Effect of Salt Stress on Plant Growth Review Ncbi

Plants (Basel). 2020 Nov; 9(11): 1574.

Evaluating the Contribution of Growth, Physiological, and Ionic Components Towards Salinity and Drought Stress Tolerance in Jatropha curcas

Muhammad Mohsin Abrar,^1, ² Muhammad Saqib,^ii, ^* Ghulam Abbas,^2, ⁱⁱⁱ Muhammad Atiq-ur-Rahman,^ii, ⁴ Adnan Mustafa,¹ Syed Atizaz Ali Shah,¹ Khalid Mehmood,⁵ Ali Akbar Maitlo,^i, ^six Mahmood-ul-Hassan,⁷ Nan Lord's day,^1, ^* and Minggang Xu¹

Ghulam Abbas

^twoFound of Soil and Environmental Sciences, University of Agriculture, Faisalabad 38040, Islamic republic of pakistan; moc.liamg@kp29a.g (1000.A.); moc.liamg@179qitaradras (G.A.-u.-R.)

³Department of Environmental Sciences, COMSATS University Islamabad, Vehari Campus, Punjab 61100, Pakistan

Muhammad Atiq-ur-Rahman

²Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad 38040, Pakistan; moc.liamg@kp29a.thou (Thousand.A.); moc.liamg@179qitaradras (G.A.-u.-R.)

⁴Soil Survey of Punjab Lahore, Lahore 54780, Pakistan

Khalid Mehmood

^fiveCollaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Key Laboratory for Aerosol-Deject-Precipitation of Communist china Meteorological Administration, School of Atmospheric Sciences Nanjing University of Information Scientific discipline and Applied science, Nanjing 210044, Cathay; moc.liamg@077dilahk.arpis

Mahmood-ul-Hassan

⁷Department of Plant Nutrition, College of Resources and Environmental Sciences, China Agronomical University, 2 W Yuanmingyuan Ave, Haidian, Beijing 100193, China; moc.liamg@71rganassah

Received 2020 Oct 10; Accustomed 2020 Nov 6.

Abstract

Salinity and drought stress, singly or in combination, are major environmental menaces. Jatropha curcas Fifty. is a biodiesel plant that tin tolerate long periods of drought. However, the growth operation and stress tolerance based on physical, chemic, and physiological attributes of this found have not yet been studied. To address this question, J. curcas seedlings were grown in a completely randomized design in plastic pots filled with soil to evaluate the effects of salinity and drought stresses on growth, ionic composition, and physiological attributes. The experiment consisted of six treatments: control (without salinity and drought stress), salinity alone (7.5 dS m⁻¹, fifteen dS 1000⁻¹), drought, and a combination of salinity and drought (7.5 dS m⁻¹+ Drought, 15 dS m⁻¹+Drought). Our results revealed that, compared with the command, both plant summit (PH) and stem diameter (SD) were reduced by (83%, lxxx%, and 77%) and (69%, 56%, and 55%) under salinity and drought combination (15 dS thou^−one+Drought) later on 3, vi, and nine months, respectively. In that location was 93% more leaf Na⁺ found in plants treated with xv dS m⁻¹+Drought compared with the control. The highest significant boilerplate membrane stability index (MSI) and relative water content (RWC) values (81% and 85%, respectively) were found in the control. The MSI and RWC were non influenced by 7.5 dS thousand^−one and drought treatments and mostly contributed towards stress tolerance. Our findings imply that J. curcas is moderately tolerant to salinity and drought. The Na⁺ toxicity and disturbance in K⁺: Na⁺ ratio were the main contributing factors for limited growth and physiological attributes in this constitute.

Keywords: Jatropha curcas Fifty., salinity, drought stress, stress tolerance, biomass, chlorophyll content, ionic composition

one. Introduction

The extreme events associated with global climate alter jeopardize sustainable establish growth and product worldwide [1]. The changes in abiotic constraints such equally common salt stress, drought, and temperature are typical examples of such alterations. Amidst abiotic stresses, soil salinization and drought extremes have been regarded equally leading stresses limiting farm production. Given that efforts had been made in the past to ameliorate the negative impacts of these environmental constraints on constitute growth [2,three,4], only a few studies are bachelor to date that explore the combined furnishings of salinity and drought stresses on Jatropha curcas [5].

Salinity and drought stresses more often than not occur concurrently [6]. The increase in dryland areas is often associated with the consumption of low-quality irrigation water. Thereby, the continuous progression of drought and salinity stress results in a decrease in the available abundant land for agronomics, especially in arid to semi-arid regions of the world [7].

Salinity and drought are 2 major environmental constraints for crop productivity and are consistently threatening agricultural systems [eight]. Salinity affects approximately 50% of irrigated lands worldwide [ix].

Soil salinity causes ion accumulation at toxic levels and osmotic stress in plants, resulting in growth and developmental reductions [10], which causes lower soil matric potential and leads to drought weather, i.e., those that cause physiological limitation for found growth [10]. It has been established that halophytes can survive under high salt concentrations (>200 mM NaCl), while glycophytes can only sustain their growth under relatively low salinity conditions [11,12]. Stunted establish growth and low crop yields are the two foremost impressions of salinity and drought stresses. Therefore, information technology becomes imperative to introduce economically efficient, environmentally friendly, and sustainable management approaches to tackle such ecology constrains to ensure nutrient security.

Stress tolerance (i.eastward., salinity or drought) can exist divers as the ability of the constitute to sustain sufficient growth under stress milieu [ten]. More precisely, the salinity tolerance tin exist termed as producing biomass on a percent basis in controls in contrast to saline treatments for a longer fourth dimension elapsing. Several attributes are associated with the physiological and developmental mechanisms of plants such every bit the buildup of osmotically active solutes, osmotic adjustment, and a partial stomatal opening for tolerating long episodes of drought stress [thirteen]. The closing of stomata is a double-edged sword, i.e., information technology decreases C uptake on ane mitt while minimizes water loss on the other manus. Hence, plants sustain osmotic adjustments in tissues under salinity and drought stress conditions. Such a type of do good (efficient water consumption) is more than significant in C₄ plants than C₃ plants [14].

Jatropha curcas (physic nut) is a C_three shrubby found (family Euphorbiaceae) [15], adaptable to marginal soils, and is capable of ameliorating problematic soils and call up soil productivity [16]. In recent times, Jatropha has gained the exceptional attention of the scientific factions because of its bioenergy, salinity [17], and drought-resistance [18] in various agricultural settings.

Little is known about the combined effect of salinity and drought stresses on the growth functioning of Jatropha. Conversely, it is well known that Jatropha is drought-resistant, since many scientists accept quantified the operation of Jatropha under water deficit conditions. For example, Maes et al. [17] demonstrated that drought considerably reduced plant growth; however, it did not affect physiological parameters (water relations). Moreover, Achten et al. [xix] have examined that biomass production of Jatropha was 57% more in well-watered atmospheric condition compared with medium water supply (40% plant bachelor h2o). Nevertheless, variations are establish regarding the imposition of drought stress in diverse studies, and the interaction of both salinity and drought stresses has not been well quantified. Moreover, Jatropha had demonstrated sufficient biomass production under the stressful environment of semi-arid areas and its overall operation to salinity and water deficit conditions has been explored. However, its stress tolerance based on biomass production, ionic composition, and physiological mechanisms under the interaction of salinity and drought is not well described. Taking this context into account, nosotros hypothesized that combined salinity and drought stresses may affect growth and development of J. curcas while their effects are farther governed by stress tolerance ability of J. curcas.

Therefore, the electric current study was carried out to unravel the furnishings of salinity and drought stresses on growth, ionic composition, and physiological attributes of J. curcas.

2. Results

2.one. Growth Parameters Affected by Salinity and Drought

Salinity, drought, and their interaction significantly affected institute height (PH) and stalk bore (SD) (p < 0.05; Table 1). Compared with the control, both the PH and SD were reduced with increasing salinity and drought. The maximum decrease (83%, eighty%, and 77%) in the PH was observed at an interactive level of salinity and drought (15 dS m⁻ⁱ+Drought) after three, six, and nine months, respectively, compared with the control. Simultaneously, a similar decreasing pattern (69%, 56%, and 55%) in SD was recorded after three, six, and 9 months, respectively. The plants died at 22.5 dS m⁻¹ and 22.five dS chiliad⁻¹+Drought, due to farthermost conditions.

Table 1

The consequence of salinity and drought stress on growth and physical parameters of Jatropha curcas.

Treatments	Plant Pinnacle (cm)			Stalk Diameter (cm)			No. of Branches			No. of Leaves
Treatments	Duration (months)			Duration (months)			Duration (months)			Duration (months)
	three	6	9	3	vi	ix	3	six	9	3	6	ix
Command	62.half-dozen ± 0.93a	68.80 ± 0.86a	72.00 ± 1.58a	1.82 ± 0.06d	1.93 ± 0.03a	2.xl ± 0.18a	12.xx ± 0.37a	fourteen.80 ± 0.86a	xvi.40 ± 0.86a	11.40 ± 0.68a	14.twenty ± 0.86a	fifteen.eighty ± 0.86a
Drought	33.4 ± 1.81b	36.20 ± 1.74b	41.xl ± 1.58b	1.07 ± 0.06bc	1.20 ± 0.11c	i.37 ± 0.05bc	9.80 ± 0.37b	12.20 ± 0.73b	13.60 ± 0.51b	seven.40 ± 0.81b	10.20 ± 0.37b	13.20 ± 0.58b
vii.v dS grand^−ane (Well-watered	21.00 ± 1.00c	22.60 ± 1.03c	26.eighty ± 0.97c	i.58 ± 0.08b	ane.63± 0.08b	i.68 ± 0.07b	nine.60 ± 0.68b	10.lxxx ± 0.86b	13.20 ± i.02bc	7.20 ± 0.80b	10.20 ± 0.86b	12.40 ± ane.33b
7.five dS k⁻¹+Drought	13.85 ± ane.92d	14.67 ± 0.93d	17.20 ± 1.58d	1.04 ± 0.07c	1.fifteen ± 0.04c	1.48 ± 0.19bc	seven.20 ± 0.66c	viii.00 ± 0.55c	11.twenty ± 0.37cd	6.60 ± 0.51b	seven.60 ± 0.51c	ix.twoscore ± 0.51c
15 dS m⁻ⁱ (Well-watered)	12.89 ± one.07d	xv.81 ± 0.97d	xviii.63 ± one.58d	1.08 ± 0.06c	1.14 ± 0.06c	ane.16 ± 0.01cd	6.80 ± 0.58c	seven.20 ± 0.66cd	10.00 ± 0.71d	half dozen.twenty ± 0.58b	6.lxxx ± 0.66c	7.lx ± 0.51cd
xv dS thousand⁻ⁱ+Drought	10.75 ± 1.95d	13.70 ± 0.93d	xvi.44 ± one.58d	0.56 ± 0.08d	0.84 ± 0.07d	1.08 ± 0.06d	four.eighty ± 0.97d	5.20 ± 0.37d	vii.60 ± 0.75e	4.00 ± 0.55c	4.40 ± 0.51d	five.60 ± 0.51e

Salinity and drought stress significantly (p < 0.05) affected both the number of branches (NOB) and number of leaves (NOL). The maximum NOB and NOL were found in the control, while the least values for both parameters were observed in 15 dS m^−one+Drought. The NOB averaged from 4.80, 5.20, and 7.60 after 3, six, and 9 months, respectively. The NOL followed a similar trend at the same level (p < 0.05; Table 1).

Compared with the control, the SFW and SDW were significantly decreased nether xv dS m^–1+Drought (p < 0.05; Figure 1). The highest SFW and SDW values (66.48 and 32.thirteen g plant^–1) were recorded in the command. At the aforementioned fourth dimension, the maximum decrease of 85% and 84% in the SFW and SDW, respectively, was noted at the fifteen dS m^–1+Drought in contrast to the control. A tendency similar to the SFW and SDW was also found in the RFW and RDW subjected to 15 dS one thousand^–1 and xv dS m^–1+Drought (Figure iB). In the control, the maximum mean values (28.02 and xiii.16 grand plant^–1) of the RFW and RDW, respectively were noted. Whereas no pregnant divergence was observed in the RDW values of plants subjected to 7.five dS m^–1+Drought (250 mL) treatments. The highest reduction in the RFW and RDW of 88% and 79% was noted at fifteen dS m^–one+Drought in contrast to the control.

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(A) Shoot fresh weight (SFW) and dry weight (SDW), and (B) root fresh and dry weight (p < 0.05), following post-hoc Duncan'south multiple range test.

Figure 2A presents the yield of J. curcas corresponding to salinity and a relative decline in relative biomass that is inversely proportional to salinity is credible. The values of electrical conductivity in the irrigation of a water reduced yield that was fifty% of the maximum yield (EC_i50) and the salinity-tolerance index (ST-index) were 10.72 dS m⁻¹ and 11.44 dS 1000⁻¹, respectively, implicating a low vulnerability of J. curcas to salinity. A relationship was developed betwixt the stress tolerance of J. curcas plants and time on the basis of the exponential decay model, A = Ao + ae^kt, where "a" is intercept "k" is the decay charge per unit. Stress tolerance showtime decreased exponentially till six months and then attained an asymptotic relationship (Figure 2B).

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(A) The issue of salinity on the plant yield (in terms of total dry mass). The yellow circle shows the ST-alphabetize, and the ECi is the electrical conductivity of the irrigation water at the yield reduced to fifty% of the absolute yield (Y). Experimental data (dots). The model bend for Twelvemonth = a*eb*ECi. EC_i50 and ST-index are the mid-yield salinity and the salinity tolerance index, respectively, as calculated by Steppuhn et al. (2005). * indicates significant differences at p < 0.05. (B) Exponential disuse model fitted on the growth-related parameters, such every bit plant pinnacle, stem diameter, and total dry mass-produced (adapted from Fernandez [xx] with slight modifications).

2.2. Ionic Concentrations

The results of this study betoken that marked variations in Na⁺ concentration in the shoot were observed in xv dS m⁻¹+Drought compared with the control. Consistent with the shoot Na⁺ results, the root followed the same tendency, and the maximum Na⁺ concentration in root and stem were determined every bit 2.33 and 2.07 mmol g⁻¹ dw, respectively, under 15 dS m⁻¹+Drought treatment. The everyman leafage, stem, and root Na⁺ mean values (0.12, 0.14, and 0.16 mmol yard⁻¹ dw, respectively) and highest K⁺ mean concentrations (i.62, 0.68, and 0.55 mmol g^–1 dw, respectively) were recorded in the control followed past the drought treatment. Contrary to the tendency in the control, the highest mean Na⁺ (1.84, two.06 and 2.32 mmol one thousand^−one dw) and everyman One thousand⁺ values (0.75, 0.36, and 0.27 mmolg⁻¹ dw) in leaf, stalk, and root, respectively, were recorded in the 15 dS m^−one+Drought treatment (Tabular array 2).

Table 2

Concentrations of Na⁺, One thousand⁺, and K⁺: Na⁺ ratio in Jatropha curcas plants subjected to the table salt and drought stresses induced by NaCl and low h2o supply, respectively. Data refer to hateful values (north = v).

Treatment	Na⁺			Yard⁺			Chiliad⁺: Na⁺ Ratio
	Leaf	Stem	Root	Leaf	Stem	Root	Leafage	Stalk	Root
Control	0.12e	0.14e	0.16e	1.62a	0.68a	0.55a	13.06a	iv.72a	iii.49a
7.5 dS m⁻ⁱ (well-watered)	0.60d	0.66d	0.79d	0.89c	0.48c	0.41b	1.483c	0.73c	0.52c
xv dS m⁻¹ (well-watered)	1.29b	1.51b	1.89b	0.83c	0.43cd	0.38b	0.643c	0.29c	0.20c
Drought	0.16e	0.18e	0.19e	i.24b	0.57b	0.49a	7.949b	iii.28b	2.53b
7.5 dS m⁻¹+Drought	ane.05c	1.12c	i.25c	0.87c	0.46c	0.39b	0.829c	0.41c	0.31c
fifteen dS k^−ane+Drought	1.84a	two.06a	ii.32a	0.75d	0.36d	0.27c	0.408c	0.18c	0.12c

The highest K⁺: Na⁺ ratios (13.06, 4.72, and iii.49) in leaf, stem, and root were constitute in the control, whereas the lowest 1000⁺: Na⁺ mean values were noted in 15 dS m⁻¹+Drought. The Drought treatment followed the control and showed 7.95, 3.28, and 2.53 of K⁺: Na⁺ ratios in leafage, stalk, and root, respectively. However, no meaning (p > 0.05) deviation in Thousand+: Na⁺ ratios of stem and root were found among 15 dS g^−one, 7.5 dS m⁻¹+Drought and 15 dS m⁻¹+Drought treatments (Table two).

2.3. Physiological Parameters and Water Relations

A significantly highest boilerplate value (81%) of MSI was establish in the control (p < 0.05; Figure 2A), whereas the smallest value (44%) of MSI was noted in 15 dS m^−ane+Drought among all treatments. The combination of salinity and drought (15 dS chiliad⁻¹+Drought) acquired the highest subtract (by 49%) in MSI. However, 7.5 dS k^−one+Drought treatments did not crusade a notable effect on the MSI (p > 0.05).

Similar MSI, the RWC was notably college (p < 0.05) in the control compared to the other treatments except 7.v dS m⁻¹+Drought treatments (Figure twoB). The highest RWC value (85%) was found in the control, followed by the drought treatment (i.e., 77.two%). Nevertheless, these were statistically non-significant. With increasing salinity, the RWC was significantly reduced in both treatments, i.east., 15 dS k⁻¹ and fifteen dS 1000^−ane+Drought, and showed the everyman values, i.e., 51.vi%, and 53.2% of RWC values, respectively.

The photosynthetic rate (PR) differed significantly (p < 0.05) among the treatments. For example, in the control, the highest PR (6.25 µmol m⁻²sec⁻¹) was observed, while the everyman PR was determined in 15 dS chiliad⁻¹+Drought. The most pregnant decrease (73%) in the PR was noticed at fifteen dS m⁻ⁱ+Drought in comparison to the control. Similarly, the highest transpiration rate (TR) (1.98 mmol 1000⁻²sec⁻¹) was adamant in the command. At the aforementioned fourth dimension, the everyman TR was found in 15 dS yard⁻¹+Drought.

In the control, the highest hateful stomatal conductance (0.64 mmol m⁻² sec⁻¹) was noted among all the treatments. Whereas the maximum decrease (87%) in the stomatal conductance was observed in xv dS thousand^−ane+Drought. The highest mean value, i.eastward., 25 (in SPAD units) of chlorophyll content, was found in the control. The maximum decrease of 80% was observed in fifteen dS m⁻¹+Drought compared with the control, followed by fifteen dS yard⁻¹ of (68%), respectively.

three. Discussion

In broad terms, salinity stress tin be composed of two components: osmotic stress and common salt specific toxicity (Na⁺ toxicity and ionic imbalance). The combined effect of salinity and drought (in the present study) had a considerable influence on Jatropha's growth and evolution (Table one).

Following the EC_i50 and ST-indexes (ten.72 dS m⁻¹; 11.41), J. curcas seems to exist more resistant to salinity (Figure iiA) than the other crops, e.g., the almond (ECi₅₀ = 3.83 dS yard⁻¹, ST-index = 4.94), apricot (EC_i50 = 3.39 dS k⁻ⁱ, ST-alphabetize = 4.63) given by Steppuhn et al. [21].

three.1. Growth Parameters Affected by Salinity and Drought

The growth reduction of plants under salinity and water deficit conditions (drought) is a common finding in the present study, and like results are also reported by the other studies [22,23,24]. The nowadays study demonstrated that the salinity negatively affects the PH and SD and may be attributed to the decline in osmotic potential and nutrient limitation [25]. Moreover, decreased osmotic potential resulted in the endmost of stomata and the deactivation of the enzyme-associated system and eventually reduced the establish growth. Moreover, reduced CO_ii fixation and N assimilation induced a depreciation in the establish growth and reduced the PH. Simultaneously, excessive salt ions in the prison cell wall manipulated the metabolism and, therefore, decreased the cell wall's elasticity and consequently express the PH [26].

Jatropha tin can sustain its growth in rainfall atmospheric condition ranging from everyman (i.e., 200 mm) to highest (1200 mm) [27]. For example, our findings suggest a 46%, 47%, and 47% reduction in PH after three, six, and nine months, respectively, in plants irrigated with 40% of soil water property capacity (WHC) (i.e., drought stressed) compared with those irrigated with lxx% of soil WHC (well-watered) (Table 1).

The type of found, plant organ, and growth stages determine the considerable variability regarding salinity impact [12]. Moreover, Díaz-López et al. [28] and Yaron et al. [20] explored whether increasing salinity reduced stem bore and leaf growth and hence attained less weight, number of branches, and leaves. Other studies reported a decrease in SD subjected to different salinity regimes [iv,29]. This reduction in SD may be attributed to the reject in the turgor potential [28]. Similarly, we reported a decrease in SD for instance (by 69%) subsequently 3 months in plants treated with combined salinity and drought stresses (15 dS 1000⁻ⁱ+Drought) compared with the control.

In line with by studies [23,24], our findings indicated a decrease in plant biomass and SFW with increasing salinity and drought. Salinity reduces biomass production and growth in many found species, and those plants that able to produce extra dry mass tin can survive for a longer time in saline plus drought atmospheric condition [25]. Furthermore, those plants are more salt-tolerant and are capable of excluding Na⁺ from shoot to roots [thirty].

In contrast to non-saline weather condition, salinity negatively impacts the SFW and SDW, which tin be proposed as an indication for salinity tolerance at initial growth phases of the plant [31], and excessive Na⁺ concentrations are considered degrading for institute growth [32]. This implies that salt stress slows down the metabolic mechanisms and leads to decreased growth, and consequently, a reduction in biomass occurs [33].

In our written report, in contrast to the command, salinity (vii.5 dS chiliad⁻¹) decreased RFW and RDW by 45% and 43%, respectively. However, drought treatment did non touch then severely, equally 7.five dS m⁻¹ affected both RFW and RDW (Figure iA). Moreover, combined salinity and drought treatments influenced the root growth relatively more than adversely; for case, in an experiment, Soda et al. [34] reported that salinity reduced the root architecture in the olive plant. A similar pattern was given past Bernstein et al. [35], who concluded that avocado root growth compared with shoot growth might be more than sensitive to salinity.

A large amount of foliage and root litter influence the physicochemical characteristics of soils [36]. The rhizodeposition is a vital energy reserve for microbes (in the form of sucrose or starch, etc.), which alternatively regulates microbial activity [37]. Saline stress solitary or in combination with drought considerably (p < 0.05; Figure oneB) reduces root fresh and dry weights [38,39]. Similarly, Carillo et al. [40] proposed that salinity depreciated fresh and dry biomass.

3.2. Chemical Parameters Afflicted by Salinity and Drought

Plants tend to maintain high 1000⁺ concentration in contrast to Na⁺ in stalk and root. Numerous researchers have ended that plants tend to achieve sufficient K⁺ levels that might effectively diffuse the toxic effects of Na⁺ in plant tissues [41,42,43]. In comparison, the elevated leaf Na⁺ concentration corresponding to the lowered leafage K⁺ concentration under salt treatments results in Yard⁺: Na⁺ ratio pass up. Nosotros found that M⁺: Na⁺ ratio decreased with an increasing salinity level. Moreover, potassium is a necessary macro-nutrient responsible for the activation of more than > l enzymes [44] inclusive of the enzymes which participated in the biosynthesis of chlorophyll. Both Na⁺ and K⁺ ions accept a very similar ionic radius and hydration energy. Therefore, under saline conditions, Na⁺ enters the jail cell by using K⁺ channels located at cell membranes [45]. The higher cytoplasmic concentration of Na⁺ leads to a lower K⁺: Na⁺ ratio, which ultimately affects plant metabolism. Hence, the capability of the plants to limit K⁺ loss and maintenance of high ionic ratio (K⁺: Na⁺) in the cytoplasm is an indication of their salt tolerance potential [46]. In the present study, we noticed a considerably higher K⁺: Na⁺ ratio in the control, as compared with the rest of the treatments, and produced more than biomass (Tabular array ii). For instance, in comparison to the command, maximum decrease (86%) in biomass was noted in combination of salinity and drought (15 dS chiliad⁻¹+Drought), whereas the everyman subtract (37%) was recorded in Drought treatment. The lowest G⁺: Na⁺ ratio at 15 dS 1000^−one+Drought treatment also afflicted physiological parameters adversely, for example, information technology reduced the photosynthetic rate, chlorophyll contents, stomatal conductance, and transpiration charge per unit by 67%, 80%, 73%, and 40%, respectively, compared with the control (Effigy three).

An external file that holds a picture, illustration, etc. Object name is plants-09-01574-g003.jpg

Event of unlike levels of salinity and drought on the (A) membrane dtability alphabetize (B) relative water content (C) photosynthetic rate (D) transpiration rate (E) stomatal conductance (F) chlorophyll content. Dissimilar letters depict a significant deviation at p < 0.05.

3.iii. Physiological Parameters Affected by Salinity and Drought

Our findings recorded a 49% and 53% reduction in the MSI and RWC, respectively, in 15 dS m⁻¹+Drought in comparison to the command; nevertheless, no statistical divergence (p > 0.05) was observed in the MSI and RWC amid the control, 7.5 dS chiliad^−one and Drought treatments (Effigy 2A,B). In nowadays study, our results validated that the MSI and RWC were the major attributes contributing towards stress tolerance, since these were less affected past salinity (7.5 dS m⁻¹) and water deficit (Drought). However, with increasing salinity and under the combined effect of salinity and drought, both of these parameters were influenced significantly. Similarly, Kotula et al. [47] noticed a forty% and 33% reduction in the MSI and RWC, respectively, due to salinity stress in comparison to the control in melon. Salinity-induced effects can serve equally an essential indicator for water relations to quantify the common salt tolerating ability of plants [48]. In our study, a greater amount of biomass was recorded in the combination of depression salinity and drought (7.5 dS one thousand^−ane+ Drought) compared with the high salinity treatment (15 dS grand⁻¹) alone. Information technology was further validated by the high value of the RWC in the same treatment.

The RWC has been proposed equally an like shooting fish in a barrel agricultural attribute to select plants for their tolerance to salinity, drought, and heavy metal contagion on the basis of a high RWC [49]. Salinity and drought are responsible for causing manipulations in MSI, which may bespeak cell damage [50]. The ability of plants to maintain normal transpiration rates nether stress weather reflects their stress tolerance, since transpiration is often associated with the normal assimilation of CO₂ for photosynthesis [51].

Chlorophyll is a green-colored pigment responsible for the vital procedure of photosynthesis to make food [52], and the chlorophyll content tin can be assessed in terms of SPAD units, which is likely to decrease in saline conditions compared with the control. The relative decrease in SPAD units was mainly driven by genetic command [53]. Nether stress conditions (i.e., salinity and drought), the relative common salt accumulation and the stress-tolerating ability of the plant determine the reduction in chlorophyll contents [54]. Additionally, Velagaleti et al. [55] concluded that the decrease in chlorophyll contents was ascribed to chloride accumulation (Cl⁻). Moreover, Rangani et al. [56] concluded that in quinoa, the turn down in chlorophyll contents was mainly attributed to the disintegration of chlorophyll construction nether higher salinity levels.

By and large, in most plants, salt stress reduces the photosynthetic charge per unit [57]. Furthermore, Yang et al. [58] reported that stomatal factors limited the net photosynthetic rate. For example, older leaves serve as the table salt-accumulating hotspots under salinity stress. Because of loftier salt concentrations, the leaf senescence took place prematurely, which lead to a reduction in the photosynthetic leafage area of a plant. Consequently, the photosynthesis charge per unit decreased [12], which led to a lower biomass [59].

A further stress enhancement resulted in a situation when the found could non tolerate the combination of salinity and drought (i.e., 15 dS m⁻¹+Drought treatment) in our study (Figure 3A), that might exist due to the extra inclusion of saline ions by plants in a bid for osmotic adjustment, which leads to the ionic imbalance or toxicity. Hence, the closing of stomata may be regarded as an approach to avoid a water deficit (or drought), leading to reduced C assimilation [59,60].

For example, a decline in photosynthetic and transpiration rates was observed in fruit crops with increasing salt stress; and that reduction was mainly attributed to the stomata closing [61,62]. Moreover, in excessive salinity, there was relatively less entrance of CO₂ into the leaves, which resulted in a reduced photosynthetic charge per unit [63].

Combined stresses such as salinity and drought reduce the water contents in soil, which farther reduces soil water and osmotic potential [64]. Moreover, high salt contents in the soil solution hampered the ability of the constitute to absorb h2o and reduced the turgor pressure of leaves [65] and ultimately limited the transpiration rate [12]. The decline in the transpiration rate reduced the ion uptake by roots, xylem conductivity, and decreased ions in leaves [66].

The combined stressors, i.eastward., salt and drought, decreased the conductance of stomata, due to the inability of the plant to excerpt water from the soil. Thus, an imbalance was developed between the uptake of water by roots and h2o lost by transpiration, which consequently resulted in the wilting of the plant [67]. While being exposed to salinity and drought, the plant closes the stomata and avoids dehydration. Notwithstanding, at the same time, the stomata closure likewise limits the CO₂ and O_ii exchange between the atmosphere and internal tissue. Again, this slows downwardly many metabolism-related mechanisms and may reduce plants' survival rate [68].

4. Materials and Methods

iv.one. Experimental Design and Ingather Establishment

The present study was performed every bit a pot experiment in a wire-house of the Institute of Soil and Ecology Sciences (ISES), Academy of Agriculture, Faisalabad (UAF), Pakistan (latitude 31.42° N, longitude 72.08° E, Top 187 thousand). The area is characterized by a mean annual temperature of 24.ii °C and mean annual precipitation of 346 mm [69]. Before the experiment, soil sampling was performed from the research area of the ISES, UAF. Parameters such as pH, ECe, SAR, soluble cations (Na⁺, G⁺), anions (CO₃ ²⁻, HCO₃ ⁻), and texture were analyzed using standard methods mentioned in USDA Handbook# sixty [seventy]. Before sieving through a 2-mm sieve, the soil was stale start, and and then eight kg of that soil was poured into each plastic pot (i.e., 25 cm in bore and 23 cm loftier).

Not-saline treatment (without NaCl and drought stress) was considered as the command (normal irrigation ~ k mL). Three levels of salinity (seven.five, 15, 22.5 dS m⁻¹ NaCl), one level of drought (250 mL), and three combined levels of salinity and drought (7.5 dS m⁻¹ NaCl+Drought, 15 dS m⁻¹ NaCl+Drought, and 22.five dS m⁻¹ NaCl+Drought) were fabricated by mixing NaCl (computed amounts). Well-watered plants were irrigated to 70% of the soil's water-holding capacity (WHC), and drought stressed plants were irrigated to twoscore% WHC. Each treatment has five replications and was arranged in a completely randomized design (CRD). Healthy and uniform seedlings (lx days old) were planted in all the pots (one seedling per pot). Tap water was used to irrigate plants.

The bones soil physico-chemical backdrop were determined before planting the seedlings into the pots. The soil texture was silt loam with 23.5% dirt, pH 7.seven, EC 2.25 dS 1000⁻¹, SAR 54.1 (mmol L⁻¹)^ane/ii, bicarbonates were 0.22 mg L⁻¹, and carbonates were absent.

4.two. Measurement of Growth and Chemical Attributes

Plant growth data for top (PH), stem bore (SD), and the number of leaves (NOL) and branches (NOB), shoot fresh weight (SFW) and shoot dry out weight (SDW), root fresh weight (RFW) and root dry weight (RDW) were quantified three times (afterward every three months) before the harvesting. A meter tape was used to measure out the plant tiptop (cm) from the base to the top of the plant. Vernier calipers were used to record the stem diameter of each plant (five cm) in a higher place the soil surface.

Plant shoots were excised, and SFW of each plant was weighed at once, and the plants were covered with paper bags and left in the oven to dry out at 60 °C for three days. Afterward drying, shoot and root samples were basis separately, shoot and root dry weights (DW) were measured, followed by the measurements of sodium (Na⁺), potassium (Thou⁺), which were measured using a flame photometer (BWB-XP5). The G⁺: Na⁺ ratios were computed in shoot and root samples.

4.3. Determination of Physiological Attributes

Physiological parameters such as chlorophyll contents of the 2nd leaf were determined with a chlorophyll meter (SPAD-502, Konica Minolta Japan). Prior to harvesting, a portable Infrared Gas Analyzer (IRGA LCA-4 ADC) (Analytical Development Company, Hoddesdon, England) was used to determine photosynthetic and transpiration rates and the stomatal conductance of Jatropha plants. All the measurements were made between 11:00 am and 2:30 pm with the adjustments mentioned in Supplementary Fabric (Table S1).

Membrane stability alphabetize (MSI) was measured following the method proposed by Sairam et al. [71] by analyzing the EC of leaf ions leaked in ultra-pure deionized water. About 100 mg of the leaf sample was taken in a exam tube containing 10 ml of ultra-pure deionized water in two parts; the start was placed in a water bathroom for thirty min (forty °C), while the other was placed in a water bath (100 °C boiled water for 15 min), and their EC values (Ci and Cii) were noted, respectively, with an EC meter (HANNA, 99301, Hanna Inst. Inc. RI, The states). The following formula was used for the adding of the membrane stability index:

For the RWC determination, a pair of leaves were cutting from each shoot, and their FW was recorded at once. Then, overnight, they were left floating in distilled water (at 4 °C), and the resaturated weight (RW) was measured. Then they were put in the oven at 70 °C overnight for drying and weighed once more for the dry weight (DW) measurement. The following formula given by Teulat et al. [72] was employed to calculate the RWC:

4.4. Quantification of Stress Tolerance

4.4.1. Stress Response Models and Salinity-Tolerance Index

Yield response variables such every bit maximum yield (Y_m) and relative yield (Y_r) were studied past Steppuhn [21]. Total institute dry mass (shoots and roots) was expressed as yield (Y), and it was converted to Y_r by using a dividing cistron Y_m that was dependent on the full biomass, which is contained of salinity. The following equation was used to compute Y_r value at each salinity level.

On the basis of the best-fitted results and maximum R^two values, an exponential model, was used to clarify the yield response to salinity after transforming the data in Equation (1):

where the electrical conductivity of irrigation water is expressed as ECi; a and b are the constants; the former depicts the curve shape, while the latter determines the model intensity. The Salinity Tolerance Alphabetize (STI) indicates the inherent power of crops to tolerate root-zone salinity by Steppuhn et al. [28]. EC_i50 can exist computed from Equation (2); it is the value of EC at which the yield was reduced to 50% of the maximum yield. The STI can be adamant as suggested by Steppuhn et al. [73]:

4.four.2. Stress Tolerance Determination

The stress tolerance was proposed for yield-related attributes. Here, nosotros have adjusted the stress tolerance (with slight modifications) for the plant meridian from Fernandez [74]. It defines the plant's ability to maintain sufficient growth in the stress surroundings respective to the control conditions in terms of the overall performance of the plant. The stress tolerance was adamant using the following formula:

$S t r e s south T o l e r a northward c e (%) = \frac{Y_{c o northward t r o fifty}}{Y_{a 5 k}} \times \frac{Y_{southward a l i due north i t y, d r o u m h t}}{Y_{a v g}} \times 100$

(4)

where Y in Equation (four) represents growth-related parameters, due east.g., plant height, stem diameter, and full dry mass-produced. Y_avg denotes the boilerplate of all the plants under control atmospheric condition for institute acme Y, stem diameter, and full dry mass-produced.

4.5. Statistical Analyses

Preliminary information was processed in MS Excel 2016 (for Windows). Data for diverse parameters were performed by calculating one-style Analysis of Variance (ANOVA) utilizing the software SPSS xx.0 Statistical Package for Windows (IBM, Chicago, IL, United states), followed by Duncan's multiple comparisons post-hoc test to decide the to the lowest degree significant differences between treatment ways. Differences in treatment means were expressed equally the standard error (±SE), come across Steel et al. [75]. The ANOVA and Duncan tests were both prepare at p < 0.05.

5. Conclusions

In summary, the data presented in this written report demonstrate that J. curcas can be considered to be a more than tolerant crop if the stressors are not combined. However, the combined stresses of salinity and drought (no affair if the salinity level was low or loftier) created more menace in less biomass production, due to decreased tolerance and disturbed physiological mechanisms. Plants treated with 15 dS g⁻¹ NaCl showed a meaning reduction in growth. The MSI and RWC contributed the nigh towards stress tolerance. Thus, it could hands be grown in saline soils of arid to semi-arid regions, admitting prospective piece of work regarding assays in field conditions is imperative for furthering insight into biomass production and quality.

Acknowledgments

The authors are thankful to the staff of the Faisalabad-Bangor Link Biosaline Laboratory and greenhouse who helped to comport the experiment. Nosotros are highly grateful to the Endowment Fund Secretariat, UAF for providing the financial assistance.

Author Contributions

Conceptualization, M.Southward., M.X., and North.S.; methodology, M.S., 1000.A., and Thousand.A.-u.-R.; software, M.A.-u.-R. and A.A.Yard; validation, G.A., A.G., and Due south.A.A.S.; formal analysis, M.-u.-H., and K.M.; investigation, Thousand.Chiliad.A., and G.A.; resources, M.S., and N.S.; data curation, M.-u.-H., and One thousand.A.-u.-R.; writing—original draft training, M.M.A.; writing—review and editing, K.A., A.M., Thousand.M., and S.A.A.S.; visualization, A.A.Chiliad. and K.M.; supervision, Grand.S. and G.X. All authors have read and agreed to the published version of the manuscript.

Funding

This inquiry received no external funding.

Conflicts of Interest

The authors declare that there are no conflicts of involvement either financially or otherwise.

Footnotes

Publisher'south Annotation: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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