Valentinas Černiauskas

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.

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.

Trees growing in urban areas face increasing stress from atmospheric pollutants, with limited attention given to the early responses of young seedlings. This study aimed to address the knowledge gap regarding the effects of simulated pollutant exposure, specifically particulate matter (PM), elevated ozone (O₃), and carbon dioxide (CO₂) concentrations, on young seedlings of five tree species: Scots pine (Pinus sylvestris L.); Norway spruce (Picea abies (L.) H.Karst.); silver birch (Betula pendula Roth); small-leaved lime (Tilia cordata Mill.); and Norway maple (Acer platanoides L.). The main objectives of this paper were to evaluate the seedling stem growth response and the biochemical response of seedling foliage to pollutant exposure. Four treatments were performed on two- to three-year-old seedlings of the selected tree species: with PM (0.4 g per seedling) under combined O₃ = 180 ppb + CO₂ = 650 ppm; without PM under combined O₃ = 180 ppb + CO₂ = 650 ppm; with PM (0.4 g per seedling) under combined O₃ < 40–45 ppb + CO₂ < 400 ppm; and without PM under combined O₃ < 40–45 ppb + CO₂ < 400 ppm. Scots pine and Norway maple showed no changes in growth (stem height and diameter) and biochemical parameters (photosynthetic pigments, total polyphenol content (TPC), total flavonoids content (TFC), and total soluble sugars (TSS)), indicating a neutral response to the combined PM, O₃, and CO₂ treatment. The chlorophyll response to PM alone and in combination with elevated O₃ and CO₂ exposure varied, with silver birch increasing, Norway maple—neutral to increasing, Scots pine—neutral to decreasing, and Norway spruce and small-leaved lime—decreasing. The TPC indicated stress responses in Scots pine, small-leaved lime, and Norway maple under increased combined O₃ and CO₂ and in Norway spruce under single PM treatment. Hence, Scots pine and Norway maple seedlings showed greater resistance to increased PM under combined O₃ and CO₂ with minimal change in growth, while silver birch seedlings showed adaptation potential with increasing chlorophyll under simulated pollutant stress.

Urban trees, integral to urban environments, demonstrate intricate responses to atmospheric pollutants like particulate matter (PM), tropospheric ozone (O3), and carbon dioxide (CO2). Notably, O3 induces oxidative stress in leaf tissues, while PM, consisting of fine airborne particles, interacts with urban trees through foliar deposition. This interaction is particularly interesting as tree canopies are highly effective filters, capturing and accumulating PM on their surfaces. The present study focused on silver birch, small-leaved lime, and Norway maple seedlings responses to elevated O3 and CO2 with and without PM. Maple seedlings exhibited the highest stem height increment, followed by lime and birch. Elevated O3 and CO2 without PM led to substantial height increments for lime and maple. Elevated O3 and CO2 without PM increased the total polyphenols in lime and maple leaves but decreased the content of total flavonoids in birch and lime leaves. Our findings underscore the adaptability of lime and maple seedlings to elevated O3 and CO2, positioning them as promising species for urban environments in the face of changing climates. Birch, while exhibiting biochemical changes, demonstrated less pronounced growth responses. This studyʼs insights into the intricate interactions between urban trees and multiple pollutants, particularly the species-specific responses, are of significant value for urban planning and environmental management.

Populus spp. is an economically valuable tree worldwide, known for its adaptability, fast growth, and versatile wood, often cultivated in short-rotation plantations. Effective propagation is crucial for rapid genetic improvement and global demand for forest products and biomass energy. This study focused on the rooting and growth of poplar cuttings, examining shoot collection timing and growth stimulant treatments across four hybrids: Populus deltoides × P. nigra (Agathe F), P. maximowiczii × P. trichocarpa (Arges), P. deltoides × P. trichocarpa (Donk), and an interspecific hybrid Populus × canadensis (F-448). The experiment used hybrid poplar cuttings collected in spring 2022 and 2023, planted in controlled climates with a randomized block design. Cuttings were soaked for 24 h in growth stimulants, namely indole-3-butyric acid, cinnamic acid, and indole-3-acetic acid. After 12 weeks, rooting percentage and seedling height were assessed. The study found that the optimal time for collecting poplar cuttings for best rooting is late winter to early spring, specifically from March to early April, with shoots collected after early April showing the lowest rooting potential. The growth stimulants significantly influenced the growth of poplar seedlings. There was a tendency for lower concentrations to increase root formation and seedling height, while higher concentrations had adverse effects. Despite variations in growth rates, a consistent growth pattern was observed across different shoot collection dates for all genomic groups.