Hydraulic limits on tree performance Transpiration, carbon gain and - PowerPoint PPT Presentation

Hydraulic limits on tree performance Transpiration, carbon gain and growth of trees by Mel Tyree USDA Forest Service Northeastern Experiment Station Burlington, Vermont USA

Soil-plant continuum model and the Cohesion-Tension Theory Connects: • Soil water potential, Ψ soil • Leaf water potential, Ψ L • Transpiration, E • Plant hydraulic resistance (R plant ) or conductance (K plant ) E Ψ = Ψ − = Ψ − R E L soil plant soil K plant

AC i curve of photosynthesis Stomatal response curve C i Lockhart growth curve

CASE ONE Does tree size affect tree hydraulics and performance? Answers from a study on sugar maple Acer saccharum

Shoot hydraulics versus basal diameter (D): K shoot = 0.06 D 1.402 Shoot leaf area versus basal diameter (D): A L = 4667 D 2.007

From the previous slide and our plant-model we can compute: Ψ L ≅ - 1.6x10 5 D 0.605 E Which means: As maple trees get larger Ψ L grows more negative. But this is a problem for stomatal conductance because ⇒

Stomatal conductance, g s , declines with Ψ L 240 g s is linked to E because: 200 Stomatal conductance, mmol s -1 m -2 E = g s ∆ X 160 120 where ∆ X is the difference 80 in ‘humidity’ between the 40 leaf and the outside air. 0 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 Leaf water potential, MPa

200 Putting all this together we 180 Theoretical maximum g s , mmol s -1 m -2 can figure out how changes 160 140 in tree size affect g s 120 100 80 60 <0.25 <0.03 <0.06 40 <0.5 <0.1 20 0.0001 0.001 0.01 0.1 K plant , kg s -1 MPa -1 200 180 Theoretical maximum g s , mmol s -1 m -2 160 140 120 100 80 60 40 20 0.8 1 2 3 5 8 10 x10 -5 K plant /A L , kg s -1 m -2 MPa -1

CASE TWO Is there evidence that short-term changes in plant conductance changes performance? Answers from a study on a pine Pinus ponderosa

Pinus ponderosa Hubbard et al 2001 Shows the effect of short term changes on plant hydraulic conductance caused by embolism = xylem dysfunction

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.

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.

40 k / DW, kg s -1 MPa -1 gDW -1 X10 -7 A comparison of light-demanding 30 Roots (fast growing) seedlings to Shoots 20 shade-tolerant (slow growing) seedling all under intermediate 10 light regime. 0 10 Fast growing: k/ A L , kg s -1 MPa -1 m -2 X10 -5 • Am = Apeiba membranacea 8 • Ma = Miconia argentia 6 Slow growing: 4 • Tt = Trichiliaq tubersculata • Pr = Pouteria reticulata 2 • Gs = Gustavia superba 0 Tt Pr Gs Am Ma Species

CONCLUSIONS Based on the above and my experiences in the tropics generally There are a number of necessary conditions for rapid tree growth  High K plant /A L  High photosynthetic capacity of leaves  Low leaf-area index  Resistance to pests (at least some)  Cold tolerance (in temperate climates)

Fast-growing Eucalyputs hybrids grown my MONDI of South Africa

Thank you! I hope that some day you will visit the beautiful State of Vermont.