrients in Arid Soils

Center for Conservation Biology, Dep. of Plant Pathology, Univ. of California, Riverside, CA 92521-0334

View larger version (115K): [in this window] [in a new window]   FIG. 1. Mycorrhizae in situ: (A) arterial arbuscular mycorrhizae (AM) hyphae extending from a root of Artemisia californica beyond the root hairs into the surrounding soil matrix, and (B) an EM infection consisting of several root tips encased in a fungal mantle, with a rhizomorph extending from those tips into the surrounding soil. Both images were acquired using a Bartz Technology Corp. minirhizotron, Model BTC-100X.

View larger version (22K): [in this window] [in a new window]   FIG. 2. The expanse of a single fungal taxa connecting a mature oak located at the 0,0 point with seedlings planted at various distances (in meters) surrounding the mature tree. Shown are two taxa, Thelephora terrestris (wide dashed lines) and Amanita sp. (narrow solid lines) based on distribution of restriction fragment length polymorphism analyses of seedling root tips (Allen and Lindahl, unpublished data, 2003).

View larger version (130K): [in this window] [in a new window]   FIG. 3. (A) An arbuscular mycorrhizae (AM) hypha bridging gaps between pumice particles on Mount St. Helens. (B) After teasing apart pumice pieces, the AM hyphae connecting pumice particles and the roots can be clearly seen. Images were taken using a Scalar Proscope USB digital microscope at 100x.

View larger version (118K): [in this window] [in a new window]   FIG. 4. Changing the tortuosity factor by crossing gaps of soil pores. Roots, rhizomorphs, and individual hyphae can reduce the by reducing the capillary length (Lc) compared with the column length (L), by providing linear units crossing soil pores. The two examples show these linear units. The left images are minirhizotron photos and the right images are from a program that identifies edges, showing the structure of the edges created by the roots and rhizomorphs. (A) shows a root stretching across a minirhizotron frame and (B) shows a rhizomorph. In both cases, the soil pores are outlined in small spherical objects, whereas the roots and fungal hyphae are linear units.

View larger version (47K): [in this window] [in a new window]   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).