PARENT SESSION
Oral Session #98: Carbon and Nitrogen Cycling: N-addition, N-flux.
Presiding: C. Hoover
Friday, August 9. 9:00 AM to 12:00 PM. Greenlee Meeting Room, TCC.

Isotopic and genetic assessments of ectomycorrhizal turnover under N-fertilization.

Treseder, Kathleen^*,1, Masiello, Caroline², Lansing, Jennifer¹, Allen, Michael³, ¹ Dept of Biology, Philadelphia, PA² Center for Accelerator Mass Spectrometry, Livermore, CA³ Center for Conservation Biology, Riverside, CA

ABSTRACT- One potential effect of anthropogenic nitrogen deposition is a shift in biomass and turnover of soil microbes, with ensuing consequences for soil carbon dynamics. Genetic analyses were coupled with radiocarbon dating to examine effects of N fertilization on age of ectomycorrhizal fungi collected from a pinyon and juniper woodland in the Sevilleta LTER. Ectomycorrhizas were frequently present on roots of pinyon pine (72–205 ectomycorrhizal tips/m root). However, their abundance did not vary significantly with fertilization treatment. Ectomycorrhizas collected in August and December 2000 had mean ¹⁴C values of 109.9 ‰ ±3.4 ‰ and 99.5 ‰ ±3.1 ‰, respectively, across all sites. These signatures correspond to tissue ages of approximately 2–3 years. Radiocarbon signatures did not vary between N treatments. In addition, the four most abundant genotypes did not differ significantly from one another in ¹⁴C signature, nor was there a significant genotype-by-fertilization interaction. However, one genotype tended to have a shorter lifespan under N-fertilization than in the control plots, whereas the other three genotypes had the opposite response. We conclude that N deposition is not likely to alter the sequestration or turnover of carbon in ectomycorrhizal fungi in this system.

KEY WORDS: RFLP, radiocarbon, soil microbes, lifespan