Relationships between wood density and hydraulic efficiency and safety (hydraulic specific conductivity and vulnerability
to cavitation, respectively) could clarify the physiological process explaining the impact of density on fitness. We have
used new, relatively high-throughput phenotyping methods to estimate genetic variation of wood hydraulic specific conductivity
s) and vulnerability to cavitation (VC) as an important step toward demonstrating the adaptive value of wood density.
The first aim of this study is to test if, in Douglas-fir, there is a relationship between wood hydraulic properties (k
s and VC) and wood density. The second objective is to estimate genetic variation of wood k
s and VC. These results could aid understanding of the role of wood density in the hydraulic properties of xylem and may clarify
the role of wood density in adaptation to drought.
Many significant relationships were found between wood density and wood hydraulic properties at clone and tree level, as well
as significant genetic variation for k
s and VC. We have also found positive correlations between tree height, specific conductivity and vulnerability to cavitation,
but no relation was found between radial growth and hydraulic variables.
Our results suggest that wood density has an adaptive value and that microdensity can be used to study adaptation to drought
in Douglas-fir. The novel methods used to measure k
s and VC proved to be interesting alternatives for localized measurement of wood hydraulic properties and were compatible with
a robust estimation of genetic variation.
KeywordsAdaptation to drought–Wood density–Douglas-fir–Hydraulic efficiency–Hydraulic safety
Annals of Forest Science 04/2012; 68(4):747-757. · 1.79 Impact Factor
Bosque 01/2011; 32(3):221-226.
ABSTRACT: Microdensity profiles of Douglas-fir's clones and weather data were used to study phenotypic plasticity (dendroplasticity). Within-ring microdensity was interpreted as the variation of tree response to drought constraints during selected growing seasons. An original norm of reaction was obtained by pairing evident points of abrupt changes in tree-ring microdensity profiles and in weather indices. The coefficients of the non-linear models adjusted to the reaction norms were analysed as dendroplasticity variables. Dendroplasticity variables were significantly different between geographical locations, years and clones. Heritability of the dendroplasticity variables ranged from low to high and was similar to heritability values of microdensity variables such as mean ring density (MRD). Coefficients of genetic variation of dendroplasticity variables were intermediate between those of wood density and growth variables. Dendroplasticity variables were phenotypically and genetically related to ring microdensity variables, more strongly to latewood variables. Dendroplasticity provides retrospective, synthetic and easy-to-interpret information about tree response to the variation of the balance between water availability and water demand during the growing season. The proposed model of dendroplasticity is described by a number of parameters that are linked to a biological meaning. Our results suggest that there is a potential for adaptation to drought in Douglas-fir, with two mechanisms involved: at individual level, short-term plastic response during the growing season and, at population level, long-term, between-generation, evolution process.
Forest Ecology and Management 258(5):860-867. · 2.49 Impact Factor
ABSTRACT: Drought response of three Douglas-fir clones (slow, intermediate and fast growing) inhabiting two different climatic regimes in France was examined. We used the hydraulic conductivity and the percent loss of conductivity due to embolism from stems and branches as well as wood microdensity measurements to determine the role of genetics in the control of embolism in this species. Conductivity and tree-ring’s microdensity variables (ring width: RW, mean ring density: MRD, minimum ring density: MID and maximum ring density: MAD) were compared in growth rings in all three clones during a typical year (2002) vs. an extremely dry year (2003). A new method was developed in order to assess axial hydraulic specific conductivity (Ks) within tree rings. The results show that branches are more resistant to embolism than stems, and that there are significant differences in embolism resistance among the clones between the two sites. Ks varied between years, sites and clones but the site exerted the most significant effect. Lartimache (more humid site during 2003) trees showed substantially higher Ks than those inhabiting Chassenoix (strongly affected by the 2003 heat and drought wave site). Wood analysis showed a significant year effect for all ring variables and a significant clone effect for all ring variables except for MAD, while the site effect was significant for MRD and MAD. The existence of a genetic control for the study traits indicates that Douglas-fir populations introduced in France may have a selection potential to face extreme climate events like the 2003 heat and drought wave.
Forest Ecology and Management.
ABSTRACT: In a global warming scenario, drought and heat waves like the one that occurred in 2003 in Europe are expected to become more intense and frequent. This extreme climate event strongly affected the hydraulic balance in many forest tree species including Douglas-fir, with symptoms ranging from partial crown necrosis to death. We studied a French Douglas-fir provenance trial, strongly affected by the 2003 drought and heat wave. Using wood X-ray microdensity profiles as a record of cambium response to environmental variations, we compared mean stem density and growth between dead and alive neighbouring trees and several microdensity characters measured over 17 growth rings previous to 2003. Special attention has been given to the sampling layout in order to minimize the micro-environmental effects. At tree level, surviving trees have a significantly higher mean stem density. At tree ring level, they have a significantly higher mean ring density, maximum ring density, latewood density and, to a lesser extent, latewood proportion. No significant difference was found for diameter growth. These results could have direct implications in the way to study and predict possible acclimation and adaptation of forest trees to climate change process. Wood could be used for the selection of genotypes with a desirable plasticity and resistance to drought induced-cavitation.
Forest Ecology and Management.