TWO PARAMETERS OF PHOTOSYNTHETIC ACTIVITY OF SIBERIAN CONIFERS (RUSSIA)

 

Galina G. Suvorova, Ludmila S. Yan’kova, Lidia D. Kopytova, Alexandra K. Phylippova

 

Siberian Institute of Plant Physiology and Biochemistry, SB RAS, Russia

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

 

Abstract

 

The relationship of maximum day time photosynthetic rate and day time photosynthetic productivity for pine (Pinus sylvestris L.) and Siberian spruce (Picea obovata Ledeb.) during spring, summer and autumn is investigated. The nature of the relation is rather steady, which indicates a possibility to use regression equations in calculation of a physiological production potential of an arbor, vegetative crown and arboreal stand.

 

Introduction

 

Maximal photosynthetic rate  of individual species of plant canopy is characterized by the values of maximal daily rate of their photosynthesis determined by field experiments. Following the sources (Zalensky, 1968; Slemnev, 1991) we define maximal daily rate of net photosynthesis as a parameter of realization of photosynthetic potential of the plant species under investigation in concrete combination of environmental conditions. Maximal values of CO₂ photosynthetic fixation and organic mass formation are related through photosynthetic productivity – carbon absorption over a certain period of time. Daily photosynthetic productivity is an index of СО₂ assimilation calculated for weight unit or a unit of plant leaf surface over 24 hours. Daily photosynthetic productivity determines the level of daily organic matter accumulation by the plant. This parameter characterizes production potential of the plant.

We hereby set out an objective to investigate the proportion between realization of photosynthetic potential and production potential of common pine and Siberian spruce during vegetation, and in the years differing in weather conditions.

 

Material and Methods

 

Peculiarities of carbon dioxide gas exchange of common pine (Pinus sylvestris L.) and Siberian spruce (Picea obovata Ledeb.) were studied in 1997 and 1999 in the forest stand, planted with two-year-old saplings in 1985 in the suburb of Irkutsk. Photosynthetic activity was determined by IK-gas analysis method modified by Shcherbatyuk (Shcherbatyuk, 1991). Cylinder-shaped polyethylene-covered assimilation cuvettes were installed on the intact needles-bearing branches of the previous year in the upper third of the crowns. Detailed description of the experiment method and registration of environmental factors has been presented earlier (Shcherbatyuk et al., 2004). 25-30 three-days weekly experiments were conducted during the vegetation season (early April – November 10). Maximal daily photosynthesis rate was selected in compliance with the graphs of daily СО₂-gas-exchange. Daily photosynthetic productivity was determined as integral assimilation during the day. Analysis of connection between maximal daily photosynthesis rate and daily photosynthetic productivity of pine is presented for four phenological periods – early-spring (April 1 – May 15), spring (May 16 – June 15), summer (June 16 – August 31) and autumn (September 1 – November 10) using software Exсel-97 for Windows. Two vegetation seasons differing in weather conditions were selected for the analysis: anomalously early warm vegetation period of 1997 and vegetation period of 1999, close to the first one in terms of warmth, but with low spring level of soil moisture and summer drought (Suvorova et al., 2002).

 

Results and Discussion

 

Realization of photosynthetic potential and daily photosynthetic productivity of pine and spruce were established to change with high degree of association in early spring  (R²=0,54-0,93) and autumn (R²=0,62-0,84) periods, when air and soil temperatures act as major limiting factors and photosynthetic activity is rigidly regulated on the whole plant level. At the same time the crown of evergreen coniferous species is not exposed to overheating.  In spring and summer more labile response of photosynthetic apparatus of the coniferous species to environmental conditions results in dissociation of link between photosynthetic activity parameters. Closeness of link between parameters of maximal rate  and daily photosynthesis productivity decreases in the following cases. In spring, on clear days with high air temperature at midday low relative air humidity is observed (down to 20-30%). Reduction of air temperature to zero at night brings down warming of soil mass. With this maximal rate of assimilation process may be low, but daily photosynthetic productivity reaches high values due to long-term light period. This peculiarity characterizes both pine and spruce. During summer drought a fairly high maximum of assimilation rate may show in the morning with optimal levels of temperature and relative air humidity. But photosynthesis depression developed at midday and n the afternoon leads to low daily productivity of photosynthesis. On the days with sharp weather change – short-term rain, thunder - closeness of link between maximal photosynthesis rate and daily photosynthetic productivity is also likely to go down. In spring 1997 with air temperature rise and decrease of soil moisture reserves in the upper 50 cm soil layer there was also observed absence of  connection between photosynthesis parameters in both species simultaneously. At the same time there is observed transfer from anomalously high rate  values and photosynthesis productivity, by 2-3 times exceeding normal values, to standard values.  In all the other cases the level of connection during spring and summer period between the parameters analyzed remained fairly high even in the years, which we did not present for the analysis.   During the drought of 1999 closeness of connection between the parameters of photosynthetic activity of spruce was high in the period of cool spring and autumn  (R²=0,78-0,82), for pine like in 1997 – in early spring period  (R²=0,93) (Table 1).

Maximal photosynthesis rate and daily photosynthetic productivity in the droughty 1999 were 3-4 times lower for pine and 2-3 times lower for spruce as compared to favorable period of 1997 (Fig. 1). But neither type of connection, nor proportions between ratios did not change significantly. This allows to infer that in Baikal Siberia the change of level of photosynthetic potential of pine and spruce during the vegetation is accompanied by adequate change of daily photosynthetic productivity. In ideal conditions we could expect that with a certain maximum value of photosynthesis rate the value of daily photosynthetic productivity would reach the plateau achieving maximal limiting value for the given species. In our case dependence of the parameters investigated is far from saturation. This allows to state that in the conditions of the studied region the production process of coniferous is limited by environmental conditions already in the earliest periods – realization of potential possibilities of photosynthetic apparatus and preservation of high level of assimilation activity during the day.

It has been earlier shown that high values of daily and seasonal photosynthetic productivity was noticed in environmental conditions characteristic of each specific species (Suvorova et al.,  2002). Ranges of conditions, at which there are observed 20% of net photosynthesis maximums, are also species-specific (Suvorova, 1992). At the same time, environmental parameters characterizing absolute seasonal maximum of net photosynthesis did not show any species specificity (Shcherbatyuk et al., 1999).

 

Conclusion

 

The above analysis of the experimental research allowed to reveal linear type of connection between maximal values of daily net photosynthesis and daily photosynthetic productivity of the coniferous species. The type of connection is similar in two periods analyzed. Dependence between the parameters investigated does not reach saturation plateau, which speaks in favor of limitation of the coniferous production process at the level of carbon fixation. With the approach selected, species specificity of the connection between photosynthetic potential and photosynthetic productivity of pine and spruce is only observed in general: pine is characterized by the highest degree of connection in early spring, spruce demonstrates reduction of photosynthesis parameters link closeness in the periods with high air temperature. 

The acquired regressive equations of connection between photosynthetic potential and photosynthetic productivity may be used for calculation of potential carbon stock to coniferous stands. In order to calculate real carbon stock it is necessary to include parts of assimilates demand not only for growth but for the growth respiration and maintenance respiration supporting crown elements and plant root system. The approach suggested results in deeper understanding of carbon stock  as a dynamic process determined by the impact of natural factors and species-specific properties of wooden plants photosynthesis.

 

Literature cited

 

1.      Zalensky O.V. Potential photosynthesis intensity of surface plants of different botanical-geographical zones of USSR // Theses of reports of the session of General meeting of the Biological  Sciences Division of the USSR as dedicated to space biology. М. 1961. P. 243-24 (in Russian).

2.      Slemnev N.N. Photosynthesis ecology in connection with regularities of vital activity of Mongolian steppe and desert plants: Abstract of D.Sc. thesis: 03.00.05. BIN named after V.L. Komarov, Leningrad, 1990. 36 p. (in Russian).

3.      Suvorova G.G. Photosynthesis and growth of coniferous species of the forest-steppe Predbaikaliye. Abstract of Ph.D. thesis. Irkutsk, 1992. 19 p. (in Russian).

4.      Suvorova G.G., Shcherbatyuk A.S., Yan’kova L.S., Kopytova L.D. Photosynthetic productivity of Pinus sylvestris, Picea obovata and Larix sibirica. Botanical Journal. 2002. V. 87. № 9. P. 99-109 (in Russian).

5.      Shcherbatyuk A.S., Suvorova G.G., Yan’kova L.S., Kopytova L.D., Philippova A. K. Role of Photosynthesis in determination of wooden plants species status // Academic Open Internet Journal, (http: //www.acadjournal.com/2005/v14).

6.      Shcherbatyuk A.S. Multi-channel installations with СО₂-gas-analyzers for laboratory and field research // Infra-red gas-analyzers in the investigation of plants gas-exchange. М.: Nauka, 1990. P. 38-54 (in Russian).

7.      Shcherbatyuk A.S., Suvorova G.G., Yan’kova L.S., Rusakova L.V., Kopytova L.D. Species specificity of coniferous photosynthesis response to environmental factors // Lesovedenie. 1999. № 5. P. 41-49 (in Russian).

 

 

 

 

Figure 1. Interconnection of maximal daily rate and daily photosynthetic productivity of common pine in 1997 (а) and 1999 (b).

 

 

 

 

 

 

 

 

 

Table 1. Equations of connection of maximal photosynthesis intensity (x) and daily photosynthetic productivity (y) of coniferous species in individual vegetation periods 

Pine			Spruce
1997 (anomalously warm, early)
Period	Connection equation	R2	Connection equation	R2
Early spring	Y=29.5x-8.9	0.91	Y=24.5x+0.7	0.65
Spring	Y=22.7x+15.5	0.10	Y=5.5x+35.1	0.12
Summer	Y=34.0x-21.6	0.79	Y=28.1x-10.9	0.71
Autumn	Y=20.7x-4.1	0.62	Y=21.9x-11.2	0.73
1999 (hot, droughty)
Early spring	Y=32.2x-4.7	0.93	Y=22.1x+2.7	0.54
Spring	Y=26.9x-5.3	0.50	Y=40.2x-12.9	0.82
Summer	Y=24.2x-2.7	0.53	Y=26.6x-4.7	0.50
Autumn	Y=18.7x-1.73	0.84	Y=16.4x-1.2	0.78

 

 

 

 

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