Blauth, James , Allen, Edith , Allen, Michael F. .
Nitrogen Deposition, Mycorrhizal Communities, and Vegetation Change in Southern California Desert.
WE have been studying arbuscular mycorrhizal (AM) fungi hypothesized to mediate between changes in soil nitrogen and vegetation change in southern California ecosystems. Anthropogenic nitrogen deposition appears to be contributing to invasion of these ecosystems by exotic annuals. We assessed the impact of nitrogen deposition on the AM fungal community in creosote bush scrub (CBS) sites in Joshua Tree National Park: a low N deposition site including fertilized plots and a high N deposition site. We sampled soil under mature creosote bushes with exotic grass understory to measure AM colonization of roots and identify AM fungal species from spores. We observed that nitrogen deposition in CBS ecosystems is correlated with changes in AM fungal community composition. We have also been testing whether increased N, changes in the AM fungal community, or an interaction between the two can explain invasion of CBS ecosystems by exotic annuals. We measured growth responses of the native shrub Larrea tridentata and the exotic grass Bromus tectorum to N addition and to inoculation with different AM fungal communities. Plants were grown in autoclaved soil from the low N deposition CBS site and inoculated with fresh soil from the low N deposition, low N deposition with N fertilization, or high N deposition sites; control plants were mock-inoculated with sterilized soil from the same sites. Half the plants received a moderate level of added N. We found that Bromus and Larrea respond differently to the combinations of N addition and AM inoculation, suggesting the interaction between increased N and altered AM fungal communities may be important for invasion. Detailed results and implications for the role of AM fungi in vegetation change in CBS ecosystems will be described.
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1 - University of Redlands, Biology, 1200 East Colton Ave., Redlands, California, 92373, USA
2 - University of California Riverside, Department of Botany & Plant Sciences, Riverside, California, 92521-0124, USA
3 - University of California, Riverside, Center for Conservation Biology, Riverside, California, 92521
creosote bush scrub
Presentation Type: Poster:Posters for Sections
Location: Auditorium/Bell Memorial Union
Date: Tuesday, August 1st, 2006
Time: 12:30 PM