size mediates ageing: merging architectural complexity with cellular senescence m. mencuccini school...
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Size mediates ageing: merging Size mediates ageing: merging architectural complexity with architectural complexity with cellular senescencecellular senescence
M. Mencuccini
School of GeoSciencesUniversity of Edinburgh (UK)
Structure of the talkStructure of the talk
• Our perspective on plant hydraulics Our perspective on plant hydraulics • The theoretical framework The theoretical framework • The approachThe approach• Some resultsSome results• Preliminary conclusions on our take of the Preliminary conclusions on our take of the
age-related declinesage-related declines
Our perspective. I: Our perspective. I: Interspecific Interspecific convergence and convergence and significance of significance of stature. stature.
Almost isometric scalingIf life forms are not considered, scaling is not isometric (WBE b=1.0)Significant intercept shifts predicted by model of biomass allocation.
(Mencuccini, 2003)
Our perspective. II: Significance of stature Our perspective. II: Significance of stature during stand development.during stand development.
(Mencuccini & Grace, 1996)
Decline in NPP in Scots pine paralleled by decline in hydraulics and leaf area index
Schulze et al (1999) Schulze et al (1999) Global Global Change BiologyChange Biology 5, 703-722 5, 703-722
Siberian forest, pine Siberian forest, pine chronosequence after firechronosequence after fire
Law et al. (2004) Global Change Biology
Our perspective. III: Ecosystem processesOur perspective. III: Ecosystem processes
Theoretical framework. I: Hydraulics Theoretical framework. I: Hydraulics and architectural complexityand architectural complexity
(West et al., 1999. Nature 400, 664-667)a i-1
l i-1
a i
l i
The plant as a fractal-like structure of order N
Theoretical framework. II: Ageing Theoretical framework. II: Ageing processes in plantsprocesses 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
the state of the artthe state of the art
Ryan e
t al.,
20
04
NPPAg = GPP - Resp. - TBCA
Results:
GPP decreases dramatically.
TBCA, if anything, decreases.
Respiration, if anything, decreases.
Hydraulic limitation hypothesis only partially
supported.
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).
We need new approaches, We need new approaches, experimental manipulationsexperimental manipulations
True senescence in True senescence in monocarpic plantsmonocarpic plants
Inherent changes in meristems do occur: in pea plants, shoot meristems have a limited growth potential; true senescence does occur(Lockhart & Gottschall, 1961).
Different ages, different sizes Different ages, same size
Scots pine
sycamore
ash
poplar
Different sizes, same age Same age, same size
Different ages, different sizes Different ages, same size
Different sizes, same age Same age, same size
1971 20032002 1998
19941975
Our results: RGROur results: RGR(RGR=NAR x SLA x LMR)(RGR=NAR x SLA x LMR)
Mencuccini et al. (Ecology Letters, in press), Martinez-Vilalta et al. (submitted)
age, yrs
0 20 40 60 80 100 120 140 160
RG
R (
kg k
g-1
yr-1
)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Sycamore graftsSycamore donors
age, yrs
0 20 40 60 80 100 120
RG
R (
kg k
g-1
yr-1
)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Ash graftsAsh donors
age, yrs
0 50 100 150 200 250 3000.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
RG
R (
kg k
g-1
yr-1
)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Scots pine graftsScots pine donors
age, yrs
0 10 20 30
RG
R (
kg k
g-1
yr-1
)
0
1
2
3
4
5
6
Poplar cuttingsPoplar donors
P<0.0001 P<0.001
P<0.0001 P<0.0001
Our results: NAROur results: NAR
Mencuccini et al. (Ecology Letters, in press), Martinez-Vilalta et al. (submitted)
age, yrs
0 20 40 60 80 100 120 140 160
NA
R (
kg m
-2 y
r-1
)
0.0
0.2
0.4
Sycamore graftsSycamore donors
age, yrs
0 20 40 60 80 100 120
NA
R (
kg m
-2 y
r-1
)
0.0
0.2
0.4
Ash graftsAsh donors
age, yrs
0 50 100 150 200 250 300
NA
R (
kg m
-2 y
r-1
)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Scots pine graftsScots pine donors
P<0.01
P<0.05
P<0.05P<0.05
age, yrs
0 10 20 30
NA
R (
kg m
-2 y
r-1
)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Poplar donorsPoplar cuttings
P<0.05
Our results: SLAOur results: SLA
Mencuccini et al. (Ecology Letters, in press), Martinez-Vilalta et al. (submitted)
age, yrs
0 20 40 60 80 100 120 140 160
SLA
(m
2 kg
-1)
5
10
15
20
25
30
Sycamore graftsSycamore donors
age, yrs
0 20 40 60 80 100 120
SLA
(m
2 kg
-1)
5
10
15
20
25
30
35
40
Ash graftsAsh donors
age, yrs
0 50 100 150 200 250 300
SLA
(m
2 kg
-1)
1.5
2.0
2.5
3.0
3.5
4.0
Scots pine graftsScots pine donors
age, yrs
0 5 10 15 20 25 30 35
SLA
(m
2 kg
-1)
5
10
15
20
Poplar cuttingsPoplar donors
P<0.05
P<0.10
P<0.01
P<0.10
Our results: Our results: ggss
Mencuccini et al. (Ecology Letters, in press), Martinez-Vilalta et al. (submitted)
age, yrs
0 20 40 60 80 100 120 140 160
g s (
mm
ol m
-2 s
-1)
0
50
100
150
200
5
10
15
20
25
Sycamore graftsSycamore donors
age, yrs
0 20 40 60 80 100 120 140
g s (
mm
ol m
-2 s
-1)
0
50
100
150
200
250
0
5
10
15
20
25
30
Ash graftsAsh donors
age, yrs
0 50 100 150 200 250 300
g s (
mm
ol m
-2 s
-1)
0
50
100
150
200
250
Scots pine graftsScots pine donors
age, yrs
0 5 10 15 20 25 30 35
g s (
mm
ol m
-2 s
-1)
0
100
200
300
400
500
Poplar cuttingsPoplar donors
P<0.01P<0.10
P=0.05P<0.05
Species/Param.
Acer pseudoplatanus
Fraxinus excelsior
Pinus sylvestris Populus trichocarpa x
deltoides
grafts donors grafts donors grafts donors cuttings donors
Anetns -0.15** ns -0.24** n/a - ns ns
%N ns -0.003* ns -0.07s ns -0.18** ns ns
13C ns 0.10* ns 0.14** ns 0.06** 0.04* ns
ResultsResults
Mencuccini et al. (Ecology Letters, in press), Martinez-Vilalta et al. (submitted)
Size mediates ageing: Size mediates ageing: mergingmerging architectural architectural complexity with cellular complexity with cellular senescencesenescence
Ryan e
t al.,
20
04
If genetic control is present at the beginning of If genetic control is present at the beginning of
the life cycle, it is not unreasonable to expect it to the life cycle, it is not unreasonable to expect it to
be present more or less throughout, and be present more or less throughout, and
especially, at the end of the life cycle especially, at the end of the life cycle
For very young plants there is or very young plants there is alwaysalways a clear a clear
decline in growth rates which is stable upon grafting.decline in growth rates which is stable upon grafting.
A mechanism for the decline in A mechanism for the decline in hydraulic conductance: size-dependent hydraulic conductance: size-dependent
hydraulic taperinghydraulic tapering
(West et al., 1999. Nature 400, 664-667)a i-1
l i-1
a i
l i
The plant as a fractal-like structure of order N
Sycamore, Edinburgh March 2005
distance from tip, cm1 10 100
hyd
rau
lic r
esi
sta
nce
to ti
p,
MP
a s
cm
-2
10
100
1000 old fieldyoung fieldyoung graftedold grafted
b=0.34
b=0.36
b=0.38
b=0.67
(Petit et al., in prep.)
Do vessel and hydraulic tapering Do vessel and hydraulic tapering depend on size and/or age?depend on size and/or age?
Petit et al. (in prep.)
ApexApexsycamoresycamore
basebase1.4m1.4m
sycamoresycamore
basebase26m26m
sycamoresycamore
SynthesisSynthesis
• 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?