HR: 1340h
AN: B43A-0893    [Abstracts]
TI: Isotopic and Reporter Techniques to Verify Links Between Plant C Flow and Denitrification
AU: * Killham, K
EM: k.killham@abdn.ac.uk
AF: University of Aberdeen, School of Biological Sciences (Plant & Soil Science) St Machar Drive, Aberdeen, AB24 3UU, United Kingdom
AU: Prendergast, M
EM: m.prendergast@abdn.ac.uk
AF: University of Aberdeen, School of Biological Sciences (Plant & Soil Science) St Machar Drive, Aberdeen, AB24 3UU, United Kingdom
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
AB: The availability of organic C is considered paramount for the production and reduction of the greenhouse gas nitrous oxide (N2O) during denitrification in the rhizosphere. Despite this, the role of organic C in the regulation of N2O- and N2-genic enzymes is poorly understood. Stable isotopes are fundamental in resolving this. Here we will present selected results from experiments in which we have applied isotopic and reporter techniques to verify the effect of plant C in driving denitrification, and the potential feedbacks of this on climate change. Changes in C input to soil, such as under elevated atmospheric CO2, is significant for N2O production and reduction. Following application of 15N-labelled fertiliser to Lolium perenne swards we showed increased denitrifier-N2O and N2 production under elevated pCO2 (60 Pa) in the Swiss FACE experiment. This was attributed to greater below ground C allocation providing the energy for denitrification, and emissions were strongly positively correlated with TOC. By converting all rhizosphere soil to Redox conditions conducive to denitrification, rhizosphere C flow was quantified via N2O flux, and estimates agreed with measurements using 13C and 14C approaches. Little is known about the effect of different C substrates in regulating N2O and N2 production nor their effects on community structure, activity or species selection of denitrifying bacteria in the rhizosphere. We provide the first evidence for differences in N2O and N2 production with different C compounds typically present in root exudate, which suggest differences in regulation of the NO and N2O reductases, or preference for different C compounds in the rhizosphere denitrifier community. Such differences in gaseous N production are being related to the function and activity of the denitrifier community associated with this root C flow, with the link between C flow and denitrifier activity being verified by stable isotope probing and NanoSIMS imaging. Further ecophysiological evidence is presented of reporter gene expression by denitrifiers in response to different substrate classes of rhizosphere C.
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