HR: 1330h
AN: C42A-1011    [PDF]
TI: Soil nitrogen dynamics during seasonal transitions: N retention and loss in ecosystems of the Sierra Nevada, California
AU: * Miller, A E
EM: amy@icess.ucsb.edu
AF: University of California, Santa Barbara, Dept. of Ecology, Evolution & Marine Biology, Santa Barbara, CA 93106 United States
AU: Sickman, J O
EM: jsickman@Uno.edu
AF: University of New Orleans, Dept. of Geology & Geophysics, New Orleans, LA 70148 United States
AU: Schimel, J P
EM: schimel@lifesci.ucsb.edu
AF: University of California, Santa Barbara, Dept. of Ecology, Evolution & Marine Biology, Santa Barbara, CA 93106 United States
AU: Melack, J M
EM: melack@lifesci.ucsb.edu
AF: University of California, Santa Barbara, Dept. of Ecology, Evolution & Marine Biology, Santa Barbara, CA 93106 United States
AU: Meixner, T
EM: tmeixner@mail.ucr.edu
AF: University of California, Riverside, Dept. of Environmental Sciences, Riverside, CA 92521 United States
AB: The maintenance of nitrogen (N) limitation in many terrestrial ecosystems may be mediated by N losses that occur during seasonal transitions. In the southern Sierra Nevada, short-duration nitrate pulses associated with spring snowmelt in the alpine, and with fall rains at lower elevations, may account for greater than 90% of annual DIN export. To evaluate the role of microbial processes in mediating such losses of N, we examined overwinter variation in soil N dynamics at a high (2800 m) and low (750 m) elevation site. The fall transition marked a period of intense nitrifier activity at both sites: field incubations showed five-fold to 30-fold increases in soil NO$_{3}$$^{-}$ pools with the onset of fall freeze-thaw and rewetting events, followed by 60%-75% decreases in total soil inorganic N and net N mineralization rates. Nitrogen held in microbial biomass decreased significantly at the alpine site but recovered to growing-season levels under snowpack, indicating biotic sequestration of N. With the onset of spring snowmelt, microbial biomass again decreased, producing an increase in soil inorganic N concentrations and a shift from net N$_{2}$O consumption to production. These results, paired with results of laboratory incubations, indicate that physical disturbances incurred during seasonal transitions may enhance nitrification and gaseous losses from soil, and that large fluctuations in microbial biomass may regulate N production and export in these systems.
DE: 0400 Biogeosciences
DE: 1806 Chemistry of fresh water
DE: 1860 Runoff and streamflow
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2003 Fall Meeting