In the present paper, the results of the research of biometric parameters and functional peculiarities of photosynthetic apparatus of Stellaria humifusa in West Spitsbergen are discussed. The study showed that the largest proportion of the mat is composed of a brown layer of dead leaves covering the assimilative organs (about 70%). Green leaves and shoots accounted for about 20%, whereas generative organs – for about 10% of the mat mass. The values of the maximum photochemical quantum yield of PS II (FV/FM) in all the studied plants were lower than the optimal values (0.83), which suggests that the plants are exposed to stress factors. The low values of chlorophyll and carotenoid content and relatively high values of the light-harvesting complex (70-80%), the sharp decrease in the quantum yield of PS II (FPSII) entailed by a marginal increase in PPFD indicative of a sufficiently high of photochemical activity within the range of low and medium values of light. It also suggests that Stellaria humifusa is well-adapted to the shaded conditions created in the mat. Besides, a considerable decrease the maximum fluorescence yield of a light-adapted leaf (FM´) at increasing PPFD was observed, which suggests that Stellaria humifusa has a well-developed mechanism of energy dissipation via the non-photochemical (NPQ) pathway. The rapid development of NPQ gives reason to assume that, under high light conditions, non-photochemical quenching is likely to serve as the main mechanism for preventing the photodamage of the photosynthetic apparatus. Thus, it was shown that the photosynthetic apparatus of Stellaria humifusa works efficiently under the conditions created in the mat, and the thick layer of dead leaves covering the assimilative organs, on the one hand, protects them from excessive light, and on the other hand, absorbs thermal energy, which raises temperature of the local habitat.

No abstract

In the present paper, the results of the research of biometric and functional parameters of photosynthetic apparatus of Bistorta vivipara from West Spitsbergen are presented and discussed. A high intraspecific variability of biometric parameters (linear dimensions and biomass) was found. The differences found in biomass suggest that biological productivity is associated with the functional activity of the plant individuals. A direct dependence of the biomass on the photosynthetic pigment content per unit dry mass of leaf has been revealed. A high variability of non-photochemical fluorescence quenching (NPQ), basic fluorescence yield (F 0), maximal fluorescence yield (F M) and variable fluorescence yield (F V) have been shown contrastingly to relatively constant values of the maximum photochemical quantum yield of PS II (F V /F M) and the coefficient of photochemical fluorescence quenching (qP). Close-to-theoretical-maximum F V /F M values indicated the absence of stress conditions and the presence of regulation systems in chloroplastic photosynthetic apparatus (PA) level functioning during varying microclimate parameters of the daily climate. The relatively constant qP indicated the same photosynthetic activity of the B. vivipara leaves, unaffected by the varying weather conditions. The NPQ data suggest that the non-photochemical quenching acts as a protective mechanism, sustaining the PA in an optimally active state and reducing probability of negative changes to PSII. The revealed high PA adaptability at the level of the plant structure and light-dependent reactions of photosynthesis makes it possible for B. vivipara to develop at a high functional level at various values of environmental factors, which provides for the successful growth of the species in the high Arctic region. The high PA flexibility suggests that B. vivipara is capable of active adaptation in the context of the forecast climate change.