Submitted to: Wildland Shrub and Arid Land Restoration Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/15/2001
Publication Date: N/A
Technical Abstract: Mycorrhizal fungi form ecologically important symbiotic associations with their host plants in every major ecosystem. The mycorrhizal status of many dominant plant species in arid ecosystems is unclear because the fungi do not form typical interfaces, sites of nutrient exchange. Dark septate endophytic (DSE) fungi also occur in all ecosystems but their function is unknown. They extensively and non-destructively colonize the roots of fourwing saltbush, Atriplex canescens (Pursh) Nutt., a dominant, ubiquitous and ecologically important shrub in arid southwestern USA rangelands. A. canescens roots were collected as plants were breaking dormancy in the spring, prepared and stained with Sudan IV, specific for lipids, and analyzed with differential interference contrast microscopy (DIC). A distinction was made between inactive and active stages of the fungus. Commonly observed stained or naturally pigmented hyphae and microsclerotia were regarded as dormant fungal structures. Active vacuolated hyaline hyphae not visible with conventional microscopy and root preparation and staining methods, were observed colonizing both cortex and the phloem tissues. The vacuolar contents stained positively with Sudan IV indicating that these hyphae were transporting and releasing lipids directly into the phloem. It is proposed that lipids are energy rich carbon source utilized by the host for the production of new spring foliage. DSE fungi differ uniquely from other mycorrhizal fungi in the way that interface with the host. The transport of lipids during peaks of metabolic activity suggests that DSE fungi function in the management and transportation of carbon in an arid ecosystem.