Relationship between hydraulic pathway
length and foliar isotopic carbon
composition in longleaf pine
Price C. McLemore III, Lisa J. Samuelson,
Greg L. Somers
School of Forestry and Wildlife Sciences
Auburn University, AL 36849
Relationship between hydraulic pathway
length and foliar isotopic carbon
composition in longleaf pine
Price C. McLemore III, Lisa J. Samuelson,
Greg L. Somers
School of Forestry and Wildlife Sciences
Auburn University, AL 36849
Hydraulic Resistance Hypothesis
• Hydraulic Limits to Tree Height and Tree Growth
(Ryan and Yoder, 1997)
• Maintenance Respiration and Stand Development
in a Subalpine Lodgepole Pine Forest (Ryan and
Waring, 1992)
• Foliar isotopic carbon discrimination decreases
with increased total hydraulic pathway length
Objectives
• Compare physiological functions and branch and
tuft morphology between younger and older
longleaf pine trees
• Establish a relationship between branch physiology
and branch morphology
Methods, Field
• Two sites
• Sampling in May and November
• 1-3 branches per tree sampled, > 5 trees/site
• Branches with varying morphology, branching
hierarchy, and age
Methods
• Pathway lengths ranged up to 21m
• Tree heights ranged from grass stage to 23m
• Sampled branch heights ranged up to 20m
• Branch lengths up to 7m
• Tree Diameters ranged from 5 to 75cm
Methods, Lab
• Branch morphology measurements
– Diameters and lengths for each section or node
– Branch order
• Needle measurements
– needle length, age, projected area, dry weight
• d13C most recent fully developed needles
Hydraulic Pathway
-24
dC13 (per mill)
-25
-26
-27
-28
-29
-30
R2=.813 p<0.001
-31
0
Site 1
5
10
15
Total Length (m)
20
25
Hydraulic Pathway
-25
dC13 (per mill)
-26
-27
-28
-29
-30
R2=.782 p<0.001
-31
0
Site 2
5
10
15
Total Length (m)
20
25
Microclimate Effects
14
N (mg g-1)
12
10
8
6
4
p=.186
2
0
Site 1
5
10
15
Total Length (m)
20
25
Microclimate Effects
14
N (mg g-1)
12
10
8
6
4
R2=.326 p=.007
2
0
Site 2
5
10
15
Total Length (m)
20
25
Branch Comparisons
dC13 (per mill)
-25
-26
-27
-28
Y= -25.95B -28.06C+0.437X
-29
0
0.5
Site 1, hts (m)=15.2,15.7,15.5,15.7
1
Length (m)
R2=.88 p=.035
1.5
2
Branch Comparisons
14
N (mg g-1)
12
10
8
6
4
p=.194
2
0
Site 1
0.5
1
Length (m)
1.5
2
Branch Comparisons
-25
dC13 (per mill)
-26
-27
-28
-29
-30
Y=-27.7A -28.9C +.546X
0
1
Site 2, hts (m)=14.2,14.3,14.4,14.9
R2=.760 p=.001
2
Length (m)
3
4
Branch Comparisons
14
N (mg g-1)
12
10
8
6
4
Y= 8.89A+7.96B+.388X
2
0
Site 2
1
R2=.269 p=.001
2
Length (m)
3
4
Conclusions
• Significant linear relationships between dC13 and
total hydraulic pathway length or branch length.
• Microclimate effects are non-significant or minimal
• Increasing hydraulic resistance with increasing
length of the hydraulic pathway may increase
stomatal limitation of photosynthesis.
Analyses Under Consideration:
• Needle Length
• Tuft Dry Weight
• Projected Needle Area
• Area to Weight Ratio
• Specific Leaf Area
• Non-Linear Regression for dC13
• Total Hydraulic Pathway Volume (sapwood and
total)
Analyses Under Consideration:
• Needle Length
• Tuft Dry Weight
• Projected Needle Area
• Area to Weight Ratio
• Specific Leaf Area
• Non-Linear Regression for dC13
• Total Hydraulic Pathway Volume (sapwood and
total)