Ecological and physiological features of the process of photosynthesis of white birch (Betula platyphylla)
in South-Eastern Yakutia
Grigorev M.R., Maximov T.Chr., Institute of Biological Problems of Cryolithozone SB RAS (Yakutia, Russia), e-mail: eidosmarat@mail.ru
INTRODUCTION
Many works have been devoted to the ecological and physiological features of the process of photosynthesis of woody plants in Siberia. Unfortunately, studies on the photosynthesis of broad-leaved trees,
namely flat-leaved birch in South Yakutia, have hardly been carried out. There are only data from episodic studies in Central Yakutia in an average productive forest and the results of phytotron studies abroad.
MATERIALS AND METODS
Field work was carried out from June 7 to August 13 at the forest station "Elgeeii" IBPC SB RAS is located
in the south-eastern part of Yakutia, Village Ust-Maya. The absolute height of the terrain is ~ 183 m. Taiga
vegetation is represented by medium-productive larch forests with a small admixture of birch, alder, and
willows; the main forest-forming species is Larix cajaderi (Fig. 1.).
Figure 1. Study site, “Elgeeii” forest station, Yakutia, Russia
For measurements, an LI-6400 infrared gas analyser with OS version Open 6.1.4 (LI-COR,
USA) was used. Studies of the content of C and N isotopes were carried out on a Delta-V mass
spectrometer, USA in the biogeochemical laboratory of the University of Hokkaido, Japan.
(Fig. 2.).
Figure 2. Infra-red gas analyser LI-6400 (LI-COR, USA)
RESULTS
To show on the graph, we used the main biochemical parameters - total leaf respiration
(Resp); the maximum rate of Rubisco carboxylase activity(Vcmax); the. maximum rate of photosynthetic electron transport (Jmax); the rate of triose phosphates utilization (TPU); According to
the main biochemical parameters of birch photosynthesis, one can notice a good relationship between various indicators (Resp, Vcmax, TPU, Jmax). All parameters have primary and
secondary peak values on June 18 and July 10, respectively, except for J max, which has
opposite peak values, on June 18 secondary and July 10 primary indicators (Fig. 3.).
Figure 5. Light curves of a white birch, forest station "Elgeeii" Ust-Maya, June-August 2018
According to the light dependence of photosynthesis throughout the summer, the range of light saturation of birch leaves ranges from 300 to 500 μmol m-2 s-1, depending on the time period, after which the
photosynthesis rate reaches a relative plateau. So the lowest point of light saturation falls on June 9,
and the maximum on August 2.(Fig. 5.).
Figure 3. The main biochemical parameters (Vcmax, Jmax, TPU, Resp)
Figure 6. Correlation coefficient of the maximum rate of carboxylation (Vc max) with the content of
carbon (A) and nitrogen (B) (mg) in the leaves of Betula platyphylla
We have found a positive correlation coefficient between the rate of carboxylation and the carbon
content in the leaves, C and Vcmax equal to R² = 0.24. Whereas, the relationship between the maximum intensity of carboxylation (Vcmax) and nitrogen (N) was low. All this suggests that nitrogen does
not strongly affect to birch photosynthesis (Fig. 6.).
Figure 4. Carbon dioxide curves of a birch, forest station "Elgeeii", Ust-Maya, June-August 2018
This graph shows relationship between assimilation and intercellular C content. The lowest CO 2
assimilation in response to Ci and PAR is traced in early June in excellent weather. CO-assimilation
in response to Ci is traced to the beginning of June and is highest on July 10th. The range of carbon
dioxide saturation is from 480 to 700 µmol mol -1. While the normal concentration of carbon dioxide
in the atmosphere is 380-400 µmol mol-1, which is evidence that carbon dioxide is not a limiting
factor in their photosynthetic activity (Fig. 4.).
According to our data, the isotopic discrimination
of flat birch in South-Eastern Yakutia was only 11
ppm (for C3 plants is in the range from 25 to 35
ppm.), which is two times lower than that of other
tree species. Therefore, it can be assumed that the
involvement of secondary compounds in the respiratory metabolism in the birch in Yakutia, deposited
in the stock in the composition of wood, is underestimated. Therefore, it is quite expected that the
carbon isotopic composition of wood becomes
heavier compared to leaves and thin roots (Fig.
7.).
Figure 7. Correlation coefficient of maximum carboxylation rate (Vc max) and isotopic discrimination
(δ13C (‰)) in leaves of Betula platyphylla
CONCLUTIONS
1. The maximum intensity of photosynthesis of white birch in South-Eastern Yakutia is 15.8 μmol CO2 m-2 s-1.The maximum rates of CO2 assimilation of woody plants in Eastern Siberia are well suited to
both theoretical (model) and experimental ranges of values for the boreal zone.
2. The seasonal maximum of birch leaf photosynthesis is observed at the end of the second decade of June, which is in good agreement with the rate of utilization of triose phosphate photosynthesis products.
3. The seasonal maximum of birch leaf respiration intensity is observed at the beginning of the growing season and is 2.56 μmol CO2 m-2 s-1. During this period, the processes of development, growth and
maintenance of birch require more energy costs.
4. In the studied species of birch, the plateau of light saturation is observed in the range of 300 - 500 μmol m-2 s-1.
5. The range of birch carbon dioxide saturation during the growing season varies from 480 to 700 µmol mol -1.
6. A good correlation was found between the maximum carboxylation rate with carbon content and with the ratio of carbon and n itrogen equal to R = 0.24, while the relationship between the maximum carboxylation rate and nitrogen is much weaker, which is primarily due to the environmental conditions of birch growth in South-Eastern Yakutia.
7. The isotopic discrimination of flat birch in South-Eastern Yakutia was 11‰, which is two times lower than that of other tree species. All this indicates a weak involvement in the respiratory metabolism of
secondary compounds deposited in the composition of birch wood.