Fig 1.
The effects of water deprivation on Engelmann spruce.
(A) Change over time in stem water potential of Picea engelmannii seedlings during a water deprivation experiment; (B) the relationship between stem water potential and photosynthetic rate (μmol m2s-1); (C) the distribution of salicylic acid (SA) concentrations in needles, roots, and stem phloem; and (D) the relationship between stem water potential and SA concentrations in needle tissues. The solid line shows a fitted regression model and dashed lines represent the 95% CI. Where lowercase letters are shown, they denote significant differences among means identified by Tukey’s HSD test. Water deprivation caused strongly negative water potentials, which corresponded to reduced photosynthesis and elevated SA in needles.
Fig 2.
Relationship between drought stress and salicylic acid (SA) levels in Engelmann spruce tissues.
(A) Variation in stem water potentials (MPa) over time in Picea engelmannii seedlings receiving ample (0.8 g H2O/g soil, white symbols) and drought (0.2 g H2O/g soil, gray symbols) watering treatments. (B) Mean concentrations of SA in needle and stem tissues of P. engelmannii seedlings relative to watering treatments. The asterisk denotes a significant difference in SA concentrations between drought-stressed and well-watered seedlings. (C) The relationship between SA concentrations in needles and stem phloem. As was the case for acute water deprivation, chronic drought stress results in elevated SA concentrations in needles.
Fig 3.
Drought stress and salicylic acid (SA) interact to affect expression of foliar monoterpenes.
The effects of (A) SA × watering treatment interaction on β-phellandrene concentrations and (B) SA alone on terpinolene concentrations. In each panel dashed lines show the 95% CI of each fit. In panel A, the gray line shows the fitted model for seedlings receiving the drought-stress treatment and the black line shows the fitted model for well-watered seedlings; in panel B, only SA was a significant predictor of secondary metabolite concentrations.
Table 1.
Summary of two-way ANOVA models.
Fig 4.
Drought stress and salicylic acid (SA) interact to affect expression of phloem monoterpenes.
The effects of SA × watering treatment interaction on the concentrations of secondary metabolites in the stem phloem of Picea engelmannii seedlings, including (A) 3-carene, (B) γ-terpinene, (C) sabinene, and (D) terpinolene. In each panel dashed lines show the 95% CI of each fit. Gray lines show fitted models for the drought-stress treatment and black lines show fitted models for well-watered seedlings. In drought-stressed seedlings, SA is positively correlated with concentration of specific stem phloem monoterpenes.
Fig 5.
Drought stress limits the ability of Engelmann spruce to form resin ducts.
The frequency of traumatic resin ducts formation in Picea engelmannii seedlings over time following exposure to the elicitor methyl jasmonate (MeJa) for (A) droughted and (B) well-watered seedlings. In well-watered seedlings a higher proportion of individuals formed traumatic resin ducts.