Seasonal Dynamics of the Chlorophyll and Carotenoid Content in the Leaves of Steppe and Forest Plants on Species and Community Level

The content of chlorophylls (Chl) a and b and carotenoids (Car) during the growing season was studied in the leaves of 31 species of steppe and forest plants. In contrast to forest plants, steppe plants possessed less chlorophylls and carotenoids per leaf mass (2 and 1.5 times, respectively), a low Chl/Car ratio, a greater (1.5 times) content of carotenoids per leaf area, and a high Chl a/b ratio. In spite of the low chlorophyll content per leaf mass in steppe plants, their content per leaf area was similar to forest species (3-4 mg/dm(2)) owing to their thicker and denser leaves. This suggests that the plants of steppe and forest communities have the same potential ability to intercept solar energy in this locality. In the period of active vegetation (mid-June -early August), parameters of the pigment complex were stable both in steppe and forest communities. However, steppe plants demonstrated the modified in content of Car and Chl b, as well as Chl/Car and Chl a/b ratios, in the beginning and at the end of the season that indicated a reorganization of the light-harvesting complex. Intraspecific variation of parameters during the season was two or three times lower than interspecific. High interspecific variation in forest plants were achieved due to the presence of species with thick long-lived leaves. It was concluded that the chlorophyll content per leaf area reflects the adaptation of plants to climatic conditions of the geographic region, whereas pigment contents per leaf mass shows adaptation to local irradiation in plant community (forest or steppe).