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.

The aim of the present study was to assess fungal and oomycete communities in the irrigation water of forest nurseries, focusing on plant pathogens in the hope of getting a better understanding of potential pathogenic microorganisms and spreading routes in forest nurseries. The study sites were at Anykščiai, Dubrava, Kretinga and Trakai state forest nurseries in Lithuania. For the collection of microbial samples, at each nursery five 100-L water samples were collected from the irrigation ponds and filtered. Following DNA isolation from the irrigation water filtrate samples, these were individually amplified using ITS rDNA as a marker and subjected to PacBio high-throughput sequencing. Clustering in the SCATA pipeline and the taxonomic classification of 24,006 high-quality reads showed the presence of 1286 non-singleton taxa. Among those, 895 were representing fungi and oomycetes. The detected fungi were 57.3% Ascomycota, 38.1% Basidiomycota, 3.1% Chytridiomycota, 0.8% Mucoromycota and 0.7% Oomycota. The most common fungi were Malassezia restricta E. Guého, J. Guillot & Midgley (20.1% of all high-quality fungal sequences), Pezizella discreta (P. Karst.) Dennis (10.8%) and Epicoccum nigrum Link (4.9%). The most common oomycetes were Phytopythium cf. citrinum (B. Paul) Abad, de Cock, Bala, Robideau, Lodhi & Lévesque (0.4%), Phytophthora gallica T. Jung & J. Nechwatal (0.05%) and Peronospora sp. 4248_322 (0.05%). The results demonstrated that the irrigation water used by forest nurseries was inhabited by a species-rich but largely site-specific communities of fungi. Plant pathogens were relatively rare, but, under suitable conditions, these can develop rapidly, spread efficiently through the irrigation system and be a threat to the production of high-quality tree seedlings.

Eurasian aspen (Populus tremula L.) is a tree species with recognised ecological and economic importance for both natural and plantation forests. For the fast cloning of selected aspen genotypes, the method of plant propagation through in vitro culture (micropropagation) is often recommended. The efficiency of this method is related to the use of shoot-inducing chemical growth regulators, among which cytokinins, a type of plant hormone, dominate. Although cytokinins can inhibit rooting, this effect is avoided by using cytokinin-free media. This study sought to identify concentrations and combinations of growth regulators that would stimulate one type of P. tremula organogenesis (either shoot or root formation) without inhibiting the other. The investigated growth regulators included cytokinin 6-benzylaminopurine (BAP), auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA), auxins indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA), gibberellin biosynthesis inhibitor paclobutrazol (PBZ), and a gibberellin mixture (GA₄/₇). Both BAP and TIBA increased shoot number per P. tremula explant and decreased the number of adventitious roots, but TIBA, in contrast to BAP, did not inhibit lateral root formation. However, for the maintenance of both adventitious shoot and root formation above the control level, the combination of PBZ and GA_4/7 was shown to be especially promising.

Background. Micropropagation of silver birch (Betula pendula Roth) is used to obtain healthy plant material for high-value plantations. The aim of this study was to evaluate the first steps of birch explant introduction and maintenance in vitro in order to make practical suggestions about the influence of these first steps on further micropropagation success. Materials and methods. Of the seven studied birch genotypes, one had been cultured in vitro for two years at the time of experiments, while six were newly planted in vitro from shoot segments disinfected after either one or two weeks of storage of collected branches. The explants were placed in glass culture tubes either on a hormone-free or cytokinin (6-benzylaminopurine)-supplemented medium. Results. A shorter branch storage time (one week instead of two) was better for the viability of explants, while external cytokinin, if used during the very first subculture in vitro, had largely a negative impact. Among the tested birch genotypes, 52BPL171 had the highest rate of viable explants and was followed in this respect by 01BPL115 which, however, contrasted strongly to the former because of its ability to maintain a green shoot apex alongside a green stem on the control medium. After 12 months in vitro, only genotype 01BPL115 was characterized by regular shoot growth and a well-developed root system. Conclusions. The green shoot apex on the control medium and, also, maintenance of viability on the medium with external cytokinin were found to be most helpful characteristics of birch explants during the first subculture, early recognition of those genotypes that would be most promising for obtaining multiple rooting shoots in vitro.

Urban trees are vital for air pollution mitigation, but their function is often compromised by exposure to particulate matter (PM), which impairs physiological processes and reduces growth. Enhancing tree resilience is therefore essential for maintaining their ecosystem services in polluted urban environments. This study examined the early growth and biochemical responses of Norway spruce (Picea abies) and Norway maple (Acer platanoides) seedlings to foliar PM exposure and assessed whether biochar (BC) soil amendment can alleviate PM-induced stress. Seedlings were cultivated outdoors under three treatments: Control (no treatment), PM (foliar exposure to particulate matter), and PM + BC (PM exposure with 10% biochar added to the substrate). Results revealed that Norway maple showed significant biochemical sensitivity to PM, including substantial reductions in chlorophyll and increases in antioxidant activity. However, Norway spruce showed more moderate pigment changes but reduced height growth. BC modulated oxidative and phenolic responses (TPC, TFC, MDA) and partially mitigated PM-induced stress, although its effectiveness varied by species. For Norway spruce, BC significantly enhanced resilience by restoring height growth, stabilizing pigments, and reducing oxidative stress compared with treatment using PM alone. In contrast, for Norway maple, BC failed to restore chlorophyll levels and increased oxidative and phenolic activity, yielding mixed outcomes. Despite physiological differences between the two species, multivariate PCA consistently showed that PM-treated seedlings diverged from the control cluster, whereas PM + BC-treated seedlings were closer to the controls, with mitigation substantially stronger in Norway spruce. These findings demonstrate that biochar can reduce PM-induced stress, but its successful implementation depends fundamentally on selecting appropriate species traits and understanding their specific metabolic response strategies.