JXB Advance Access originally published online on June 20, 2005
Journal of Experimental Botany 2005 56(418):2003-2010; doi:10.1093/jxb/eri198
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Published by Oxford University Press [2005] on behalf of the Society for Experimental Biology.
RESEARCH PAPER |
Cavitation vulnerability in roots and shoots: does Populus euphratica Oliv., a poplar from arid areas of Central Asia, differ from other poplar species?
1UMR INRA-UHP Ecologie-Ecophysiologie Forestières, INRA Nancy, F-54280 Champenoux, France
2UMR INRA-UBP Physiologie Intégrée des Arbres Fruitiers et Forestiers, INRA, Site de Crouëlle, F-63039 Clermont-Ferrand, France
* To whom correspondence should be addressed. Fax: +33 3 83 39 40 22. E-mail: triboulo{at}nancy.inra.fr
Populus euphratica is a poplar species growing in arid regions of Central Asia, where its distribution remains nevertheless restricted to river-banks or to areas with an access to deep water tables. To test whether the hydraulic architecture of this species differs from that of other poplars with respect to this ecological distribution, the vulnerability to cavitation of P. euphratica was compared with that of P. alba and of P. trichocarpaxkoreana. The occurrence of a potential hydraulic segmentation through cavitation was also investigated by assessing the vulnerability of roots, stems, and leaf mid-rib veins. Cryo-scanning electron microscopy (cryo-SEM) was used to assess the level of embolism in fine roots and leaf mid-ribs and a low pressure flowmeter (LPFM) was used for stems and main roots. The cryo-SEM technique was validated against LPFM measurements on paired samples. In P. alba and P. trichocarpaxkoreana, leaf mid-ribs were more vulnerable to cavitation than stems and roots. In P. euphratica, leaf mid-ribs and stems were equally vulnerable and, contrary to what has been observed in other species, roots were significantly less vulnerable than shoots. P. euphratica was by far the most vulnerable. The water potential inducing 50% loss of conductivity in stems was close to –0.7 MPa, against 
–1.45 MPa for the two others species. Such a large vulnerability was confirmed by recording losses of conductivity during a gradual drought. Moreover, significant stem embolism was recorded before stomatal closure, indicating the lack of an efficient safety margin for hydraulic functions in this species. Embolism was not reversed by rewatering. These observations are discussed with respect to the ecology of P. euphratica.
Key words: Drought, embolism, hydraulic architecture, hydraulic segmentation, phreatophyte, Populus, stomatal conductance, water relations
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