Adjustments in hydraulic architecture of Pinus palustris maintain similar stomatal conductance in xeric and mesic habitats

doi:10.1111/j.1365-3040.2005.01430.x

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Wiley InterScience

Plant, Cell & Environment

Volume 29 Issue 4, Pages 535 - 545

Published Online: 17 Oct 2005

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Adjustments in hydraulic architecture of Pinus palustris maintain similar stomatal conductance in xeric and mesic habitats

R. N. ADDINGTON ^1,2 , L. A. DONOVAN ¹ , R. J. MITCHELL ² , J. M. VOSE ³ , S. D. PECOT ² , S. B. JACK ² , U. G. HACKE ⁴ , J. S. SPERRY ⁴ & R. OREN ⁵

¹ Department of Plant Biology, University of Georgia, Athens, GA 30602, USA, ² Joseph W. Jones Ecological Research Center, Newton, GA 39870, USA, ³ USDA Forest Service, South-eastern Forest Experiment Station, Coweeta Hydrologic Laboratory, Otto, NC 28763, USA, ⁴ Department of Biology, University of Utah, Salt Lake City, UT 84112, USA and ⁵ Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC 27708, USA

Correspondence to Robert Addington. Present address: The Nature Conservancy, P.O.Box 52452, Fort Benning, GA31995, Phone: +1 706 5447515 Fax: +1 706 5446570; e-mail: raddington@tnc.org

KEYWORDS

habitat structure • hydraulic conductance • leaf water potential • longleaf pine • stand density • tree height • water relations

ABSTRACT

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 (Ψ_S − Ψ_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 Ψ_S − Ψ_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.