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Size mediates ageing: merging architectural complexity with cellular senescence M. Mencuccini

Size mediates ageing: merging architectural complexity with cellular senescence M. Mencuccini School of GeoSciences University of Edinburgh (UK). Structure of the talk. Our perspective on plant hydraulics The theoretical framework The approach Some results

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Size mediates ageing: merging architectural complexity with cellular senescence M. Mencuccini

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  1. Size mediates ageing: merging architectural complexity with cellular senescence M. Mencuccini School of GeoSciences University of Edinburgh (UK)

  2. Structure of the talk • Our perspective on plant hydraulics • The theoretical framework • The approach • Some results • Preliminary conclusions on our take of the age-related declines

  3. Our perspective. I: Interspecific convergence and significance of stature. • Almost isometric scaling • If life forms are not considered, scaling is not isometric (WBE b=1.0) • Significant intercept shifts predicted by model of biomass allocation. (Mencuccini, 2003)

  4. Our perspective. II: Significance of stature during stand development. Decline in NPP in Scots pine paralleled by decline in hydraulics and leaf area index (Mencuccini & Grace, 1996)

  5. Our perspective. III: Ecosystem processes Schulze et al (1999) Global Change Biology 5, 703-722 Law et al. (2004) Global Change Biology Siberian forest, pine chronosequence after fire

  6. a i l i l i-1 (West et al., 1999. Nature400, 664-667) a i-1 Theoretical framework. I: Hydraulics and architectural complexity The plant as a fractal-like structure of order N

  7. Theoretical framework. II: Ageing processes in plants • Maturation: progressive changes in the habitual behaviour of meristems leading up to adult reproductive maturity • Senescence: progressive loss of function accompanied by decreasing fertility and increasing mortality rate with age (population and individual) • Cellular senescence: irreversible changes in leaf physiological activity and growth triggered by gene expression with age

  8. the state of the art Ryan et al., 2004 NPPAg = GPP - Resp. - TBCA • Controlled study quantifying the complete carbon budget of developing stands for over six years (a full rotation) in replicated Eucalyptus plantations in Hawaii (final tree height ~ 25 m). • Results: • GPP decreases dramatically. • TBCA, if anything, decreases. • Respiration, if anything, decreases. • Hydraulic limitation hypothesis only partially supported.

  9. We need new approaches, experimental manipulations

  10. True senescence in monocarpic plants Inherent changes in meristems do occur: in pea plants, shoot meristems have a limited growth potential; true senescence does occur (Lockhart & Gottschall, 1961).

  11. Scots pine sycamore ash Different ages, different sizes Different ages, different sizes Different ages, same size Different ages, same size poplar 1994 1971 2003 1998 1975 2002 Different sizes, same age Different sizes, same age Same age, same size Same age, same size

  12. Our results: RGR(RGR=NAR x SLA x LMR) Mencuccini et al. (Ecology Letters, in press), Martinez-Vilalta et al. (submitted)

  13. Our results: NAR Mencuccini et al. (Ecology Letters, in press), Martinez-Vilalta et al. (submitted)

  14. Our results: SLA Mencuccini et al. (Ecology Letters, in press), Martinez-Vilalta et al. (submitted)

  15. Our results: gs Mencuccini et al. (Ecology Letters, in press), Martinez-Vilalta et al. (submitted)

  16. Species/ Param. Acer pseudoplatanus Fraxinus excelsior Pinus sylvestris Populus trichocarpa x deltoides grafts donors grafts donors grafts donors cuttings donors Anet ns -0.15** ns -0.24** n/a - ns ns %N ns -0.003* ns -0.07s ns -0.18** ns ns d13C ns 0.10* ns 0.14** ns 0.06** 0.04* ns Results Mencuccini et al. (Ecology Letters, in press), Martinez-Vilalta et al. (submitted)

  17. Size mediates ageing: merging architectural complexity with cellular senescence Ryan et al., 2004 • For very young plants there is alwaysa clear decline in growth rates which is stable upon grafting. • If genetic control is present at the beginning of the life cycle, it is not unreasonable to expect it to be present more or less throughout, and especially, at the end of the life cycle

  18. a i l i l i-1 (West et al., 1999. Nature400, 664-667) a i-1 A mechanism for the decline in hydraulic conductance: size-dependent hydraulic tapering The plant as a fractal-like structure of order N

  19. Do vessel and hydraulic tapering depend on size and/or age? Apex sycamore base 1.4m sycamore base 26m sycamore Petit et al. (in prep.)

  20. Synthesis • The “age-related” decline in growth is not an effect of age per se (i.e., cellular senescence) • Effect of tree height on tree hydraulics and water use possibly on all four species, but it does not seem to be the only driver of the decline in growth. • …a single cause for the “size-related” decline? • We have a potential mechanism to explain effects of height on tree hydraulics. Can we reconcile WBE with the data? • Do trees EVER age?

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