The research presents the results of studying the dynamics of chlorophyll a and b accumulation over three growing seasons under varying weather conditions on the Southern Coast of Crimea in the leaves of three native deciduous and one introduced evergreen species of the genus Quercus L. It was found that the concentration of chlorophylls in leaf tissues depends on the hydrothermal conditions of the year. During periods of hot and dry weather, their content decreases. The highest pigment concentration was characteristic of Quercus robur, while the lowest was observed in Quercus ilex.

The study describes the state of the photosynthetic apparatus in the examined species under controlled wilting conditions at different combinations of temperature and air humidity. It was established that when the water deficit level in the tissues of deciduous Quercus species reaches 20–28%, exposure to high temperature and low air humidity leads to more significant changes in photosynthetic processes compared to lower temperature and higher humidity conditions.

Notably, the level of thermal dissipation of excitation energy increases substantially, the number of chlorophyll molecules associated with PSII reaction centers decreases, and the reoxidation processes of primary electron acceptors are disrupted. The most informative parameters of the photoinduction curve for diagnosing heat resistance and drought tolerance in Quercus species were identified.