The role of ectomycorrhizal fungi in nitrogen acquisition in California oak woodlands

In northeastern California oak woodland, we measured nitrogen uptake by ectomycorrhizal (ECM) oak roots (Quercus douglasii, blue oak, Q. wislizeni, live oak). In February 2005, after sampling fine roots of 5 blue and 5 live oaks, we added ¹⁵NH₄ to soils, waited one month then re-sampled. ECM root tips were separated into 21 morphotypes and analyzed for ¹⁵N. Blue oak ECM diversity was higher than that in live oak. Few morphotypes (33%) were common to both oak species. More abundant morphotypes took up less ¹⁵N than less abundant morphotypes. We hypothesized that ECM species more active in N uptake would be more frequent in soil cores. However, our data did not support our hypothesis; and ECM species present in few cores were more enriched in ¹⁵N than species present in many soil cores. We believe our data are the first to demonstrate functional biodiversity of ECM fungi for N uptake.