VEGETOS: An International Journal of Plant ResearchOnline ISSN: 2229-4473
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Research Article, Vegetos Vol: 30 Issue: 2

Transpiration of Woody Plants in the Desert Zone of Mangistau

Belozerov IF* and Imanbayeva AA
RSE Mangyshlak Experimental Botanical Garden of SC MES RK, Aktau, Kazakhstan
Corresponding author : Belozerov IF
RSE “Mangyshlak Experimental Botanical Garden” of SC MES RK, Aktau, Kazakhstan
E-mail: [email protected]
Received: February 28, 2017 Accepted: April 19, 2017 Published: April 21, 2017
Citation: Belozerov IF, Imanbayeva AA (2017) Transpiration of Woody Plants in the Desert Zone of Mangistau. Vegetos 30:2. doi: 10.5958/2229-4473.2017.00141.0

 

Abstract

Transpiration of Woody Plants in the Desert Zone of Mangistau

Objective: The present research on the transpiration flow conducted in the arid conditions of Mangistau allowed three groups of introduced species to be distinguished: low transpiration (3 types of trees); average transpiration (7 types of trees and shrubs) and high transpiration (3 types of trees). Methods: The research subjects included 22 introduced species of trees and shrubs of the different geographical origin, degree of biological resistance and growth forms, among them 4 conifers, 15 deciduous trees, and 3 fruit trees. The following methods were applied in the physiological research: the total water content and the transpiration rate. The selection of leaves was made in the middle part of the crown in the 5-10-fold repetition. Results: According to the correlation analysis, a close relationship has been set between the transpiration rate and the water content of leaves. Soil moisture determines from 11.6% to 43.6% of the transpiration rate variation. Reliable at the 5% significance level is the ratio of correlation with the relative moisture and the air temperature. The conjugation with the value of illumination is statistically unreliable. Seasonal dynamics in the majority of introduced species is seen as a unimodal curve with a peak value in June. Three types have been determined for the daily transpiration rhythm: "rising", "falling" and "variable". Conclusion: The intensity of the transpiration process, due to its considerable variability and multifactor nature, cannot be referred to the resistance criteria of woody plants, but at the same time, there is a noticeable connection between the biological stability of introduced species and the coefficient of transpiration variation. With the increase of its values, the resistance of introduced species to the arid habitat conditions is generally enhanced due to their increased ability to the self-regulation of water exchange..

Keywords: Woody plants; Transpiration rate; Correlation; Water content; Regression

Keywords

Woody plants; Transpiration rate; Correlation; Water content; Regression

Introduction

Transpiration is one of the main environmentally improving indicators of tree plantations for the desert conditions of Mangistau. Physiological water return is also relevant because in the conditions of the soil moisture limit, the process of maximizing the productivity of plants comes down to a simultaneous optimization of solar radiation absorption and water flow through transpiration. The amount of water evaporated by the plant is very often many times greater than the volume of water contained in it. At the same time, the economical water consumption is one of the most important phyto introduction problems in the arid regions. Transpiration in regular sizes is indeed not necessary. Thus, if plants are grown in the conditions of the low and high soil moisture, naturally, in the first case transpiration will be much less intensive. However, the growth of plants in a certain moisture range will be about the same (within statistical accuracy bounds). Therefore, it is necessary to find a balance by selecting a specific spectrum and regulating the irrigated soil regime. Moreover, transpiration is an indispensable physiological process of the plant body and is essential to its life activity as a defense mechanism against overheating in direct contact with the sunlight and as a creator of the continuous flow of water and mineral nutrients from the root system to other anatomical organs. Due to the special importance of this physiological parameter for the desert habitat, Mangyshlak Experimental Botanical Garden (MEBS) conducted a detailed study of the transpiration moisture rate for the prevailing types of trees and shrubs in the garden and parkland of the region in 2012-2014. Its purposes were to identify the regularities of its daily and seasonal dynamics, to establish the correlation and regression relationship with the soil moisture supply and the main meteorological factors, and to determine the possibility of using woody introduced species as an indicator of biological resistance.

Materials and Methods

The research subjects included 22 introduced species of trees and shrubs of the different geographical origin, degree of biological resistance and growth forms, among them 4 conifers, 15 deciduous trees, and 3 fruit trees. The following methods were applied in the physiological research: the total water content - by drying leaves to a constant weight at a temperature of 100ºC -105ºC; the transpiration rate - by the method of rapid weighing proposed by A.A. Ivanov [1,2]. The selection of leaves was made in the middle part of the crown in the 5-10-fold repetition. The statistical processing of the findings was performed by the method of G.F. Lakin with the use of statistical software package - Statgraphics Centurion XVI.I. [3].

Results and Discussion

According to the average three-year data, all the introduced species were divided into three groups by the values of the transpiration rate (Table 1): 1) low transpiration (less than 250 mg/g of the weight of moist leaves per hour) - all conifers (Platycladus orientalis (L.) Franco, Juniperus virginiana L. and Pinus pallasiana Lamb.); 2) average transpiration (250-500 mg/g of the weight of moist leaves per hour) - Gleditsia triacanthos L., Maclura aurantiaca Nutt., Elaeagnus oxycarpa Schlecht., Populus bolleana Lauche, Populus diversifolia Schrenk., Amygdalus nana L., Betula verrucosa Ehrh., Berberis vernae Schneid., Fraxinus sogdiana Bunge, Armeniaca vulgaris Lam.; and 3) high transpiration (more than 500 mg/g of the weight of moist leaves per hour) - Crataegus ambigua C. A. Mey, Quercus robur L., Malus sieversii (Ldb.) M.Roem. The absolute maximum of the transpiration rate (TR) was observed in the water-loving tree - Populus bolleana (1,578 mg/g per hour), and other woody plants of the mesophytic and mesohydrophytic species: Betula verrucosa (1,115). Crataegus ambigua (1,546), Berberis vernae (1,011), Gleditsia triacanthos (1,428) and Quercus robur (1,313 mg/g per hour).
Table 1: Correlation of the transpiration rate with the number of month of the vegetation season and the main meteorological factors in the study of seasonal dynamics.
Transpiration has daily and seasonal dynamics. There are several approaches to the interpretation of the seasonal dynamics of transpiration. Most researchers, associating the course of physiological water return with a set of meteorological factors, indicate a close correlation only if there is a sufficient moisture supply of woody plants [4-6]. According to the authors’ observations, the transpiration rate increases from spring to mid-summer and then drops to autumn. Another approach is based on the gradual aging of biocolloids of the leaves’ protoplasm, resulting in a natural reduction in the transpiration flow during the vegetation season [7,8]. Sudnitsyn also observed such dynamics of transpiration but explained it with a steady depletion of soil moisture reserves [9]. In the present research, in each vegetation month soil moisture varied in a strictly defined range - from the antecedent irrigation level (70- 75%) to the value of the full field moisture capacity (100%). That was because all the introduced species of woody plants are grown only in the conditions of systemic irrigation, and sampling was carried out in the middle of the inter-irrigation period. There was a change only in meteorological factors and the physiological state of woody plants. The resulting picture of the TR seasonal dynamics in the vast majority of introduced species is given as a unimodal curve with a peak value in June, which is conditioned by the depression of physiological water return in July-August due to a high temperature and insolation, in September – due to leaf apparatus aging, temperature deterioration and moisture increase (Table 2).
Table 2: Transpiration rate and water content in the leaves of woody plants (average three-year data for 2012-2014).
The TR seasonal dynamics is very unusual in one of the most biologically resistant types - Elaeagnus oxycarpa (Table 2). Its value strictly corresponds to the course of temperature variation, therefore, a maximum is observed in July, and a minimum - in May and September. This is also confirmed by the correlation analysis, according to which this species has the highest negative correlation (r=-0.64) with the air temperature (Table 3).
Table 3: Seasonal dynamics of the transpiration rate of woody plants (three-year average data for 2012-2014, in mg/g of the weight of moist leaves per hour).
According to the average data, the correlation ratio of the transpiration rate is statistically reliable in the study of seasonal dynamics only with the number of month from the beginning of the vegetation season (r=-0.91). With the air temperature (r=0.13) and moisture (r=0.49), as well as illumination (r=-0.37), the correlation is unimportant at the 5% significance level (Table 3).
In the seasonal and timing aspect, the TR correlation between the selected taxa is estimated to be high only between the representatives of one morphological and taxonomic group or when the stability and confinement of the natural habitat is similar. For example, the types of conifers – r=0.91-0.92, Elaeagnus oxycarpa and Populus diversifolia - 0.70.
According to the TR variability, during the vegetation season woody plants were divided as follows (Table 4): 1) Low variability (Cv<10%): Betula verrucosa; 2) Average variability (Cv=10-20%): Amygdalus nana, Quercus robur, Populus diversifolia, Fraxinus sogdiana; and 3) High variability (Cv>20%): Platycladus orientalis, Juniperus virginiana, Pinus pallasi-ana, Crataegus ambigua, Gleditsia triacanthos, Maclura aurantiaca, Elaeagnus oxycarpa, Populus bolleana. The most common taxa in the green areas of Mangistau fall into the groups with a higher variability due to a better adaptation to the desert growing conditions. Unlike the seasonal development of transpiration, daily dynamics is influenced by a smaller number of endogenous and exogenous factors. However, its character is very heterogeneous and depends both on the change in weather conditions, and on the biology of species (Table 5). According to the averaged data, the following types of the TR daily rhythm were identified: 1) "rising" (from the morning to the evening) - Platycladus orientalis, Juniperus virginiana, Betula verrucosa; 2) "falling" (from the morning to the evening) - Gleditsia triacanthos; 3) "variable" (with a maximum at noon) - Pinus pallasi-ana, Crataegus ambigua, Quercus robur, Maclura aurantiaca, Amygdalus nana, Elaeagnus oxycarpa, Populus bolleana, Populus diversifolia, Fraxinus sogdiana.
Table 4: Seasonal dynamics of the transpiration rate of woody plants (three-year average data for 2012-2014, in mg/g of the weight of moist leaves per hour).
Table 5: Daily dynamics of the transpiration rate (average data for 2013, in mg/g of the weight of moist leaves per hour).
However, in July, the hottest and driest month, most of the plants should be attributed to the "variable" type with a minimum at noon. Transpiration curves seem to be flattened. The variation of the transpiration rate stops to comply with the daily course of meteorological factors. There is an asymmetry of transpiration curves towards the antemeridian or afternoon hours. Alekseyenko and Khashes also pointed out this feature. The latter explains the shift of the maximum transpiration rate with endogenous causes [10,11]. Without the regulatory activity of plants themselves, the transpiration flow should gradually increase by 1400, and then just as slowly decrease. However, at some period of the day the plant starts not to be able to provide the leaves with the quantity of water necessary for evaporation in accordance with the supply of energy.At this time, there is a maximum of transpiration, after which it is weakened, no longer corresponds to the course of meteorological conditions, and is defined by the physiological state [10]. Thus, even in the conditions of the high relative water supply, the desert climate makes the plant to actively adjust its water exchange. On average, all of the test plants (Figure 1) in May, June, August and September have a fixed maximum of the transpiration rate at 1430 with a reduction and increase towards the morning and evening hours. In July, the transpiration rate gradually falls during the day, but only slightly - by 5-12%.
Figure 1: Dependence diagram of the TR and the water content of leaves (WC), η = 0,79; ηcr05 = 0,42.
As far as transpiration is the final stage of the cycle of irrigation water in the soil and the plant, its correlation with soil moisture and the water content of leaves is unquestionable even from a logical point of view Gunn and Kolov [12]. Experimentally, it is confirmed by a number of authors [13-17]. With the decrease in soil moisture, the transpiration level decreases [18]. The less water is in the soil, the less water is in the plant. The reduction of the water content in the plant body automatically decreases the transpiration process due to a stomatal and non-stomatal adjustment [19]. In our studies, even with the use of the composite power connection (Figure 2), the correlation of the transpiration rate and the water content of leaves is statistically reliable at the 5% significance level (η=0.79). Soil moisture determines 11.6% of the TR variation (r=0.34), primarily due to its dependence on other factors, particularly, meteorological (Table 6). Moreover, for a variety of taxa, the correlation coefficient varies in a very wide range - from 0.17 to 0.56. On average, for all of the test plants, the most reliable equation of regression between the TR and soil moisture in order of importance has a square-power form (Figure 3), and the correlation ratio (η) is 0.66. In addition to soil moisture reserves, the main environmental factors influencing transpiration include the illumination intensity, the relative air moisture and temperature, and the wind speed. The internal factors are as follows: area, location, and structure of leaves, behavior of stomata and effectiveness of the root absorption surface. There are also complex interactions between different factors Garnier, Berger and Martin [20]. The higher the air moisture stress is, the lower (more negative) its water potential is, and the faster the evaporation is. This is also true for transpiration, but it should be noted that when there is a shortage of water in the leaf, there is a stomatal and non-stomatal adjustment, by virtue of which the effect of external conditions is made in a moderate form. Analysis of study materials showed the presence of a significant close correlation between the TR and the relative air moisture (η>ηcr05) for almost all the woody plants selected for the experiment (Table 7). The diagram of the multiplicative correlation between the TR and the relative air moisture demonstrates an explicit tendency of the transpiration flow reduction with the increase of the water content in the air (Figure 1). Another investigated factor influencing the process of transpiration is the air temperature. As known, when the temperature increases, there is a significant increase in the amount of water vapor which fills this space. The growth of the water vapor pressure leads to the moisture stress, which in turn increases the amount of transpiration moisture. Both by the value of the correlation coefficient - r=0.46 (Table 7), and by the correlation ratio (0.40) of the complex multiplicative power equation (Figure 4), there is a statistically reliable correlation between the TR and the AT. During the research, the equation of the correlation between the TR and illumination was derived for the first time for the conditions of Mangistau. As seen from the diagram in Figure 5, in the studied range from 29.1 to 75.6 klx, an increase in illumination does not lead to the depression of the transpiration process due to the protection of stomata against strong solar radiation and overheating. The transpiration rate also depends on the development phase. With the increase of the plant’s age, transpiration tends to fall. High evaporation rates in young leaves can occur by increasing the level of cuticular transpiration, as far as the cuticle is still poorly developed during this period. Thus, according to Henkel [21], cuticular transpiration in young birch leaves is about 50%, and in old leaves - only 20% of the total evaporation. It should also be taken into account that young leaves have higher water content. It is interesting that the evaporation rate is affected not only by the leaf ’s own age, but also by the overall age of the plant body. P.L. Henkel believes that a gradual decrease in the transpiration rate in the process of ontogeny of both the body and the plant in total may serve as a confirmation of the biogenetic law (ontogeny recapitulates phylogeny) [21]. Indeed, there is a correspondence between the way of adaptation of the plant to terrestrial life in phylogeny and the better retention of moisture in ontogeny. In our experiments, even in the age range of 2 - 20 years a pattern of the reduction of the transpiration rate with age is observed for the majority of woody plants, but in a mild form. On average, for all the introduced species, even with the use of the S dependence curve (Figure 6), the correlation ratio is 0.38 at the critical value of 0.47.
Figure 2: Dependence diagram of the TR and soil moisture (SM), η = 0,66; ηcr05 = 0,42.
Table 6: Daily dynamics of the transpiration rate (average data for 2013, in mg/g of the weight of moist leaves per hour).
Figure 3: Dependence diagram of the TR and the relative air moisture (RAM), η = 0.59; ηcr05 = 0.39
Table 7: Correlation of the transpiration rate with the time of the day and the main meteorological factors in the study of daily dynamics for 2013.
Figure 4: Dependence diagram of the TR and the air temperature (AT), η = 0.40; ηcr05 = 0.39
Figure 5: Dependence diagram of the TR and illumination (IL), η = 0.38; ηcr05 = 0.39.
Figure 6: Dependence diagram of the TR and the plant age (A), η = 0.48; ηcr05 = 0.88.
The variability and multifactor nature of the transpiration process does not allow it to be referred to the number of biological markers of plant resistance. The one thing, noted in the analysis of the collected materials, is a certain conjugate resistance to dry environmental conditions with a coefficient of variation of the TR. The more it is, the more stable the introduced species are due to the autoregulation of the water regime. For example, a number of plants with the greatest variation of physiological evaporation (38.2-47.2%) included such resistant species in local conditions as Platycladus orientalis, Elaeagnus oxycarpa, Populus bolleana and Populus diversifolia. To the contrary, the less resistant species are Betula verrucosa, Crataegus ambigua, Gleditsia triacanthos and Fraxinus sogdiana, which have a coefficient of variation by 5-15% less.

Conclusion

Thus, based on the results of the three-year study on the values of the transpiration flow of moisture, three groups of introduced species were distinguished: low transpiration (3 types of trees), average transpiration (7 types of trees and shrubs) and high transpiration (3 types of trees). According to the correlation analysis, a close correlation between the TR and the water content in the leaves of woody plants was set (r=0.79). Soil determines from 11.6% to 43.6% of the transpiration rate variation (r=0.34; η=0.66). Reliable at the 5% significance level is the ratio of correlation of the TR with the relative moisture (r=-0.59) and the air temperature (r=0.46). Its conjugation with the value of illumination is statistically unreliable (r=0.19). Seasonal dynamics in the majority of introduced species is seen as a unimodal curve with a peak value in June. Three types were determined for the daily transpiration rhythm: "rising" (from the morning to the evening - 3 types of trees), "falling" (from the morning to the evening - one type of trees) and "variable" (with a maximum at noon - 9 types of trees and shrubs). According to the research material, the intensity of the transpiration process, due to its considerable variability and multifactor nature, cannot be referred to the resistance criteria of woody plants. However, at the same time, there is a noticeable connection between the biological stability of introduced species and the coefficient of variation of the TR. With the increase of its values, the resistance of plants to the arid habitat conditions is generally enhanced due to their increased ability to the self-regulation of water exchange.

References

 

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