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OXYGEN ISOTOPE IN PHOSPHATE: CAN IT WORK IN THE SOIL/PLANT SYSTEM?

OXYGEN ISOTOPE IN PHOSPHATE: CAN IT WORK IN THE SOIL/PLANT SYSTEM?. F.Tamburini, SM. Bernasconi, V. Pfahler, E. Frossard. Why d 18 O-PO 4 in soils?.

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OXYGEN ISOTOPE IN PHOSPHATE: CAN IT WORK IN THE SOIL/PLANT SYSTEM?

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  1. OXYGEN ISOTOPE IN PHOSPHATE: CAN IT WORK IN THE SOIL/PLANT SYSTEM? F.Tamburini, SM. Bernasconi, V. Pfahler, E. Frossard

  2. Why d18O-PO4 in soils? • Stable isotopes are used to identify biogeochemical and physical processes and trace sources. They also allow to study long-term evolution of signals and are not dangerous for the environment. • P has only one stable isotope (31P)… • But phosphate has 4 oxygen atoms. This is the only stable isotope approach to study P cycling. • Different sources have distinctived18O-PO4 signatures (e.g. mineral fertilizer vs manure). • At conditions found in soils, only biologically-driven processes can change the d18O-PO4 signature.

  3. How does this work? 18O P 16O

  4. Theory - 1 • There is little fractionation associated to inorganic processes such as adsorption, precipitation and dissolution. • Inorganic hydrolysis of condensed phosphates promotes incorporation of water oxygen w/out any fractionation. • Organisms preferentially take up the lighter isotopologue.df – di = e ln(x)

  5. Theory - 2 • Intracellular phosphatases promote a T-dependent equilibrium between PO4 and H2O T (°C) = 111.4 – 4.3(d18OPO4 – d18OH2O) • PO4 released by extracellular phosphatases will partly inherit O from the original molecule and partly exchange and fractionate O with H2O.df = x(di) + (1-x)(d18OH2O + e)

  6. d18O-PO4 in the soil/plant system

  7. Preparation and analysis TCEA/IRMS Tamburini et al., EJSS (early view)

  8. Case study 1 – Plant uptake PDC-20 Verena Pfahler et al. Effects of plant uptake on the δ18O signature of phosphate ??? ‰ Organisms preferentially take up the lighter isotopologue. df – di = e ln(x) e for E. coli = -3 ‰ (Blake et al., 2005)

  9. Case study 2- Soil development BigLink Project 2007-2010 Damma glacier forefield (Switzerland)

  10. Case study 2- Soil development Pase data (2007) from E. Bünnemann Apatite signature OM signature T-dependent equilibrium biological cycling Imprint from extracell. enzymes

  11. Case study 2- Soil development Resin-P 07.2010 Resin-P 09.2007 HCl-P d18O-PO4 in plant > +20‰ d18O-PO4 atT-equilibrium +11.5‰ __ +15‰ d18O-PO4 in apatite ~ +6‰

  12. Case study 3 – Source tracing COST Action 869 Prediction of contributing areas for P-losses from agricultural land (Claudia Hahn) Baldeggersee (Switzerland)

  13. Case study 3 – Source tracing d18O-PO4 in plant residues > +20‰ d18O-PO4 in soils (res-P) +18‰ __ +19‰ d18O-PO4 at T-equilibrium +13.5‰ __ +14.8‰ d18O-PO4 in manures +11‰ __ +13‰

  14. Wrapping up • The answer is YES • The use of d18O-PO4 in the soil/plant system is really promising, but it is still in its infancy. • The developed conceptual models are giving a good prediction on what to expect. • As for other isotopic systems, the “good” use of d18O-PO4 to understand the dynamics of P in soils is bound to our knowledge of the individual fractionation processes and of the complex interplay between them.

  15. 2012 in Ascona Developments in the understanding of processes in the P cycle: new concepts from the use of isotopic tracers

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