Irrigation water salinity effects on oregano (Origanum onites L.) water use, yield and quality parameters

Scientia Horticulturae 247 (2019) 327–334

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Irrigation water salinity effects on oregano (Origanum onites L.) water use, yield and quality parameters

T

⁎

Nurten Esen Hancioglua, Ahmet Kurunca, , Ismail Tontulb, Ayhan Topuzc a

Faculty of Agriculture, Akdeniz University, Campus, 07058, Antalya, Turkey Faculty of Engineering and Architecture, Necmettin Erbakan University, 42060, Konya, Turkey c Faculty of Engineering, Akdeniz University, Campus, 07058, Antalya, Turkey b

A R T I C LE I N FO

A B S T R A C T

Keywords: Oregano (Origanum onites L) Salinity Salinity threshold value Yield Yield quality

Irrigation water salinity effects on oregano growth, water use, yield and quality parameters were investigated. For this aim, eight irrigation water salinity levels including 0.54 (control), 1.2, 1.8, 2.5, 3.5, 5.0, 7.0 and 10 dS/ m were utilized. The plants in all of 7 and 10 dS/m and two out of five replications of 5 dS/m treatment could not survive until the end of the experiment. The mean soil salinity and seasonal averaged drainage water salinity values increased with increasing salinities of applied irrigation water. Compared to control 27, 33, 44 and 74% reductions in total dry yields, and 27, 38, 49, and 77% decreases in dry leaf yields were calculated for 1.8, 2.5, 3.5 and 5 dS/m treatments, respectively. In general, increased irrigation water salinity caused increases in total phenolic content, total flavonoid content, extract yield which shows the amount of water extractable matter from the plants and antioxidant activity whereas significant decreases in total oil content. Among the essential oil components, carvacrol, β-cymene and γ-terpinene contents decreased with increasing water salinities up to 2.5 dS/m and after this level sharply increased but linalool content showed a reversed pattern. A threshold value of 0.50 dS/m was calculated for total fresh yield of oregano but it was not possible to determine a threshold salinity value for total dry yield, dry leaf yield and total oil content. Based on these results, oregano is a very sensitive plant to salinity.

1. Introduction Salt stress is the second most prevalent abiotic stress after drought in the world that adversely impacts plant growth (Pessarakli, 1991). Even though, most of the salinity and all of the sodicity is natural, a significant proportion of recently cultivated land has become saline because of land clearing and irrigation. Food and Agriculture Organization (FAO) has estimated that approximately 45 million ha (20%) out of 230 million ha of irrigated land in the world are salt affected (FAO, 2005). In general, soil salinization can be caused by shallow saline water tables, but also results from the saline irrigation water especially coupled with poor irrigation management. However, saline water available in different regions of the world has been used successfully for irrigation purposes with proper scheduling (Rhoades et al., 1992). Accurate scheduling of irrigation, essential for maximizing crop production, requires a good knowledge of water demand and salinity tolerance of the crop in addition to soil water characteristics (Theiveyanathan et al., 2004).

⁎

Soil salinity response and tolerance of plants vary widely. Crop salt tolerance is based on the crop’s ability to maintain the effects of excess salt in the root zone. Threshold, the maximum salinity level at which crop yield or growth is not decreased, and slope values, percent reduction in relative yield or growth for per soil salinity increase, of many crops including fiber, grain, grasses, forage, vegetables, fruits, woody, ornamental shrubs, trees, ground cover etc., were determined under experimental conditions. Although experimental data on crop salt tolerance exists for more than 130 crop species, there are many crops which lack definitive data (Shannon and Grieve, 1998). It is claimed that secondary metabolites in the medicinal and aromatic plants are strongly influenced by environmental factors (Eman et al., 2008; Heydari et al., 2008). As a perennial medicinal and aromatic plants, oregano is one of the common species of origanum and a genus of the mint (Lamiaceae). It is native to the Mediterranean region. Among the species, Origanum onites is one of the most exported species in Turkey (Can Baser, 2008; Yaldiz et al., 2005) and has been used for gastrointestinal complaints and also in medicine as analgesic, antiparasitic, antihelminthic antitussive, expectorant, sedative and

Corresponding author. E-mail address: [email protected] (A. Kurunc).

https://doi.org/10.1016/j.scienta.2018.12.044 Received 1 November 2018; Received in revised form 12 December 2018; Accepted 21 December 2018 0304-4238/ © 2018 Elsevier B.V. All rights reserved.

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stimulant (Dundar et al., 2008). Alpha-terpinene, gamma-terpinene, borneol, carvacrol, linalool, p-cymene and thymol are the main components for essential oil of Origanum onites (Demirci et al., 2004; Yaldiz et al., 2005). Its cultivation has been increased in recent years especially in Mediterranean and Aegean regions. Cultivated areas of oregano are 4700 ha in 2005, 8535 ha in 2010 and 12147 ha in 2017 with the average yields of 1.36, 1.31 and 1.19 tons per hectare, respectively, in Turkey (TUIK, 2017). There is no literature existing on the tolerance of this plant to water and salinity stresses. The purpose of the present research was to generate realistic data on oregano grown under irrigation water salinity levels up to 10.0 dS/m in an attempt to determine salinity effect on oregano growth and yield parameters, irrigation water use efficiency and crop quality parameters including essential and total oil, total phenolic and flavonoid contents, extract yield and antioxidant activity and essential oil components such as carvacrol, linalool, βcymene and γ-terpinene.

Table 2 Some physical and chemical properties of the experimental soil. Physical Properties

Chemical Properties

Particle size distribution

Electrical cond. (paste) (dS/ m) pHe (paste) Organic matter (%) N (%) P (ppm)

7.8 2.0 0.1 60

K (ppm) Ca (ppm) Mg (ppm) Na (ppm)

79 4818 312 68

Sand (%) Silt (%) Clay (%) Soil water contents (dry weight basis) Saturation (%) Field capacity (%) Wilting point (%) Bulk density (g/cm3)

The experiment was realized in lysimeters at Akdeniz University Experimental Research Area of Agricultural Faculty. The geographic coordinate of the experimental area is 36° 53' 15" N latitude and 30° 38' 53" E longitude. In order to protect plants from rainfall, the lysimeters were located in the experimental area under a polyethylene cover which was 3.5 m height from the surface. Local cultivar of Origanum onites L. was used as a plant material. It is, generally, known as İzmir Oregano, Turkish Oregano or White Oregano. This cultivar can grow up to 65 cm in height and develop many widely spread branches with opposite leaves 1–4 cm long (Davis, 1982). Essential oil of this plant contains phenolic compounds including carvacrol and thymol whereas the other chemical compounds contributing to the flavor are caryophyllene, limonene, ocimene and pinene. It can grow in all soils, but the best in clay soils (Baydar, 2002). The experiment was arranged as a randomized complete block design with five replications per treatments and three plants per replication. There were eight irrigation waters with different electrical conductivities (ECw) including S1 = 0.54 (tap water as a control), S2 = 1.2, S3 = 1.8, S4 = 2.5, S5 = 3.5, S6 = 5.0, S7 = 7.0 and S8 = 10.0 dS/m. Sodium adsorption ratio (SAR) of each irrigation water treatment was kept less than 5.2 in order to eliminate the adverse effect of SAR on gas movement, soil structure and water (Ünlükara et al., 2010, 2008). Saline irrigation waters were prepared by mixing calculated amounts of CaCl2, NaCl and MgSO4 to obtain targeted salinity level for each treatment. The chemical characteristics of the irrigation water for each treatment were given in Table 1. The soil used in the experiment was sieved with a 4 mm screen in order to remove large particles. An air-dried soil of 38 kg was placed in lysimeter pots having 36 dm3 in volume. Properties of the experimental soil used in the experiment were presented in Table 2. At the beginning of the experiment, soil in each lysimeter was saturated with water and

I=

(Wfc − W ) ρw 1 − LF

IWUE =

pHw

Ca (me/L)

Mg (me/L)

Na (me/L)

SAR

S1 S2 S3 S4 S5 S6 S7 S8

0.54 1.2 1.8 2.5 3.5 5.0 7.0 10.0

7.60 7.85 7.77 7.58 7.45 7.26 7.21 7.05

4.4 5.8 7.5 11.8 16.8 29.2 41.2 62.1

1.4 3.0 5.9 7.5 10.9 15.4 29.5 50.7

0.9 6.1 9.3 13.1 17.7 23.3 30.2 38.7

0.5 2.9 3.6 4.2 4.8 4.9 5.1 5.2

(1)

where: LF is leaching fraction, which was set to a target of 0.25 as suggested by Ayers and Westcot (1985), Wfc and W are the weights of lysimeter at field capacity and just before water application, and ρw is bulk density of water (1 kg/l). A container underneath each lysimeter pot was used to collect the leachate. Amount of collected drainage water volume in the drain pan of each replication was measured after the drainage ceased in order to control targeted leaching fraction of 0.25 and adjust field capacity changes of lysimeters due to plant growth. Also, in situ EC and pH analyses of the leachate water (ECdw and pHdw) were measured with an EC-pH meter after each irrigation. Before the experiment started, oregano seeds obtained from West Mediterranean Agricultural Research Institute were sown into viols having 50% peat and 50% perlite under glasshouse conditions. Then raised uniform oregano seedlings with 3 leaves were selected and 3 seedlings were transferred to each lysimeter pot. In order to allow high survival ratio of seedlings, each lysimeter pot were irrigated with tap water two times after transplanting. Two weeks after transplanting each plant were pruned to a standard height with 8 cm from the soil surface to provide homogeneity on plant heights and stimulate development of side branches and then treatment applications were started. Throughout the experiment, 250 ml foliar application of nitrogen fertilizer was applied to each lysimeter every month. In addition, in order to fight diseases and pests, lambda-cyhalothrine and acetamiprid cyhalothrine formulated powder pesticides were used. Irrigation water use efficiency, amount of applied irrigation water to produce one-unit dry matter, was obtained by using the equation (2):

Table 1 Composition of the saline irrigation waters used in the experiment. ECw (dS/m)

33.6 19.4 8.9 1.4

then covered to prevent evaporation. After the drainage stopped, the weights of the lysimeters were assumed as field capacity. Throughout the growing season, irrigation practices were performed at 3- to 14-day intervals and all treatments were irrigated when 45–55% of available water was consumed in the control treatment. The amount of applied irrigation water (I) was determined by weighting the lysimeter pots just before irrigation and calculated by the following equation:

2. Materials and methods

Treatment

40.1 37.5 22.4

0.2

DM Is

(2)

where: DM is total dry matter production (g) and Is is seasonal irrigation water applied (mm/season). Plant heights were measured every two weeks and certain physical and physiological changes were recorded. According to literature (Baydar, 2002), the best harvest time for oregano is the 50% flowering time. At the harvest, the plants were cut and then fresh and dry weights (air dried for 8–10 days) of stem and leaves from each replication were obtained. Dried oregano leaf samples were used to determine moisture content (TSE, 2008), essential oil (TSE, 2011), total phenolic content (Škerget et al., 2005), total flavonoid content (Chang et al., 2006), extract yield (TSE, 1997), antioxidant activity (Maisuthisakul et al., 2007), carvacrol linalool, β-cymene and γ-terpinene contents (Kizil

ECw: electrical conductivity of irrigation water. pHw: pH value of irrigation water. SAR: Sodium Adsorption Ratio. 328

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and leaves were dried and dropped.

et al., 2008). Immediately after the harvest, soil samplings from lysimeters were realized. These samples were air-dried and sieved. Saturation extracts were obtained from saturated soil pastes, then electrical conductivities of the extracts (ECe) and pH values (pHe) were measured by using an EC and pH meter (Richards, 1954). The threshold soil salinity and slope values for yield and/or growth parameter were obtained by using salt tolerance model (Maas and Hoffman, 1977). The suggested model is:

Ya b =1− × (ECe − ECe threshold ) Ym 100

3.1. Soil and drainage water In the experiment, even though a 25% leaching fraction was targeted, realized leaching fractions ranged from 23% (for S7) to 24% (for other treatments). However, no significant difference was obtained among leaching fractions of the irrigation water salinity treatments indicating a constant leaching fraction with variable water consumption was maintained as aimed (Table 3). Significant differences among treatments were observed for soil K, Mg and Na contents, saturation extract ECe and pHe values and also drainage water ECdw and pHdw values at a 0.01 probability level, whereas changes in soil Ca content was significant at 0.05 probability level (Table 3). In general, all of these parameters increased with increasing salinities of applied water. The K content of 79.0 ppm (Table 2) at the beginning of the experiment decreased down to 35.2 ppm at the end of the experiment. The highest K content was obtained from S7 (47.8 ppm) and S8 (47.2 ppm) in which plants died, which differed statistically from other treatments. Since the Na, Ca and Mg salts were used in order to obtain different concentrations of irrigation water salinity treatments, higher concentrations of these elements were expected in higher irrigation water treatments at the end of the experiment. The highest values were obtained from S7 (4280 ppm) and S8 (4706 ppm) treatments for Ca, and from S8 treatment for Mg (673 ppm) and Na (1010 ppm) (Table 3). Duncan’s test results showed that soil ECe value of control (S1) treatment was not significantly different from those of S2, S3 and S4. The highest soil ECe value (25.64 dS/m) was existed in S8 treatment. The change in average ECdw values throughout the growing season is presented for all treatments in Fig. 1. Differences in average ECdw values among the treatments started to form at the beginning of the

(3)

where: Ym and Ya are the maximum and actual yields (g) from the control (non-saline) and the saline treatments, respectively, b is the slope value (%/dS/m), ECe threshold and ECe are threshold soil salinity and soil salinity beyond the threshold value (dS/m). SPSS statistical analysis software (IBM SPSS Inc., 2012) was used to analyze the obtained data. All statistical tests were performed at P < 0.01 significance level. Where appropriate, mean separations of the data were realized by Duncan test at a P < 0.05 level of significance. Considering correlation coefficient (R) values, the strengths of the linear relationships between investigated parameters were evaluated as strong (R ≥ 0.8), moderate (0.5 < R < 0.8) and weak (R ≤ 0.5) (Peck and Devore, 2012). 3. Results Statistical analysis results for the investigated parameters were given in Table 3. It is important to mention that the plants in all replications of S7 (7 dS/m) and S8 (10 dS/m) and two out of five replications of S6 (5 dS/m) treatments could not survive until the end of the experiment. For these replications, plant growth obviously stopped

Table 3 Effect of irrigation water salinity on the experimental soils, water use, growth, yield and quality parameters of Origanum onites. Analysis

Irrigation water salinity treatments in dS/m S1 (0.54)

Leaching fraction (%) Saturation extract (ECe, dS/m) Saturation extract (pHe) Drainage water (ECdw, dS/m) Drainage water (pHdw) Soil K (ppm) Soil Ca (ppm) Soil Mg (ppm) Soil Na (ppm) Applied water (mm/season) Plant height (cm) Total fresh yield (g/plant) Total dry yield (g/plant) Dry leaf yield (g/plant) Irrigation water use efficiency (g/mm) Leaf moisture content (g/100 g dw) Essential oil content (g/100 g dw) Total essential oil yield (g/plant) Total phenolic content (mg GAE/g dw) Total flavonoid content (mg CE/g dw) Extract yield (g/100 g dw) Antioxidant activity (mg dw/mgDPPH) Carvacrol (mg/100 mg essential oil) Linalool (mg/100 mg essential oil) β-cymene (mg/100 mg essential oil) γ-terpinene (mg/100 mg essential oil)

0.24 0.63 8.38 0.93 8.21 35.2 3911 266 67 1131.0 57.0 135.1 58.2 28.6 0.16 8.50 1.70 0.49 2.22 1.65 15.4 5.32 54.0 18.4 6.7 7.6

S2 (1.2) #

dŧ a e a b bc e e a a a a a a a a a cd b c a ab b ab bc

0.24 1.41 8.24 2.86 8.03 39.6 3887 303 213 1065.0 56.4 122.3 49.0 26.3 0.14 8.60 1.75 0.46 2.10 1.50 16.5 5.27 48.3 29.9 4.9 4.8

P>F

S3 (1.8)

d b de b b bc e de ab a ab ab a ab a a ab d b c a ab b b c

0.24 2.25 8.06 4.41 7.99 35.8 3937 312 267 1012.6 59.4 111.9 42.6 20.9 0.12 8.10 1.82 0.38 2.79 1.85 18.2 4.12 49.1 29.6 4.5 6.2

S4 (2.5)

cd c cd c b bc de cd ab a ab bc b b a a ab bc b c ab ab b b bc

0.24 4.28 7.97 6.05 7.90 38.8 3836 366 325 964.8 57.6 107.9 39.2 17.7 0.12 8.30 1.74 0.31 3.25 2.47 22.9 3.50 36.1 41.3 5.4 4.3

S5 (3.5)

cd c bc d b bc de cd ab a b bc bc b a a bc ab a b bc b a b c

0.24 5.90 7.78 8.31 7.83 38.2 3768 412 377 890.6 53.0 98.4 32.8 14.5 0.11 8.10 1.58 0.23 3.79 2.57 28.4 2.53 65.8 4.3 7.8 8.8

S6 (5.0)

c d ab e b c cd cd b ab b c c b a a c a a a c a c ab b

0.24 11.69 7.60 8.52 7.80 39.7 3762 496 452 528.8 47.0 58.4 15.2 6.7 0.06 4.75 1.84 0.12 3.15 1.65 28.2 2.38 64.0 0.8 9.6 13.4

S7 (7.0)

b e ab ef b c bc c c b c d d c b a d b b a c a c a a

0.23 15.19 7.55 10.09 7.77 47.8 4280 577 788 395.2 0.0 0.0 0.0 0.0 0.00 0.00 0.00 0.00 0.00 0.00 0.0 0.00 0.0 0.0 0.0 0.0

£

S8 (10.0)

b e a f a ab b b cd c d d e d c b e e c d d c d c d

0.24 25.64 7.55 10.87 7.73 47.2 4706 673 1010 224.4 0.0 0.0 0.0 0.0 0.00 0.00 0.00 0.00 0.00 0.00 0.0 0.00 0.0 0.0 0.0 0.0

£

a e a g a ab a a d c d d e d c b e e c d d c d c d

ns ** ** ** ** ** * ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** **

: Each value is the mean of five replications. : Within rows, means followed by the same letter are not significantly different according to Duncan’s multiple range test at 0.05 significance level. £ : There is no yield and quality parameters for S7 and S8 treatments since plants for all replications of these treatments could not survive until end of the study. **,*: Significant at the 0.01 and 0.05 probability levels, respectively. ns: Non-significant. # ŧ

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Fig. 1. Changes on drainage water EC values throughout the growing period of oregano.

Fig. 2. Changes on plant heights (cm) throughout the growing period of oregano.

experiment. Throughout the growing season, ECdw values of the S1 treatment followed relatively a stable trend whereas an increasing trend, in general, for other treatments was observed between January and April (Fig. 1). The lowest seasonal average ECdw was obtained for S1 treatment (0.93 dS/m) which was not significantly different from that of S2 (2.86 dS/m), whereas the highest values of 10.87, 10.09, 8.52 and 8.31 dS/m were obtained from S8, S7, S6 and S5 treatments, respectively (Table 3). Unlike ECe values, increasing salinity levels caused decreases in both pHe and seasonal averaged pHdw values. The highest pHe and pHdw values were obtained from S1 (8.38 and 8.21) whereas the lowest values from S7 (7.55 and 7.77) and S8 treatments (7.55 and 7.73) (Table 3).

respectively. Similarly, the highest total dry (58.2 g/plant) and dry leaf yields (28.6 g/plant) were obtained from the control, which were not significantly different from S2 treatment (Table 3). Compared to control treatment, 27, 33, 44 and 74% reductions in total dry yields, and 27, 38, 49 and 77% decreases in dry leaf yields were calculated for S3, S4, S5 and S6 treatments, respectively.

3.4. Quality parameters The air dry based leaf moisture contents for the first 5 treatments ranged from 8.10 to 8.60 g/100 g dw (dry weight) which are not significantly different from each other but this value significantly decreased to 4.75 g/100 g dw in S6 treatment (Table 3). Except S7 and S8 treatments (no plant survived), essential oil contents were ranged from 1.58 (for S5 treatment) to 1.84 g/100 g dw (for S6 treatment), however there was no significant differences among these treatments (Table 3). The highest total essential oil yield, calculated by multiplying dry leaf yield and essential oil content, was obtained from S1 (0.49 g/plant) which was not significantly different from S2 (0.46 g/plant) and S3 treatments (0.38 g/plant) while the lowest value was calculated for S6 treatment (0.12 g/plant) which was significantly different from other treatments (Table 3). Compared to control treatment 38, 51 and 78% reductions in total oil contents were calculated for S4, S5 and S6 treatments, respectively. In general, slight increases in irrigation water salinity up to 3.5 dS/ m caused increases in both total phenolic and flavonoid contents. The lowest total phenolic content values were obtained from S1 and S2 treatments (2.22 and 2.10 mg GAE/g dw, respectively) whereas the highest values from S4 and S5 treatments (3.25 and 3.79 mg GAE/g dw, respectively). Similarly, total flavonoid contents from S4 and S5 treatments (2.47 and 2.57 mg CE/g dw, respectively) were significantly different from the other treatments (Table 3). Compared to control treatment an increase of 46 and 71% in total phenolic, and 50 and 56% in total flavonoid contents was calculated for S4 and S5 treatments, respectively. Accordingly increased salinity in irrigation water (except S7 and S8 treatments due to death of all plants) caused an increase in extract yields of oregano. The highest extract yields were observed from S5 (28.4 g/100 g dw) and S6 (28.2 g/100 g dw) treatments whereas the lowest from S1 (15.4 g/100 g dw), S2 (16.5 g/100 g dw) and S3 (18.2 g/ 100 g dw) treatments (Table 3). The antioxidant activity of the Origanum onites samples was determined as IC 50 (inhibiton concentration for 50%). The higher antioxidant activity, thereby lower IC50 value, were determined in S6, S5, S4 treatments, respectively (Table 3). This was expected since the total phenolic and flavanoid contents of these treatments were, in general, higher than other treatments. In general, carvacrol, linalool, β-cymene and γ-terpinene as essential oil components constitute more than 80% of the essential oil for the Origanum onites. Even though the essential oil content did not

3.2. Irrigation water use efficiency Statistical analysis results show that under a 25% leaching fraction I and IWUE values of oregano plant were affected from irrigation water salinity at 0.01 significance. Both I and IWUE decreased with increasing irrigation water salinity. The highest I (1131 mm/season) value was obtained from the control treatment but Duncan’s test results indicated that this value did not differ from 1065 (S2), 1013 (S3) and 965 (S4) mm/season. These results are consistent with the obtained soil salinities (Table 3). Compared to the control treatment, I value decreased by 21, 53, 65 and 80% for S5, S6, S7 and S8 treatments, respectively. Irrigation water use efficiency values for S7 and S8 treatments could not be calculated since there is no yield obtained from these treatments due to the death of all plants. Therefore, the lowest IWUE value (0.06 g/ mm) was calculated for S6 treatment whereas the highest values (0.16 and 0.14 g/mm) for the control and S2 treatments (Table 3). Compared to the control treatment, IWUE values decreased by 19, 24, 30 and 61% for S3, S4, S5 and S6 treatments, respectively. 3.3. Growth and yield parameters Throughout the growing season, changes on oregano plant heights under different irrigation water salinity levels were presented in Fig. 2. Relatively no increases on plant height were observed during the winter period, but it started to increase after January. In general, there were agreements between ECe’s and plant heights and also between I’s. There are no big differences among the plant heights of S1, S2, S3 and S4 treatments throughout all season. Since all replications died before terminating the experiment, the last 8 and 2 plant height measurements could not be realized for S8 and S7 treatments, respectively (Fig. 2). Considering the last measurements, the highest average plant height (59.4 cm) was measured for S3 but it was not significantly different from those of S1 (57.0 cm), S2 (56.4 cm), S4 (57.6 cm) and S5 (53.0 cm) (Table 3). The highest total fresh yield (135.1 g/plant) was observed from the control, which was not significantly different from S2 and S3 treatments (Table 3). Compared to control treatment, 20, 27 and 57% reductions in total fresh yields were calculated for S4, S5 and S6 treatments, 330

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Fig. 3. Salt tolerance models for fresh and dry yields, dry leaf yield and total oil content of oregano.

significantly differ among treatments (except S7 and S8), these essential oil components showed significant differences. Among those, carvacrol, β-cymene and γ-terpinene contents decreased with increasing water salinities up to 2.5 dS/m and after this salinity level sharply increased but linalool content showed a reversed pattern (Table 3). Compared to the lowest carvacrol and γ-terpinene contents (for S4 treatment), 82 and 77% increases in carvacrol and 104 and 211% increases in γ-terpinene content obtained for S5 and S6 treatments, respectively. However, 90 and 98% decreases in linalool contents were calculated for S5 and S6 treatments compared to S4 treatment.

investigated parameters. Other than these to parameters (ECe and ECdw), all of the parameters showed significantly important (except pHdw versus extract yield and γ-terpinene content, linaool versus total phenolic content, extract yield and antioxidant activity, β-cymene and γ-terpinene contents) strong-, moderate- or weak- positive linear correlations with each other. In general, the correlations were significant at 0.01 probability level for most parameters (applied water, all of the growth and yield parameters in addition to IWUE, leaf moisture content, essential oil content, total essential oil yield, antioxidant activity and carvacrol content versus all investigated parameters).

3.5. Salt tolerance model and salinity related yield response factor

4. Discussion

The threshold salinity and slope after threshold values for total fresh, total dry and dry leaf yields in addition to total essential oil yield of oregano were attempted to determine by generating salt tolerance models of these parameters. As it can be seen in Fig. 3, total fresh yield of oregano has a threshold value of 0.50 dS/m and a slope value of 6.09. However, it is important to note that it was not possible to find a threshold salinity value for total dry, dry leaf and total essential oil yields of oregano, since the slope lines of these parameters cuts the Y axis below 100% (about 95% for relative total dry yield and relative dry leaf yield, and 98% for relative total essential oil yield), but the slope (decline yield in unit salinity increase) values could be determined. The slope values for total dry, dry leaf and total essential oil yields were 6.17, 6.39 and 6.64, respectively. These linear models revealed that there was a reduction in relative total fresh and dry leaf yields and total essential oil yields even for the control (ECe = 0.63 dS/m) treatment.

Considering the SAR value of the irrigation water source, CaCl2, MgSO4 and NaCl salts were used in the preparation of saline water treatments and thus, the SAR value of all treatments were kept close to each other as much as possible. Therefore, by preventing the dominant effect of a particular ion, the effect of SAR on the results was eliminated and only the effects of total salinity were investigated. It was expected that significant differences in mineral composition of soils would be occured due to differences among applied irrigation water salinities. Although K was not used as fertilizer or in the preparation of saline water treatment, it was thought that the statistical difference in the K content of the soil at the end of the experiment might be caused by the plant use of significant amounts of K and/or by removal of the K via drainage water from the root zone (Wulff et al., 1998). The fact that the soil Na content of the control treatment was close to each other at the beginning and end of the experiment (67.5 ppm) indicates that the plant probably did not make Na intake. The ratios of ECe/ECw were 1.17, 1.18, 1.25, 1.71, 1.69, 2.34, 2.17 and 2.56 for treatments from S1 to S8, respectively. Ayers and Westcot (1985) declared that, assuming ECe = 0.5 × ECsw, (EC of soil water), expected ECe/ECw ratio is 1.2 under a leaching fraction of 0.25. Therefore, it can be concluded that ECe/ECw ratios for treatments having irrigation water salinities greater than 1.8 dS/m were higher than expected. Higher soil salinities may be due to edge (bypass) flow

3.6. Relationship between parameters Statistical evaluation results (R and P values) of the linear relationships between investigated parameters are presented in Table 4. As expected, there were significantly important (except ECdw versus extract yield, β-cymene and γ-terpinene contents) and negative (except ECe versus ECdw) correlations between ECe or ECdw versus other 331

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Table 4 Relationship between investigated parameters.

pHe ECdw pHdw I PH TFY TDY DLY IWUE LMC EOC TEOY TPC TFC EY AA CAR Lin Cym Ter

ECe

pHe

ECdw

pHdw

I

PH

TFY

TDY

DLY

IWUE

LMC

EOC

TEOY

TPC

TFC

EY

AA

CAR

Lin

Cym

−0.82 ** 0.72 ** −0.77 ** −0.89 ** −0.87 ** −0.88 ** −0.85 ** −0.84 ** −0.87 ** −0.86 ** −0.82 ** −0.82 ** −0.69 ** −0.70 ** −0.65 ** −0.81 ** −0.67 ** −0.40 * −0.52 ** −0.52 **

−0.83 ** 0.93 ** 0.85 ** 0.76 ** 0.87 ** 0.91 ** 0.93 ** 0.88 ** 0.76 ** 0.70 ** 0.91 ** 0.41 * 0.46 ** 0.35 * 0.88 ** 0.54 ** 0.37 * 0.40 * 0.36 *

−0.85 ** −0.61 ** −0.67 ** −0.76 ** −0.82 ** −0.84 ** −0.78 ** −0.70 ** −0.60 ** −0.82 ** −0.32 * −0.39 * −0.25 ns −0.82 ** −0.41 * −0.40 * −0.28 ns −0.21 ns

0.79 ** 0.66 ** 0.78 ** 0.85 ** 0.87 ** 0.80 ** 0.68 ** 0.60 ** 0.85 ** 0.33 * 0.38 * 0.26 ns 0.81 ** 0.46 ** 0.34 * 0.33 * 0.31 ns

0.91 ** 0.96 ** 0.94 ** 0.92 ** 0.95 ** 0.91 ** 0.86 ** 0.90 ** 0.73 ** 0.77 ** 0.67 ** 0.86 ** 0.72 ** 0.40 * 0.55 ** 0.55 **

0.91 ** 0.85 ** 0.83 ** 0.90 ** 0.93 ** 0.93 ** 0.81 ** 0.84 ** 0.84 ** 0.83 ** 0.83 ** 0.75 ** 0.46 ** 0.62 ** 0.61 **

0.98 ** 0.96 ** 1.00 ** 0.92 ** 0.85 ** 0.94 ** 0.72 ** 0.75 ** 0.66 ** 0.85 ** 0.70 ** 0.42 ** 0.52 ** 0.51 **

0.98 ** 0.99 ** 0.87 ** 0.78 ** 0.96 ** 0.61 ** 0.66 ** 0.53 ** 0.86 ** 0.63 ** 0.42 ** 0.44 ** 0.43 **

0.96 ** 0.85 ** 0.75 ** 0.96 ** 0.55 ** 0.59 ** 0.47 ** 0.88 ** 0.60 ** 0.43 ** 0.39 ** 0.38 **

0.91 ** 0.84 ** 0.95 ** 0.70 ** 0.73 ** 0.63 ** 0.86 ** 0.69 ** 0.42 ** 0.51 ** 0.49 **

0.88 ** 0.82 ** 0.80 ** 0.83 ** 0.76 ** 0.83 ** 0.67 ** 0.51 ** 0.51 ** 0.51 **

0.80 ** 0.86 ** 0.83 ** 0.86 ** 0.77 ** 0.79 ** 0.38 * 0.64 ** 0.69 **

0.57 ** 0.61 ** 0.49 ** 0.83 ** 0.63 ** 0.38 * 0.40 * 0.42 **

0.98 ** 0.97 ** 0.48 ** 0.75 ** 0.31 ns 0.63 ** 0.69 **

0.92 ** 0.47 ** 0.66 ** 0.41 * 0.54 ** 0.56 **

0.47 ** 0.78 ** 0.25 ns 0.69 ** 0.73 **

0.68 ** 0.31 ns 0.55 ** 0.48 **

−0.20 ** 0.87 ** 0.89 **

−0.29 ns −0.25 ns

0.91 **

ECe: soil salinity,pHe: soil pH,ECdw: drainage water salinity,pHdw: drainage water pH,I: applied water,PH: plant height,TFY: total fresh yield,TDY: total dry yield,DLY : dry leaf yield, IWUE: irrigation water use efficiency,LMC : leaf moisture content,EOC : essential oil content, TEOY: total essential oil yield,TPC : total phenolic content, TFC: total flavonoid content,EY : extract yield, AA: antioxidant activity,CAR : carvacrol content, Lin : linalool content, Cym: β-cymene content,Ter : γ-terpinene content, **: significant at 0.01 probability level,* : significant at 0.05 probability level, ns : non-significant.

salinity which is defined as the difference between amount of total salinity and precipitable salts should be used instead of the total salinity of irrigation water. The reason for decreases on IWUE’s was due to higher reductions on yield than the amount of applied irrigation water at high salinities (Table 3). Beltrão and Asher (1997) showed that at high salinity conditions, the water content at wilting point is higher than at low salinity conditions, resulting in an insufficient amount of available water, and therefore, a reduced yield. Also Rhoades et al. (1992) stressed that excess salinity within the plant root zone has a deleterious effect on plant growth rates and therefore decreases plant water consumption. At the end of the experiment, plant height, total fresh and dry yields and dry leaf yield of oregano were affected from salinity levels. Increased salinity of the applied water resulted in decreases in these parameters. Salinity-induced reductions in growth parameters are usually due to only an osmotic effect for tolerant plants, but sensitive ones are more likely to show additional ion toxicity (Bajji et al., 2002). Rhoades et al. (1992) concluded that plant growth is reduced due to excessive salinity, because, instead of plant growth and yield, it diverts energy to make the biochemical adjustments necessary to survive under stress. In a study related to the effect of salinity stress on daisy (matricaria chamomila) plant, Dadkhah (2010) concluded that plant heights are significantly decreased due to the increased salinity. De Herralde

through soil-lysimeter interface caused decreases in leaching effectiveness. However, all of the lysimeters used in the experiment were the same, then constant ECe/ECw values should have been resulted for constant leaching fraction (Ünlükara et al., 2010). Another reason for high soil salinities than expected may also be due to salt precipitation in soils especially for high ECw treatments (Doneen, 1954). Considering calculated ECdw/ECe ratios of the treatments, it can be seen that effectiveness of leaching was decreased from 2.04 (for S2 treatment) to 0.42 (for S8 treatment). According to these results, it can be concluded that salt precipitations occurred in soils received irrigation water with ECw > 5 dS/m. In addition to these, using real LF values from Table 3, ECdw values were calculated (ECdw = ECw / LF) as 2.3, 5.0, 7.5, 10.5, 14.4, 20.4, 30.1 and 41.6 dS/m for treatments from S1 to S8, respectively. However, real ECdw values were 2.4, 1.8, 1.7, 1.7, 1.7, 2.4, 3.0 and 3.8 times less than those of the calculated ECdw values, respectively. The reason for these differences may be due to salt (especialy K, Ca and Mg) uptake of plant from soil, existing important changes on soil physical properties caused by high soil salinities such as infiltration rate which may influence leaching efficiency and/or more importantly precipitation of some salts such as CaCO3, Ca(HCO3)2, MgCO3, Mg(HCO3)2 and CaSO4 which are less soluble in the soil after application of saline irrigation water. Doneen (1954) proposed that, for the assessment of soil salinity caused by irrigation water, effective 332

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5. Conclusions

et al. (1998) claimed that salt stress encourage reductions in leaf biomass due to death of leaves. It is reported that dry matter reduction under salt stress is due to the reduction in mineral nutrients uptake and utilization by plants (Razmjoo et al., 2008). Several researchers also noticed an increasing degree of reduction in dry matter production with increasing salinity levels (Bar-Tal et al., 1991). Salinity level of applied irrigation water significantly affected all quality parameters of oregano including essential and total oil, total phenolic and total flavonoid contents, extract yield, and antioxidant activity in addition to essential oil components such as carvacrol, linalool, β-cymene and γ-terpinene contents at 0.01 probability level (Table 3). In a study in which some medicinal plant (Lepidium sativum L., Linum usitatissimum L., Plantago ovata Forssk. and Trigonella foenumgraecum L.) seeds were exposed to various salinity levels, it was observed that there were large differences in moisture content of the species. While the moisture content was found to be close to the control treatment in all but the highest salinity in Lepidium, Plantago and Trigonella, there was a decrease in moisture content of Linum with increasing salinities except for low salinity treatments (Muhammad and Hussain, 2012). With the increasing salinity stress, it has been proven that some growth parameters and essential oil content in daisy (Matricaria chamomile) (Razmjoo et al., 2008) and in lemon balm (Ozturk et al., 2004) were decreased. However, Fatima et al. (1999) reported that secondary products such as essential oils can be stimulated in restricted environmental conditions. Decrease in the essential oil yield may occur due to restriction of photosynthesis and carbohydrate production under stress conditions (Flexas and Medrano, 2002). Compared to control treatment 49, 84 and 83% increases in extract yields were observed for S4, S5 and S6 treatments, respectively. Similar results has also been demonstrated in a study on short-term saline water application in Gemlik olive (Olea europaea) (Demiral et al., 2011). Holtzer et al. (1988) claimed that stress can increase, decrease or not affect the secondary metabolites of the plant, depending on plant species and plant genotype. Many researchers agree that the synthesis and accumulation of phenolic compounds in plants are usually stimulated by biotic and abiotic stresses (Dixon and Paiva, 1995; Naczk and Shahidi, 2004). However, it is also argued that the relationship between salinity and total phenolic content in the leaves is probably related to the tolerance of the plant to salinity. On the other hand, as Agastian et al. (2000) reported, in different mulberry varieties, high phenolic content was found at low salinity levels. Similar results on higher antioxidant activity with increasing water salinity was also reported for different plants such as Mentha pulegium (Oueslati et al., 2010), Salvia officinalis (Ben Taârit et al., 2012), Rosmarinus officinalis (Kiarostami et al., 2010) and Salvia mirzayanii (Valifard et al., 2014). On the other hand, Ksouri et al. (2007) determined that the effect of salinity on the antioxidant activity of Jarka and Tabarka cultivars of sea rocket (Cakile maritima Scop.) as a halophyte plant was very high. They concluded that considering the control treatments, antioxidant activity was similar in both cultivars. It was observed that the saline water application had a weak effect on the antioxidant activity of the Jerba cultivar whereas it decreased significantly in the Tabarka cultivar (Ksouri et al., 2007). Baranauskaite et al. (2016) declared that carvacrol contents from oregano herbs depended on the oregano species (O. vulgare L., O. onites L. ir O. vulgare spp. hirtum) and also different types of extraction methods had a big influence on the extraction yield of essential oil compounds. Similarly, Ozdemir et al. (2018) claimed that essential oil yield, oil composition and antioxidant activity of O. vulgare and O. onites plants were strongly influenced by the drying methodology. The relative yield or oil content decreases for the parameters were between 6.09 and 6.64. Based on these results, oregano plant is very sensitive to salinity. This may be due to fact that oregano naturally grown under rain-fed conditions for many years has not developed a resistance against saline conditions.

In this study, effects of irrigation water salinity on growth (plant height), yield parameters (total fresh, total dry and dry leaf yields), irrigation water use efficiency, and quality parameters (leaf moisture content, essential oil content, total essential oil yield, total phenolic content, total flavonoid content, extract yield, antioxidant activity, carvacrol content, linalool content, β-cymene content and γ-terpinene content) of oregano were investigated. Irrigation water use efficiency of oregano decreased with increasing irrigation water salinity. In general, increasing salinity of the applied water caused significant decreases in total fresh, total dry and dry leaf yield in addition to total essential oil yield whereas increases in total phenolic content, total flavonoid content, extract yield and antioxidant activity values of oregano. Among the essential oil components, carvacrol, β-cymene and γ-terpinene contents decreased with increasing water salinities up to 2.5 dS/m and after this level sharply increased but linalool content showed a reversed pattern. Since a very low threshold value (0.50 dS/m) for total fresh yield data was obtained and/or threshold values for total dry yield, dry leaf yield and total oil content could not be identified, the plant is classified as very sensitive to salinity. Acknowledgement The authors acknowledge support of the funding by the Scientific Research Projects Coordination Unit of Akdeniz University. References Agastian, P., Kingsley, S.J., Vivekanandan, M., 2000. Effect of salinity on photosynthesis and biochemical characteristics in mulberry genotypes. Photosynthetica 38, 287–290. https://doi.org/10.1023/A:1007266932623. Ayers, R.S., Westcot, D.W., 1985. Water Quality for Agriculture - FAO Irrigation and Drainage Paper 29. FAO - Food and Agriculture Organization of the United Nations, Rome. https://doi.org/ISBN92-5-102263-1. Bajji, M., Kinet, J.-M., Lutts, S., 2002. Osmotic and ionic effects of NaCl on germination, early seedling growth, and ion content of Atriplex halimus (Chenopodiaceae). Can. J. Bot. 80, 297–304. https://doi.org/10.1139/B02-008. Baranauskaite, J., Jakštas, V., Ivanauskas, L., Kopustinskiene, D.M., Drakšiene, G., Masteikova, R., Bernatoniene, J., 2016. Optimization of carvacrol, rosmarinic, oleanolic and ursolic acid extraction from oregano herbs (Origanum onites L., Origanum vulgare spp. Hirtum and Origanum vulgare L.). Nat. Prod. Res. 30, 672–674. https:// doi.org/10.1080/14786419.2015.1038998. Bar-Tal, A., Feigenbaum, S., Sparks, D.L., 1991. Potassium-salinity interactions in irrigated corn. Irrig. Sci. 12, 27–35. https://doi.org/10.1007/BF00190706. Baydar, H., 2002. Isparta koşullarında İzmir kekiğinin (Origanum onites L.) verimi ve uçuçu yağ kalitesi üzerine araştırmalar (Researches on the yield and essential oil quality of oregano (Origanum onites L.) under the condition of Isparta province). Süleyman Demirel Üniversitesi Fen Bilim. Enstitüsü Derg. J. Basic Appl. Sci. Suleyman Demirel Univ. 6, 15–21. Beltrão, J., Asher, J.B., 1997. The effect of salinity on corn yield using the CERES-maize model. Irrig. Drain. Syst. Eng. 11, 15–28. Ben Taârit, M., Msaada, K., Hosni, K., Marzouk, B., 2012. Physiological changes, phenolic content and antioxidant activity of Salvia officinalis L. Grown under saline conditions. J. Sci. Food Agric. 92, 1614–1619. https://doi.org/10.1002/jsfa.4746. Can Baser, K., 2008. Biological and pharmacological activities of carvacrol and carvacrol bearing essential oils. Curr. Pharm. Des. 14, 3106–3119. https://doi.org/10.2174/ 138161208786404227. Chang, Q., Zuo, Z., Chow, M.S.S., Ho, W.K.K., 2006. Effect of storage temperature on phenolics stability in hawthorn (Crataegus pinnatifida var. major) fruits and a hawthorn drink. Food Chem. 98, 426–430. https://doi.org/10.1016/j.foodchem.2005.06. 015. Dadkhah, A., 2010. Effect of salt stress on growth and essential oil of Matricaria chamomila. Res. J. Biol. Sci. 5, 643–646. Davis, P.H., 1982. Flora of Turkey and the East Aegean Islands Vol.7 Edinburgh University Press, Edinburgh. De Herralde, F., Biel, C., Savé, R., Morales, M.A., Torrecillas, A., Alarcón, J.J., SánchezBlanco, M.J., 1998. Effect of water and salt stresses on the growth, gas exchange and water relations in Argyranthemum coronopifolium plants. Plant Sci. 139, 9–17. https:// doi.org/10.1016/S0168-9452(98)00174-5. Demiral, M.A., Uygun, D.A., Uygun, M., Kasırğa, E., 2011. Biochemical response of Olea europaea cv. Gemlik to short-term salt stress. Turk. J. Biol. 35, 433–442. Demirci, F., Paper, D.H., Franz, G., Baser, K.H.C., 2004. Investigation of the Origanum onites L. Essential oil using the chorioallantoic membrane (CAM) assay. J. Agric. Food Chem. 52, 251–254. https://doi.org/10.1021/jf034850k. Dixon, R.A., Paiva, N.L., 1995. Stress-induced phenylpropanoid metabolism. Plant Cell 7, 1085–1097. https://doi.org/10.2307/3870059.

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