PARENT SESSION
Symposium #22: Species Interactions in Desert Communities: Dynamics of Resource Supply and Utilization .

Organized by: M Price and RJ Smith
Wednesday, August 7. 1:00 PM to 4:30 PM. Turquoise Ballroom, TCC.

Mycorrhizae and Nutrient Supply in Deserts.

Snyder, Season^*,1, Allen, Michael¹, Gosz, James², Pregitzer, Kurt³, ¹ Center for Conservation Biology, Riverside, CA² University of New Mexico, Albuquerque, NM³ Michigan Technological University, Houghton, MI

ABSTRACT- Mycorrhizal dynamics were observed in response to nutrient availability at the Sevilleta LTER. The 3 dominant vegetation transitions are from Chihuahua Desert-Larrea tridentata Scrub, to Great Plains-Bouteloua gracilis and B. eriopoda grassland, to Pinus edulis- Juniperus monosperma woodland. L. tridentata (creosote bush) forms arbuscular mycorrhizae (AM) and only Glomus spp. has been found. B. gracilis (blue grama) and B. eriopoda (black grama) also both form AM. In the grasslands, Glomus and hyphae of Acaulospora spp. have been found. J. monosperma (juniper) forms AM and Scutellospora spp have been added to the Glomus and Acaulospora. Finally, P. edulis (pinyon) forms ectomycorrhizae (EM) with about 30 fungal species. AM enhance uptake of NH₄⁺ whereas EM transport both organic N and NH₄⁺. In L. tridentata, root density is low but the AM hyphae appear to be sustained by hydraulically-lifted water. ¹⁵N values support an open cycle apparently taking up newly released N. Both grass species have dense roots and associated AM hyphae. Little N probably escapes contributing to a higher ¹⁵N value. In other studies, N fertilization reduced AM activity and species richness. In juniper, more roots and a diverse array of AM fungi contribute to N uptake. N fertilization increased plant growth, but had little impact on the AM activity. N fertilization increased respiration and root turnover, but increased longevity of mycorrhizal fungi. In transition zones, the ability of different rooting strategies and mycorrhizal associations determine which plants are likely to survive the changing local environmental conditions. Moreover, while many processes in deserts are driven by pulse dynamics associated with precipitation, the longer-term vegetation shifts may be more associated with longer-scale nutrient transformations.

KEY WORDS: mycorrhizal fungi, biome transition, nutrient cycling, vegetation change