Oecologia (2004) 141: 468–476 DOI 10.1007/s00442-004-1622-3 ECOSYSTEM ECOLOGY Jennifer N.Bennett . Cindy E.Prescott Organic and inorganic nitrogen nutrition of western red cedar, western hemlock and salal in mineral N-limited cedar–hemlock forests Received: 26 January 2004 / Accepted: 14 May 2004 / Published online: 20 August 2004 # Springer-Verlag 2004 AbstractWesternred cedar(Thuja plicata Donn.), western hemlock (Tsuga heterophylla Raf. Sarge)and salal(Gaultheria shallon Pursh) are the main species growing in cedar–hemlock forests on Vancouver Island, Canada. Based on the dominance of organic N in these systems, we tested the hypotheses that: (1) organic N can be utilized by the three plant species; and (2) salal, which is ericoid mycorrhizal and has high tannin concentration in its tissues, would absorb more N from the complex organic N compounds than the other two species. The abilities of cedar,hemlock and salal to take up 15 N, 13 C-labelled glutamic acid were measured and the capacities of the three species to use nitrate (NO 3 − ), ammonium (NH 4 + ), glutamicacid, protein and protein–tanninN were compared over a 20-day period. Based on 13 C enrichment, all three species absorbed at leasta portion of glutamic acid intact. Cedar, hemlock and salal also showed similar patterns of N uptake from the NO 3 − , NH 4 + , glutamic acid, protein and protein–tannin treatments. The largest propor- tions of applied N were taken up from the NO 3 − and NH 4 + treatments while smaller amountsof N were absorbed from the organic N compounds. Thus organic N was accessed to a modest degree by all three species, and salal did not have a greater capacity to utilize protein and protein–tannin–N. KeywordsProtein . Tannin . Mycorrhizae . Isotope Introduction Mycorrhizal and non-mycorrhizal plants from a variety o ecosystems have shown the capacity to take up organic forms of N, without the necessity of mineralization prior uptake. Nasholm et al. (1998)examined the uptake of 15 N, 13 C-labelled glycine by two trees, a shrub and a grass in a borealforest,and allfourwere found to contain enriched levels of the two isotopes, strongly suggesting thatatleasta portion ofthe amino acid was absorbed intact(Nasholm et al. 1998).Similar investigations have been conducted with plants in arctic tundra (Schimel an Chapin 1996), boreal (Nordin etal. 2001;Persson et al. 2003),alpine (Lipson and Monson 1998; Lipson etal. 1999;Miller and Bowman 2003), and sub-tropical Euca- lyptusforest(Turnbullet al. 1995) and agricultural (Nasholm etal. 2000)systems, and all the examined species demonstrated the ability to take up amino acids Based on uptake kinetics and soil amino acid concentra- tions,simple organic N compounds are thought to meet 50–100% of the N required by plants in alpine ecosystem (Lipson et al. 2001)and account for 10–82% of N potentiallyabsorbedby plantsin arcticecosystems (Chapin etal. 1993;Kielland 1994). In some studies, applied amino acids were taken up in similar quantities NH 4 + or NO 3 − , further highlighting the potential impor- tance of simple organic N in some systems (Schimel and Chapin 1996; Nasholm et al. 2000;Nordin etal. 2001; Miller and Bowman 2003). More complexorganiccompoundsmay also be important sources of N. In controlled laboratory studies using plants infected with single strains of fungi, ecto- a ericoid mycorrhizal plants were able to grow on a variet of organic N compounds including amino sugars (Kerley and Read 1995), chitin (Kerley and Read 1995), peptides (Bajwa and Read 1985) and larger proteins (Abuzinadah and Read 1986; Finlay et al. 1992). Griffiths and Caldwe (1991)showedthat ectomycorrhizal fungi found in coniferous forests were able to utilize N from insoluble protein–tannin complexes. However, four ectomycorrhiz fungistudied by Bending and Read (1996) did not show J. N. Bennett (*) Forestry Department, North Carolina State University, 3106 Jordan Hall, Raleigh, NC, 27601-8008, USA e-mail: jbennett@ncsfnc.cfr.ncsu.edu Fax: +1-919-513-4041 C. E. Prescott Forest Sciences Department, University of British Columbia, 3041-2424 Main Mall, Vancouver, BC, Canada, V6T 1Z4