The role of light in the adaptation of Thymus praecox Opiz subsp. praecox for diverse habitat conditions

The light decides about the course and efficiency of photochemical processes, being an important component of the surrounding environment shaping the plant composition in specific conditions. Thymus praecox subsp. praecox belongs to endangered taxa due to preferences for open habitats, which as a result of natural succession are exposed to overgrowth and shading with forest-scrub vegetation. In this study, an attempt was made to check the physiological activity of creeping thyme in changing environmental conditions prevailing on isolated stands in the Ojców National Park (Southern Poland). The increase in fresh and dry mass and the percentage of water in plants were determined, the content of chlorophyll a and b was measured, the intensity of chlorophyll a fluorescence was examined and the degree of electrolytes leakage through cell membranes was checked. The main aim was to determining the optimal habitat conditions for this taxon, which could help protect it. Based on the conducted research it was found, among others higher mass increase in plants from a sunny stand. Regardless of the measurement period, an increase in chlorophyll a and b content and a higher degree of cell membranes destabilisation in plants from a partially shaded stand was observed. The obtained results show, that T. praecox subsp. praecox characterises small habitat flexibility - even partial shade is not a convenient habitat for it. To optimal development, this subspecies requires conditions with high light availability. Creeping thyme is a heliophilic and thermophilic taxa and the sunny stands are optimal for it.