Effect of Drought, Salinity, and Defoliation on Growth Characteristics of Some Medicinal Plants of Iran

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Effect of Drought, Salinity,and Defoliation on GrowthCharacteristics of SomeMedicinal Plants of IranAlireza Koocheki a , Mehdi Nassiri-Mahallati a &Golsoomeh Azizi aa Faculty of Agriculture , Ferdowsi University ofMashhad , P.O. Box 91775-1163, Mashhad, IranPublished online: 12 Dec 2008.

To cite this article: Alireza Koocheki , Mehdi Nassiri-Mahallati & Golsoomeh Azizi(2008) Effect of Drought, Salinity, and Defoliation on Growth Characteristics of SomeMedicinal Plants of Iran, Journal of Herbs, Spices & Medicinal Plants, 14:1-2, 37-53,DOI: 10.1080/10496470802341201

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Journal of Herbs, Spices & Medicinal Plants, Vol. 14(1–2) 2008Available online at http://www.haworthpress.com© 2008 by The Haworth Press. All rights reserved.

doi:10.1080/10496470802341201 37

WHSM1049-64751540-3580Journal of Herbs, Spices & Medicinal Plants, Vol. 14, No. 1, August 2008: pp. 1–32Journal of Herbs, Spices & Medicinal Plants

Effect of Drought, Salinity, and Defoliation on Growth Characteristics of Some

Medicinal Plants of IranKoocheki, Nassiri-Mahallati, and AziziJournal of Herbs, Spices & Medicinal Plants Alireza Koocheki

Mehdi Nassiri-MahallatiGolsoomeh Azizi

ABSTRACT. The effects of water stress, salinity, and defoliation ongrowth of four medicinal plants—Shiraz thyme (Zataria multiflora),kakooti (Ziziphora clinopodioides), garden thyme (Thymus vulgaris), andcat thyme (Teucrium polium)—were evaluated in greenhouse experiments.Water stress and defoliation were studied using a completely randomizedfactorial design with three replications and four levels of water potential(−0.03, −0.5, −1.0, and −1.5 megapascals) and three levels of defoliation(0%, 25%, 50%). Salinity and defoliation were studied in a split plot with acompletely randomized block design and three replications using three lev-els of salinity (0, 5, 10 ds.m−1) in the main plots and a combination of threelevels of defoliation (0%, 25%, 50%) for four plant species allocated insubplots. Measurements on relative chlorophyll content (SPAD readings),stomatal resistance, temperature within the plant community, leaf-to-stem

Alireza Koocheki, Professor, Faculty of Agriculture, Ferdowsi University ofMashhad, P.O. Box 91775-1163, Mashhad, Iran. (E-mail: [email protected]).

Mehdi Nassiri-Mahallati, Associate Professor, Faculty of Agriculture, FerdowsiUniversity of Mashhad, Iran.

Golsoomeh Azizi, PhD Student, Faculty of Agriculture, Ferdowsi University ofMashhad, Iran.

Address correspondence to: Alireza Koocheki, Department of Agronomy,Faculty of Agriculture, Ferdowsi University of Mashhad, P.O. Box 91775-1163.(E-mail: [email protected]).

Received: January 8, 2007.

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38 JOURNAL OF HERBS, SPICES & MEDICINAL PLANTS

ratio, specific leaf weight, and root-to-top ratio indicated drought stressincreased chlorophyll content in kakooti, specific leaf weight in Shirazthyme, and kakooti and temperature in Shiraz thyme and cat thyme as com-pared with controls. Defoliation, however, reduced chlorophyll in Shirazthyme, kakooti, and cat thyme, specific leaf weight in Shiraz thyme, kakootiand garden thyme, and leaf-to-stem ratio in Shiraz thyme as compared withcontrols. Increased salinity levels reduced chlorophyll content andincreased stomatal resistance in all species. A significant negative correla-tion was noted between salinity and leaf-to-stem ratio and between droughtstress and leaf-to-stem ratio for all species. With increased defoliationintensity, the root-to-top ratio for Shiraz thyme and garden thyme decreasedbut was increased in kakooti and cat thyme. A significant positive correlationwas observed between the root-to-top ratio and drought levels. Kakooti wasthe most drought-resistant, and garden thyme had lowest resistance todrought and defoliation stresses but was the most resistant to salinity.

KEYWORDS. Cat thyme, garden thyme, herb, kakooti, Shiraz thyme,Thymus vulgaris, Teucrium polium, water stress, Zataria multiflora,Ziziphora clinopodioides

INTRODUCTION

Water deficit is an important factor affecting plant growth and develop-ment and hence global plant distribution (11). Water stress has been found toreduce growth of root and above-ground parts of plants (9,12,21,30) andnegatively affect leaf area, height, and dry matter (11); to interfere with sto-matal behavior (11,29), photosynthesis (11,12,17), and transpiration (12,29);to destroy enzymes (11) and proteins; to change the synthesis of protein (12)and amino acids; and to reduce chlorophyll contents (11). Salinity has beenshown to cause early maturity and reduce growth, dry matter accumulation,and stomatal conductance (21,22), and interfere in protein synthesis (22).Soil salinity may also affect plant growth indirectly through inhibition ofbiological process, such as nitrogen mineralization and nitrification in soil(21). Membrane interference, metabolic poisoning, photosynthesis inhibi-tion, and reduced nutrient uptake are results of salinity (10).

Although a wide range of studies on the effect of environmentalstresses on growth and yield of field crops have been done, such studiesare scare for medicinal plants and, therefore, more research is needed (7).Hasani and Omid-beigi (11) found that a water deficit has a significant

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Koocheki, Nassiri-Mahallati, and Azizi 39

negative effect on growth, yield, chlorophyll content, and essential oil ofsweet basil (Ociumum basilicum), reducing available soil water and plantheight, leaf numbers and area, fresh and dry leaf, stem, and root weights,leaf area index, leaf area, chlorophyll a and b content, total chlorophyll,and essential oil yield, while the root-to-shoot ratio and the essential oilcontent per plant were increased. Lebaschi et al. (15) showed that waterdeficit reduced yield and quality of St. John’s Wort (Hypericum perfo-ratum). Misra and Sricastatva (16) have demonstrated that in mint(Mentha sp.), water stress significantly reduced leaf area, fresh and dryweight, chlorophyll, and essential oil yield. In a study on the effects ofsodium chloride and calcium chloride on growth and yield of cumin(Cuminum cyminum), Nabizadeh (19) observed that plant growth wasreduced under increasing salinity but that essential oil was not affected. Anegative effect of salinity on cumin has also been reported by Zahtab-Salmasiet al. (30). Salim et al. (26) noted that environmental stresses mayenhance foliar damage by insects, but a contradictive result has beenreported by Sadras et al., (24). Herbivores do, however, enhance thenegative effects of drought and salinity (28).

The present investigation evaluated the effects of environmentalstresses, including drought, salinity, and simulated herbivore defoliationon medicinal plants.

MATERIALS AND METHODS

Plant Material

Shiraz thyme (Zataria multiflora), kakooti (Ziziphora clinopodioides),garden thyme (Thymus vulgaris), and cat thyme (Teucrium polium) wereused in this study. For determining the effects of water deficit and defoli-ation on growth, plants were sown initially in polythene pots (19 cm indiameter × 25 cm deep) filled with 4 kg of soil. Moisture content of the soil,based on weight, was measured at −0.03, −0.5, −1.0, and −1.5 megapascalby pressure plate, and a moisture content curve was drawn for the soil.Moisture content of soil at −0.03 megapascal (on weight bases) was 13%and at −1.5 megapascal was 5.5%.

For salinity and defoliation experiments, the same plant materials wereused. Seeds were planted in polythene boxes 60 cm long × 40 cm wide ×30 cm deep and filled with fine sand. Salinity was imposed after plantestablishment, and defoliation was imposed at flowering.

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Experimental

The water deficit and defoliation experiment was done in a greenhouse.Treatments consisted of four water deficit levels (−0.03, −0.5, −1.0, and −1.5 megapascal) and defoliation of 0%, 25%, and 50%. The pots contain-ing the experimental plant material were weighed daily, and the necessaryquantity of water was added to maintain the desired moisture level. Waterstress was initiated after the plants were established. Defoliation was byhand on the vegetative tissues (stem and leaves) to remove 0% (control),25%, or 50% of the above-ground growth.

Leaf chlorophyll concentration in the upper leaves was estimatedbiweekly using a chlorophyll meter (SPAD 502, Konica Minolta Sensing,Inc., Tokyo); plant temperature inside the plant community was measuredby an infrared thermometer and stomatal conductance by a porometer onbiweekly bases. Other variables, such as specific leaf weight, leaf-to-stemratio, and root-to-top ratio, were determined at the final stage of plantgrowth after harvesting. The experiment was a factorial in a complete ran-domized block design with three replications

The salinity and defoliation experiment was done in the greenhouseusing salinity levels of 0 ds.m−1, 5 ds.m−1, and 10 ds.m−1. Defoliation treat-ments and procedures were the same as those used with the water deficitstudy. Janson nutrient solution and salinity were pumped into the system.Chlorophyll concentration in the upper leaves and stomatal conductancewere measured as described. The experiment was a complete randomizedblock design with a split plot arrangement and three replications

Statistical analysis was done using Mstatc, Minitab, and Excel.

RESULT AND DISCUSSION

Water stress showed a significant positive effect on chlorophyll con-centration only in the Kakooti (Table 1). Other reports have also indicateda positive effect of water stress on chlorophyll concentration reading inplant tissues (11,25). Contrasting results have also been reported (1,13).Antolin et al. (2) noted that with increasing water stress, leaf chlorophylldecreased. Peng et al. (20) and Monje and Bugbee (18) found a positiverelationship between leaf chlorophyll and nitrogen content.

Defoliation reduced SPAD reading in Shiraz thyme, kakooti, and catthyme (see Table 1). This was also true for salinity and, in this case, nega-tive effect was more pronounced in Shiraz thyme in such a way that with

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–10 ds.m−1, SPAD reading was reduced by 76.9% compared with control(see Table 1). This finding is also confirmed by other results (6,14).

Interactive effects of water stress and defoliation on chlorophyll con-tent reading for Shiraz thyme, kakooti and cat thyme were significant(Table 2). Apparently, the effects of these types of environmental stresseson chlorophyll are cumulative. In general, the negative effect of defolia-tion was more pronounced on chlorophyll content in kakooti. No interac-tive significant effect between salinity and defoliation on chlorophyll wasobserved.

A positive correlation between water stress and stomatal resistance wasobserved (Table 3). This correlation has been associated with differentmechanisms in the literature (1,5,16,25,29). Wang et al. (29) stated thatwater deficit decreased cell turgidity and increased abscisic acid andhence caused stomatal closure. Defoliation caused reduction in stomatalresistance only in Shiraz thyme (see Table 3), wherein with 25% defolia-tion, stomatal resistance was 27%, and with 50% defoliation, stomatalresistance was 39% as compared with the unstressed control plants.

In plants such as cotton, damage caused by insects has interfered withstomatal function and reduced stomatal conductance (24). A positive corre-lation between salinity and stomatal resistance was also noted for plants inthe current study, similar to the results of an earlier study in sunflowers by

TABLE 1. Relative chlorophyll content of species at selected stress levels

Stress Treatment

StressLevel

Shiraz Thyme

Kakooti Garden Thyme

Cat Thyme

(Relative chlorophyll level, Spad units)1

Drought (MPa) −0.3 52.48 a 42.35 a 41.50 a 42.33 a−0.5 51.60 a 38.18 b 41.20 a 43.43 a−1.0 52.80 a 42.28 a 41.23 a 43.93 a−1.5 53.30 a 43.88 a 43.30 a 44.58 a

Defoliation (%) 0 54.60 a 44.58 a 41.08 a 45.88 a25 52.75 a 40.25 b 41.93 a 42.15 b50 50.25 b 40.20 b 42.48 a 42.65 b

Salinity (ds.m−1) 0 43.39 ab 41.35 ab 50.10 a 41.77 ab5 21.66 cd 20.80 cd 41.39 ab 26.36 c

10 10.01 d 19.07 cd 30.82 bc 19.89 cd

1Means with the same letter within the same stress column section are not significantlydifferent at p = 0.05.

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Sohan et al. (27). Except for garden thyme, the interactive effect of waterstress and defoliation on stomatal resistance was not significant (Table 4).

An increasing water stress tended to increase temperatures within theplant communities, but this trend was inconsistent within species (Table 5).An increasing temperature inside a plant community by exposure todrought has been reported (1). The temperature increase in the canopyappears to be due to closure of stomata inhibiting transpirational coolingand increased respiration by leaves under temperature stress, although.defoliation had no effect on temperature within the plant community. Nointeractive effect of water potential and defoliation on temperature withinthe canopy was observed for cat thyme (Table 6).

Water stress reduced leaf to stem ratio for all species as compared withunstressed controls (Figure 1). This reduction was more pronounced forcat thyme than other plants. The reduction of leaf-to-stem ratio appearslogical because water stress induces leaf senescence and thus a reductionin leaf weight on plants (11,13). Defoliation also decreased leaf to stemratio in Shiraz thyme (Figure 2) and produced an insignificant decreasingtrend in the ratio in other species. A reduction in leaf-to-stem ratio by

TABLE 2. The effect of combined defoliation and water stress on chlorophyll level in selected species

Defoliation Water Stress Shiraz Thyme Kakooti Garden Thyme Cat Thyme

(%) (MPa)(Relative chlorophyll level, Spad units)1

0 −0.03 52.5 a 44.4 ab 45.4 bcd 42.3bcd–0,5 53.3 a 43.4abc 41.8 bcd 51.1 a−1.0 55.3 a 45.7 a 40.3 ab 38.9 c−1.5 55.3 a 44.8 a 42.4 a 51.2 aMean 54.1 44.6 42.5 45.9

25 −0.03 52.7 a 38.3 c 39.3bcd 42.6 bcd−0.5 50.5 a 38.1 cd 42 de 42.3 bcd−1.0 53.3 a 41.1 abc 40.3 bcd 48.2 ab−1.5 54.5 a 43.4 abc 46 abc 35.5 dMean 52.8 40.2 41.9 42.2

50 −0.03 52.1 a 44.3 a 39.8 bcd 42 bcd−0.5 50.9 a 32.9 d 29.8 cde 36.9 d−1.0 49.8 a 39.4 bc 43.1 de 44.7 abc−1.5 48.1 a 42.7 ab 41.5 e 46.9 abMean 50.2 39.8 41.0 42.6


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TABLE 3. Stomatal resistance of species at selected stress levels

Stress Treatment Stress Level Shiraz Thyme Kakooti Garden Thyme Cat Thyme

(Rs)1

Water stress (MPa) −0.03 7.10 a 7.36 a 16.20 a 10.57 a−0.5 8.20 a 7.30 a 16.44 a 11.81 a−1.0 8.30 a 7.83 a 20.20 a 12.73 a−1.5 8.30 a 8.37 a 17.33 a 13.47 arb 0.65 0.65 0.24 0.98

Defoliation (%) 0 10.07 a 7.4 a 19.57 a 10.07 a25 7.40 b 7.77 a 17.04 a 7.40 a50 6.13 b 7.93 a 16.01 a 6.13 arb 0.96 0.95 0.94 0.81

Salinity (ds.m–1) 0 3.54 a 2.12 a 1.58 a 1.65 a5 4.93 a 2.16 a 3.57 a 3.09 a

10 4.74 a 2.90 a 3.03 a 5.05 ar2 0.63 0.78 0.50 0.99


TABLE 4. The effect of combined defoliation and water stress on stomatal resistance in selected species


(%) (MPa)(Rs)

1

0 −0.03 9.4 a* 23.4 a 7.9 a 11.4 a−0.5 9.9 a 23.1 a 7.0 a 11.5 a−1.0 11.1 a 17.4 abc 7.2 a 12.9 a−1.5 9.9 a 14.3 bc 7.6 a 14.5 aMean 10.1 19.6 7.4 12.6

25 −0.03 6.7 a 11.7 cd 8.2 a 8.8 a−0.5 8.2 a 15.4 abcd 6.7 a 12.6 a−1.0 7.2 a 22.8 a 7.3 a 14.1 a−1.5 7.6 a 18.3 abcd 8.8 a 14.4 aMean 7.4 17.1 7.8 12.5

50 −0.03 5.3 a 13.5 bc 5.9 a 11.5 a−0.5 6.4 a 10.8 d 8.2 a 11.4 a−1.0 6.5 a 20.4 ab 9.0 a 11.2 a−1.5 7.5 a 19.8 abc 8.7 a 11.4 aMean 6.4 16.1 8.0 11.4


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TABLE 5. Plant community temperature of species at selected stress levels

Stress Treatment StressLevel Shiraz Thyme Kakooti Garden Thyme Cat Thyme

(°C)1

Water stress (MPa) −0.03 28.58 a 30.53 a 27.43 c 27.1 b−0.55 28.60 a 30.53 a 28.45 bc 27.35 b−1.0 29.03 a 30.58 a 28.6 b 28.7 a−1.5 28.67 a 31.05 a 29.12 a 27.3 b

Defoliation (%) 0 28.83 a 30.55 a 28.38 a 27.75 a25 28.78 a 30.53 a 28.35 a 27.05 a50 28.55 a 30.93 a 28.48 a 27.38 a


TABLE 6. The effect of combined defoliation and water stress on temperature within plant community


(%) (MPa)(°C)1

0 −0.03 28.8 a* 31.3 a 27.6 a 26.4 de−0.5 28.5 a 30.0 a 28.8 a 28.3 ab−1.0 29.2 a 29.7 a 28.1 a 28.3 ab−1.5 28.8 a 31.2 a 29.2 a 28.0 abcMean 28.8 30.6 28.4 27.7

25 −0..03 28.4 a 29.6 a 27.3 a 27.3 bcde−0.5 28.5 a 30.0 a 27.5 a 27.8 bcd−1.0 29.8 a 30.7 a 29 a 28.6 ab−1.5 28.6 a 31.7 a 29.7 a 28.1 abcMean 28.8 30.5 28.4 27.9

50 −0.03 28.5 a 30.6 a 27.6 a 27.5 bcd−0.5 28.8 a 31.0 a 29.0 a 26.0 e−1.0 28.1 s 31.3 a 28.7 a 29.3 a−1.5 28.8 a 30.2 a 29.2 a 26.7 cdeMean 28.4 30.8 28.6 27.4


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defoliation could be expected, but because defoliation in our study wasremoval of both leaves and associated stems of the plant, the lack of anythe significant effect of defoliation on the ratio is not surprising.

FIGURE 1. Leaf-to-stem ratio at selected water stress levels.

FIGURE 2. Leaf-to-stem ratio at selected defoliation levels.

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In both Shiraz thyme and cat thyme, salinity stress at 5 ds.m−1 reducedleaf-to-stem ratio significantly as compared with unstressed controls(Figure 3). Similar reductions for the other species were observed at a10 ds.m−1 salinity stress. No interaction effects of water stress and defoli-ation on leaf to stem ratio were observed (Table 7).

Water stress increased leaf weight, as compared with nonstressed con-trols in kakooti and garden thyme (Table 8). The increased water stressapparently induced thicker leaves, an effect of water stress noted withother plant species (11,23,24). Hasani and Omid-Beigi (11) reported thatwater stress increased specific leaf weight in basil as compared withunstressed controls. In contrast, increased defoliation reduced leaf weightfor all species, especially in kakooti. The decrease in leaf weight of ourtest species under salinity stress was unexpected as the opposite resultshave been reported (1,25). An interactive effect of water stress and defoli-ation on leaf weight for kakooti and garden thyme did occur with thelowest specific leaf weight observed with 50% defoliation and −0.3 mega-pascal soil water potential (Table 9).

Increasing water stress increased the plant root-to-top ratio as com-pared with unstressed control plants, an effect pronounced for Shirazthyme and less pronounced for kakooti (Figure 4). In general, root-to-top

FIGURE 3. Leaf-to-stem ratio at selected salinity levels.

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TABLE 7. The effect of combined defoliation and water stress on leaf to stem ratio


(%) (MPa)(Leaf-to-stem ratio)1

0 −0.03 1.7 ab 0.7 a 1.0 a 3.5 de−0.5 1.8 a 0.8 a 0.6 a 2.9 ab−1.0 1.7 bcde 0.7 a 0.9 a 2.8 ab−1.5 1.9 abc 0.8 a 0.9 a 2.6 abcMean 1.8 0.8 0.9 3.0

25 −0.03 1.5 abcd 1.0 a 0.5 a 4.2 bcde−0.5 0.8 e 0.7 a 0.9 a 1.9 bcd−1.0 0.8 e 0.6 a 0.5 a 2.6 ab−1.5 0.9 e 0.6 a 0.4 a 0.9 abcMean 1.0 0.7 0.6 2.4

50 −0.03 1.2 abcd 0.9 a 0.7 a 2.2 bcd−0.5 1.0 cde 0.9 a 0.5 a 2.7 e−1.0 1.1 ab 0.8 a 0.4 a 2.2 a−1.5 0.9 de 0.5 a 0.6 a 1.9 cdeMean 1.1 0.8 0.6 2.3


TABLE 8. Leaf weight of species at selected stress levels

Stress Treatment Water Stress Shiraz Thyme Kakooti Garden Thyme Cat Thyme

(MPa)(g/m–2)1

Water stress (MPa) −0.03 83.8 a 63.3 a 80.1 a 84.4 a−0.5 80.5 a 850.0 a 81.3 a 90.3 a−1.0 79.1 a 79.0 a 83.3 a 93.3 a−1.5 79.3 a 101.0 a 86.3 a 100.2 a

Defoliation (%) 0 87.6 a 95.0 a 88.6 a 101.7 a25 76.1 b 85.0 b 81.0 b 89.3a50 78.3 ab 66.0 c 78.8 c 85.3 a

Salinity (ds.m–1) 0 44.0 a 77.0 a 134.0 a 60.0 a5 3.0 a 19.0 a 89.0 a 22.0 a

10 5.0 a 0.0 a 28.0 a 7.0 a


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TABLE 9. The effect of combined defoliation and water stress on leaf weight


(%) (MPa)(g/m–2)1

0 −0.03 90.8 a 62.0 hi 90.3 b 92.7 a−0.5 83.0 a 120.0 b 90.0 b 109.7 a−1.0 83.3 a 98.0 d 90.0 b 94.0 a−1.5 93.5 a 100.0 c 84.0 c 110.3 aMean 90.2 95.0 88.6 101.7

25 −0.03 75.8 a 70.0 f 90.0 b 86.3 a−0.5 77.8 a 70.0 f 84.0 c 77.0 a−1.0 72.0 a 61.0 i 80.0 d 105.0 a−1.5 79.0 a 140.0 a 70.0 e 89.0 aMean 76.2 85.3 81.0 89.3

50 −0.03 85.0 a 58.0 j 60.0 f 74.3 a−0.5 80.8 a 65.0 g 70.0 e 84.3 a−1.0 82.0 a 78.0 e 80.0 d 81.0 a−1.5 65.5 a 63.0 h 105.0 a 101.3 aMean 78.3 66.0 78.8 85.2


FIGURE 4. Root-to-top ratio at selected water stress levels.

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ratios at field capacity were higher for Shiraz thyme and lower forkakooti, an effect widely reported in previous studies (3,4,11,23). Underwater stress, more photosynthetic material is apparently allocated to theplant roots, leading to increased penetration of the soil and biomass accu-mulation in the roots. In some cases, however, drought has been reportedto reduce the root to top ratio (12).

No consistent effects of defoliation on root to top ratio for the testedspecies were observed (Figure 5), although defoliation has been shown tocause a reduction in root to top ratio due to a reduction in photosyntheticarea (8,21). Feiz (8) has reported that severe grazing reduces root biom-ass. In general, defoliation from drought and salinity reduce dry matteryield for all species, although the severity differs (8,21).

A reduction in dry matter yield with water stress of −1.5 megapas-cal, as compared with unstressed controls, was lowest for kakooti andthe highest for garden thyme (Figure 6). This did not match with salin-ity stress, except for kakooti, which had an almost similar response towater stress and salinity. The reduction in yield to 10 ds.m−1 salinity,as compared with unstressed controls, was highest for Shiraz thyme,cat thyme, and kakooti and lowest for garden thyme. Defoliationaffected growth of garden thyme more negatively than other testedspecies (Figure 7).

FIGURE 5. Root-to-top ratio at selected defoliation levels.

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FIGURE 6. Dry matter at selected soil moisture levels.

FIGURE 7. Dry matter production at selected defoliation levels.

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CONCLUSION

All plants tested responded to water deficit, but the negative effectswere more pronounced in kakooti and Shiraz thyme than in other species.Garden thyme demonstrated better tolerance to salinity stress than theother species.

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FIGURE 8. Total dry matter at selected salinity levels.

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Documents

Effect of Drought, Salinity, and Defoliation on Growth Characteristics of Some Medicinal Plants of Iran