HR: 1340h
AN: B43A-0894    [Abstracts]
TI: Recent Advances in Stable Isotope Techniques for N2O Source Partitioning in Soils
AU: * Baggs, E
EM: e.baggs@abdn.ac.uk
AF: University of Aberdeen, School of Biological Sciences (Plant & Soil Science) St Machar Drive, Aberdeen, AB24 3UU, United Kingdom
AU: Mair, L
EM: l.mair@abdn.ac.uk
AF: University of Aberdeen, School of Biological Sciences (Plant & Soil Science) St Machar Drive, Aberdeen, AB24 3UU, United Kingdom
AU: Mahmood, S
EM: s.mahmood@abdn.ac.uk
AF: University of Aberdeen, School of Biological Sciences (Plant & Soil Science) St Machar Drive, Aberdeen, AB24 3UU, United Kingdom
AB: The use of 13C, 15N and 18O enables us to overcome uncertainties associated with soil C and N processes and to assess the links between species diversity and ecosystem function. Recent advances in stable isotope techniques enable determination of process rates, and are fundamental for examining interactions between C and N cycles. Here we will introduce the 15N-, 18O- and 13C-enrichment techniques we have developed to distinguish between different N2O-producing processes in situ in soils, presenting selected results, and will critically assess their potential, alone and in combination with molecular techniques, to help address key research questions for soil biogeochemistry and microbial ecology. We have developed 15N- 18O-enrichment techniques to distinguish between, and to quantify, N2O production during ammonia oxidation, nitrifier denitrification and denitrification. This provides a great advantage over natural abundance approaches as it enables quantification of N2O from each microbial source, which can be coupled with quantification of N2 production, and used to examine interactions between different processes and cycles. These approaches have also provided new insights into the N cycle and how it interacts with the C cycle. For example, we now know that ammonia oxidising bacteria significantly contribute to N2O emissions from soils, both via the traditionally accepted ammonia oxidation pathway, and also via denitrification (nitrifier denitrification) which can proceed even under aerobic conditions. We are also linking emissions from each source to diversity and activity of relevant microbial functional groups, for example through the development and application of a specific nirK primer for the nitrite reductase in ammonia oxidising bacteria. Recently, isotopomers have been proposed as an alternative for source partitioning N2O at natural abundance levels, and offers the potential to investigate N2O production from nitrate ammonification, and overcomes the need to apply 18O-H2O to determine nitrifier denitrification. However, this only provides an estimated, not a quantified, contribution, and further developments are required for quantification using isotope enrichment. Despite some limitations, such techniques become even more powerful when linked with other recent developments, such as nanoSIMS, gene expression and 13C-stable isotope probing of microbial RNA, and when linked to other disciplines. These may help address remaining questions such as: which microbes are producing N2O in soil, what is the influence of plants and mycorrhizal fungi on rhizosphere processes, and where is denitrification occurring in soil?
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0469 Nitrogen cycling
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting