Journal Article

Atmospheric and soil drought reduce nocturnal conductance in live oaks

Jeannine Cavender-Bares, Lawren Sack and Jessica Savage

in Tree Physiology

Volume 27, issue 4, pages 611-620
Published in print April 2007 | ISSN: 0829-318X
Published online April 2007 | e-ISSN: 1758-4469 | DOI: http://dx.doi.org/10.1093/treephys/27.4.611
Atmospheric and soil drought reduce nocturnal conductance in live oaks

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Nocturnal and daytime whole-canopy transpiration rate (E) and conductance (g = E/VPD, where VPD is leaf to air vapor pressure difference) were assessed gravimetrically in drought-treated and well-watered 3-year-old saplings of live oak species (Quercus series Virentes Nixon) from the southeastern USA (Quercus virginianaMill.) and Central America (Q. oleoides Cham. and Schlecter). Our objectives were to: (1) quantify nocturnal and daytime E and g in a controlled environment; (2) determine the impact of severe drought on nocturnal E and g; and (3) examine whether unavoidable water loss through the epidermis could account for nocturnal water loss. We calculated daytime E during peak daylight hours (between 0930 and 1330 h) and nocturnal E during complete darkness (between 2200 and 0500 h). In addition to reducing E and g during the daytime, drought-treated plants reduced nocturnal E and g on a whole-canopy basis by 62−64% and 59−61%, respectively, and on a leaf-level basis by 27−28% and 19−26%, respectively. In well-watered plants, nocturnal g declined with increasing VPD, providing evidence for stomatal regulation of nocturnal transpiration. In drought-treated plants, g was low and there was no relationship between nocturnal g and VPD, indicating that water loss could not be reduced further through stomatal regulation. Both daytime and nocturnal g declined curvilinearly with predawn water potential for all plants, but nocturnal g was unrelated to predawn water potentials below −1 MPa. The reductions in daytime and nocturnal E and g during drought were associated with decreases in whole-plant and leaf hydraulic conductances. Observed nocturnal g was within the same range as epidermal conductance for oak species determined in previous studies under a range of conditions. Nocturnal E rose from 6−8% of daytime E for well watered plants to 19−20% of daytime E for drought-treated plants. These results indicate that, during drought, saplings of live oak species reduce g to a minimum through stomatal closure, and experience unavoidable water loss through the epidermis.

Keywords: epidermal conductance; hydraulic conductance; leaf hydraulic properties; nocturnal conductance; Quercus oleoides; Quercus virginiana; stomatal pore index

Journal Article.  0 words. 

Subjects: Plant Sciences and Forestry

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