Research Highlights: For the first time, the Pinus sibirica Du Tour and Abies sibirica L. conifer forest at the West Sayan ridge timberline has been explored to reveal which species is likely to react to climate change and a shift of the timberline. Such a shift may modify the ecological functions of the forests. Background and Objectives: Long-term climate change has become obvious in the mountains of southern Siberia. Specifically, a half-century rise in annual mean temperatures has been observed, while precipitation remains unchanged. Trees growing at the timberline are likely to strongly react to climate alterations. The objective was to estimate which of the two species sharing the same habitat would benefit from climate alteration and shifting of the timberline. Materials and Methods: At several altitudes (from 1413 to 1724 m a.s.l.), samples of P. sibirica and A. sibirica needles have been collected and contents of chlorophyll a and b as well as carotenoids were measured in June 2019. The temperature of needles of the two species was measured in both cloudy and sunny weather conditions. Results: The studied species have been shown to have different patterns of pigment variations with the growth of altitude. The decline of chlorophylls and carotenoids was more pronounced in P. sibirica (ratio at timberline ca. 2.2) than in A. sibirica (ratio ca. 3.1). Accordingly, the electron transport rate decreased more strongly in P. sibirica at the timberline (ca. 37.2 μmol of electrons/m−2 s−1) than in A. sibirica (56.9 μmol of electrons/m−2 s−1). The temperatures of needles in both cloudy and sunny weather were higher in A. sibirica (10.5 and 43.3 °C, respectively) than in P. sibirica (3.8 and 24.2 °C, respectively). Conclusions: The considered physiological and ecological traits show that P. sibirica is better protected from higher-altitude hazards (excess insolation, rise of temperature etc.) than A. sibirica. P. sibirica may be therefore a more likely winner than A. sibirica in the movement of the mountain timberline under climate warming in the area.

No abstract

Traditionally the registration of seasonal changes in plant growth and development has been carried out phenologically, i.e., qualitatively using visual inspection. However, since the process of plant acclimatization to winter dormancy involves reversible biochemical and physiological changes at the level of cells, quantitative methods can be applied to determine the duration and the depth of winter dormancy in perennial plants. We used a method based on detecting thermally induced changes in the zero-level fluorescence (TICZF) on needles from four Siberian coniferous trees. Needles of Picea obovata Ledeb. and Abies sibirica Ledeb. recover from the state of winter dormancy much faster than those of Pinus sibirica Du Tour and Pinus sylvestris L. The photosynthetic apparatus in the needles of A. sibirica may be damaged during the spring period, characterized by unstable weather, when after several days of warm weather, the plants prematurely recover from winter dormancy. We conclude that under conditions of climate warming tree, species like A. sibirica may suffer from severe diebacks due to desiccation caused by premature break of winter dormancy.

No abstract

During the attack of a forest fire, the vegetative organs of plants are affected by high temperatures, which lead to their stressful state. At the time of burning, it is quite difficult to record temperature changes in the tree crown and the associated reactions in the photosynthetic needle apparatus. This article presents the results of modelling a high-temperature effect simulating a convective flow from a ground fire. Experimental heating at 55° C lasted for 5 and 10 minutes. Evaluation of the response was carried out by the parameters of rapid fluorescence (Fv / Fm, ETR), the state of the pigment complex, the relative water content in the needles. To characterize the degree of heat endurance and short-term effects concerning thermal damage, saplings of Scots pine (Pinus sylvestris L.) in different periods of the vegetation phase were used. The researchers have discovered different levels of heat resistance of the needle assimilation apparatus. Usually heat resistance is rising by the end of the vegetation season. The data obtained in June show that heating of the saplings led to a significant suppression of the photosynthesis rate. In subsequent periods (July, August, September), the photochemical quantum yield (Fv / Fm) was restored to 75% and 60% from the initial level on average, after 5and 10-minute heating respectively. The values of the electron transport rate (ETR) for saplings selected in September restored to the initial level within 3 days after a short heat exposure. For the study of long-term effects after high-temperature exposure during the vegetation season, the undergrowth of Scots pine was used. Restoration of the photosynthetic activity in needles from model trees was observed only after a short-term (5-minute) impact, but by the end of the studied period the restoration had not reached the control values. A longer heating (during 10 minutes) resulted in an irreversible suppression of photosynthesis and destruction of the photosynthetic apparatus, as evidenced by the decrease in the number of photosynthetic pigments.