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ŠUMARSKI LIST 7-8/2023 str. 71     <-- 71 -->        PDF

Stojnić et al., 2019; Stojnić et al., 2022; Kebert et al., 2022a; Vuksanović et al., 2022). The only studies which assessed oxidative stress and other parameters while being exposed to intense biotic stress (pest attacks) were conducted by Kebert et al. (2022a) (lipid peroxidation, total non-protein thiol compounds, Trolox Equivalent Antioxidant Capacity, FRAP, TP, TF and condensed tannins) and Pilipović et al. (2020) (combined stress experiment – drought and herbivore attack – where nitrate reductase and chlorophyll a content was measured, among others). These efforts were contributing to the selection activities, in order to identify individuals and provenances resilient to abiotic and biotic stress, in order to further develop breeding programmes of targeted species and contribute to climate smart forestry management practices in Serbia.
Depending on the species, other researchers have found contradictory results when studying the impact of drought and osmotic stress on polyphenol levels (Cheruiyot et al., 2007; Petridis et al., 2012; Griesser et al., 2015; Cherit-Hacid et al., 2015). For example, Štajner et al., (2011) investigated oxidative and drought stress tolerance in selected melliferous plant species (Populus alba, Robinia pseudoacacia, Sophora japonica, Euodia hupehensis, Tilia sp., Fraxinus sp.). During July, proline content and malondialdehyde quantity increased and soluble proteins decreased in all investigated species. The high and permanent antioxidant activity during the whole investigated period was observed in P. alba, but it was insufficient to protect its leaves from oxidative injury during the period of drought in July. The highest ability to accumulate proline and highest protein content under severe drought stress in July was observed in Fraxinus sp. Other investigated antioxidant parameters (total antioxidant and DPPH radical scavenger capacities) were high and accumulation of malondialdehyde was low which indicate high drought oxidative stress tolerance (Štajner et al., 2011). The study of Stojnić et al. (2016) showed that the content of free proline, FRAP units and the amount of malondialdehyde had increased values in Q. robur and Carpinus betulus trees subjected to soil water deficit. Stojnić et al. (2019) used oxidative stress parameters to identify traits that might be utilized to improve leaf-level intrinsic water use efficiency (WUEi), and therefore be used in breeding programmes to enhance drought adaptation of Q. robur. They analysed morphological, anatomical and oxidative stress parameters, where they screened total phenolics content, total flavonoids content, ferric reducing antioxidant power, total soluble protein content, radical scavenger capacity against ABTS•+, radical scavenger capacity against NO radical and radical scavenger capacity against DPPH free radical. However, the results of examined biochemical characteristics, presumably related to tolerance of oxidative stress, did not have considerable significance in conditions of moderate drought. Indeed, only FRAP was selected by stepwise regression analysis and, according to the results of path coefficient analysis, showed significant effect on the WUEi, both directly and indirectly through stomatal density and leaf dry mass per unit leaf area (Stojnić et al., 2019). Popović et al. (2017) investigated different poplar clones subjected to water stress and pointed out that phenolic compounds significantly or slightly decreased depending on the genotype. On the other hand, in the same paper, the increased biosynthesis of specific phenolic compounds, such as myricetin, chrysin, kaempferol and isoferulic acid etc., as well as increased activity of biosynthetic enzyme (PAL-phenylalanin ammonium lyase) under induced drought stress in poplar clones was reported. Recent research, however, has been in line with the results from our investigation that drought, among other stress factors, may cause the baseline level of phenolics to rise (Yoshida et al., 2015). However, the rise of phenolic compounds content and most of the antioxidant parameters was not significant in our groups of damaged oak. An exception was the ABTS radical scavenger test which discriminated damaged pooled early oak from vital, with a 66% increase of the scavengers of ABTS radical.
Trudić and Draškić et al. (2021b) described different candidate gene expression responses of two pedunculate oak phenological groups, characterized by different physiological status (vital vs damaged) and flushing period [early (var. praecox) vs late (var. tardissima)]. The most significant differen­ces in relative gene expression levels are shown between the flushing period [tardissima (8 genes upregulated) vs praecox (3 genes upregulated)], more than a physiological status (vital vs damaged). This was also the case with our measurements of total phenol and protein content. Only three genes wrky53, rd22 and sag21 show­ed upregulated expression pattern in damaged physiological groups, indicating their possible role in the coping mecha­nisms of oak in stressed environment (Trudić and Draškić et al., 2021b).
Forest genetic monitoring, i.e. tracking of temporal changes in the genetic variation and structure of tree populations, is the only way to verify how well genetic diversity is maintained over time, and how this diversity is shaped by climate change and management practices. One of the first collaborative initiatives on defining comprehensive methodological framework of forest genetic monitoring on European continent was done by EUFORGEN group of experts (Aravanopoulos et al., 2015), although there was a history of similar initiatives in the past, mostly in other parts of the world (Namkoong et al., 1996; Boyle, 2000; Namkoong et al., 2002 (unpublished); Konnert et al., 2011). When detailing proper marker system and molecular data, Aravanopoulos et al. (2015) focused mainly on parameters accessible from DNA sequences, parameters of genetic diversity available from such data and quantitative