Drought effects on hydraulic conductivity and xylem vulnerability to embolism in diverse species and provenances of Mediterranean cedars

Abstract

We studied hydraulic traits of young plants of the Mediterranean cedar species Cedrus atlantica (Endl.) G. Manetti ex Carrière (Luberon, France), C. brevifolia (Hook. f.) Henry (Cyprus), C. libani A. Rich (Hadeth El Jebbe, Lebanon) and C. libani (Armut Alani, Turkey). With an optimum water supply, no major differences were observed among species or provenances in either stem hydraulic conductivity (Ks) or leaf specific conductivity (Kl) measured on the main shoot. A moderate soil drought applied for 10 weeks induced marked acclimation through a reduction in Ks, particularly in the Lebanese provenance of C. libani, and a decrease in tracheid lumen size in all species. Cedrus atlantica, which had the smallest tracheids, was the species most vulnerable to embolism: a 50% loss in hydraulic conductivity (PsiPLC50) occurred at a water potential of -4.4 MPa in the well-watered treatment, and at -6.0 MPa in the moderate drought treatment. In the other species, PsiPLC50 was unaffected by moderate soil drought, and only declined sharply at water potentials between -6.4 and -7.5 MPa in both irrigation treatments. During severe drought, Ks of twigs and stomatal conductance (g(s)) were measured simultaneously as leaf water potential declined. For all species, lower vulnerability to embolism based on loss of Ks was recorded on current-year twigs. The threshold for stomatal closure (10% of maximum g(s)) was reached at a predawn water potential (Psi(pd)) of -2.5 MPa in C. atlantica (Luberon) and at -3.1 MPa in C. libani (Lebanon), whereas the other provenance and species had intermediate Psi(pd) values. Cedrus brevifolia, with a Psi(pd) (-3.0 MPa) close to that of C. libani (Lebanon), had the highest stomatal conductance of the study species. The importance of a margin of safety between water potential causing stomatal closure and that causing xylem embolism induction is discussed.

Temperate forest trees and stands under severe drought: a review of ecophysiological responses, adaptation processes and long-term consequences

“…Positive values correspond to a safety margin, negative ones reveal a lack of control of stomata over cavitation. Data from [109]; [47]; [81]; Huc et al, unpublished; [92]; [31]; [28]; [3]; Cochard et Ameglio, unpublished. margin [135]. In most tree species, this margin is narrow, meaning that tree transpiration operates close to the cavitation induction point (Fig.…”

“…Within an organ, wider conduits are generally more susceptible to drought-induced cavitation, but across organs or species this trend is very weak [64,81]. This is probably because the cavitation threshold is generally not determined by vessel diameter but by the pore diameter in conduit walls [156].…”

“…Drought frequently results in decreases of xylem conduit dimensions in the short term [5,45,81,91,128]. In the long term, the main consequence of drought at tree level is a reduction of sapwood section due to enhanced duraminisation in the sapwood to heartwood transition zone and therefore of K S .…”

High genetic diversity and significant population structure in Cedrus brevifolia Henry, a narrow endemic Mediterranean tree from Cyprus

“…brevifolia is well-differentiated from other species of the genus based on morphological and ecophysiological traits such as short needles and slow growth, resistance to aphids, and the highest tolerance to drought in all cedar species (e.g. Vidakovic 1991;Ladjal et al 2005). In contrast, phylogenetic studies on cedar species have shown a strong genetic relationship between C. brevifolia and its widespread congener C. libani, especially with populations from Turkey (Scaltsoyiannes 1999;Fady et al 2000;Bou Dagher-Kharrat et al 2007;Qiao et al 2007).…”

Morpho-Anatomical Changes in Roots of Chickpea (Cicer arietinum L.) under Drought Stress Condition

“…Roots are the primary organ for the absorption of water and minerals, and drought greatly affects the number and size of water conducting elements, a functional aspect related to root anatomy [12]. Reduction in cortical cell size and number, lignification of epidermal and exodermal cells and layering of sclerenchymatous cells in neighbour of cortical cells are due to the deposition of lignin, and suberins is one of another modifications under water deficit condition [13].…”