PARENT SESSION
Poster Session # 14: Forest Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Acquisition of nitrogen from decomposing plant residues by ectomycorrhizal bishop pine (Pinus muricata) and ericoid mycorrhizal evergreen huckleberry (Vaccinium ovatum).

Rains, Kai^{*,1, 2}, Bledsoe, Caroline ², ¹ University of South Florida, Tampa, FL² University of California, Davis, CA

ABSTRACT- Ericoid mycorrhizas are generally considered more adept than ectomycorrhizas at acquiring N from organic sources. This may be particularly important in ecosystems where nutrient cycling occurs primarily in surface organic-rich horizons. We contrasted the ability of an ericoid mycorrhizal shrub and a co-occurring ectomycorrhizal tree to obtain N from decomposing plant residues. Plants were grown individually and in pairs, including all intraspecific and interspecific combinations, in soil collected from the O/A horizon of a California mixed conifer forest. Pots were amended with one of four ¹⁵N-enriched plant residues: bishop pine needles, bishop pine roots, evergreen huckleberry foliage, or evergreen huckleberry roots. Plants grown individually were harvested after 2, 5, and 12 months, while those grown in pairs were harvested after 12 months. The quantity of N obtained from all residue types increased for both species between 2 and 5 months. At both harvests, we found pines and huckleberries had accumulated greater amounts of N from pine root residues than from the other residue types. After 5 months, pines had obtained more N than had huckleberries from decomposing pine needles and pine roots, while huckleberries had obtained more N than had pines from decomposing huckleberry foliage. Both species obtained similar amounts of N from decomposing huckleberry roots. Thus, during the initial stages of decomposition, ectomycorrhizal bishop pines, as opposed to ericoid mycorrhizal huckleberry, may have greater access to the N found in the abundant pine litter layer in these forests. The results from the 12 month harvest also will be presented.

Key words: organic, competition, mycorrhiza, nitrogen