Picea Abies Seedlings Research Articles

Winter warming response of gas-exchange and growth of Abies alba and Picea abies seedlings

Winter warming response of gas-exchange and growth of Abies alba and Picea abies seedlings

Contrasting effects of two hydrogels on biomass allocation, needle loss, and root growth of Picea abies seedlings under drought

Adapted management methodologies are required to alleviate increasing and/or more frequent water stress under climate change, enabling successful tree seedling establishment after planting. Hydrogel amendments have been suggested to increase soil water holding capacity, tree seedling growth and survival. However, the effect of a non-uniform addition of hydrogels to tree planting pits as compared to homogenously admixed hydrogels in agricultural soils, as well as effects of hydrogels on woody root system establishment, have been poorly studied.Here we studied the effect of two commercial hydrogels (Polyter and Stockosorb) on the above- and belowground growth of Picea abies seedlings during a ∼ 5-weeks-long drought period. Rhizoboxes with a non-uniform distribution of nutrients and hydrogels were used to monitor root system development in a stratified soil. Biomass allocation, root morphology and root elongation rates were related to evapotranspiration rates. Proximity effects of hydrogels on root traits were determined.Total plant biomass was significantly greater if plants were grown in Polyter-amended soil (+16, 17 %) compared to the Stockosorb and control treatments, respectively. Dead needle mass was significantly greater in Stockosorb than in Polyter (+719 %) and control (+274 %). Root elongation was faster in both hydrogel treatments compared to the control during the first part of the drought period, but subsequently ceased to the order Polyter > control > Stockosorb. Root morphological changes in relation to hydrogels were limited.The better performance of Polyter-amended seedlings was related to a slow water release from the hydrogel, while Stockosorb released the additional soil water content prematurely. The latter might have imposed a “false sense of security”, and the subsequent lack of acclimation responses early in the drought resulted in an even more severe drought stress and a higher needle loss of Stockosorb-amended seedlings as compared to control. However, both hydrogels did not result in preferential growth towards or away from the hydrogel, suggesting that roots did neither sense the hydrogel-bound water nor that secondary compounds hampered root growth. A deeper root system placement and thus potential advantages for drought events at later growth stages were not encountered, asPolyter also had a strong positive effect on root growth in the fertile top soil. As hydrogel amendments may influence root system establishment and seedling vitality differently during drought, further studies are urgently needed before large scale applications to mitigate climate change effects on forest regeneration / restoration can take place.

Outbreak of Pityogenes chalcographus and Pityophthorus pityographus on Spruce Seedlings Resulting from Inappropriate Management in a Forest Nursery

In this report, we describe a local outbreak of small bark beetles on 4-year-old seedlings of Picea abies in a forest nursery in Central Europe in 2021. In March 2022, 10–50% of the seedlings were “dry” (i.e., with dry and easily broken twigs and with easily peeled bark) in each 4-row bed in the nursery. Half of the dry plants were completely covered by galleries of bark beetles and another 35% of the seedlings were with one or two bark beetle galleries. Almost 90% of the beetles found on the affected seedlings were Pityogenes chalcographus, and only 10% were Pityophthorus pityographus (we studied 100 seedlings in the second bed). The chipping of Picea pungens in previous years had left many felled trunks, branches, and other logging residues in the area. These residues are covered by galleries of both bark beetles. We suggest that, after multiplying on the logging residues, the beetles could not find suitable material for reproduction and were lured to the nursery seedlings, which had been weakened by location (a location that provided inadequate shade and no wind protection) and by repeated replanting.

FEATURES OF THE ROOT SYSTEM DEVELOPMENT IN PICEA ABIES (L.) H. KARST. SEEDLINGS PLANTED UNDER SHELTERWOOD IN A MOIST BILBERRY SPRUCE FOREST DEPENDING ON SOIL PREPARATION METHODS

The effect of soil preparation (no soil preparation (control), mounding, and removal of the humus layer) on the parameters of root systems of Picea abies seedlings was analyzed. The soil preparation methods have not influenced the total root biomass. Seedlings growing on mounds demonstrated both extensive and intensive mechanisms of utilizing soil resources (increasing the length of conducting roots and the average length of last-order roots, enlarging the surface area of last-order roots by increasing the diameter of ectendomycorrhiza (EEM) and its share among last-order roots). Many parameters had similar values in the control plots and in the plots with the removed humus layer (length of conducting roots, average length of last-order roots, surface area of one ectomycorrhiza (EM), total surface area of tips (TSA), percentages of EM, EEM, and roots with disturbed structure among last-order roots, the ratio of EM and EEM surface areas in the TSA). The differences between the root systems of P. abies seedlings in the plots with removed humus and those in the control are manifest in the intensification of the use of soil resources (by increasing the EEM diameter and the density of last-order roots). The soil preparation methods have not influenced the formation of EM. The surface area of EM in plots with mounding and humus removed did not change versus the control, but the intensity of EM mycorrhization among last-order roots was different. The diameter and the intensity of mycorrhization of EEM were the parameters the most significantly altered by soil preparation. All the examined cross-sections of last-order roots had endotrophic features.

Влияние Amanita muscaria (класс Agaricomycetes, сем. Amanitaceae) иFlammulina velutipes(классAgaricomycetes, сем. Physalacriaceae) на рост и развитие сеянцев Picea abies (класс Pinophyta, сем. Pinaceae) и Abies sibirica (класс Pinophyta, сем. Pinaceae)

The article presents studies of the influence of Amanita muscaria and Flammulina velutipes on the growth and development of seedlings of species of the Pinaceae family. The positive effect of mycorrhization by these fungi species on the growth and development of Picea abies and Abies sibirica was established. Thus, the presence of Flammulina velutipes and Amanita muscaria in the substrate accelerated the appearance of the first shoots by 4–8 days. Mycorrhization of Amanita muscaria influenced the morphometry of the seedlings of Picea abies and Abies sibirica. The main root length changed: in Picea abies it increased by 17.2%, in Abies sibirica it decreased by 12.9%, compared with the control group. In the presence of Amanita muscaria, the length of lateral roots increased by 51.0% in Picea abies seedlings, and by 32.4% in Abies sibirica seedlings, compared with the control group. The height of the aerial part in the presence of Flammulina velutipes increased in comparison with the control group in Picea abies seedlings by 52.2% and in Abies sibirica seedlings by 18.3%. Mycorrhization of Amanita muscaria seedlings caused an increase in the stem diameter at the root collar of Picea abies seedlings by 13.6%, and Abies sibirica seedlings by 12.1%.

Transcriptome analysis shows nicotinamide seed treatment alters expression of genes involved in defense and epigenetic processes in roots of seedlings of Picea abies

Nicotinamide treatment of plants and plant cell cultures has been shown to promote defense and decrease levels of DNA methylation. In the present study, we used RNA-seq technology to study overall changes in gene expression induced in roots of 3-month-old spruce (Picea abies) seedlings grown from nicotinamide-treated seeds to examine the molecular mechanisms underlying the defense promotion. Approximately 350 genes were identified as differentially expressed in roots after the seed treatment. Stress response genes, including transcription factors MYB77 and LHY and two chitinase enzymes, were generally upregulated, whereas genes thought to be involved in epigenetic regulation such as DDM1, known to promote DNA methylation, were present at high frequency among the downregulated genes. Across all samples, the expression of downregulated epigenetic-related genes was highly correlated with the nicotinamide treatment, indicating a common regulation. Our results support an earlier hypothesis regarding a potential role of nicotinamide as a defense-signal mediator.

Constitutive and inducible chemical defences in nursery-grown and naturally regenerated Norway spruce (Picea abies) plants

Nursery-grown Norway spruce Picea abies seedlings are often heavily attacked by the pine weevil Hylobius abietis on clear-cuts the first years after planting. Because the seedlings are not resource-limited during the growing phase in the nursery they are expected to invest less in defence than naturally regenerated seedlings already present on the clear-cuts. The latter have had to cope with various environmental stressors that could make them invest more in defence. We tested if naturally regenerated plants have stronger chemical defences than nursery-grown plants. Nursery-grown plants were planted in-between naturally regenerated plants on fresh clear cuts, and phenolic and terpene compounds in the stem bark were measured after one growing season. To test both constitutive and inducible defences, plants were either wounded, painted with methyl jasmonate (MeJA) to induce defences, or given a combination of both treatments. Growth and pine weevil attacks of the plants were registered.Nursery-grown plants had higher total concentrations of phenolic compounds and lower concentrations of terpenes than naturally regenerated plants. These opposite responses were reflected in very different compound profiles in the two plant types. We suggest the differences between plant types to be results of differences in plant age, stress level, genetic origin or possibly a combination of these factors. Most compounds showed no response to wounding, MeJA-treatment or wounding and MeJA-treatment combined, but the terpenes 3-carene, eucalyptol, limonene and para-cymene had higher concentrations in MeJA-treated nursery-grown plants than in control plants. These compounds are known to be effective in conifer resistance against weevils and bark beetles. Overall, 27% of our 400 study plants had signs of pine weevil damage after 3 ½ months in the field. However, treatment or plant type had no significant effect on whether plants were attacked or not and this might have been a result of the relatively low overall level of attacks in this study. Further studies are needed to disentangle the importance of plant age, stress level, genetic origin and resource availability for chemical defence mechanisms of young Norway spruce plants, as strengthening the natural resistance of nursery plants may be increasingly important in a future with less pesticide use.

DNA-Metabarcoding of Belowground Fungal Communities in Bare-Root Forest Nurseries: Focus on Different Tree Species.

The production of tree seedlings in forest nurseries and their use in the replanting of clear-cut forest sites is a common practice in the temperate and boreal forests of Europe. Although conifers dominate on replanted sites, in recent years, deciduous tree species have received more attention due to their often-higher resilience to abiotic and biotic stress factors. The aim of the present study was to assess the belowground fungal communities of bare-root cultivated seedlings of Alnus glutinosa, Betula pendula, Pinus sylvestris, Picea abies and Quercus robur in order to gain a better understanding of the associated fungi and oomycetes, and their potential effects on the seedling performance in forest nurseries and after outplanting. The study sites were at the seven largest bare-root forest nurseries in Lithuania. The sampling included the roots and adjacent soil of 2–3 year old healthy-looking seedlings. Following the isolation of the DNA from the individual root and soil samples, these were amplified using ITS rRNA as a marker, and subjected to high-throughput PacBio sequencing. The results showed the presence of 161,302 high-quality sequences, representing 2003 fungal and oomycete taxa. The most common fungi were Malassezia restricta (6.7% of all of the high-quality sequences), Wilcoxina mikolae (5.0%), Pustularia sp. 3993_4 (4.6%), and Fusarium oxysporum (3.5%). The most common oomycetes were Pythium ultimum var. ultimum (0.6%), Pythium heterothallicum (0.3%), Pythium spiculum (0.3%), and Pythium sylvaticum (0.2%). The coniferous tree species (P. abies and P. sylvestris) generally showed a higher richness of fungal taxa and a rather distinct fungal community composition compared to the deciduous tree species (A. glutinosa, B. pendula, and Q. robur). The results demonstrated that the seedling roots and the rhizosphere soil in forest nurseries support a high richness of fungal taxa. The seedling roots were primarily inhabited by saprotrophic and mycorrhizal fungi, while fungal pathogens and oomycetes were less abundant, showing that the cultivation practices used in forest nurseries secured both the production of high-quality planting stock and disease control.

Effect of site preparation under shelterwood on Norway spruce seedlings

ABSTRACT The effect of site preparation (mixed mounding and removal of the humus layer) under a shelterwood of mixed boreal forest along a forest interior-edge gradient on Norway spruce (Picea abies) seedlings was studied two years after planting. Mounds had a positive effect on root development, ectomycorrhiza formation and the absorption of nitrogen (N) and phosphorus (P) in the seedlings, and augmented their survival, growth and biomass. Humus removal had an adverse effect on the root biomass and ectomycorrhiza formation. A decreased soil fertility after the removal of humus led to a low N and P content in the seedlings. Two years after planting, humus removal had not affected the growth of the seedlings, but reduced their biomass. The influence of the forest edge, compared to the interior plot, was mostly associated with a decrease in the stand density, reduced amount of litter and increased light availability for the seedlings.

Red Light Controls Adventitious Root Regeneration by Modulating Hormone Homeostasis in Picea abies Seedlings.

Vegetative propagation relies on the capacity of plants to regenerate de novo adventitious roots (ARs), a quantitative trait controlled by the interaction of endogenous factors, such as hormones and environmental cues among which light plays a central role. However, the physiological and molecular components mediating light cues during AR initiation (ARI) remain largely elusive. Here, we explored the role of red light (RL) on ARI in de-rooted Norway spruce seedlings. We combined investigation of hormone metabolism and gene expression analysis to identify potential signaling pathways. We also performed extensive anatomical characterization to investigate ARI at the cellular level. We showed that in contrast to white light, red light promoted ARI likely by reducing jasmonate (JA) and JA-isoleucine biosynthesis and repressing the accumulation of isopentyl-adenine-type cytokinins. We demonstrated that exogenously applied JA and/or CK inhibit ARI in a dose-dependent manner and found that they possibly act in the same pathway. The negative effect of JA on ARI was confirmed at the histological level. We showed that JA represses the early events of ARI. In conclusion, RL promotes ARI by repressing the accumulation of the wound-induced phytohormones JA and CK.

Seasonal timing and recurrence of methyl jasmonate treatment influence pine weevil damage to Norway spruce seedlings

Defense can be induced in conifer seedlings to reduce pine weevil (Hylobius abietis) damage, by treatment with the plant hormone methyl jasmonate (MJ). Few studies have addressed important practical issues regarding the use of MJ such as treatment incidence and timing, seedling age and its compatibility with plant nursery practices. We examined if levels of pine weevil damage depend on seasonal timing and recurrence of MJ treatment, and if the observed effects depend on plant age. Norway spruce (Picea abies) seedlings from two age cohorts (1 year and 1.5 years old) received four MJ treatments: MJ application before winter storage in the previous year, after winter storage but before spring/summer planting, repeated MJ application (both before winter storage, and before planting) or no MJ application at all. Pine weevil damage was evaluated in a lab and field experiment. We found that the timing and recurrence of MJ treatment affected the amount of damage inflicted by pine weevils in different ways, but these effects were consistent among age cohorts. MJ application before winter storage provided the most effective protection, and this reduction in damage was comparable to that provided by a currently used physical protection method against pine weevil feeding. Our results indicated that MJ can be applied in line with nursery practices (before winter storage) and provides adequate protection for two growing seasons.

First report of Calonectria montana causing damping‐off disease on pine and spruce seedlings in Europe

AbstractIn 2015–2016, damping‐off symptoms were observed on Pinus sylvestris and Picea abies seedlings in four forest nurseries in Poland. Some Calonectria isolates were obtained from symptomatic seedlings by culturing pieces of necrotic tissue on malt extract agar.Morphological and molecular analyses revealed that isolates represent Calonectria montana, a recently described species from natural forests in China. The isolates represent the first detection of this species outside of Asia. Pathogenicity tests demonstrated that C. montana is a severe pathogen of P. sylvestris seedlings.

Light Shock Stress after Outdoor Sunlight Exposure in Seedlings of Picea abies (L.) Karst. and Pinus sylvestris L. Pre-Cultivated under LEDs—Possible Mitigation Treatments and Their Energy Consumption

Year-round cultivation under light emitting diodes (LEDs) has gained interest in boreal forest regions like Fenno-Scandinavia. This concept offers forest nurseries an option to increase seedling production normally restricted by the short vegetation period and the climate conditions. In contrast to some horticultural crops which can be cultivated entirely under LEDs without sunlight, forest seedlings need to be transplanted outdoors in the nursery at a very young age before being outplanted in the field. Juvenile plants are less efficient using absorbed light and dissipating excess energy making them prone to photoinhibition at conditions that usually do not harm mature plants. The outdoor transfer can cause stress in the seedlings due to high sunlight intensity and exposure to ultraviolet (UV) radiation not typically present in the spectra of LED lamps. This study tested possible treatments for mitigating light shock stress in seedlings of Picea abies (L.) Karst. and Pinus sylvestris L. transplanted from indoor cultivation under LEDs to outdoor sunlight exposure. Three sowings were carried out in 2014 (May and June) and 2015 (May) cultivating the seedlings during five weeks under LED lights only. Afterwards, higher light intensity or UV radiation treatments were applied during one week in order to adapt the seedlings to natural outdoor conditions. After transplanting a transition phase was introduced using shading cloths for one or three weeks as outdoor treatments for light shock mitigation. Chlorophyll fluorescence (ChlF) levels and CO2 assimilation rates were measured before transplanting and followed outdoors during 5 weeks. The ChlF results revealed stress symptoms in the photoreceptors during the first days after transplanting. After five weeks outdoors the ChlF levels had recovered and the light saturation points had shifted, allowing higher CO2 assimilation rates. By the end of the vegetation period the morphological attributes showed no major differences between treatments.

Treatments for induction of cold hardiness in Picea abies (L.) Karst. and Pinus sylvestris L. seedlings pre-cultivated under light-emitting diodes – impact of photoperiod and temperature including energy consumption and seedling quality after cold storage

ABSTRACTIn Nordic climates, the weather allows a narrow time window during spring and summer for forest seedlings to be transplanted from indoor growth to outdoor conditions. If a new method for year-round cultivation under LED lamps is to be successfully introduced in forest nurseries, a cold storage phase for batches produced outside of the vegetation period needs to be included in the concept. Different short-day treatments for induction of cold hardiness in very young seedlings of Picea abies and Pinus sylvestris cultivated solely under LED lamps were investigated. The study compared a combination of two photoperiods (5 h or 8 h) at three different temperatures (5°C, 10°C or 20°C) applied during five weeks. Chlorophyll fluorescence, shoot electrolyte leakage and molecular testing for gene expression of cold acclimation were used to assess the treatments. After a period of three months in cold storage at 2°C, the vitality of the seedlings was evaluated using a root growth capacity test. Lower temperatures during the treatments, especially for Pinus sylvestris, had a significant effect on inducing cold hardiness. The results showed that the photoperiod should not be overly reduced to allow photosynthesis and generation of carbohydrate reserves but it could be optimized to reduce electricity consumption.

Pathogenicity of Thekopsora areolata from seed orchards in Finland on Prunus spp. and Picea abies

AbstractPathogenicity of cherry‐spruce rust, Thekopsora areolata, was investigated by inoculations with aeciospores from seven Norway spruce, Picea abies, seed orchards that had suffered from successive severe rust epidemics in the 2000s in Finland. Detached leaves of Prunus spp. were inoculated in the laboratory using aeciospores from cones of various ages. In the greenhouse, live Prunus padus plants were inoculated, and possible autoecism of the rust was tested by inoculations of Picea abies seedlings. Thirty‐five spore sources from the seed orchards formed uredinia on Prunus spp. in the laboratory 2 weeks after incubation, but no telia developed. In the greenhouse, uredinia developed on live P. padus, but no rust symptoms, cankers or sporulation were detected on Picea abies. Thus, no evidence of autoecism was observed among the T. areolata populations and therefore all populations, suggesting all those tested from the Finnish seed orchards were heteroecious.

Can methyl jasmonate treatment of conifer seedlings be used as a tool to stop height growth in nursery forest trees?

A plant's induced defense system can be triggered by the application of the plant hormone methyl jasmonate (MeJA), and recent research suggest that MeJA treatment may become a tool for protection of conifer seedlings against insect herbivory (e.g. by the pine weevil Hylobius abietis). A side-effect of MeJA application is temporarily reduced height growth. This has generally been considered as negative, but in forest tree nurseries this could instead be beneficial since it is commonly desired to stop the growth of nursery seedlings in late summer. Artificially longer dark periods (long nights/short days) are widely used in high-latitude nurseries to terminate height growth and induce freezing tolerance. However, long night treatment requires specialized nursery equipment and are labor intensive. Therefore alternatives are sought after. We compared long-night and MeJA treatments by following the growth of Norway spruce (Picea abies) seedlings throughout one season. The regulatory effect of MeJA on height growth was similar if not even better than that of long nights, i.e. it was terminated faster. However, MeJA treatment also reduced root growth and delayed the development of freezing tolerance. MeJA may therefore not replace long-night treatments, but it could facilitate a more flexible application of long nights by gaining a longer time interval during which this treatment can be used without risking the seedlings growing too large.

Above- and belowground growth response of Picea abies seedlings exposed to varying levels of soil relative bulk density

During mechanized forest operations, machines with high wheel loads are operated directly on the soil and can pose serious concerns for the integrity and quality of soil properties. Simply relying on absolute soil density (g cm−3 or t m−3) as a measure of qualitative assessment remains site specific. Instead of absolute soil density, the aim of this study was to assess and quantify the above- and belowground biomass growth response of Norway spruce (Picea abies [L.] Karst) seedlings exposed to varying relative bulk densities (RBD), expressed as a ratio between field bulk density and maximum bulk density achieved through the standard Proctor test. In the laboratory study, silt loam collected from a forest stand located near Munich, Germany, was placed inside 24 chambers (30.6 cm in length, 8.2 cm in width, and 42.0 cm in height) and compacted layerwise with a hydraulic press until the target RBD levels (0.67, 0.72, 0.77, and 0.82) were reached. After compaction, 120 Norway spruce seeds were sown and growth was monitored for 156 days. Morphologic measurements of 102 seedlings were performed after the growing period where root, shoot, and needle growth characteristics and mass were recorded. Detailed root analysis was performed with the WinRHIZO software, and nutrient analysis was performed on the soil as well as the root, shoot, and needle components of seedlings. Results indicate statistically lower average root (48%), shoot (43%), and needle (43%) mass per seedling for seedlings growing on the RBD 0.82 as compared to those growing on the RBD 0.67. Most analyses revealed no statistical differences between the two lower RBD levels, while statistical differences were detected as the RBD increased to 0.77 and 0.82. The use of RBD as a means of qualitative assessment of soil properties showed promise and should be investigated further for other economically important European tree species, while taking into consideration a longer monitoring period.

Biosynthesis of Protoilludene Sesquiterpene Aryl Esters by Siberian Strains of the Genus Armillaria Fungi

Secondary metabolites of the basidiomycetes of Armillaria borealis Marxm. and Korhonen, A. cepistipes Velen., A. gallica Marxm., A. ostoyae (Romagn.) Herink, and A. sinapina Berube and Dessur isolated in Southern Siberia (Krasnoyarsk region and Tyva Republic) and in the Far East (Sikhote-Alin) were studied. Metabolites belonging to the class of protoilludene sesquiterpene aryl esters of the melleolides group have been identified in the species A. borealis, A. cepistipes, and A. sinapina. The strains differ in the spectrum of synthesized melleolides. A. borealis strain 74g synthesized a wider range of melleolides than other strains of the species: melleolides B, C, D and H, melledonals B and C, 5'-O-methylmelledonal, 13-hydroxy-5'-O-methylmelledonal, and armillarinin. It was shown that the composition of the medium influenced the amount of synthesized metabolites. All of the studied strains synthesizing melleolides exhibited a toxicogenic and phytopathogenic effect on seeds and seedlings of Picea abies (L.) H. Karst. and Abies sibirica Ledeb. A significant decrease in seed germination energy, laboratory and ground seed germination, the development of the root system of conifer seedlings was revealed. The maximum inhibitory effect was shown by the culture fluid of A. borealis 74g with the greatest amounts and variety of melleolides in the metabolome profile.

Comparative analysis of abscisic acid levels and expression of abscisic acid-related genes in Scots pine and Norway spruce seedlings under water deficit

Abscisic acid (ABA) is one of the main participants in the regulation of plant responses to water deficiency. Knowledge of the ABA signal transduction pathways in gymnosperms is rather limited, especially in comparison with those in angiosperms. Seedlings of Scots pine and Norway spruce are known for their contrasting behaviour strategies under water deficit. To characterize the possible role of ABA in these differences, ABA dynamics were investigated under conditions of water deficit in seedlings of these two species. The content of ABA and its catabolites was followed in the roots and needles of seedlings of Pinus sylvestris and Picea abies under conditions of polyethylene glycol (PEG)-induced water deficiency (−0.15 and −0.5 MPa) for 10 days. The expression of the main genes for ABA-biosynthetic enzymes was also analysed. ABA showed more pronounced stress-dependent dynamics in pine roots than in spruce roots, whereas in needles, the response was greater for spruce than pine. The ABA increase during drought was mainly due to de novo synthesis and the shift in the balance between ABA synthesis and catabolism towards synthesis. The ABA-glucosyl ester did not serve as a reserve for the release of free ABA under water deficiency. The expression levels of the main ABA biosynthetic genes showed a weak or no correlation with changes in ABA content under water stress, i.e., the ABA content in the seedlings of both species was not directly linked to the transcript levels of the main ABA biosynthetic genes. Less-pronounced stress-induced changes in ABA in pine needles than in spruce needles may be related to pine seedlings having a less conservative strategy of growth and maintenance of water balance under water deficit.

Morphology and phenology in Picea abies seedlings in response to split short day treatments

Short-day (SD) treatment is used by forest nurseries to induce growth cessation in Picea abies seedlings. SD treatment may however increase the risk of reflushing in autumn and earlier bud break the following spring. We tested how different starting dates and durations of SD treatment influenced on morphological and phenological traits. Regardless of timing and duration of the SD treatment, height growth was reduced compared to the untreated controls. Seedlings given split SD (7+7 days interrupted with two weeks in long days) had less height growth than all other treatments. Root collar diameter growth was significantly less in control seedlings than in seedlings exposed to early (7 or 14 days) or split (7+7 days) SD treatment. There were also differences in the frequency of reflushing and bud break timing among the SD treated seedlings, dependent on duration and starting date. If the SD treatment started early, a continuous 14-day SD treatment was not sufficient to avoid high frequencies of reflushing. However, by splitting the SD treatment into two periods of 7+7 days these negative effects were largely avoided, although spring bud break occurred earlier than in the controls.