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)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)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 lengthFoliar 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 treesCompare physiological functions and branch and tuft morphology between younger and older longleaf pine trees Establish a relationship between branch physiology and branch morphologyEstablish a relationship between branch physiology and branch morphology

Methods, Field Two sitesTwo sites Sampling in May and NovemberSampling in May and November 1-3 branches per tree sampled, > 5 trees/site1-3 branches per tree sampled, > 5 trees/site Branches with varying morphology, branching hierarchy, and ageBranches with varying morphology, branching hierarchy, and age

Methods Pathway lengths ranged up to 21mPathway lengths ranged up to 21m Tree heights ranged from grass stage to 23mTree heights ranged from grass stage to 23m Sampled branch heights ranged up to 20mSampled branch heights ranged up to 20m Branch lengths up to 7mBranch lengths up to 7m Tree Diameters ranged from 5 to 75cm Tree Diameters ranged from 5 to 75cm

Methods, Lab Branch morphology measurements Branch morphology measurements –Diameters and lengths for each section or node –Branch order Needle measurements Needle measurements –needle length, age, projected area, dry weight  13C most recent fully developed needles  13C most recent fully developed needles

Hydraulic Pathway R 2 =.813 p<0.001 R 2 =.813 p<0.001 Total Length (m) Site 1  C13 (per mill)

Hydraulic Pathway R 2 =.782 p<0.001 Site 2 Total Length (m)  C13 (per mill)

Microclimate Effects Total Length (m) N (mg g -1 ) p=.186 Site 1

Microclimate Effects Total Length (m) N (mg g -1 ) Site 2 R 2 =.326 p=.007

Branch Comparisons Site 1, hts (m)=15.2,15.7,15.5,15.7  C13 (per mill) Length (m) Y= B C+0.437X R 2 =.88 p=.035 Y= B C+0.437X R 2 =.88 p=.035

Branch Comparisons Length (m) N (mg g -1 ) Site 1 p=.194

Branch Comparisons Length (m)  C13 (per mill) Site 2, hts (m)=14.2,14.3,14.4,14.9 Y=-27.7A -28.9C +.546X R 2 =.760 p=.001

Branch Comparisons Length (m) Site 2 N (mg g -1 ) Y= 8.89A+7.96B+.388X R 2 =.269 p=.001

Conclusions Significant linear relationships between  C13 and total hydraulic pathway length or branch length.Significant linear relationships between  C13 and total hydraulic pathway length or branch length. Microclimate effects are non-significant or minimalMicroclimate effects are non-significant or minimal Increasing hydraulic resistance with increasing length of the hydraulic pathway may increase stomatal limitation of photosynthesis.Increasing hydraulic resistance with increasing length of the hydraulic pathway may increase stomatal limitation of photosynthesis.

Analyses Under Consideration: Needle LengthNeedle Length Tuft Dry WeightTuft Dry Weight Projected Needle AreaProjected Needle Area Area to Weight RatioArea to Weight Ratio Specific Leaf AreaSpecific Leaf Area Non-Linear Regression for  C13Non-Linear Regression for  C13 Total Hydraulic Pathway Volume (sapwood and total)Total Hydraulic Pathway Volume (sapwood and total)

Analyses Under Consideration: Needle LengthNeedle Length Tuft Dry WeightTuft Dry Weight Projected Needle AreaProjected Needle Area Area to Weight RatioArea to Weight Ratio Specific Leaf AreaSpecific Leaf Area Non-Linear Regression for  C13Non-Linear Regression for  C13 Total Hydraulic Pathway Volume (sapwood and total)Total Hydraulic Pathway Volume (sapwood and total)