Early selection improves clonal performance and reduces intraclonal variation of Norway spruce plants propagated by somatic embryogenesis

Height growth during the first and second growth periods (i.e., the June-September period in consecutive years) and intraclonal variation were assessed in 13 Norway spruce (Picea abies (L.) Karst.) clones propagated by somatic embryogenesis. The plants were acclimatized and grown in a greenhouse until mid-July and then transferred outdoors. The clonal mean heights after the first and second growth periods were lower for somatic embryo plants than for seedlings from corresponding families sown at the time of somatic embryo plant ex vitro transfer, because a large proportion of somatic embryo plants were small. We determined whether certain selection criteria at ex vitro transfer can be used to identify somatic embryo plants with height growth characteristics comparable with those of seedlings. Epicotyl length and presence of lateral roots proved to be important parameters for selection, whereas main root length was less useful. A combined selection for somatic embryo plants with lateral roots and with an epicotyl length exceeding 8 mm resulted in taller plants and reduced intraclonal variation after the first and second growth periods. The growth of somatic embryo plants selected in this way was similar to that of seedlings from the corresponding families. We conclude that selection according to these criteria at ex vitro transfer can result in improved performance of clonal stock propagated by somatic embryogenesis.     

Metabolite profiling reveals clear metabolic changes during somatic embryo development of Norway spruce (Picea abies)

Progress on industrial-scale propagation of conifers by somatic embryogenesis has been hampered by the differences in developmental capabilities between cell lines, which are limiting the capture of genetic gains from breeding programs. In this study, we investigated the metabolic events occurring during somatic embryo development in Norway spruce to establish a better understanding of the fundamental metabolic events required for somatic embryo development. Three embryogenic cell lines of Norway spruce (Picea abies (L.) Karst) with different developmental capabilities were studied during somatic embryo development from proliferation of proembryogenic masses to mature somatic embryos. The three different cell lines displayed normal, aberrant and blocked somatic embryo development. Metabolite profiles from four development stages in each of the cell lines were obtained using combined gas chromatography-mass spectrometry. Multivariate discriminant analyses of the metabolic data revealed significant metabolites (P ≤ 0.05) for each development stage and transition. The results suggest that endogenous auxin and sugar signaling affects initial stages of somatic embryo development. Furthermore, the results highlight the importance of a timed stress response and the presence of stimulatory metabolites during late stages of embryo development.     

Storage protein changes during zygotic embryogenesis in interior spruce

The major storage proteins isolated from protein bodies of embryo tissues of interior spruce Picea glauca (Moench) Voss/Picea engelmanii Parry had apparent molecular weights of 41, 35, 33, 24 and 22 kD. Minor proteins of 30 and 27.5 kD were also observed. Based on their solubility characteristics, the 41 kD protein was identified as a water and buffer-soluble albumin, and the 35, 33, 24 and 22 kD proteins were characterized as buffer-insoluble, high salt-soluble globulins. Two-dimensional electrophoresis revealed each protein was composed of several isoelectric variants. Developmentally specific accumulation of storage proteins was observed during embryogenesis. The 41 kD protein only accumulated during the later stages of cotyledon maturation, whereas the other storage proteins began to accumulate during the early stages of embryo development. All storage proteins showed major accumulations during cotyledon maturation.     

Silvicultural measures to increase the mechanical stability of pure secondary Norway spruce stands before conversion

This study evaluates the effect of two different thinning treatments (2 and 3), and a control without thinning (1), on stand stability of secondary even-aged Norway spruce stands, in relation to the main risk factors of snow and wind, which should be considered in the period of stand conversion. Treatment 2 is a heavy thinning at top heights of 10, 12.5 and 15 m; treatment 3 starts with the first heavy thinning at the top height of 10 m, but the second and third treatments are delayed till a top height of 20 and 22.5 m are reached. The experimental stands are in secondary Norway spruce forest growing on a site considered unsuitable for that species and especially at risk from snow and storm damage. The investigated thinning variants significantly influenced the stability of the experimental stands. Both thinning treatments encouraged diameter increment and therefore their h/d ratio reached lower levels than the control. In treatment 2, the h/d ratio stabilized in the period of intensive treatment at around 80; i.e., it is the most suitable treatment from the viewpoint of stem-break resistance. Treatment 3 did not stop h/d ratio increase, but slowed it compared to the control variant without thinning. Subsequently the later interventions at the top heights of 20 m and, especially, 22.5 m stopped the increase of the h/d ratio and kept it under the critical value of 90.     

Modelling the epigenetic response of increased temperature during reproduction on Norway spruce phenology

Temperature during seed maturation can induce an epigenetic memory effect in growth phenology of Norway spruce (Picea abies (L.) Karst.) that lasts for several years. To quantify the epigenetic modifications induced by natural climatic variation, common garden experiments with plants originating from different provenances and seed years were performed. Plants from warmer seed years showed delayed phenology with later bud flush, bud set and growth cessation. This effect was quantified by linear models of phenology traits as a function of climate indices for the origin and seed year of the plants. Significant effects of the temperature during seed production (seed year) was found for the bud set in seedlings in their first growing season and for bud flush and growth cessation in the 7th-8th growing season from seed. The models suggest that growth start and growth cessation are delayed 0.7–1.8 days per 100 additional degree days experienced by the seed during embryo development and seed maturation. Models that include factors that are known to induce epigenetic effects could be used to better predict future performance of forest reproductive material.     

Effects of seed pre-soaking on the emergence and early growth of containerized Norway spruce seedlings

To study the effects of seed soaking on seedling emergence and development in Norway spruce [Picea abies (L.) Karst.] two commercial seed lots were soaked for 15 h in aerated water. After soaking, floating and sunken seeds were separated and analyzed prior to being sown in peat-filled containers. Seedling development was followed for one growing season. All sunken seeds were viable according to radiography whereas the floating seeds contained a considerable number of larvae filled and empty seeds. Mean time of emergence of the sunken seeds was approximately 1.5 days shorter than control (i.e. dry) seeds and floating seeds. Soaking had no effect on the time taken for most germinants to emerge in both seed lots, thus failing to synchronize seedling emergence. The later a seedling would emerge, the more likely it was for it to die during the growing season or to be culled at the end of the growing season. Soaking had an inconsistent effect on stem diameter at the end of the growing season and no effect on stem or root biomass. Seedling size uniformity was equal in all treatments. This study suggests that soaking and seed sorting does not guarantee a more uniform seedling crop, but this technique may be useful in upgrading poor quality seed lots of Norway spruce containing a high number of empty or larva infested seeds.     

Potential production of Norway spruce in Sweden

In this paper, the potential stem wood production for Norway spruce was estimated for different regions in Sweden. This was done by using basic physiological relationships of intercepted radiation versus biomass production and knowledge of how a water deficit reduces the potential production, derived from results of field experiments on nutrient optimisation. To scale these relationships up to regional and national levels, data of incident radiation and humidity during the growing season for all of Sweden were used. The figures for potential and attainable production indicate that the temperate to boreal climate allows considerably higher production than the current production, if availability of water and nutrients is non-limiting. In northern Sweden, the attainable production is ca. 300% higher than the current production and in southern Sweden, the yield can be increased by ca. 100%. In absolute numbers, as a mean for a whole rotation period, it is possible to achieve an annual stem-wood dry mass production of 7–9 Mg ha⁻¹ in southern and central and ca. 5–6 Mg in northern Sweden. This increased production would mean that rotation periods can be shorter than they are now by 20–30 years in southern Sweden and by ca. 50–60 years in northern Sweden.     

Storage lipid dynamics in somatic embryos of Norway spruce (Picea abies): histochemical and quantitative analyses

Adequate storage compounds are a prerequisite for successful development during the later stages of somatic embryogenesis; however, the critical amount of reserves below which somatic embryos fail to mature and germinate has not been determined. We analyzed storage lipids during Norway spruce (Picea abies (L.) Karst.) somatic embryogenesis. As maturation progressed, lipids, which were stored as lipid bodies in the cytoplasm, were localized first in suspensor cells of the early embryos, and later in the embryonic root pole, superficial layers of the hypocotyl and in cotyledons. The concentration of total lipids exhibited marked variation, with values peaking during cotyledon development and then decreasing during maturation. Linoleic (18:2), oleic (18:1), palmitic (16:0) and 5,9-octadecenic (5,9-18:2) acids were the most abundant fatty acids in embryos. As embryos developed, linoleic acid concentration increased slightly, whereas oleic acid concentration decreased. Oleic acid was the most prominent component of the fatty acid spectrum in isolated dormant zygotic embryos and megagametophytes. Addition of 5% polyethylene glycol to the medium during somatic embryo maturation caused a shift in the fatty acid spectrum toward that of zygotic embryos. During maturation, changes in the exogenous carbohydrate supply had no significant effect on total lipid concentration in mature embryos. A marked decrease in lipid concentration was detected during desiccation, indicating the importance of adequate lipid reserves during this developmental stage. The lipid content of zygotic embryos differed considerably with harvest year and location, suggesting that zygotic embryo data cannot be an indicator of somatic embryo quality.     

Sap flow of birch and Norway spruce during the European heat and drought in summer 2003

In this study the hydrological regime of Norway spruce (Picea abies) and birch (Betula pendula) growing on heavy soils in the south east of Austria was analysed. Results from the year 2003 characterised by an extremely hot and dry summer are presented in this paper. Due to the extreme weather conditions the soil water content in August 2003 was very low (0.10–0.25 m³ m⁻³) in the topsoil (0–50 cm) with no explicit difference between both tree species.     

Wood defects during industrial-scale production of thermally modified Norway spruce and Scots pine

This research investigates wood defects, particularly the formation of surface cracks, during the production of thermally modified wood and its exposure to cyclic moisture changes. Boards of Norway spruce and Scots pine originating from different steps within the production of ThermoWood® were collected and wood defects were investigated at macroscopic and microscopic scale. Subsequently, the wood was exposed to capillary wetting cycles to record its sensitivity towards cracking. After the modification process, typical anatomical defects of conventional kiln-drying became more frequent and severe, with the magnitude being to some extent depending on the presence of defects in the raw material. At microscopic scale, damages to ray parenchyma and epithelial cells as well as longitudinal cracks within the cell walls of earlywood tracheids were evident in thermally modified wood. Despite a lower water uptake and higher dimensional stability, thermally modified wood was more sensitive to surface cracking during wetting cycles than unmodified wood, i.e. at the outside face of outer boards (near bark). For limiting surface cracking of thermally modified wood during service life, the use of high-quality raw material, the exposure of the inside face of the boards (near pith) and the application of a surface coating are considered beneficial.     

Ascorbic acid changes the pattern of purine metabolism during germination of white spruce somatic embryos

It has previously been shown that exogenous applications of ascorbic acid (AA) increase the conversion frequency of somatic embryos of white spruce (Picea glauca (Moench) Voss). To determine whether ascorbic acid alters purine metabolism during the early phases of embryo germination, the relative rates of purine salvage and degradation were investigated by following the metabolic fates of exogenously applied [8-14C]adenine, [8-14C]adenosine, and [8-14C]inosine, and the activities of several key enzymes. We demonstrated that both the salvage and the degradation pathways operate during germination. Specifically, adenine and adenosine were mainly salvaged to nucleotides and nucleic acids, whereas an appreciable amount of inosine was degraded to CO2 and ureides. Comparisons of purine metabolism between control and AA-treated embryos showed that exogenous applications of ascorbic acid enhanced the ability of the embryos to take up adenine and adenosine throughout the germination period. Furthermore, the higher enzymatic activities of adenosine kinase and adenine phosphoribosyltransferase were responsible for the larger proportion of adenine and adenosine being salvaged in AA-treated embryos compared with control embryos. Thus, there was a positive correlation between the ability to anabolize purine precursors and successful embryo conversion.     

Role of hydrogen peroxide in stress-induced programmed cell death during somatic embryogenesis in Fraxinus mandshurica

We examined how reactive oxygen species, in the form of hydrogen peroxide (H2O2), affect osmotic stress–induced programmed cell death during somatic embryogenesis from cotyledon explants of Manchurian ash (Fraxinus mandshurica Rupr.). We found that substantial osmotic stress was essential for Manchurian ash somatic cells to obtain embryogenic competence. The explant cells displayed hallmarks of programmed cell death, chromatin condensation, and DNA fragmentation to oligonucleotides during somatic embryogenesis. Increasing concentrations of plant growth regulators and sucrose in the medium increased osmotic stress thereby inducing H2O2 accumulation in the explant cells. We found that H2O2 concentration was significantly decreased in explant cells when the induction medium was modified, i.e., when reducing the concentration of sucrose, which reduces the osmotic pressure of the medium, or by withdrawing plant growth regulators at mid-culture. These treatments also decreased the proportion of explant cells undergoing programmed cell death. Accordingly, a decreased rate of somatic embryo induction was observed. These results show that PCD occurred during tissue browning and death of some explant cells during somatic embryogenesis in F. mandshurica. The ROS contributed to PCD in abiotic stress stimulated F. mandshurica cells.     

Life cycle of Lophodermium piceae in Norway spruce needles

The spruce needle inhabiting ascomycete Lophodermium piceae can live symptomless for several years, before it completes its life cycle within less than one year as detailed studies have shown.     

Effects of repeated fertilization in young Norway spruce forests

Several studies have shown the positive effect of nitrogen fertilization on conifer growth. In young Norway spruce (Picea abies) stands, an additional effect of including a mixture of other nutrients has often, but not always, been found. We studied effects of repeated fertilization in 28 stands with young Norway spruce in central Norway. The treatments consisted of plots without nutrient addition (Control), fertilization with 150?kg?N?ha^?1 (150?N), and fertilization with 150?kg?N plus addition of P, K, Mg, B, Mn and Cu (150?N?+?mix), repeated three times with approximately eight years interval. There was a clear positive effect on volume increment of the 150?N and 150?N?+?mix treatments compared to Control, and the effect was significantly higher for 150?N?+?mix than for 150?N. Fertilization had a stronger effect in the first fertilization period than in the second, while the third period was intermediate. The effect of 150?N?+?mix was strongest at plots?>?300?m a.s.l. However, this correlation may be due to geological conditions rather than elevation. Further studies are needed to find out under which edaphic conditions a nutrient mixture will increase growth substantially in young spruce stands.     

Early drought-induced changes to the needle proteome of Norway spruce

To elucidate early drought responses in needles of Norway spruce (Picea abies (Karst.) L.), we subjected 1-year-old seedlings to gradual desiccation for 6 weeks. Four weeks of drought treatment caused a small but significant decrease in photosystem II quantum yield of light-adapted needles (phi(a)) compared with that of well-watered controls. Six weeks of drought treatment reduced phi(a) and the photosystem II quantum yield of dark-adapted needles (phi) by 50 and 8%, respectively, and reduced shoot water potential by 0.7 MPa, but had no measurable effect on needle relative water content. After two weeks of drought treatment, and before there was a discernible effect of drought on phi or a statistically significant effect on shoot water potential, needles were analyzed for changes in protein composition. Five out of several hundred detected proteins in needles of drought-treated plants showed consistent changes compared with control leaves. The proteins were identified by LC-MS/MS as components of the oxygen-evolving complex (oxygen evolving enhancer protein 2), ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit, and one protein of unknown function, whose mRNA was found in a previous screen of wound- and methyl-jasmonate-induced bark proteins.     

Crown density changes of Norway spruce and the influence from increased age on permanent monitoring plots in Norway during 1988–1997

On the ‘local county monitoring plots’ located throughout Norway a reduction of crown density has been noted during the period 1988–1997. The aim of this study was to determine whether this change could be attributed to normal effects due to the increased age of trees in the plots. The dataset comprised around 580 plots and 27 000 single trees of Norway spruce (Picea abies), with 10 years of crown density measurements available for each tree. A two-step approach was used, first to search for an expectancy for normal reduction of crown density by age derived from the dataset, and then to compare this with the actual reduction. The interpretation was somewhat complicated as the various results were dependent upon each other. Highly significant correlations were found between crown density and age. The relationship indicated an annual reduction of crown density of around 0.12%. However, the relationship varied both between years and between regions, and it was not possible to definitely determine whether the relationship was best described by linear or nonlinear models. Of major importance here is that the relationship appeared to be influenced by the presence of stresses, whose effects tended to be more severe in old stands. On this basis it seems questionable whether an expectancy for normal ageing can be properly defined. In the present study, however, it could still be definitely determined that the mean crown density change of—0.41% annually was too negative to be attributed to normal ageing, as it was clearly below all the suggested expectancies from the various models. This suggests that the amount of stress in the period under study has been higher than normal, and this encourages the search for causal agents in further studies. Changes in silviculture may have had some influence. The results were valid for most of Norway, with the exception of western and northern regions. Crown density assessments are subjective, which may possibly give erroneous time trends. However, it is argued that this is less likely to be of major importance in the present data.     

Summer drought: a driver for crown condition and mortality of Norway spruce in Norway

Summer drought, i.e. unusually dry and warm weather, has been a significant stress factor for Norway spruce in southeast Norway during the 14 years of forest monitoring. Dry and warm summers were followed by increases in defoliation, discolouration of foliage, cone formation and mortality. The causal mechanisms are discussed. Most likely, the defoliation resulted from increased needle‐fall in the autumn after dry summers. During the monitoring period 1988–2001, southeast Norway was repeatedly affected by summer drought, in particular, in the early 1990s. The dataset comprised 455 ‘Forest officers’ plots’ with annual data on crown condition and mortality. Linear mixed models were used for estimation and hypothesis testing, including a variance–covariance structure for the handling of random effects and temporal autocorrelation.