Tracing the Responses of Pedunculate Oak (Quercus Robur L.) Trees to Drought Stress by Analyzing the Antioxidant System

The influence of different groundwater table depths on pre-dawn water potential (PWP), soil moisture content and antioxidant activity (FRAP, RSC against DPPH•, NO and ABTS radicals) of adult pedunculate oak (Quercus robur L.) trees was assessed in three managed stands (localities 1-3) and one unmanaged (locality 4 -forest reserve).The study sites were located within single forest complex at different distances from the Sava riverbed.The measurements were performed during July 2015, when the first evidence of drought was evidenced.We hypothesised that the trees at locations farther from the river would be more drought-stressed due to lower groundwater depth and will show higher antioxidant capacity.Indeed, trees at localities 2 and 3 were more drought-stressed as compared to trees at locations 1 and 4, as indicated by the PWP results.Since antioxidant capacity can be directly correlated to drought tolerance, the present results indicate a higher antioxidant capacity in leaf extracts from locality 3, but also good oxidative adaptation in leaf extracts from locality 4, where the obtained values for almost all examined antioxidant tests were without statistically significant differences compared to those on locality 3. Obtained results may help to explain differences in biochemical responses to water deficit stress of pedunculate oak trees from different microsites within the single forest complex and provide us valuable information about intra-species drought resistance.Therefore, this can be an important tool for the improvement of breeding strategies and artificial regeneration plans for pedunculate oak in dry lowland regions.