ABSTRACT:

PHYSIOLOGICAL ANALYSIS OF HYDRAULIC CONSTRAINTS ON TREE HEIGHT IN Pinus strobus

John C. Kamman

 The extent to which hydraulic limitation of tree height can be applied as a general constraint to growth is incompletely understood. To test the hydraulic limitation theory’s regional applicability, four mature White Pine trees (Pinus strobus) in Northern Minnesota, approaching the regional species-specific height maximum, were analyzed for the presence of two water stress signatures with height: water potential gradients and carbon isotope discrimination (¹³C).  Midday water potentials decreased with height, reaching pressures approaching -2.0 MPa at the top of each canopy.  The water potentials measured may be sufficiently negative to induce stomatal closure and inhibit photosynthesis in the upper fraction of the canopies.  Carbon isotope analysis results showed decreasing ¹³C discrimination with height, indicative of stress-induced stomatal closure over longer time scales.  The results are consistent with the hydraulic limitation hypothesis and suggest that the regional asymptotic maximum height of Pinus strobus may be strongly constrained by water relations.