The phenotypic and genetic effects of drought-induced stress on wood specific conductivity and anatomical properties in white spruce seedlings, and relationships with growth and wood density

Abstract

Drought frequency and intensity are projected to increase with climate change, thus amplifying stress on forest trees. Resilience to drought implicates physiological traits such as xylem conductivity and wood anatomical traits, which are related to growth and wood density. Integrating drought-stress response traits at the juvenile stage into breeding criteria could help promote the survival of planted seedlings under current and future climate and thus, improve plantation success. We assessed in greenhouse the influence of drought-induced stress on 600 two-year-old white spruce (Picea glauca) seedlings from 25 clonal lines after two consecutive growing seasons. Three levels of drought-induced stress were applied: control, moderate and severe. Seedlings were also planted at a 45° angle to clearly separate compression from normal wood. We looked at the phenotypic and genetic effects of drought stress on xylem specific hydraulic conductivity, lumen diameter, tracheid diameter and length, and the number of pits per tracheid in the normal wood. We detected no significant effects of drought stress except for tracheid length, which decreased with increasing drought stress. We found low to high estimates of trait heritability, which generally decreased with increasing drought stress. Genetic correlations were higher than phenotypic correlations for all treatments. Specific conductivity was genetically highly correlated positively with lumen diameter and tracheid length under all treatments. Tracheid length and diameter were always negatively correlated genetically, indicating a trade-off in resource allocation. Moderate to high genetic correlations sometimes in opposite direction were observed between physico-anatomical and productivity traits, also indicating trade-offs. A large variation was observed among clones for all physico-anatomical traits, but clonal ranks were generally stable between control and drought-induced treatments. Our results indicate the possibility of early screening of genetic material for desirable wood anatomical attributes under normal growing conditions, thus allowing to improve the drought resilience of young trees.

Keywords: conifer; drought-induced stress; heritability; phenotypic and genetic correlations; tracheids; xylem specific hydraulic conductivity.

Figure 1

Samples of macerated white spruce wood showing tracheids and pits. The tracheid samples shown here were taken from the same tree. (A) Whole tracheids and (B) tracheids zoomed on the pits. The reference bar represents 10.0µm. The picture was taken on a Keyence VHX-700 digital microscope.

Figure 2

Comparison of tree responses to different levels of drought-induced stress for specific conductivity (A), lumen diameter (B), number of pits per tracheid (C) and tracheid diameter (D) and length (E). Means with different letters indicate significant differences at P< 0.05 (Tukey tests).

Figure 3

(A) Matrices of phenotypic correlations between the different traits for each treatment, i.e. the control, moderate and severe drought stress treatments. (B) Matrices of genetic correlations between the different traits for each treatment. The higher the correlation, the larger the size of the dot and intensity of the color. The color gradients indicate the direction and level of correlations (blue for positive and red for negative correlations). Corresponding values and their standard errors can be found in Supplementary Tables 1 and 2 .

Figure 4

Linear relationships (P< 0.05) between tracheid length and apical growth (A) and ring width (B) under severe drought conditions, at the phenotypic level.

Figure 5

Broad-sense heritability estimates for specific conductivity (A), lumen diameter (B), number of pits per tracheid (C), tracheid diameter (D) and tracheid length (E). Error bars represent the standard errors. Narrow-sense heritability values and their standard errors can be found in Supplementary Table 3 .

Figure 6

Spearman’s rank-order correlation coefficients of clonal values that consider additive and non-additive genetic effects between treatments, (A) control and moderate drought, (B) control and severe drought, (C) moderate and severe drought, for specific conductivity, lumen diameter, tracheid length, tracheid diameter and the number of pits per tracheid. Error bars represent the standard errors.