Plant Physiology Preview
Published on November 14, 2008; 10.1104/pp.108.129783
OPEN ACCESS ARTICLE
Received September 10, 2008
Accepted November 11, 2008
Hydraulic failure defines the recovery and point of death in water stressed conifers
Tim J Brodribb * and Herve Cochard
University of Tasmania, Hobart, Australia; INRA, Clermont-Ferrand, France
* Corresponding author; email: timothyb{at}utas.edu.au.
This study combines existing hydraulic principles with recently developed methods for probing leaf hydraulic function to determine whether xylem physiology can explain the dynamic response of gas exchange both during drought and in the recovery phase after rewatering. Four conifer species from wet and dry forests were exposed to a range of water stresses by withholding water and then rewatering to observe the recovery process. During both phases midday transpiration (Emd) and leaf water potential ( leaf) were monitored. Stomatal responses to leaf were established for each species and these relationships used to evaluate whether the recovery of gas exchange after drought was limited by post-embolism hydraulic repair in leaves. Furthermore the timing of gas-exchange recovery was used to determine the maximum survivable water stress for each species and this index compared with data for both leaf and stem vulnerability to water-stress-induced dysfunction measured for each species. Recovery of gas exchange after water stress took between 1 and >100days and during this period all species showed strong 1:1 conformity to a combined hydraulic-stomatal limitation model (r2=0.70 across all plants). Gas exchange recovery time showed two distinct phases, a rapid overnight recovery in plants stressed to <50% loss of Kleaf, and a highly leaf dependent phase in plants stressed to >50% loss of Kleaf. Maximum recoverable water stress (minimum leaf) corresponded to a 95% loss of Kleaf. Thus we conclude that xylem hydraulics represents a direct limit to the drought tolerance of these conifer species.
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