Transcript Oxygen isotope in phosphate: Can It Work in the soil/plant
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?
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 ( 31 P)… But phosphate has 4 oxygen atoms. This is the only stable isotope approach to study P cycling.
Different sources have distinctive mineral fertilizer vs manure).
d 18 O-PO 4 signatures (e.g.
At conditions found in soils, only biologically-driven processes can change the d 18 O-PO 4 signature.
How does this work?
P 16 O 18 O
Theory - 1
① There is little fractionation associated to inorganic processes such as adsorption, precipitation and dissolution. ② Inorganic hydrolysis of condensed phosphates promotes incorporation of water oxygen w/out any fractionation. ③ Organisms preferentially take up the lighter isotopologue.
d f – d i = e ln(x)
Theory - 2
④ Intracellular phosphatases promote a T-dependent equilibrium between PO 4 and H 2 O T ( ° C) = 111.4 – 4.3( d 18 O PO4 – d 18 O H2O ) ⑤ PO 4 released by extracellular phosphatases will partly inherit O from the original molecule and partly exchange and fractionate O with H 2 O.
d f = x( d i) + (1-x)( d 18 O H2O + e ) d
18 O-PO 4 init.
+15 ‰ +15 ‰ d
18 O-H 2 O
-2 ‰ -2 ‰
T
°
C
15 ° C e
(fract. factor)
-30 ‰ (Apase) d
18 O-PO 4 fin.
+20.4 ‰ +3.3 ‰
d 18
O-PO
4
in the soil/plant system
Preparation and analysis
TCEA/IRMS
Tamburini et al., EJSS (early view)
Case study 1 – Plant uptake
??? ‰
PDC-20 Verena Pfahler et al.
Effects of plant uptake on the δ 18 O signature of phosphate
Organisms preferentially take up the lighter isotopologue.
d f – d i = e ln(x) e for
E. coli
= 3 ‰ (Blake et al., 2005)
[PO 4 3 ] PO 4 3 used
45% d
18 O-PO 4 initial
+12.4 ‰ d
18 O-PO final
+11.3 ‰
4
e
(fract. factor)
0.5 mM (4 mmoles) 0.05 mM (0.4 mmoles) 0.02 mM (0.16 mmoles) 98% 96% +12.4 ‰ +12.4 ‰ +17.7 ‰ +21.9 ‰ -2.5 ‰ -3.1 ‰
Case study 2- Soil development
BigLink Project 2007-2010 Damma glacier forefield (Switzerland)
Case study 2- Soil development
Apatite signature T-dependent equilibrium biological cycling Pase data (2007) from E. Bünnemann OM signature Imprint from extracell.
enzymes
Case study 2- Soil development
Resin-P 07.2010
Resin-P 09.2007
HCl-P d 18 O-PO 4 in plant > +20‰ d 18 O-PO 4 at T-equilibrium +11.5‰ __ +15‰ d 18 O-PO 4 in apatite ~ +6‰
Case study 3 – Source tracing
COST Action 869 Prediction of contributing areas for P-losses from agricultural land (Claudia Hahn) Baldeggersee (Switzerland)
Case study 3 – Source tracing
d 18 O-PO 4 in plant residues > +20‰ d 18 O-PO 4 in soils (res-P) +18‰ __ +19‰ d 18 O-PO 4 at T-equilibrium +13.5‰ __ +14.8‰ d 18 O-PO 4 in manures +11‰ __ +13‰
Wrapping up
The answer is YES The use of d 18 O-PO 4 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 d 18 O PO 4 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.
2012 in Ascona
Developments in the understanding of processes in the P cycle: new concepts from the use of isotopic tracers