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Volume 14, 2005

ROLE OF PHOTOSYNTHESIS IN DETERMINATION OF WOODEN PLANTS SPECIES STATUS

Alexey S. Shcherbatyuk, Galina G. Suvorova, Ludmila S. Yankova,

Lidia D. Kopytova, Alexandra K.Phylippova

Siberian Institute of Physiology and Biochemistry of Plants, SB RAS

P. Box 1243, 664033, Irkutsk, Russia, e-mail: suvorova@sifibr.irk.ru

Abstract

The relationship between assimilation activity of Larix sibirica Ledeb., Pinus sylvestris L. and Picea obovata Ledeb. and environmental factors was studied. Soil and air temperature and the available soil water supply were found to be the leading factors of photosynthesis in the forest zone of lake Baikal. All parameters of carbon dioxide exchange can be used to reveal ecological characteristics (ecological status) of particular species of wooden plants. The species specificity of the assimilation activity is primarily revealed at the initial periods of stress conditions.

Key words: net-photosynthesis, pine, spruce, larch, environmental factors, ecological characteristics

Ecophysiological studies of plants photosynthetic function were traditionally primarily aimed at increasing their productivity. However, Slemnev N.N. [8,9,10], Gerasimenko et al [1] and Larcher [2] have recently identified the study of indicator role of the assimilation process as a more promising approach. It has become obvious that disposing of the data on the character of photosynthetic function changes under environmental conditions one can not only reveal ecological status of the plants, but assess their competitiveness and adaptation capabilities, as well as resistance to unfavorable impact of natural and anthropogenic factors. The development of this trend appears to be quite promising for understanding of functioning of ecological mechanisms ensuring species diversity of plant communities. The key objective of the present report is to justify the possibility of resolving these problems, which are particularly critical under global environmental pollution.

Material and Methods

The observations were performed in the community, started up in May – November 1983 over the vegetation seasons of 1995-1996. Photosynthesis was identified via multi-channel equipment with infra-red gas analyzer “Infralyt-4” [4]. The process was recorded on a continuous basis for 4-5 days weekly using intact branches of 3 model trees of each species. Simultaneously to determining the photosynthesis intensity there was carried out continuous recording of air and soil temperature, solar radiation and air humidity. Precipitation was registered by rain-gauges, soil humidity was determined in each 10-cm layer for the depth of 100 cm on a decade-basis by thermogravimetric method. The methods and facilities applied are described in more detail in the previous publications [4,6,7].

Results and Discussion

The weather over the observation period was characterized by soil drought in July – first ten days of August 1995. Soil humidity in the most root-inhabited layer (0-50 cm) at this time was close to wilting humidity (Fig. 1). The first half of the vegetation season 1996 was characterized by rains. Decrease of precipitation in autumn caused soil dehydration. Nevertheless, it was not as intense as in summer 1995 and did not affect the plants’ state and photosynthetic activity. It should also be noted that in June-September 1996 soil temperature at the depth of 20 cm was by about 1^oC lower than in the corresponding period of 1995.

These weather peculiarities to a large extent predetermined seasonal photosynthesis of the coniferous species under study. Thus, seasonal photosynthetic productivity course of 1995 (Fig. 2) was characterized by July “depression”, which coincided in time with soil drought – reduction of the reserves of available soil moisture in the upper 50 cm soil layer down to 27 mm.

Being more exigent for moisture, spruce [3] demonstrated in this period (normally at the temperature exceeding 25° С) СО₂ release in the light. This drought appears to have affected photosynthesis throughout the whole vegetation period of 1995. At lower humidity and heat in August-October 1996 it was considerably higher (Fig. 3).

The analysis of seasonal dynamics of photosynthetic productivity during the observation period showed that the response the reaction of individual plant species to soil drought demonstrated itself in strict correspondence with their ecological peculiarities. Spruce photosynthetic productivity in 1995 due to the drought impact was 2.2. times lower than in 1996; photosynthetic productivity of larch, indifferent to this factor – 1.6 times lower, and the photosynthetic productivity of pine xerophyte was, on the contrary, 1.1 times higher. Specific response to moisture of the coniferous trees under investigation is well confirmed by the data of Table 1.

Under water stress conditions in summer the daily photosynthesis productivity of hydrophilous spruce reduced by 9.8 times, that of pine – by 4.7 times, that of highly flexible larch [5] – by 2.4 times only. It is characteristic that in autumn (larch needles were already yellow by then) the impact of soil drought on evergreen coniferous photosynthesis demonstrated to lesser extent – for fir-tree it reduced by 1.5 times, for pine - by 1.3.

Practically all the parameters of assimilation activity may be used to confirm the conclusion on the relevance of investigating photosynthetic function with the view to identify plants ecological status. Along with the above parameters very informative in this sense are maximal values of photosynthesis and peculiarities of daily dynamics of this process. Practically through the whole observation period the plants responded to the changes of external conditions in strict correspondence to their ecological peculiarities. Thus, larch characterized by amazing adaptability to various habitats, stands out compared to evergreen coniferous by highest stability of the assimilation process level in diverse stress situations.

Nevertheless, the most convincing proof of the possibility of appropriateness of using plants assimilation activity parameters for evaluation of the plants resistance to various unfavorable impacts is the correlation analysis of the connection between photosynthesis productivity and environmental factors (Table 2).

Despite the complexity of the interpretation of individual coefficients, on the whole the Table material is the most weighty argument in favor not only of the indicator role of the photosynthesis, by it acts as a proof of efficiency of the determination of plant ecological status by this index. Key ecological peculiarities of the species studied showed most in the course of this analysis: light-requiring properties of pine and larch, shade requirement and lack of heat demands of hydrophilous spruce, high flexibility of larch in respect of these factors.

Key factors identified by the correlation coefficient exceeding 0.50 are as follows: for pine - light and soil moisture reserve, for spruce – soil moisture reserve, for larch – light, air and soil temperature. Key factors for each species studied are kind of lines of its connection with the environment. The more they are the more diverse are habitation conditions of the species, the more ecological niches may be relevant for it, the wider its natural habitat is.

Thus, determination of the character of photosynthesis association with environmental factors allows to obtain a full picture of the plants ecological status. With a solid block of data on the character of reactions of assimilation processes to the environmental factors, alteration the species status may be more completely characterized than on the basis of conventional geobotanical methods.

Coincidence of ecological-physiological characteristics of the coniferous studied, compiled on the basis of the analysis of their photosynthetic functions, with forestry description of ecological peculiarities of these species confirms the statement regarding indicator role of photosynthesis. At the same time it confirms the efficiency of using parameters of assimilation process in order to diagnose the state of the plants, to evaluate their resistance of unfavorable impact of natural and anthropogenic factors, as well as to decipher ecological mechanisms ensuring species diversity in different habitats. Topicality of developing this research trend under global technogenic stress and exceedingly high role of habitat-protecting function of plant communities is without doubt.

Literature cited

1. Gerasimenko Т.V., Koibeiyainen E.L.., Filatova N.I. СО₂-gas-exchange of some vascular plants of the Polar (environmental aspects) // Russian Journal of Plant Physiology. 1996, v. 43,  № 3, p. 380-398 (in Russian).

2. LarcherW. // Ecophysiology of photosynthesis. Berlin: Heidelberg: Springer-Verlag. 1994, p. 261-277.

3. Orlov A.Ya. // Russian Journal of Dendrology 1996, № 1, p. 84-93 (in Russian).

4. Shcherbatyuk A.S. // Infrared gas-analyzers in the study of plants gas exchange. М.: Nauka. 1990, p. 38-54 (in Russian).

5. Shcherbatyuk A.S., Kaplin V.M., Yan’kova L.S. Rusakova L.V. //Ecological-physiological studies of photosynthesis and water regime of plants in field. Irkutsk. 1983, p. 37-43 (in Russian).

6. Shcherbatyuk A.S., Rusakova L.V., Suvorova G.G., Yan’kova L.S. Carbon dioxide gas exchange in coniferous of Predbaikaliye. Novosibirsk: Nauka. Siberian Division 1991, 135 p. (in Russian).

7. Shcherbatyuk A.S., Rusakova L.V., Yan’kova L.S. // Russian Journal of Dendrology. 1991, №4, p. З-10 (in Russian).

8. Slemnev N.N. // Ecological-physiological studies of photosynthesis and respiration of plants. L.: Nauka. Leningrad Division. 1989, p. 14-26 (in Russian).

9. Slemnev N.N. Thesis D.Sc. Biology. L. 1990, 36 p (in Russian).

10. Slemnev N.N. // Russian Journal of Plant Physiology. 1996, v. 43, №3, p.418-436 (in Russian).

Fig.1. Seasonal changes of available soil water supply in the upper 50 cm soil layer.

Figure 2. Seasonal course of  photosynthetic daily productivity of conifers in 1995. Total pine productivity (1) – 9,18; larch productivity (2) – 3,08; spruce productivity (3) – 3,10 mol СО₂ m^-2 season^-1.

Figure 3. Seasonal course of  photosynthetic daily productivity of conifers in 1996. Total pine productivity (1) – 8,71, larch productivity (2) – 4,88, spruce productivity  (3) – 6,760 mol СО₂ m^-2season^-1.

Table 1. Influence of environmental factors on conifers photosynthetic productivity
Date	Environmental factors								Photosynthesis productivity, mmol СО2 m^-2day^-1^'
	Available soil water supply, mm	Air temperature average at day, ^oС		Light availability мol* m^-1day^-1		Air humidity average at day, %	Soil temperature (h=20cm) ^oC		Pine	Spruce	Larch
Experiment (summer period)
18.07 19.07 01.08 02.08 03.08 08.08	34 36 41 39 37 35		25,8 27,8 24,1 24,1 24,5 18,2		102 107 123 115 112 106	62 58 58 58 63 75	15 16 16 16 16 15	22,3 11,5 13,1 22,9 19,7 31,3		-1,8 -3,2 3,5 8,4 2,5 7,7	18,3 12,2 63,6 58,7 18,9 17,4
Control (summer period)
22.06	120		17,3		125	61	10	113,2		27,8	74,1
Experiment (autumn period)
24.09 25.09	39 38		14,1 15,1		68 71	60 60	9 9	56,7 49,5		36,8 34,5	- -
Control (autumn period)
03.09	50		15,0		79	78	11	69,8		52,6	-

Table 2. Relationship of daily photosynthetic productivity and environmental factors (г – correlation coefficient). Environmental factors as the same in table 1.
Species	Year	Light availability	Air temperature average at day	Air humidity average at day	Soil temperature at the depth (cm)			Available soil water supply, in layer (cm)
					5		20		10	50
Pine	1995	0,64	0,34	-0,44	0,31		0,11		0,42	0,52
	1996	0,64	0,46	-0,23	0,50		0,34		0,31	0,10
Spruce	1995	0,35	0,19	-0,20	0,11		-0,06		0,47	0,56
	1996	0,49	0,36	-0,15	0,42		0,27		0,28	0,56
Larch	1995	0,74	0,65	-0,29		0,53	0,23		0,08	0,16
	1996	0,65	0,74	0,18		0,85	0,73		0,50	0,40

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