The change of germination percentages under various water stress conditions.
Abstract
Especially the use of drought‐resistant plant species reduces maintenance and irrigation costs, and plants increase the retention and success to continue its life in arid landscape. In this study, some plant species used have been studied to determine their tolerance to drought stress in gardens and parks in Kastamonu. For this purpose, germination trials have been in conducted -2, -4, -6, and -8 Bar water stress. Landscaping applications commonly used some species such as Cupressus sempervirens L., Ailanthus altissima (Mill.) Swingle, Pyracantha coccinea Roem, Thuja orientalis, Pinus sylvestris L., Sophora japonica, Cedrus libani A. Rich., Acer pseudoplatanus L., Pinus brutia Ten., and Pinus nigra Arnold. ssp. pallasiana (Lamb.) Holmboe. Their seeds were evaluated different levels of water stress in the germination percentage. PEG 6000 solution was used in the formulation of water stress. The seeds were exposed to constant temperature of 25°C for a period of 35 days at germination cabinet. As a result, this experiment calculated germination in different water stress levels what percentage has fallen, so the least affected by increased water stress was studied to determine the species. Also results showed increased water stress and reduce the percentage of germination in all species. The highest level of water stress -8 Bar, which was also obtained stress level proportional germination values Pinus nigra Arnold. ssp. pallasiana (Lamb.) Holmboe (64.8%) and Pinus brutia Ten. (46.5%).
Keywords
- polyethylene glycol
- germination percentage
- PEG
- drought stress
- plants
- seed
1. Introduction
Rapidly increasing population in the world, limitless industrialization process, poor urbanization activities, regional wars, pesticides which are used to increase crops, and unconscious use of fertilization and chemicals such as detergents have started to contaminate the environment, which results in damage for living beings as a result of extensive air, water, and soil pollutions. The use of fossil fuels has been on the increase since the industrial revolution. With the addition of rapid deforestation, these factors have yielded a serious situation nearly beyond prevention [1, 2]. Throughout history, the amount of CO2 concentration in the air did not exceed 320 ppm. However, current concentration is above 385 ppm and it keeps on increasing [3]. This situation has led to a concern and long debates in relation to the effects of global warming [1].
It is inevitable that climate change manifests its effects all around the world due to global warming. The increase in temperature and changing precipitation are expected to increase water problems, which are already felt in certain regions. It is estimated that there will be changes in the frequency and severity of droughts and floods, which may lead to serious loss of lives and properties throughout Europe [4].
Drought is a phenomenon resulting from certain variables such as precipitation, temperature, humidity, evaporation, and transpiration. Basically, drought refers to water deficit resulting from below‐average emergence of natural water assets, which are used by various systems, in some regions for a particular time period [5]. When drought is mentioned, precipitation and water deficit come to one's mind first. It can be defined as having higher levels of water loss due to evaporation than the water supplied by precipitation in a certain region [6].
Twenty‐eight percentage of usable territories on the world are affected by drought [5]. Due to greenhouse gas accumulation in the atmosphere, a climate change will take place in the upcoming years, which is likely to leave us with arid and sub‐arid territories. These, in turn, will add to the water problems in urban areas, and there will be an increase in the demand for water for both agricultural and drinking purposes. Hence, in addition to the expansion of arid and sub‐arid territories, there will be an increase in summer drought period and severity accompanied by desertification, salinization, and erosion processes [7]. Undoubtedly, one of the most vulnerable territories to drought is green and outdoor spaces in cities.
The drought increasing day by day and the thirstiness as a result of this make their destructive effects felt in green fields as it is in all parts of our lives. Almost all of the green fields constituted with the approach of classical landscaping design, which requires great amounts of water especially in our metropolitan cities, were damaged greatly in a few months in which water usage was restricted [8–11].
While the purpose was healing the environment‐ambience quality in the applications of landscaping architecture and repairing the damaged environment conditions in previous years, the wise usage of water for the worries depending on the climate change and herbal applications resistant to drought have come to the fore recently [12–16]. The plants used in landscaping fields are desired to be resistant to drought, and this becomes the most important criterion, which affects the choice of plants in some regions even [17–21]. It is of great importance for the wise usage of water that species and origins resistant to drought are identified first and these kinds of species and origins is used for the landscaping designs.
Different methods are used for identifying the resistances of species against drought. One of these methods is to conduct PEG applications on the seeds in different concentrations. PEG applications have been used in many species for identifying their resistance to drought, and it has given very successful results [22, 23].
In this study, it was aimed at identifying the water stress tolerance for some plants, which are used in landscaping works. Trials have been conducted on nine species chosen for this purpose, and the water stress reactions of the species in different levels were determined.
2. Material and methods
In the study, a total of 10 species have been used which are
Germination tests were performed in 11‐cm‐diameter glass petri dishes on two layers of filter paper saturated with water solutions. Fifty pieces of seeds have been placed in each petri dish in a way that the seeds will not have a touch with each other, and the study has been conducted with 4 repetitions. In this way, a total of 9000 seeds consisting of 50 pieces of seeds, 4 repetitions, 5 applications, and 9 species have been used in the study.
The seeds have been subject to germination with the period of 35 days in 25 ± 1.0°C constant–temperature in germination cabinet, and the filter papers have been renewed in each 3 days.
At the end of 35‐day period, non‐germinated seeds were cut and checked. Unfilled seeds were excluded from the evaluation, and germination percentage (GP) was calculated by proportioning the number of germinated seeds to healthy ones.
Germination percentage results were subjected to factorial variance analysis. The differences between species and the degrees of significance of such differences were revealed. In order to eliminate the misleading effects of the germination capability differences between the species included in the experiment in checking operations (0 Bar) on the analysis results, the values of these operations were proportioned to 100, and cumulative germination percentages (CGP) were calculated. Thus, the differences between the species were tried to be demonstrated more rationally. The data to be subjected to variance analysis were entered as they were proportioned to 100.
SPSS 17.0 statistics program was used to evaluate the data obtained through experiments. When statistically significant differences (P < 0.05) were found through analyses of variance, Duncan's test was performed to form homogeneous groups. Duncan's test showed that the operations were in the same or different categories in terms of the measured characteristics [26]. Multivariate analysis of variance (ANOVA) employs two or more factors and attempts to reveal significant differences between the mean scores of many groups according to these factors. In other words, multivariate analysis of variance is used to test the difference between the mean scores of k‐dependent groups [27]. In order to interpret study results with more ease, Excel program was used to create graphs.
3. Findings
Table 1 shows the end‐of‐study values regarding the change in the germination percentages of species under water stress conditions.
Species | Water stress conditions | ||||
---|---|---|---|---|---|
Control | -2 Bar | -4 Bar | -6 Bar | -8 Bar | |
45,2 | 40,0 | 36,3 | 24,5 | 21,0 | |
81,9 | 71,0 | 65,5 | 62,3 | 53,1 | |
62,6 | 54,3 | 45,8 | 36,7 | 19,7 | |
60,2 | 50,0 | 12,2 | 1,2 | 0,0 | |
51,2 | 32,5 | 26,6 | 10,2 | 5,6 | |
70,2 | 65,3 | 48,0 | 35,2 | 15,6 | |
72,6 | 66,7 | 41,3 | 28,6 | 12,3 | |
55,5 | 45,0 | 30,5 | 7,1 | 1,2 | |
32,3 | 30,7 | 18,0 | 7,2 | 2,4 | |
38,7 | 28,6 | 20,2 | 5,1 | 0,0 |
Considering the values in Table 1, the highest germination was observed in
Another species experiencing a rapid fall in germination percentage due to increasing water stress level was
Though its germination percentage was below 50% in the control group,
The purpose of this study was to reveal the changes in the germination percentages of species depending on the water stress and to determine which species are least influenced by increasing water stress. However, not only the germination percentages of species but also to what extent they experience a fall in germination depending on the increasing water stress are of importance in order to make an evaluation in this matter. As a matter of fact, the germination percentage of a species may be low due to its biology or environmental conditions. For instance, Khera and Singh [28] studied various origins in their studies. They reported that
Species | Water stress conditions | ||||
---|---|---|---|---|---|
Control | -2 Bar | -4 Bar | -6 Bar | -8 Bar | |
100 | 88,5 | 80,3 | 54,2 | 46,5 | |
100 | 86,7 | 80 | 76,1 | 64,8 | |
100 | 86,7 | 73,2 | 58,6 | 31,5 | |
100 | 83,1 | 20,3 | 2 | 0 | |
100 | 63,5 | 52 | 19,9 | 10,9 | |
100 | 93,0 | 68,4 | 50,1 | 22,2 | |
100 | 91,9 | 56,9 | 39,4 | 16,9 | |
100 | 81,1 | 55 | 12,8 | 2,2 | |
100 | 95,0 | 55,7 | 22,3 | 7,4 | |
100 | 73,9 | 52,2 | 13,2 | 0 |
The values in the table show that the germination percentage reduced in all of the species due to increasing water stress. The minimum change took place in
However, most of the species experienced great falls in their germination percentages starting from -4 Bar water stress level. The minimum change under -2 Bar water stress level was observed in
Not a big difference occurred in these results under -6 Bar water stress level. The species had similar ranks to the ranks under -4 Bar water stress level. Once again, the highest values in the comparison of germination percentages to the control group percentages were observed in
Under -8 Bar water stress, which is the highest water stress level,
4. Discussion and conclusion
In today's modern life, it has been accepted that the presence of plants in cities is an indicator of their quality and inhabitability [29]. Plants reduce the air pollution and noise in their surrounding areas [30–35]. They also increase aesthetic value [36], have a good influence on psychology [37, 38], save energy [39, 40], prevent erosion [41], and decrease the speed of winds. Since they penetrate into soil with their roots, they prevent transportation of soil by precipitation and streams. They also protect wild life and hunting resources. Green and open areas surrounded by plants are important activity areas for both adults and children [42, 43]. In addition, indoor plants increase the productivity of people working in these places [44]. They relieve people psychologically and reduce stress and negative feelings [45–47].
Due to these functions of plants, a lot of issues such as plants’ spread areas, [48–52], protection [53–59], production [60–64], tolerance against stress factors [65, 66], use in various areas [67–69], genetic variability [70–72], relationships with environment and other living beings [73–79], and raising awareness about them, as well as their legal aspects [80–82] have become main study areas. Therefore, a lot of studies have been conducted on these subjects.
In addition to these functions of plants, their contributions to the aesthetic aspect of the places they are in should be dwelt on under a separate title. Landscape practices for which various species and varieties are used have gained a distinct importance in the modern world. The desire to use diverse species has led to an intense use of plants outside their natural spread areas. The species which are not part of the natural flora of the region draw more attention when they are used for landscape practices and increase landscape quality. However, these practices also cause such plants to deal with ecological and climatic conditions which they are not used to. Therefore, maintenance and watering costs of such species are higher. However, global warming makes it necessary to have a reasonable and thrifty attitude in the use of water.
It is inevitable that climate change manifests its effects all around the world due to global warming. It is expected that the increase in temperature and changing precipitation will increase water problems. It is expected that there will be changes in the frequency and severity of droughts and floods throughout Europe, which may result in loss of lives and property [83]. Therefore, there is a need to determine species which are tolerant to water stress and use such species in both landscaping and forestation practices.
This study is an attempt to reveal the tolerances of certain plant species, which are commonly used for landscape practices, against drought stress. The results of the study indicate that increasing water stress reduced the germination percentage in all the species examined. Many previous studies have reported similar results for many other species so far. Sevik and Cetin [84] conducted a study to determine species’ tolerances towards water stress and reported that the species which were most affected by water stress were
Falusi et al. [85] analyzed the influence of increasing water stress on the germination percentages of four origins of
Tilki and Dirik [86] performed experiments on various origins of
Boydak et al. [87] conducted a study with
Ahmadloo et al. [88] conducted
-5, -10, -15, and -20 Bar water stress levels were created in order to reveal the influence of water stress on the germination percentages of
Boydak et al. [87] conducted a study with 6 different origins of
Kaufmann and Eckard [89] stated that water stress at a level of -8 Bar may reduce the germination percentages of Pinus
Semerci et al. [5] studied the influence of water stress on various
The same study also reported that proportional germination percentages largely vary between the origins. For instance, proportional germination percentage in seeds originating in Tavsanlı Ballıköy was 77% under -2 Bar, 53% under -4 Bar, and 17% under -6 Bar water stress levels. Similarly, proportional germination percentage in seeds originating in Mengen Daren was 75% under -2 Bar, 63% under -4 Bar, and 16% under -6 Bar water stress levels. However, the same study revealed that the proportional germination percentage of seeds originating in Göksun B. Çamurlu and Andırın Akifiye was only 2% under -2 Bar water stress level. Topacoglu et al. [91] reported that
Buyurukçu [27] compared the tolerance of Anatolian pinus nigra (
5. Recommendations
The plants used for parks and recreational areas consist of a wide variety. Previous studies report that water stress works in which PEG solution is used yield successful results. It is possible to have an idea about the water stress tolerance of alternative species to be used in an area where landscape work will be practiced through a 1‐month preliminary work performed in this area. Thus, it will be possible to use species which are tolerant to water stress. However, if researchers conduct such studies and provide the practitioners with ready‐to‐use information, this will bring a great ease for them. Therefore, such studies should be varied and increased in number.
Due to global warming, drought and scarcity of water make their devastating effects felt in all aspects of our lives including green areas. Therefore, the water should be used reasonably, which makes drought‐tolerant plants and their practices crucial. The plants to be used in landscape areas are required to be drought‐tolerant. It sometimes functions as a crucial criterion determining plant choice in some areas. In order to use water reasonably, the species and origins which are tolerant to drought should be determined. Using the seeds and saplings of such species and origins in landscape arrangements is of great importance. In this sense, species should be subjected to drought stress under equal conditions and compared. Accordingly, selecting the species which are most tolerant to drought for landscape practices is important.
The fact that species have rather variable tolerance against water stress has been revealed in previous studies. Even the regions and territories where water scarcity has not influenced the growth of tree species much yet may experience problems due to drought stress in near future. Hence, it is even important to compare the drought stress tolerances of populations in the same climatic regions. Therefore, the situation of local origins is not guarantees, which makes the identification of relatively tolerant species important as part of decision‐making on future forestation strategies.
Therefore, it is very important to perform experiments on the origins of the species that have been proved to be drought‐tolerant in order to determine their most drought‐tolerant origins through studies focusing on extreme fields and to produce seeds from them. Hence, these seeds can be used for landscape practices, which may yield great benefits in future. The use of such species, particularly in areas where maintenance will be performed after mining activities, areas prone to erosion, areas involving forestation on side slopes and traffic islands, urban forests in arid areas, and so on, will both reduce watering, maintenance, fertilization, etc. costs and extend the lifespan of saplings.
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