**2. Material and methods**

**1. Introduction**

44 Water Stress in Plants

of lives and properties throughout Europe [4].

usage was restricted [8–11].

Rapidly increasing population in the world, limitless industrialization process, poor urbaniza‐ tion 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 environ‐ ment, 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 ofrapid deforestation,these factors have yielded a serious situation nearly beyond prevention [1, 2].Throughout history,the amount of CO2 concentration in the airdidnot 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

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

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 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

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 impor‐

due to evaporation than the water supplied by precipitation in a certain region [6].

the most vulnerable territories to drought is green and outdoor spaces in cities.

In the study, a total of 10 species have been used which are *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 and which are frequently used in landscaping applications. The fruits and cones of above‐mentioned species were gathered in October in the parks and gardens in Kastamonu, and seeds were attained after cleaning the cones and fruit fleshes. The seeds are except the ones of *Pinus nigra* and *Pinus brutia* which have been subject to stratification for a period of 8 weeks, and then, germination trials have been conducted in -2, -4, -6, and -8 Bar water stress, and in addition to these, control group has been used. The water potential of the germination substrates (0, -2, -4, -6 and -8 Bar) was determined using PEG‐6000 solution and prepared as described by Michel and Kaufman [24, 25].

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 propor‐ tioning 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 propor‐ tioned 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.
