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JXB Advance Access published online on February 2, 2009
Journal of Experimental Botany, doi:10.1093/jxb/ern367
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Patterns of nocturnal rehydration in root tissues of Vaccinium corymbosum L. under severe drought conditions

Luis R. Valenzuela-Estrada1, James H. Richards2, Andres Diaz3 and David M. Eissensat1,*

1Department of Horticulture, Penn State University, 218 Tyson Building, University Park, PA, 16802-4200 USA
2Department of Land, Air, and Water Resources, University of California Davis, Davis, CA 95616, USA
3Department of Electrical Engineering, Penn State University, University Park, 16802 PA, USA

* To whom correspondence should be addressed: E-mail: dme9{at}psu.edu

Although roots in dry soil layers are commonly rehydrated by internal hydraulic redistribution during the nocturnal period, patterns of tissue rehydration are poorly understood. Rates of nocturnal rehydration were examined in roots of different orders in Vaccinium corymbosum L. ‘Bluecrop’ (Northern highbush blueberry) grown in a split-pot system with one set of roots in relatively moist soil and the other set of roots in dry soil. Vaccinium is noted for a highly branched and extremely fine root system. It is hypothesized that nocturnal root tissue rehydration would be slow, especially in the distal root orders because of their greater hydraulic constraints (smaller vessel diameters and fewer number of vessels). Vaccinium root hydraulic properties delayed internal water movement. Even when water was readily available to roots in the wet soil and transpiration was minimal, it took a whole night-time period of 12 h for the distal finest roots (1st to 4th order) under dry soil conditions to reach the same water potentials as fine roots in moist soil (1st to 4th order). Even though roots under dry soil equilibrated with roots in moist soil, the equilibrium point reached before sunrise was about –1.2 MPa, indicating that tissues were not fully rehydrated. Using a single-branch root model, it was estimated that individual roots exhibiting the lowest water potentials in dry soil were 1st order roots (distal finest roots of the root system). However, considered at the branch level, root orders with the highest hydraulic resistances corresponded to the lowest orders of the permanent root system (3rd-, 4th-, and 5th-order roots), thus indicating possible locations of hydraulic safety control in the root system of this species.

Key words: Blueberry, hydraulic redistribution, root water potential, split-pot

Received 29 October 2008; Revised 15 December 2008 Accepted 22 December 2008


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