Photosynthesis and anatomic–morphological characteristics of sea aster leaves on the white sea coast

Anatomic–morphological and functional features of sea aster (Aster tripolium L.) leaves were investigated in the field study on the northern limit of A. tripolium’s range of distribution, using plants growing in the intertidal zone on the Pomorsky coast of the White Sea. The largest leaf area was found in plants grown close to the shore, near the high tide mark. In plants grown near the low tide mark, the leaf area decreased fourfold, while the leaf thickness increased by 30%. The plants sampled near the low and high tide marks showed different rates of photosynthesis and transpiration; they also differed in stomatal conductance and the number of stomata on the upper and lower leaf sides. Analysis of carbon dioxide plots of photosynthesis revealed the habitat-related differences in photosynthetic characteristics. Under saturating concentrations of carbon dioxide, the plants grown near the shore exhibited larger rates of photosynthetic electron transport and carboxylation. Characteristics of plants in the examined transect were found related to the local environmental conditions. A hypothesis is put forward that A. tripolium possesses an inducible CO2 concentrating mechanism during the growing season under northern summer conditions.