Rapid nitrogen transfer from ectomycorrhizal pines to adjacent ectomycorrhizal and arbuscular mycorrhizal plants in a California oak woodland

Nitrogen transfer among plants in a California oak woodland was examined in a pulse-labeling study using 15N. The study was designed to examine N movement among plants that were mycorrhizal with ectomycorrhizas (EM), arbuscular mycorrhizas (AM), or both. Isotopically enriched N (K15NO3-) was applied to gray pine (Pinus sabiniana) foliage (donor) and traced to neighboring gray pine, blue oak (Quercus douglasii), buckbrush (Ceanothus cuneatus) and herbaceous annuals (Cynosurus echinatus, Torilis arvensis and Trifolium hirtum). After 2 wk, needles of 15N-treated pines and foliage from nearby annuals were similarly enriched, but little 15N had appeared in nontreated (receiver) pine needles, oak leaves or buckbrush foliage. After 4 wk foliar and root samples from pine, oak, buckbrush and annuals were significantly 15N-enriched, regardless of the type of mycorrhizal association. The rate of transfer during the first and second 2-wk periods was similar, and suggests that 15N could continue to be mobilized over longer times.