HR: 1340h
AN: B23D-1597    [Abstracts]
TI: Abiotic Immobilization of Nitrate in Forest Soils: a Double Label Approach
AU: * MacLean, R W
EM: rwb5@cisunix.unh.edu
AF: Complex Systems Research Center University of New Hampshire, Morse Hall 39 College Way, Durham, NH 03820, United States
AU: * MacLean, R W
EM: rwb5@cisunix.unh.edu
AF: Department of Natural Resources University of New Hampshire, 215 James Hall 56 College Rd, Durham, NH 03820, United States
AU: Ollinger, S V
EM: scott.ollinger@unh.edu
AF: Complex Systems Research Center University of New Hampshire, Morse Hall 39 College Way, Durham, NH 03820, United States
AU: Ollinger, S V
EM: scott.ollinger@unh.edu
AF: Department of Natural Resources University of New Hampshire, 215 James Hall 56 College Rd, Durham, NH 03820, United States
AU: Hobbie, E A
EM: hobbie@solo.sr.unh.edu
AF: Complex Systems Research Center University of New Hampshire, Morse Hall 39 College Way, Durham, NH 03820, United States
AU: Frey, S D
EM: Serita.Frey@unh.edu
AF: Department of Natural Resources University of New Hampshire, 215 James Hall 56 College Rd, Durham, NH 03820, United States
AU: Dail, D B
EM: bryan.dail@maine.edu
AF: Department of Plant, Soil, and Environmental Sciences University of Maine, 5722 Deering Hall, Orono, ME 04469, United States
AB: Mechanisms of soil nitrogen (N) retention remain a key uncertainty in the terrestrial N cycle. During recent work at the Harvard Forest Chronic N Experiment, ¹⁵N added to soils as ammonia nitrate was observed to be rapidly immobilized after addition to soil on a time scale of minutes. In published results it was hypothesized that the rapid time of immobilization could be explained by abiotic immobilization of both ammonia and nitrate. The possibility of abiotic immobilization of nitrate has been studied since the first half of the 20th century, mainly using ideal compounds and soil sterilization techniques. However, critics of these studies have argued that while in vitro studies may indicate the possibility of an abiotic reaction, they cannot demonstrate its plausibility in soils. Soil sterilization methods have been criticized, because they are not effective enough to eliminate biotic interactions within an experimental treatment. Isotopic tracer studies have also been used but also have problems differentiating biotic and abiotic reactions. This study is an attempt to demonstrate abiotic immobilization of nitrate in soil samples through the use of double labeled nitrate (¹⁵N¹⁸O₃^- ). The resolution of this method depends on the biochemistry of microbial immobilization of nitrate; reduction of nitrate to nitrite, then ammonia and glutamine before incorporation into microbial biomass. Reduction of ¹⁵N¹⁸O₃^- before microbial utilization of the ¹⁵N implies that retention of both heavy isotopes in the soil can only occur through abiotic reaction of ¹⁵N¹⁸O_x species. In biotic immobilization the ¹⁸O is lost to the system in water. While nitrate has proven unreactive in soils, its reduced product, nitrite, is known to be readily reactive with various soil compounds. Nitrite can be introduced into the soil environment naturally by both ‘leakiness' in nitrification and denitrification and may possibly be generated abiotically through methods such as the proposed Ferrous Wheel hypothesis. Samples of the O-horizon of Harvard Forest red pine soils were incubated at several short intervals (15 m, 1 h, 4 h), based on previous observations made at Harvard Forest, under both anoxic and oxygenated conditions. Following incubation, KCl extraction of available N, and freeze drying, isotopic enrichment was determined by EA/TCEA Mass Spectroscopy. Preliminary results showed a significant enrichment in ¹⁵N and a small but significant enrichment in ¹⁸O. The full results of the experiment will be available by the Fall meeting.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0463 Microbe/mineral interactions
DE: 0469 Nitrogen cycling
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting