Photosynthetic Pigments in Siberian Pine and Fir under Climate Warming and Shift of the Timberline

Abstract

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.

Alpine and Polar Treelines in a Changing Environment

“…They found that, at the treeline, Pinus canariensis displays a drought avoidance strategy due to a great plasticity in gas exchange, antioxidants, and pigments. Pakharkova et al [18] demonstrated that Pinus sibirica Du Tour and Abies sibirica L. showed different patterns of photosynthetic pigments along an elevational gradient in the West Sayan ridge, Siberia. As the decline in photosynthetic pigments with increasing elevation was more pronounced in Pinus sibirica needles than in Abies sibirica needles, the authors conclude that under conditions of future climate warming, Pinus sibirica trees will have an advantage in colonizing zones above the present treeline.…”

Two-Species Forests at the Treeline of Siberian Mountains: An Ecophysiological Perspective under Climate Change

“…At the beginning of the growing season, the critical conditions of treeline habitats are a combination of negative soil temperatures, low positive air temperatures, and high illumination, aggravated by the reflection of light from spots of the snow cover. All this leads to burns and drying out of needles, which are especially pronounced in fir and prevent the advancement of its seedlings above the treeline [ 13 ]. Siberian pine partially compensates for these factors by increasing the content of carotenoids in needles and by later resumption of photosynthetic activity [ 12 ], which allows Siberian pine seedlings to occupy habitats above the forest boundary.…”

“…The sampling and measurements were performed in mid-April 2020, which was the end of the growing season in the area. Thus, the methods slightly differed from those applied in a previous study [ 13 ], in which sampling was done at the very beginning of the growing season.…”

“…Pakharkova et al [ 12 , 13 ] used another approach to foresee how two-species mountain forests may alter their dominant species composition and the treeline position in the West Sayan ridge. The authors measured the content of photosynthetic pigments and the rate of electron transport in needles of codominating Pinus sibirica and Abies sibirica .…”

“…In this study, we continue to extend the approach used in previous studies [ 12 , 13 ] over a different geographic area. The goal of the study was to project the possible alteration at the treeline ecotone in a rather remote and heavily underexplored area of East Sayan under current climate change.…”