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.

Changes in Biologically Active Compounds in Pinus sylvestris Needles after Lymantria monacha Outbreaks and Treatment with Foray 76B.

Due to climate warming, the occurrence of Lymantria monacha outbreaks is predicted to become more frequent, causing repeated and severe damage to conifer trees. Currently, the most effective way to control the outbreaks is aerial spraying with the bioinsecticide Foray 76B. The present study aimed to determine the impact of both: (i) L. monacha outbreaks and (ii) treatment with Foray 76B on tree resistance through the synthesis of polyphenols (TPC), flavonoids (TFC), photosynthetic pigments (chlorophyll a and b, carotenoids), lipid peroxidation (MDA), and soluble sugars (TSS) in Pinus sylvestris needles. Samples were collected from visually healthy (control), damaged/untreated, and damaged/Foray 76B-treated plots in 2020 and 2021 (following year after the outbreaks). The results revealed that L. monacha outbreaks contributed to the increase in TPC by 34.1% in 2020 and 26.7% in 2021. TFC negatively correlated with TPC, resulting in 17.6% and 11.1% lower concentrations in L. monacha-damaged plots in 2020 and 2021, respectively. A decrease in MDA was found in the damaged plots in both 2020 and 2021 (10.2% and 23.3%, respectively), which was associated with the increased synthesis of photosynthetic pigments in 2021. The research results also showed that in the following year after the outbreaks, the increase in the synthesis of photosynthetic pigments was also affected by the treatment with Foray 76B. Moreover, the increase in the synthesis of TPC and photosynthetic pigments in the damaged plots in 2021 illustrates the ability of pines to keep an activated defense system to fight biotic stress. Meanwhile, a higher synthesis of photosynthetic pigments in Foray 76B-treated plots indicates a possible effect of the treatment on faster tree growth and forest recovery after L. monacha outbreaks.

Seed Treatment with Electromagnetic Field Induces Different Effects on Emergence, Growth and Profiles of Biochemical Compounds in Seven Half-Sib Families of Silver Birch.

In the context of climate change, strategies aimed at enhancing trees' resistance to biotic and abiotic stress are particularly relevant. We applied an electromagnetic field (EMF) seed treatment to observe changes in the establishment and content of biochemical compounds in silver birch seedlings induced by a short (1 min) seed exposure to a physical stressor. The impact of EMF treatment was evaluated on seedling emergence and growth of one-year-old and two-year-old seedlings from seven half-sib families of silver birch. The effects on numerous biochemical parameters in seedling leaves, such as total phenolic content (TPC), total flavonoid content (TFC), amounts of photosynthetic pigments, total soluble sugars (TSS), level of lipid peroxidation level, antioxidant activity and activity of antioxidant enzymes, were compared using spectrophotometric methods. The results indicated that, in one-year-old seedlings, two of seven (60th and 73rd) half-sib families exhibited a positive response to seed treatment with EMFs in nearly all analyzed parameters. For example, in the 60th family, seed treatment with EMFs increased the percentage of emergence by 3 times, one-year-old seedling height by 71%, leaf TPC by 47%, antioxidant activity by 2 times and amount of chlorophyll a by 4.6 times. Meanwhile, the other two (86th and 179th) families exhibited a more obvious positive response to EMF in two-year-old seedlings as compared to one-year-old seedling controls. The results revealed that short-term EMF treatment of silver birch seeds can potentially be used to improve seedling emergence and growth and increase the content of secondary metabolites, antioxidant capacity and photosynthetic pigments. Understanding of the impact of EMFs as well as the influence of genetic differences on tree responses can be significant for practical applications in forestry. Genetic selection of plant genotypes that exhibit positive response trends can open the way to improve the quality of forest stands.

Phenolic and Antioxidant Compound Accumulation of Quercus robur Bark Diverges Based on Tree Genotype, Phenology and Extraction Method.

Oak bark is a rich niche for beneficial bioactive compounds. It is known that the amount of the compounds found in plant tissues can depend on species, genotype, growth site, etc., but it is unclear whether oak phenology, i.e., late or early bud burst, can also influence the amount of phenols and antioxidants that can be extracted. We tested two Quercus robur populations expressing different phenology and five half-sib families in each population to see how phenology, genotype, as well as extrahent differences (75% methanol or water) can determine the total phenol, total flavonoid content, as well as antioxidant activity. Significant statistical differences were found between half-sib families of the same population, between populations representing different oak phenology and different extrahents used. We determined that the extraction of flavonoids was more favorable when using water. So was antioxidant activity using one of the indicators, when significant differences between extrahents were observed. Furthermore, in families where there was a significant difference, phenols showed better results when using methanol. Overall, late bud burst families exhibited higher levels in all parameters tested. Thus, we recommend that for further bioactive compound extraction, all these factors be noted.

Genotype-Dependent Jasmonic Acid Effect on Pinus sylvestris L. Growth and Induced Systemic Resistance Indicators.

Due to temperature changes, forests are expected to encounter more stress than before, both in terms of biotic factors, such as increased insect attacks, and abiotic factors, such as more frequent droughts. Priming trees to respond to these changes faster and more effectively would be beneficial. Induced systemic resistance (ISR) is a mechanism that is turned on when plants encounter unfavorable conditions. Certain elicitors, such as jasmonic acid (JA) are known to induce plants' metabolic response. However, even though studies on ISR in herbaceous species are common and varied ISR elicitors can be used in agriculture, the same cannot be said about trees and forestry enterprises. We aimed to investigate whether JA used in different concentrations could induce metabolic changes (total phenol content, total flavonoid content, photosynthesis pigment content, antioxidant enzyme activity) in Pinus sylvestris seedlings and how this varies between different pine half-sib families (genotypes). After six weeks with a single application of JA, pine seedlings in several pine genetic families exhibited increased antioxidant enzyme activity, total phenol content and carotenoid content that correlated positively with JA concentrations used. Results from other genetic families were varied, but in many cases, there was a significant response to JA, with a noticeable increase as compared to the unaffected group. The impact on chlorophyll content and flavonoids was less noticeable overall. A positive effect on seedling growth parameters was not observed in any of the test cases. We conclude that JA can induce systemic resistance after a single application exogenously in P. sylvestris seedlings and recommend that the use of JA needs to be optimized by selecting appropriate concentrations.