Enrichment of leaf & leaf-transpired water – beyond Craig & Gordon –

1. Enrichment of leaf & leaf-transpired water – beyond Craig & Gordon – Matthias Cuntz Research School of Biological Sciences (RSBS), ANU, Canberra, Australia Jérôme Ogée, Philippe Peylin Laboratoire des Sciences du Climat et de l’Environnement (LSCE), Gif-sur-Yvette, France Graham D. Farquhar, Lucas A. Cernusak Research School of Biological Sciences (RSBS), ANU, Canberra, Australia

2. Leaf water enrichment? • Strong influence on atmospheric water vapour (18O, D) • Partition evaporation from transpiration • Dew uptake • Water redistribution in soils by trees • Water recycling • Determines isotopic composition of plant organic matter (18O, D) • Determine physiological and genetic changes in stomatal conductance and crop yield • Resource utilisation of mistletoes • Paleo-climatic reconstructions (e.g. tree rings) • Important determinant of 18O in O2 (Dole effect) • Paleo-reconstructions of terrestrial vs. marine productivity • Synchronisation tool between different paleo records • Important determinent of 18O in CO2 • Partition net CO2 exchange in assimilation and respiration

3. Steady-state: Craig & Gordon Rv RE Re or Re RE RE stoma Craig & Gordon equation: Re Steady-state: RE=Rs Two compartments: RL=f1Re+(1-f1)Rs RL=Re xylem Rs

4. Steady-state: Péclet effect RE stoma x Re Rs xylem R

5. The effective length: Leff RE stoma x Re LL Leff=k·LL Rs xylem

6. Leaf geometry à la Farquhar & Lloyd RE stoma Re Dx D=Dx LL Leff=kLL Rs v=vxk vx=E/C xylem

7. The effective length à la Farquhar & Lloyd: Leff RE stoma Re k1·LL k4·LL k2·LL LL k3·LL Rs xylem

8. The effective length à la Cuntz (or à la soil): Leff RE stoma Re k1·LL k4·LL k2·LL LL k3·LL Rs xylem

9. Leaf geometry à la Cuntz (or à la soil) RE Cuntz Farquhar stoma Re D LL vxki vx=E/C Rs xylem

10. Leaf geometry of dicotyledon leaf • Tortuous path: • air space  QL • through aquaporines • or around mesophyll • cells  t •  k = QL·t • Leff(t) if QL(t) or t(t) For example: leaf water volume aquaporine stimulation

11. Experimental determination of Leff #1 valid only if Leff = const  E

12. Experimental determination of Leff #2 up down with Leff,up = const and Leff,down = const • Is one Leff enough to describe the problem? •  Can we take Leff=const?

13. One Leff? #1 (lupinus angustifolius - clover)

14. One Leff? #2

15. Take Leff=const? The answer to this exciting questions is just a few slides away.

16. Isotopic leaf water balance E·RE stoma Re, De RL, DL VL xylem Js·Rs

17. Farquhar & Cernusak (in press) E·RE stoma Re, De RL, DL VL xylem Js·Rs

18. Advection-diffusion equation Advection: v·R Diffusion: D·dR/dx Boundary conditions: at xylem: vRs at stoma: vRE

19. Comparison of different descriptions

20. Is the brave assumption (f1 always valid) justified?Is taking VL=const, i.e. Leff=const justified?

21. Comparison of different descriptions (repeat)

22. Summary (up to now) • Revise thinking about leaf geometry • i.e., one cannot think about the leaf water isotope path • as tortuous tubes because there is mixing between tubes. • It is the reduced diffusion in x-direction that determines • Leff not the enhanced advection speed. • There are several Péclet effects inside one leaf (upper/lower). • Measurements give the water volume weighted average. • Leff is not constant in time anymore. But: • Taking just one single Leff seems to be sufficient. • Taking also Leff=const in time seems to be justifiable. • The assumption that f1 of the Péclet effect holds for non-steady-state is valid during most of the time, except for for late afternoon/early evening. This leads to an under- estimation of leaf water enrichment during afternoon and night.

23. Saving private Dongmann Dongmann et al. (1974), Bariac et al. (1994): Cernusak et al. (2002): Farquhar & Cernusak (in press):

24. Difference between Dongmann and Farquhar Farquhar & Cernusak (in press): Dongmann et al. (1974):

25. Dongmann-style solving

26. Dongmann-style solutions

27. Evaporating site ≡ evaporated water

28. Isoflux

29. Summary (for second part) • Leaf water volume change seems to be negligible for DL • Gradient in leaf is important for DL (Péclet effect, f1) • The error done in the afternoon when using Farquhar & Cernusak’s equation for DL is passed on to evening and night • For water at the evaporating site De: Dongmann and Farquhar give essentially the same results and both compare well with observations • For the isoflux EDE: even steady-state Craig & Gordon appropriate Beware of high night-time stomatal conductance

30. FIN