Abies Seedlings Research Articles

Seed Treatment with Cold Plasma and Electromagnetic Field: Changes in Antioxidant Capacity of Seedlings in Different Picea abies (L.) H. Karst Half-Sib Families.

In the context of climate change, methods to improve the resistance of coniferous trees to biotic and abiotic stress are in great demand. The common plant response to exposure to vastly different stressors is the generation of reactive oxygen species (ROS) followed by activation of the defensive antioxidant system. We aimed to evaluate whether seed treatment with physical stressors can activate the activity of antioxidant enzymes and radical scavenging activity in young Picea abies (L.) H. Karst seedlings. For this, we applied seed treatment with cold plasma (CP) and electromagnetic field (EMF) and compared the response in ten different half-sib families of Norway spruce. The impact of the treatments with CP (1 min-CP1; 2 min-CP2) and EMF (2 min) on one-year-old and two-year-old P. abies seedlings was determined by the emergence rate, parameters of growth, and spectrophotometric assessment of antioxidant capacity (enzyme activity; DPPH and ABTS scavenging) in needles. The results indicated that the impact of seed treatment is strongly dependent on the genetic family. In the 577 half-sib family, the activity of antioxidant enzymes catalase (CAT), ascorbate peroxidase (APX), peroxidase (POX), and glutathione reductase (GR) increased after EMF-treatment in one-year-old seedlings, while similar effects in 477 half-sib family were induced by CP2 treatment. In two-year-old seedlings, CP1-treatment increased CAT, APX, POX, GR, SOD, DPPH, and ABTS activity in the 457 half-sib family. However, no significant impact of the treatment with CP1 was determined in one-year-old seedlings in this family. The application of novel technologies and the consideration of the combinatory impact of genetic and physical factors could have the potential to improve the accumulation of compounds that play an essential role in the defense mechanisms of P. abies. Nevertheless, for different resistance and responses to stressors of plants, their genetic properties play an essential role. A comprehensive analysis of interactions among the stress factors (CP and EMF), genetic properties, and changes induced in the antioxidant system can be of importance both for the practical application of seed treatment in forestry and for understanding fundamental adaptation mechanisms in conifers.

Elevation-Dependent Natural Regeneration of Abies georgei var. smithii Forest in Southeastern Tibet

The comprehensive impacts of biotic and abiotic factors on the natural regeneration of Abies georgei var. smithii (Abies) forests in Tibet are not thoroughly understood. To address this gap, our study focused on the regeneration densities of Abies seedlings, saplings, and small trees across 21 plots (each 20 m × 20 m) along an elevation gradient from 3730 m to 4330 m in the Sygera Mountains of Southeastern Tibet. We meticulously measured a suite of 11 variables that describe stand structures and ecological conditions. Through analyses using Spearman’s correlation analysis, hierarchical partitioning, and multiple linear regression, we identified key ecological drivers for successful Abies regeneration. Our results highlighted a peak in the abundance of seedlings, saplings, and small trees at an elevation of 3930 m. As the elevation rose from 3730 m to 4330 m, we observed an initial increase followed by a decrease in canopy cover (canopy), mother tree density (MotherT), 1000-seed weight (SeedW), litter thickness (LitterT), moss cover (MossC), moss thickness (MossT), soil moisture (SM), and soil bulk density, while mean annual temperature and soil depth to permafrost consistently decreased. The critical ecological drivers for Abies natural regeneration were identified as follows: MossT was pivotal for seedling density; canopy and MossC were influential for sapling density, and MotherT was the main factor affecting the density of small trees. This study suggests that a high density of mother trees and a thick and highly covered layer of moss are conducive to the natural regeneration of Abies in the Sygera Mountains. Understanding the current status of regeneration is vital for informing conservation and management strategies for Abies forests in Tibet.

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.

Evaluating foliar characteristics as early indicators of plant response to biochar amendments

Biochar amendments are widely promoted for increasing soil nutrient availability and plant yield, and although many plant species show positive growth responses, neutral to negative effects can also occur. Although biochar effects on plant yield may not yet be evident in the first growing season after amendment, foliar characteristics such as nitrogen (N) and chlorophyll concentrations are known to respond to changes in soil fertility and therefore may provide an early indication of plant performance. In this study, we investigated the effects of contrasting biochar treatments on soil nitrogen (N) forms and plant chlorophyll, and the relationships between soil and plant nitrogen status, for two economically important conifer species, Abies balsamea (L.) Mill and Picea pungens Englem., as well as forb and grass weeds. We applied two types of pyrolysis biochars (hereafter, USB and BGR) that differed in feedstock type (pine wood versus mixed forest harvesting residue) at contrasting application rates (low, high, and untreated control) to a fine sandy loam soil. We measured soil water content (SWC), pH, and inorganic nitrogen (NH4+, NO3−, and total inorganic N (TIN)), as well as plant foliar N, and chlorophyll content (Chl-a, -b, -ab), and fluorescence (Fv/Fm). SWC response was variable whereas all treatments except USB low increased pH. All treatments decreased inorganic N concentrations relative to the control, although differences diminished over the study period. USB high decreased Picea foliar N concentration whereas all treatments decreased grass foliar N. BGR decreased Abies Fv/Fm (low) and Picea Chl-a, Chl-ab (both levels), and Chl-b (low), whereas USB increased Abies Chl-ab (high). There was a weak positive relationship between foliar N and soil NH4+ (r2 = 0.14) and NO3− (r2 = 0.11) in Abies seedlings, and between foliar N and TIN (r2 = 0.16, 0.11) in both conifers. Abies foliar N showed a weak positive effect on Chl-a (r2 = 0.22), Chl-b (r2 = 0.10), and Chl-ab (r2 = 0.22). Soil NO3− (r2 = 0.14) and TIN (r2 = 0.14) showed a weak negative correlation with Picea foliar Fv/Fm. This study shows that biochar type and amendment level influence soil and plant nitrogen responses, as well as their relationships, and responses may differ between plant species. Evaluating foliar characteristics shows promise as an early indicator of plant response to biochar, and may provide additional important information for evaluating contrasting biochars as potential sustainable soil amendments.

Using associational effects of European beech on Norway spruce to mitigate damage by a forest regeneration pest, the pine weevil Hylobius abietis

Forest regeneration can be compromised by insect damage to newly-planted conifer seedlings, with the pine weevil, Hylobius abietis, being the most economically important pest in Europe. Seedling protection strategies include physical barriers, silvicultural measures and insecticides, while the potential benefits of Associational Effects (AE) have been little explored. Associational Resistance (AR) or Susceptibility (AS) arise when neighbouring plants decrease or increase, respectively, the likelihood and extent of attack on a focal plant. We investigated the potential of European beech, Fagus sylvatica, to mediate AE for Norway spruce, Picea abies, seedlings against pine weevil damage. First, we examined the effects of neighbor identity on damage to P. abies at a small scale, using choice arenas in the lab. Then, in the field, we examined these effects at a larger scale using plots containing only Norway spruce, or both species. We found that P. abies seedlings were attacked and damaged less by weevils when beech was their close neighbor, relative to having another Norway spruce as a neighbor in the lab. Yet, no difference in damage between only spruce and mixed seedling plots was found in the field. Our results indicate that the susceptibility of P. abies to H. abietis can be influenced by neighbor identity, and effects can vary with inter-plant distance. In close proximity, the presence of the non-host F. sylvatica can alter pine weevil feeding behaviour and thus, has the potential to mediate AR. However, these associational effects appear not to provide enhanced seedling protection at a larger scale.

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.

Drivers of forest regeneration patterns in drought prone mixed-species forests in the Northern Calcareous Alps

In temperate mountain forests of Northern Calcareous Alps, shallow soils, in combination with steep slopes and high radiation input on sun-exposed slopes, imply severe conditions for tree regeneration. Considering the remarkable trend of temperature increase and related climatic extremes in the Greater Alpine Area, it is likely that conditions for successful regeneration further deteriorate at these sites. Hence, investigating the relation of regeneration patterns to site conditions is crucial for recent and future forest management. Spatial point process models are appropriate tools to test the effect of environmental covariates in plant pattern generation. By applying these methods, we aim at identifying driving factors of forest regeneration dynamics of Fagus sylvatica, Abies alba and Picea abies. We used tree regeneration data from two sample sites along transects from closed canopy to forest gaps of natural origin. A set of spatially continuous explanatory variables (light environment, rock outcrops, microrelief, distance to mature trees, estimated seed density and presence of already established saplings) were generated. We fitted nonstationary parametric intensity functions with Poisson point process models and Thomas cluster point process models. The first and second order processes were analysed with pair correlation summary statistics. Interactions between regeneration patterns of different species and height classes were assessed with cross-pair correlation summary statistics. Successful germination and growth, at least at some microsites, is possible for any of the investigated species when ungulate browsing is prevented by fencing. Light is the most important environmental factor for describing the regeneration patterns. As higher shading has a positive influence, it is apparently not a limiting resource but rather a proxy for other, latent unfavourable conditions like drying of seedbeds. We thus propose to limit canopy opening sizes to a maximum of 10–12 m. No indications of seed limitation as a cause for regeneration failure of any of the main tree species were detected. Conditions for A. alba seedlings and partly also for P. abies seedlings are more favourable under the canopy of F. sylvatica than under the canopies of conspecifics or the other conifer species. Therefore, we conclude that at our study sites with the current species mixture, at least for the two conifer species, safe microsites are more important than seed availability. With increasing height of P. abies, the spatial segregation of small A. alba and F. sylvatica seedlings became stronger, indicating that competition for resources becomes more dominant and determinant for species coexistence.