Journal
PLANT CELL AND ENVIRONMENT
Volume 29, Issue 4, Pages 535-545Publisher
BLACKWELL PUBLISHING
DOI: 10.1111/j.1365-3040.2005.01430.x
Keywords
habitat structure; hydraulic conductance; leaf water potential; longleaf pine; stand density; tree height; water relations
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We investigated relationships between whole-tree hydraulic architecture and stomatal conductance in Pinus palustris Mill. (longleaf pine) across habitats that differed in soil properties and habitat structure. Trees occupying a xeric habitat (characterized by sandy, well-drained soils, higher nitrogen availability and lower overstory tree density) were shorter in stature and had lower sapwood-to-leaf area ratio (A(S):A(L)) than trees in a mesic habitat. The soil-leaf water potential gradient (Psi(S) - Psi(L)) and leaf-specific hydraulic conductance (k(L)) were similar between sites, as was tissue-specific hydraulic conductivity (K-S) of roots. Leaf and canopy stomatal conductance (g(S) and G(S), respectively) were also similar between sites, and they tended to be somewhat higher at the xeric site during morning hours when vapour pressure deficit (D) was low. A hydraulic model incorporating tree height, A(S):A(L) and Psi(S) - Psi(L) accurately described the observed variation in individual tree G(Sref) (G(S) at D = 1 kPa) across sites and indicated that tree height was an important determinant of G(Sref) across sites. This, combined with a 42% higher root-to-leaf area ratio (A(R):A(L)) at the xeric site, suggests that xeric site trees are hydraulically well equipped to realize equal - and sometimes higher - potential for conductance compared with trees on mesic sites. However, a slightly more sensitive stomatal closure response to increasing D observed in xeric site trees suggests that this potential for higher conductance may only be reached when D is low and when the capacity of the hydraulic system to supply water to foliage is not greatly challenged.
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