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ŠUMARSKI LIST 7-8/2023 str. 70     <-- 70 -->        PDF

radical scavenger activity (Table 3). However, the results were affirmative for all other tested parameters, especially in combined effect of tested variables (based on the F test).
Principal Component Analysis (PCA) and Correlation Matrix – Analiza Glavnih Komponenti (PCA) i Korelacijska Matrica
The effect of phenological variety (early and late) and physiological groups (vital or damaged) on tested biochemical parameters were tested using PCA and Pearson`s correlation matrix for p < 0.05 (Figures 3A and 3B). Treatments were placed in different quadrants and samples distribution across both principal components (PC1 and PC2) was such that no grouping was observed. The PCA of tested parameters in oak samples (Figure 3A) explained that the first two principal components summarized 74.3% of the total variance in the parameters. FRAP and phenolic compounds showed a positive influence and DPPH-test showed negative influence on the PC1 coordinate, while ABTS-test showed a positive influence to PC2 coordinate computation. The late samples (PLOV and PLOD) highly corresponded with total phenolic compounds and TF parameters. A positive correlation was confirmed among proteins, total phenolic compounds and FRAP-test (Figure 3B).
DISCUSSION
RASPRAVA
The differences among early and late oak genotypes were more significant regarding the total phenolics and flavonoids contents, as well as ferric-reducing antioxidant power. This observation was also confirmed by PCA analysis where all three parameters were grouped together with a slight difference in the most dominant PC1 component. Phenolics found in plants are considered “quantitative” defenses due to their consistently high levels in plant tissue (Ruuhola et al., 2001). Genetically determined higher levels of phenolics in late oak genotypes represent constitutive protection against a wide range of abiotic and biotic challenges (Kebert et al., 2022b, 2022c). Two-way ANOVA in our case showed that physiological grouping had no influence on total phenolics content and subsequently on FRAP, ABTS- and NO- radical scavenger activity. Bojović et al. (2022) also examined several oxidative stress parameters in their study on pedunculate oak (FRAP, RSC against DPPH·, NO and ABTS radicals). Their results contributed to explaining differences of pedunculate oak mature trees in response to oxidative stress due to the intensity of the drought. Antioxidant capacities of examined individuals not only depend on plant, but also on the drought adaptation, which is closely related to the environmental factors in each microsite.
So far, in the forest research in Serbia, oxidative stress parameters were used in two cases: a) in the assessment of the phytoremediation potential of fast growing species from Salicaceae family (genera Populus and Salix) (Kebert et al., 2011; Trudić et al., 2012; Trudić et al., 2013; Pilipović et al., 2019) and b) in the efforts of the oxidative stress capacity assessment of certain broadleaved species (e.g. Q. robur, F. sylvatica, C. betulus, P. avium) while being exposed to osmotic and drought stress in controlled, semi controlled and open conditions (Štajner et al., 2013; Stojnić et al., 2016;