SLIDE 1 Hydraulic limits on tree performance
Transpiration, carbon gain and growth
by
Mel Tyree
USDA Forest Service Northeastern Experiment Station Burlington, Vermont USA
SLIDE 2 Soil-plant continuum model
and the Cohesion-Tension Theory Connects:
- Soil water potential, Ψsoil
- Leaf water potential, ΨL
- Transpiration, E
- Plant hydraulic resistance (Rplant) or conductance (Kplant)
plant soil plant soil L
K E E R − Ψ = − Ψ = Ψ
SLIDE 3 Ci
Stomatal response curve ACi curve of photosynthesis Lockhart growth curve
SLIDE 4
SLIDE 5
CASE ONE Does tree size affect tree hydraulics and performance?
Answers from a study on sugar maple Acer saccharum
SLIDE 6
Shoot hydraulics versus basal diameter (D): Kshoot = 0.06 D1.402 Shoot leaf area versus basal diameter (D): AL = 4667 D2.007
SLIDE 7
From the previous slide and our plant-model we can compute:
ΨL ≅ - 1.6x105 D0.605 E Which means: As maple trees get larger ΨL grows more negative. But this is a problem for stomatal conductance because⇒
SLIDE 8 Stomatal conductance, gs, declines with ΨL
0.0 40 80 120 160 200 240 Stomatal conductance, mmol s-1m-2 Leaf water potential, MPa
gs is linked to E because: E = gs ∆X where ∆X is the difference in ‘humidity’ between the leaf and the outside air.
SLIDE 9 Kplant, kg s-1MPa-1
0.0001 0.001 0.01 0.1
Theoretical maximum gs, mmol s-1m-2
20 40 60 80 100 120 140 160 180 200 <0.03 <0.06 <0.1 <0.25 <0.5
Kplant/AL, kg s-1m-2MPa-1
0.8 2 3 5 8 1 10
Theoretical maximum gs, mmol s-1m-2
20 40 60 80 100 120 140 160 180 200
x10-5
Putting all this together we can figure out how changes in tree size affect gs
SLIDE 10
CASE TWO Is there evidence that short-term changes in plant conductance changes performance?
Answers from a study on a pine Pinus ponderosa
SLIDE 11
Pinus ponderosa Hubbard et al 2001 Shows the effect of short term changes on plant hydraulic conductance caused by embolism = xylem dysfunction
SLIDE 12
CASE THREE Is there an observable relationship between plant hydraulic conductance and tree performance?
Answers from surveys of sapling to mature trees in field studies.
SLIDE 13
SLIDE 14
CASE FOUR Are differences in plant hydraulic conductance manifested from the seedling stage?
Answers from comparisons of slow growing and fast growing seedlings of tropical trees.
SLIDE 15 k / DW, kg s-1MPa-1gDW-1X10-7 10 20 30 40
Roots Shoots Species
Tt Pr Gs Am Ma
k/ AL, kg s-1MPa-1m-2X10-5
2 4 6 8 10
A comparison of light-demanding (fast growing) seedlings to shade-tolerant (slow growing) seedling all under intermediate light regime.
Fast growing:
- Am = Apeiba membranacea
- Ma = Miconia argentia
Slow growing:
- Tt = Trichiliaq tubersculata
- Pr = Pouteria reticulata
- Gs = Gustavia superba
SLIDE 16 CONCLUSIONS
Based on the above and my experiences in the tropics generally
There are a number of necessary conditions for rapid tree growth
High Kplant/AL High photosynthetic capacity of leaves Low leaf-area index Resistance to pests (at least some) Cold tolerance (in temperate climates)
SLIDE 17
Fast-growing Eucalyputs hybrids grown my MONDI of South Africa
SLIDE 18
Thank you! I hope that some day you will visit the beautiful State of Vermont.
