An assessment of soil enrichment by actinorhizal N2 fixation using [delta]15N values in a chronosequence of deglaciation at Glacier Bay, Alaska

Issue Title: Frankia Symbiosis. Proceedings of the 12th International Meeting on Frankia and Actinorhizal plants, Carry-le-Rouet, France, June 2001 The extent of transfer of fixed N between N^sub 2^-fixing and non-N^sub 2^-fixing plant species is largely unknown in successional studies. In order to redress this deficiency at a locale intensively studied ecologically, leaf tissue samples were collected from actinorhizal N^sub 2^-fixing (Alnus, Shepherdia, and Dryas) and two non-N^sub 2^-fixing (Salix) woody species within research plots located along a chronosequence of deglaciated fjord in Glacier Bay National Park, Alaska. The tissue samples were analyzed for δ^sup 15^N content, and the resulting data analyzed for trends in plant tissue N. Among the non-N^sub 2^-fixing Salix species, δ^sup 15^N values increased from the most recently deglaciated sites to converge with the temporally more-stable values for the symbiotic N^sub 2^-fixing species on sites at about 40 years after deglaciation. The lower δ^sup 15^N values of sequestered N in plant tissues suggested that N derived from N^sub 2^-fixing plants accounts for the major portion of N in associated plants up to 40 years after deglaciation. The ^sup 15^N isotopic data also suggested that Shepherdia canadensis depends least on soil N, D. drummondii the most, and A. viridis ssp. sinuata somewhere between those two species. The presence of a sere dominated by dense thickets of A. viridis ssp. sinuata at the convergence of δ^sup 15^N values for the N^sub 2^-fixing and non-N^sub 2^-fixing species indicated that this species is most responsible for accumulation of fixed N in soil at Glacier Bay. This paper is dedicated to the memory of Steven J. Kohls who died prior to publication of this research.[PUBLICATION ABSTRACT]