HR: 0830h
AN: B41C-0903    [PDF]
TI: Variation in Gross Nitrogen Mineralization and Microbial Communities Along a Chronosequence of Lodgepole Pine ({\it Pinus contorta}) Stands, Yellowstone National Park
AU: * Smithwick, E A
EM: easmithwick@wisc.edu
AF: Department of Zoology University of Wisconsin-Madison, Birge Hall 430 Lincoln Drive, Madison, WI 53706 United States
AU: Turner, M G
EM: mgt@mhub.zoology.wisc.edu
AF: Department of Zoology University of Wisconsin-Madison, Birge Hall 430 Lincoln Drive, Madison, WI 53706 United States
AU: Metzger, K M
EM: klmetzger@wisc.edu
AF: Department of Zoology University of Wisconsin-Madison, Birge Hall 430 Lincoln Drive, Madison, WI 53706 United States
AU: Balser, T C
EM: tcbalser@facstaff.wisc.edu
AF: Department of Soil Science University of Wisconsin-Madison, 1525 Observatory Drive, Madison, WI 53706 United States
AB: Soils and vegetation were analyzed in 20 forest stands in Yellowstone National Park, Wyoming, USA that varied in age from 50 to 350 years and had initiated following stand-replacing fire. Our goal was to determine how nitrogen (N) availability (NH$_{4}$$^{+}$) varied among post-fire, mature lodgpole pine ({\it Pinus contorta}) stands and to determine whether that variability was related to stand age, stand tree density, microbial community composition and aboveground net primary productivity (ANPP). Gross N mineralization was measured using a laboratory isotopic dilution technique, and microbial community composition was measured using a hybrid Fatty-Acid-Methyl-Esther/ Phospho-Lipid Fatty Acid procedure. Gross nitrogen mineralization rates ranged from 0.3 to 4.2 $\mu$gN g soil$^{-1}$ d$^{-1}$ (average=1.44$\pm$0.24 $\mu$gN g soil$^{-1}$ d$^{-1}$). Gross N mineralization rates declined with increasing stand age: 2.11 $\pm$ 0.41 (50-100 yr), 1.83 $\pm$ 0.75 (125-175 yr), 0.99 $\pm$ 0.24 (200-250 yr), 0.82 $\pm$ 0.21 (300-350 yr). Gross mineralization rates in the 50-100 age class were significantly higher than in the 200-250 and 300-350 age classes. Gross mineralization was positively related to stand ANPP (p=0.0186, R$^{2}$=0.96), negatively related to stand foliar N averaged by age-class (p=0.0219, R$^{2}$=0.96), and was not significantly related to tree density. The first principal component (PC1), which explained 53% of the variation in microbial community composition, was correlated with age class. PC1 was strongly controlled by a fungal lipid (18:2 $\omega$6c). The proportion of microbial lipids in specified functional guilds differed among age classes but did not differ with stand density. These results are consistent with other studies reporting declines in N availability with increasing time-since-fire, which we attribute to changes in ANPP and changes in microbial community composition.
DE: 0400 Biogeosciences
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting