HR: 16:45h
AN: B34A-04 INVITED    [Abstracts]
TI: Beyond CO₂: Changes in Limiting Resources in California Oak Woodland
AU: * Hasselquist, N
EM: nhass001@ucr.edu
AF: Center for Conservation Biology, University of California, Riverside, Riverside, CA 92521, United States
AU: Allen, M
EM: michael.allen@ucr.edu
AF: Center for Conservation Biology, University of California, Riverside, Riverside, CA 92521, United States
AB: As atmospheric CO₂ continues to increase, other resources become even more limiting to plants and the wildland ecosystems they support. Traditionally, California Mediterranean-type ecosystems are limited by water, then N. In these ecosystems, CO₂ enrichment causes a minor increase in production associated with enhanced water-use efficiency, but N rapidly becomes the limiting factor to both production and to soil organism dynamics. In urbanizing areas, such as southern California, strong gradients in NOx deposition are also created by vehicular pollution. We have studied the regulation of N uptake by mycorrhizae in Coast Live Oak (Quercus agrifolia) using information with natural abundance from the early 1900s, current plants and fungi, and modeling change. Contrasts were made from a high NOx deposition site, a low deposition site, and a site where NOx deposition is rapidly increasing. We examined natural abundance δ¹⁵ N of current and past plant material (leaves, wood), mycorrhizal and saprobic fungal fruiting bodies, and soil. We modeled relative N uptake, fractionation, and transport between soil, fungus and plant. Our data show complex interactions between increasing NOx deposition and increasing atmospheric CO₂ on mycorrhizal-plant interactions. There is a significant shift in N sources and reduction upon mycorrhizae with NOx deposition. However, the elevated CO₂ appears to also have created a greater N demand on the trees, increasing dependence on mycorrhizae and the ability of the fungi to acquire organic N and NH₄. The individual fungal species differ among sites, but complex trends between fungal genera and trees can be seen. Projections of increasing atmospheric CO₂ and regional NOx deposition suggest strong but complex gradients in fungal-oak interactions with decreasing dependence on mycorrhizae near urbanizing areas, mediated by the rate of increasing CO₂ and inorganic NOx deposition, and paradoxically, increasing dependency on mycorrhizae and organic N acquisition in lower N deposition areas.
DE: 0429 Climate dynamics (1620)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0469 Nitrogen cycling
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting