ECOLOGICAL PLASTICITY OF THE PHOTOSYNTHETIC APPARATUS OF HIBISCUS SYRIACUS L. UNDER PRESSURE OF HIGH TEMPERATURE, INSOLATION AND AIR POLLUTION

Integrated effect of high temperature, insolation and anthropogenic pollution on pigment content, net oxygen production and dark respiration rates of Hibiscus syriacus L. is described in the paper. There were three observation sites under the study: Tashkent Botanical Garden, public garden in central part of Tashkent city and mountain holiday camp. High adaptive potential of H. syriacus L. was revealed; it is recognized as well adapted to environmental stress factors of arid and semiarid zone under good irrigation. Ecological plasticity of photosynthetic apparatus of hibiscus plays key role in the adaptation. It was revealed, that plants under the shade (in Tashkent Botanical Garden) had long, wide and thin leaves, recognized as manifestation of sciomorphosis. Heliomorphosis features of hibiscus’ leaves were identified in mountains under the high solar irradiation; there were thickened and compacted leaves of small sizes. Such leaf structure modifications have adaptive significance – it is for strengthening of photosynthetic capacity to compensate deficiency in sun light (in case of sciomorphosis); and on the contrary, – it is for shading of sensitive to redundant solar radiation photosynthetic elements to protect from oxidative damages (in case of heliomorphosis). Thus, the plant needs in carbon dioxide assimilation and organic matter production for maintenance of constant energy balance under different stress environment are provided. It was revealed that unfavorable (extreme) environment improved the resistance of dark respiration and net production of oxygen to temperature injuries (the worse environment, the higher plant resistance to temperature injuries). Besides, the higher resistance was detected for mature age leaves of H. syriacus in comparison with young ones. Thus, plants adapt to probable temperature drops gradually during their ontogenesis. Net oxygen production rate of H. syriacus (measured at optimal conditions – +27°C and 635–650 nm) was of the same level in different sites under the study during all the time of active vegetation; it was about 0,20±0,05 μmol О2/(dm2·s). It is considered as norm of reaction of net production (visible photosynthesis) rate of H. syriacus and as specific feature of its photosynthetic apparatus.

Hibiscus syriacus L., pigments, net oxygen production, dark respiration, ecological plasticity, high temperature, insolation

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