PARENT SESSION
Oral Session 15: Soil Ecology I: Mycorrhizal Communities.
Presiding: V Borowicz and X He
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room D 137.
Teasing apart different functional groups of soil microbiota.
Lucas, Richard*,1, Jackson, John2, 1 University of Pennsylvania, Philadelphia, PA2 Stroud Water Research Center, Avondale, PA
ABSTRACT- Soil microbiota such as ectomycorrhizal fungi are known to be important in nitrogen cycling in forest ecosystems. However, it has been very difficult to examine the functional responses of ectomycorrhizal fungi in isolation in field experiments. This study used in-growth mesh bags (30 
m mesh size) and root trenching with PVC pipe in combination with six different nitrogen fertilization treatments (glutamic acid, creatine, N-acetylglucosamine, nitrate, ammonium, and control) in a two-way factorial arrangement to isolate separate functional groups of the soil microbial community and evaluate their response to different forms of nitrogen fertilization in the field. Using a hybrid phospholipid fatty acid (PLFA) — fatty acid methyl ester (FAME) technique, lipids from soil samples were extracted, identified, and quantified to give a fingerprint of the soil microbial community in each treatment. Two fatty acids typically used as markers specific to fungi (18:1 
9c and 18:2 6,9c) comprised a large proportion of the soil microbial community (26 ± 4% and 7 ± 1% respectively) and were significantly greater in samples taken from within in-growth bags than samples taken from outside in-growth bags both before and after nitrogen treatments were applied. Following nitrogen addition, fungal biomass from samples taken within in-growth bags significantly increased in treatments receiving glutamic acid, nitrate and ammonium nitrogen additions. Results show that it is possible to separate functional groups of soil microbial communities in field experiments, and that natural fungal communities are able to make use of organic sources of nitrogen.
Key words: PLFA, ectomycorrhizae, organic nitrogen