Assessment of the thermotolerance of leaves of spontaneous oak species in northern and central Republic of Moldova

Understanding how the leaves of oak species trees respond to the action of thermal stress is essential in assessing their ability to adapt and in predicting their spread in the conditions of future increase in ambient temperature. In this study, the thermotolerance of tree leaves of the species was investigated: pedunculate oak, sessile oak and downy oak after the exposure of limb foliate samples to thermal shock with a temperature of 59° C for different periods of time. With the help of the electrolyte leakage method, the functional resistance of the leaves to the oak species was compared, not avoiding the avoidance phenomena. Based on the index of relative leakage of electrolytes from the tissues, the functional features of the leaves of oak species, which grow under certain environmental conditions in the Republic of Moldova, were examined. It has been shown that the thermotolerance of oak species changes depending on their biological characteristics and the environmental conditions in which the trees grow. Based on the lethal dose values (LD50), it was established that in the northern part of the Republic of Moldova the leaves of pedunculate oak are characterized by a slightly higher resistance, while those of downy oak show a somewhat higher sensitivity. In the stands in the center of the Republic of Moldova, the resistance of the downy oak leaves has obviously increased and the tolerance of the pedunculate oak ones has decreased.