Correlations between tree resource change and resistance following inoculation of the fungus <i>Ceratocystis polonica</i>.

<p>Percentage change in phloem non-structural carbohydrates (left panels) and sapwood lipids (right panels) from May to October is shown. Norway spruce resistance was measured as phloem lesion length (upper panels) and percentage necrotic phloem around the stem circumference (lower panels). Shorter lesions and less necrotic phloem signify a more resistant tree. Dotted lines show equal resource levels in May and October, whereas positive values denote a decline in resource levels over time (i.e. resource depletion). Linear trend lines are shown for clarity.</p

Predictions illustrating possible changes in tree stored resources in relation to tree resistance.

<p>(A) If stored resources are more beneficial to the tree than the fungus, trees with higher initial resource concentrations and more resource depletion over time will be more resistant to fungal colonization. (B) Tree resistance may be independent of initial resource concentrations and cause complex changes in tree resources over time. Independent of initial resource concentrations, more resistant trees may have more resource depletion and successfully resist fungal colonization (solid line). Alternatively, less resistant trees may have more resource depletion because fungi consume resources (dashed line). (C) If stored resources are overall more beneficial to the fungus than to the tree, trees with higher initial resource concentrations and more resource depletion over time will be less resistant to fungal colonization.</p

Treatment details and outcome for individual Norway spruce trees attacked by <i>Ips typographus</i>, inoculated with the fungus <i>Ceratocystis polonica</i>, or left untreated as control.

a<p>Control trees were not measured, but healthy trees generally have no necrotic phloem (e.g. Krokene and Solheim 1998).</p>b<p>Phloem lesion length is mean ± standard deviation.</p>c<p>Outcome is a qualitative assessment of tree health one year after the start of the experiment.</p

General linear model with repeated measures showing effects on resource concentrations in Norway spruce sapwood and phloem.

<p>Treatment (control, beetle attack, fungal inoculation) is a factor, sampling date is a repeated measures factor, and tree diameter is a covariate. Degrees of freedom (df) are numerator, denominator. Bold p-values indicate significant effects.</p

Change in tree resources following treatment.

<p>Change in non-structural carbohydrates (NSC) and nitrogen (N) in the phloem and sapwood and change in lipids in the sapwood is shown for control, fungal-inoculated, and beetle-attacked trees. Error bars indicate ±1 standard error. Significant ANOVA effects are indicated in the lower left corner of the panels. Note differences in y-axis scale between the sapwood and phloem for NSC and nitrogen.</p

Image_1_Methyl jasmonate, salicylic acid, and oxalic acid affects growth, inducible defenses, and pine weevil resistance in Norway spruce.tif

The large pine weevil (Hylobius abietis) is a major regeneration pest in commercial forestry. Pesticide application has historically been the preferred control method, but pesticides are now being phased out in several countries for environmental reasons. There is, thus, a need for alternative plant protection strategies. We applied methyl jasmonate (MeJA), salicylic acid (SA) or oxalic acid (OxA) on the stem of 2-year-old Norway spruce (Picea abies) plants to determine effects on inducible defenses and plant growth. Anatomical examination of stem cross-sections 9 weeks after application of 100 mM MeJA revealed massive formation of traumatic resin ducts and greatly reduced sapwood growth. Application of high concentrations of SA or OxA (500 and 200 mM, respectively) induced much weaker physiological responses than 100 mM MeJA. All three treatments reduced plant height growth significantly, but the reduction was larger for MeJA (~55%) than for SA and OxA (34-35%). Lower MeJA concentrations (5-50 mM) induced comparable traumatic resin duct formation as the high MeJA concentration but caused moderate (and non-significant) reductions in plant growth. Two-year-old spruce plants treated with 100 mM MeJA showed reduced mortality after exposure to pine weevils in the field, and this enhanced resistance-effect was statistically significant for three years after treatment.</p

Image_2_Methyl jasmonate, salicylic acid, and oxalic acid affects growth, inducible defenses, and pine weevil resistance in Norway spruce.tif

The large pine weevil (Hylobius abietis) is a major regeneration pest in commercial forestry. Pesticide application has historically been the preferred control method, but pesticides are now being phased out in several countries for environmental reasons. There is, thus, a need for alternative plant protection strategies. We applied methyl jasmonate (MeJA), salicylic acid (SA) or oxalic acid (OxA) on the stem of 2-year-old Norway spruce (Picea abies) plants to determine effects on inducible defenses and plant growth. Anatomical examination of stem cross-sections 9 weeks after application of 100 mM MeJA revealed massive formation of traumatic resin ducts and greatly reduced sapwood growth. Application of high concentrations of SA or OxA (500 and 200 mM, respectively) induced much weaker physiological responses than 100 mM MeJA. All three treatments reduced plant height growth significantly, but the reduction was larger for MeJA (~55%) than for SA and OxA (34-35%). Lower MeJA concentrations (5-50 mM) induced comparable traumatic resin duct formation as the high MeJA concentration but caused moderate (and non-significant) reductions in plant growth. Two-year-old spruce plants treated with 100 mM MeJA showed reduced mortality after exposure to pine weevils in the field, and this enhanced resistance-effect was statistically significant for three years after treatment.</p

Bark beetle damage in Norwegian forests: a study of model suitability and projected impact under climate change

Bark beetle (Ips typographus) outbreaks have the potential to damage large areas of spruce-dominated forests in Scandinavia. To define forest management strategies that will minimize the risk of bark beetle attacks, we need robust models that link forest structure and composition to the risk and potential damage of bark beetle attacks. Since data on bark beetle infestation rates and corresponding damages does not exist in Norway, we implement a previously published meta-model for estimating I. typographus damage probability and intensity. Using both current and projected climatic conditions we used the model to estimate damage inflicted by I. typographus in Norwegian spruce stands. The model produces feasible results for most of Norway’s climate and forest conditions, but a revised model tailored to Norway should be fitted to a dataset that includes older stands and lower temperatures. Based on current climate and forest conditions, the model predicts that approximately nine percent of productive forests within Norway’s main spruce-growing region will experience a loss ranging from 1.7 to 11 m3/ha of spruce over a span of five years. However, climate change is predicted to exacerbate the annual damage caused by I. typographus, potentially leading to a doubling of its detrimental effects.</p

Table_3_Epitype-inducing temperatures drive DNA methylation changes during somatic embryogenesis in the long-lived gymnosperm Norway spruce.xlsx

An epigenetic memory of the temperature sum experienced during embryogenesis is part of the climatic adaptation strategy of the long-lived gymnosperm Norway spruce. This memory has a lasting effect on the timing of bud phenology and frost tolerance in the resulting epitype trees. The epigenetic memory is well characterized phenotypically and at the transcriptome level, but to what extent DNA methylation changes are involved have not previously been determined. To address this, we analyzed somatic epitype embryos of Norway spruce clones produced at contrasting epitype-inducing conditions (18 and 28°C). We screened for differential DNA methylation in 2744 genes related mainly to the epigenetic machinery, circadian clock, and phenology. Of these genes, 68% displayed differential DNA methylation patterns between contrasting epitype embryos in at least one methylation context (CpG, CHG, CHH). Several genes related to the epigenetic machinery (e.g., DNA methyltransferases, ARGONAUTE) and the control of bud phenology (FTL genes) were differentially methylated. This indicates that the epitype-inducing temperature conditions induce an epigenetic memory involving specific DNA methylation changes in Norway spruce.</p

Attack densities (Left) and gallery lengths (Right) in 20 Norway spruce trees with different induced terpene levels in the bark.

<p>Chemical samples were taken from the reaction zone 35 days after inoculation with the bluestain fungus <i>Ceratocystis polonica.</i> Dotted lines show two potential thresholds in terpene levels (200 and 100 mg g⁻¹ dry wt) with different inhibitive effects on beetle colonization. Solid lines show the fitting of a two-parameter single exponential decay function to the data. Trees were classified as resistant (black dots), susceptible (white dots) or intermediate (black and white dots) with respect to beetle colonization success (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026649#pone-0026649-g002" target="_blank">Figure 2</a> for details).</p