Journal of Soil and Plant Biology

ISSN: 2652-2012

Research Article

Efficiency of Different Amendments for the Mitigation of Cadmium Toxicity in Sunflower (Helianthus annuus L.)

Muhammad Ashraf1*, Ahsan Aziz2, Rizwana Kausar3, Sher Muhammad Sahazad4, Muhammad Imtiaz5, Muhammad Asif2, Muhammad Abid1 and Naeem Akhtar6

1Department of Soil Science, Bahauddin Zakariya University, Multan, Pakistan

2Department of Agronomy, College of Agriculture, University of Sargodha, Sargodha, Pakistan

3Soil and Water Testing Laboratory for Research, Sargodha, Punjab, Pakistan

4Department of Soil & Environmental Sciences, College of Agriculture, University of Sargodha, Sargodha, Pakistan

5Soil and Environmental Biotechnology Division, National Institute for Biotechnology and Genetic Engineering, Faisalabad, Pakistan

6Department of Plant Breeding and Genetics, College of Agriculture, University of Sargodha, Sargodha, Pakistan

Received: 28 May 2019

Accepted: 24 June 2019

Version of Record Online: 04 July 2019

Citation

Ashraf M, Aziz A, Kausar R, Sahazad SM, Imtiaz M, et al. (2019) Efficiency of Different Amendments for the Mitigation of Cadmium Toxicity in Sunflower (Helianthus annuus L.). J Soil Plant Biol 2019(1): 73-86.

Correspondence should be addressed to
Muhammad Ashraf, Pakistan

E-mail: mashraf_1972@yahoo.com
DOI: 
10.33513/JSPB/1901-08

Copyright

Copyright © 2019 Muhammad Ashraf et al. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and work is properly cited.

Abstract

Mitigation of metal toxicity by the use of different amendments may be an important strategy for improving the plant growth and yield in metal polluted soils. Present study aimed to evaluate the efficiency of different amendments including Phosphate Rock (PR), Silicon (Si), Farmyard Manure (FYM) and Bacterial Inoculation (BI) either individually or integratedly for the detoxification of Cadmium (Cd) in sunflower (Helianthus annuus L.). Experimental plan consisted of three Cd levels (control, 20 and 40 mg kg-1), two PR levels (control and 5 g kg-1), two Si levels (control and 100 mg Si kg-1 as sodium silicate), two FYM levels (control and 5% w/w of soil), two BI levels (non-inoculated and inoculated) and integrated use of PR+Si+FYM+BI. Results revealed that Cd concentration increased by 14.3 and 16.5 times in roots, 12.0 and 21.6 times in stems, 17.0 and 45.0 times in upper leaves while 21.0 and 34.0 times in lower leaves, and 6.6 and 11.0 times in achenes at Cd-1 and Cd-2, respectively compared with control, with the subsequent reduction in plant growth, yield and physiological characteristics of sunflower. All the four amendments were effective to mitigate the deleterious effects of Cd on sunflower growth, yield and physiological behavior in the order of PR+Si+FYM+BI > Si > BI > PR > FYM. Integrated use of PR+Si+FYM+BI reduced Cd concentration by 77.1 and 83.3% in roots, 76.0 and 82.1% in stems, and 85.4 and 85.9% in achenes, while reduced malondialdehyde by 69.7 and 67.4%, with a corresponding improvement in chlorophyll 51.0 and 79.4%, photosynthetic rate 30.5 and 79.4% while achene yield 65.8 and 76.7% at Cd-1 and Cd-2, respectively compared with respective Cd treatments without amendments. In conclusion, integrated use of different organic and inorganic amendments could be an important strategy to mitigate Cd toxicity in sunflower.

Keywords

Amendments; Bacterial Inoculation; Cadmium; Farmyard Manure; Phosphate Rock; Silicon

Introduction

The buildup of heavy metals in soils resulting from different anthropogenic activities triggered by socio-economic development and urbanization may pose a big challenge for human and animal life, plant growth [1] as well as environmental quality [2]. Among heavy metals, Cadmium (Cd) is the 3rd dangerous element in the world after mercury and lead [3]. Cadmium is known to involve in human health crises in different parts of the world where many people were suffered from various health problems [4]. Cadmium is commercially used in paints, cosmetics, batteries, television screens and lasers. In agricultural soils, Cd mostly enters through pesticides [5] and phosphatic fertilizers [6]. Beyer [7] reported the release of about 4000-13000 tons of Cd per year into the environment as the result of anthropogenic activities. Average Cd concentration in the lithosphere is around 0.098 mg kg-1 [8]. According to He et al., Cd toxicity may possibly occur in most crop plants when total Cd in soil is greater than 8 mg kg-1 or bioavailable Cd is more than 0.001 mg kg-1 or plant Cd concentration reaches 3-30 mg kg-1 [9]. Cadmium is not an essential element but is absorbed by plants in relatively higher amount due to its persistence and mobility in soil. Cadmium accumulation in plant beyond the critical level may interfere with different growth and metabolic processes by disturbing the water absorption by plants [10], nutrient absorption and assimilation [11], synthesis of chlorophyll and efficiency of photosystems [12], respiration [13], gene expression [14], generation of reactive oxygen species [15], enzyme activities and hormonal balance [16]. Plants generally accumulate Cd in their bodies at a level which is usually non-toxic for them, but may harm the animals after feeding on such plants [17]. Cadmium toxicity is generally more pronounced in humans because of its deposition in vital organs. Cadmium deposition in human body at a level greater than 200 mg kg-1 f.w. is considered injurious [18]. Bone demineralization, cancer of lungs, blood, kidneys, testes and liver are the main lethal effects of Cd in humans [19].

Metal immobilization in soil by the use of inorganic and organic amendments might be an important strategy for the metal detoxification. These materials may include Phosphorus (P) [20], Silicon (Si) [21], Calcium (Ca) [22], Sulfur (S) [23], Selenium (Se) [24], Iron (Fe) [25], Proline [26], Farmyard Manure (FYM) [27] and Bacterial Inoculation (BI) [28]. In addition to metal immobilization, these amendments can enhance plant growth and development in metal stress environment by improving plant physiological characteristics such as proline, chlorophyll content, photosynthesis, glutathione synthesis, Relative Water Content (RWC) and enzyme activities, while reducing Malondialdehyde (MDA), electrolyte leakage and Reactive Oxygen Species (ROS) [20,22,26]. Wang et al., reported that adequate P availability in soil interfered with metals and reduced metal mobility, phytoavailability and accumulation by plants through metal complexation, precipitation and adsorption [29]. Bolan et al., suggested that P could mitigate the harmful effects of metals, particularly Cd by reducing its mobility in soil [30]. Chen et al., also reported that metal-phosphates complexes are more stable and relatively insoluble in soil, leading to reduced metal availability to plants [31]. Therefore, application of P-enriched material to metal polluted soils might be efficient to detoxify metals in soil and alleviate their toxic effects on living organisms [32]. Silicon can ameliorate metal toxicity by reducing metal mobility and uptake by plants [33], metal precipitation [34], activation of antioxidant defense system [35], metal complexation and compartmentalization [36], improving photosynthesis [37] and altering gene expression [38].

Bacterial inoculation may also be helpful to mitigate the toxic effects of different metals including Cd [39]. According to Tremaroli et al., metal complexation, metal efflux, changing of metal to relatively less toxic form, resistance to membrane perturbation and production of oxidative stress response are the major mechanisms induced by bacterial inoculation for improving plant tolerance to metal toxicity [40]. Pages et al., also found that changing of metals to non-toxic form, metals complexation and activation of efflux pumps are the major tolerance mechanisms induced by bacteria against metal toxicity [41]. Farmyard manure can improve the productivity of metal polluted soils by improving soil properties [42], metal complexation and precipitation [43], changing metal form [44] and increasing the availability of plant nutrients [45].

Here, a pot experiment is planned to evaluate the role of different amendments including Phosphate Rock (PR), Si, FYM and BI either alone or in combination for mitigating the deleterious effects of Cd on growth, yield and physiological characteristics of sunflower (Helianthus annuus L.).

Materials and Methods

The present study evaluated the efficiency of individual and integrated use of PR, Si, FYM and BI for mitigating the deleterious effects of Cd on growth, yield and physiological characteristics of sunflower (Helianthus annuus L.). The soil used in the experiment was collected from top 20 cm layer of a cultivated field. The soil was air dried, sieved and analyzed for texture [46], organic matter [47], saturation percentage [48], CaCO3 [49], Sodium Adsorption Ratio (SAR), Electrical Conductivity (EC) and pH [50], Cation Exchange Capacity (CEC) [51], total N [52], total P [53], available P [54], extractable K [55], extractable Al, Fe and Mn [56], total Cd [57] and available Cd [58]. Pre-sowing soil analysis is given in table 1.

Soil characteristic Unit Value
Sand % 37.6
Silt % 36.5
Clay % 25.9
Texture   Loamy
Saturation percentage % 30.7
Organic matter % 0.58
Soil pH   7.9
CEC Cmol (+) kg-1 19.8
EC dS m-1 0.59
SAR (mmol L-1)1/2 6.65
CaCO3 % 12.4
Total N % 0.19
Fe mg kg-1 5.54
Al mg kg-1 0.86
Mn mg kg-1 0.26
Total P mg kg-1 176
Available P mg kg-1 6.13
Extractable K mg kg-1 122
Total Cd mg kg-1 0.45
Available Cd mg kg-1 0.06
 

Table 1: Physical and chemical properties of experimental soil.

Experimental plan consisted of three Cd levels [control, Cd-1 (20 mg kg-1) and Cd-2 (40 mg kg-1) as cadmium sulfate], two PR levels (control and 5 g kg-1; Kakul, Abbottabad, Pakistan 34°23′30″ N latitude, 73°28′30″ E longitude, 1791 m altitude ), two Si levels (control and 100 mg Si kg-1 as sodium silicate), two FYM levels (control and 5% w/w), two BI levels (non-inoculated and inoculated) and integrated use of PR+Si+FYM+BI. The treatments were arranged according to completely randomized design and replicated for five times. The selected characteristics of FYM and PR are given in tables 2 and 3, respectively.

Characteristics

Unit

Value

N

%

0.42

P2O5

%

0.19

K2O

%

0.57

Cu

mg kg-1

6.88

Fe

mg kg-1

1147

Zn

mg kg-1

53.10

Mn

mg kg-1

41.65

Cd

mg kg-1

0.24

C:N ratio

-

17.00

Water content

%

64.80

Organic matter

%

13.42

Organic carbon

%

7.14

pH

-

8.4

 Table 2: Chemical composition of farmyard manure used in the experiment.

Characteristics

Unit

Value

Total P

%

12.62

Mg

%

0.29

Ca

%

0.22

Cd

mg kg-1

5.32

Mn

mg kg-1

0.16

Fe

mg kg-1

0.11

Zn

mg kg-1

0.04

Cu

mg kg-1

0.03

Pb

mg kg-1

0.01

 Table 3: Chemical composition of phosphate rock used in the experiment.

Four healthy and uniform seeds of sunflower (cv. Hybrid FH-621) were sown in each earthen pot having 12 kg soil. Amendments were thoroughly mixed in soil before filling the pots, according to treatment plan. For seed inoculation, a pre-isolated bacterial strain Serratia marcescens - SF3 was used, and inoculation was done as described by Shahzad et al. [59]. After germination, two seedlings were maintained in each pot. The uprooted plants were incorporated into respective pots. Recommended dose of nitrogen (52 mg N kg-1 as urea), phosphorus (36 mg P2O5 kg-1 as single superphosphate) and potassium (36 mg K2O kg-1 as potassium sulfate) were applied. The full dose of phosphorus and potassium and one third nitrogen were applied at the time of sowing, and remaining nitrogen was applied in two equal splits, at 30 and 70 days after sowing. Moisture level in pots was maintained at 60% of field capacity on weight loss basis. Relative humidity ranged from 56-85% while total rainfall was 250 mm during the crop growth period. Maximum temperature ranged between 15.2 and 40.6°C while, minimum between 7.6 and 26.8°C. Weeds were controlled by hoeing. At forty days after germination, leaf chlorophyll content was measured by Arnon [60] using spectrophotometer (Shimadzu UV-1600, UK), photosynthetic rate by Photosynthesis meter (CI-340 hand-held Photosynthesis meter), RWC [61], electrolyte leakage [62] and MDA [63]. Forty-five days after germination, one plant from each pot was harvested, washed with distilled water and separated into roots, stems and leaves. The 1-5 leaves from top and bottom of the plant were collected separately as upper and lower leaves, respectively. These plant samples were dried at 70ºC in an oven (EYELA WFO-600ND; Tokyo Rikaikai Co., Ltd., Tokyo, Japan) till constant weight, and ground to 40 mesh. A 0.1 g of ground samples of roots, stems and leaves were digested with di-acid mixture of HNO3 and HClO4 in the ratio of 2:1 (v/v) at 250ºC [64]. Cadmium in roots, stems and leaves was estimated using atomic absorption spectroscopy (Hitachi Polarized Zeeman AAS, Z-8200, Japan). Second plant was grown till maturity and used for recording growth and yield characteristics. After harvesting, ripened achenes were analyzed for Cd concentration by wet digestion as described in previous item.

Bioaccumulation Factor (BF) was calculated in accordance with Abdul and Thomas [65]:

BF = [Cdroots]/[Cdsoil]

Cdroots and Cdsoil are the concentration of Cd in mg kg-1 in sunflower roots and the soil, respectively.

Translocation Factor (TF) was calculated in accordance with Malik et al. [66]:

TF = [Cdshoots]/[Cdroots]

Cdshoots and Cdroots are the concentrations of Cd in mg kg-1 in sunflower shoots and roots, respectively.

Mstat-C was used for data analysis, while Analysis of Variance (ANOVA) for comparing the treatments [67]. Least significant difference test was used to compare the means at p ≤ 0.05.

Results

Cadmium concentration and accumulation

Cadmium concentration in different plant parts was significantly (p ≤ 0.05) influenced by Cd, PR, Si, FYM and BI when applied either individually or integratedly (Table 4). Root Cd concentration increased by 14.3 times at Cd-1 and 16.5 times at Cd-2 compared with control. However, application of different amendments significantly (p ≤ 0.05) reduced root Cd concentration. It was found that root Cd reduced by 34.6 and 49.7% with PR, 71.8 and 77.3% with Si, 54.2 and 35.7% with FYM, 60.1 and 52.7% with BI and 77.1 and 83.3% with PR+Si+FYM+BI at Cd-1 and Cd-2, respectively compared with Cd stressed plants without any amendment. Stem Cd increased by 12 times at Cd-1 and 21.6 times at Cd-2 compared with control. However, stem Cd reduced by 32.0 and 40.5% with PR, 70.6 and 73.4% with Si, 48.9 and 47.6% with FYM, 53.7 and 57.5% with BI and 76.0 and 82.1% with PR+Si+FYM+BI at Cd-1 and Cd-2, respectively compared with Cd stressed plants without any amendment. Leaf Cd increased by 17.0 times in upper leaves and 21.0 times in lower leaves at Cd-1 while 45 times in upper leaves while 34 times in lower leaves at Cd-2 compared with control. However, different amendments interacted with Cd and reduced its transfer from soil to plants. In upper leaves, Cd concentration decreased by 20.0 and 34.9% with PR, 69.0 and 62.4% with Si, 17.7 and 25.0% with FYM, 27.4 and 40.7% with BI, and 85.9 and 74.8% with PR+Si+FYM+BI at Cd-1 and Cd-2, respectively compared with Cd stressed plants without any amendment. In lower leaves, Cd concentration decreased by 15.0 and 49.0% with PR, 69.0 and 67.8% with Si, 28.7 and 45.7% with FYM, 34.8 and 48.9% with BI and 79.0 and 78.1% with PR+Si+FYM+BI at Cd-1 and Cd-2, respectively compared with Cd stressed plants without any amendment. Achene Cd increased by 6.6 times at Cd-1 and 11.0 times at Cd-2 compared with control. Different amendments were significantly (p ≤ 0.05) effective in mitigating Cd toxicity. At Cd-1, achene Cd reduced by 16.3, 67.6, 50.6, 44.9 and 85.4% by PR, Si, FYM, BI and PR+Si+FYM+BI compared with Cd-1 treated plants without any amendment. At Cd-2, achene Cd reduced by 29.4, 75.9, 67.0, 68.1 and 85.9% by PR, Si, FYM, BI and PR+Si+FYM+BI compared with Cd-2 treated plants without any amendment. Cadmium accumulation in shoot increased by 7.9 times at Cd-1 and 11.9 times at Cd-2 compared with control (Table 2). However, Cd accumulation in shoot reduced by 24.7% and 34.07% with PR, 59.6 and 64.1% with Si, 42.6 and 21.4% with FYM, 50.8 and 61.4% with BI and 64.1 and 68.6% with PR+Si+FYM+BI at Cd-1 and Cd-2, respectively compared with Cd treated plants without any amendment. When comparing the Cd concentration in different plant parts, maximum Cd concentration was found in roots followed by leaves, stems and achenes in descending order at both levels of Cd contamination. Among these amendments, Si proved most effective in reducing Cd concentration in plant tissues. However, highest reduction in Cd concentration in plant tissues was found with PR+Si+FYM+BI compared with their individual application.

Treatment

Leaf Cd (mg kg-1)

Stem Cd

(mg kg-1)

Root Cd

(mg kg-1)

Achene Cd

(mg kg-1)

Cd accumulation in shoot

Upper leaf

Lower leaf

Control

0.42g

0.65g

1.23h

2.25f

0.74h

14.76h

Cd-1

7.8e

8.10e

16.50cd

34.55a

5.63d

132.0d

Cd-1+PR

6.24ef

6.88ef

11.22ef

22.60c

4.71de

99.44ef

Cd-1+Si

2.10fg

2.46fg

4.84gh

9.72ef

1.82fg

53.24g

Cd-1+FYM

6.42ef

5.77ef

8.42fg

15.82de

2.78ef

75.70fg

Cd-1+ BI

5.66ef

5.28ef

7.63fg

13.78de

3.10def

64.85fg

Cd-1+PR+Si+FYM+BI

1.10fg

1.70fg

3.95gh

7.90ef

0.82h

47.4g

Cd-2

19.50b

23.20a

27.80a

39.42a

8.95a

190.43a

Cd-2+PR

12.69ed

11.82de

16.52cd

19.80cd

6.32cd

125.55cd

Cd-2+Si

7.32e

7.45e

7.38fg

8.92ef

2.15fg

68.38fg

Cd-2+FYM

14.62cd

12.60d

14.55d

25.32bcd

2.95ef

149.65c

Cd-2+ BI

11.55de

11.85de

11.80e

18.63d

2.84ef

73.39fg

Cd-2+PR+Si+FYM+BI

4.90ef

5.10ef

5.22gh

6.55f

1.26fg

59.76g

Table 4: Cadmium concentration in different parts of sunflower (Helianthus annuus L.) grown in cadmium contaminated soil by applying different amendments.

Values in a column followed by the same letter are not significantly different at P ≤ 0.05. (Control: No cadmium addition; Cd-1: Cadmium @ 20 mg kg-1; Cd-2: Cadmium @ 40 mg kg-1; PR: Phosphate Rock @ 5g kg-1; Si: Silicon @100 mg kg-1; FYM: Farmyard Manure @ 5% w/w of soil; BI: Bacterial Inoculation).

Bioaccumulation and translocation factors

Bioaccumulation factor reduced by 37.5, 73.3, 53.9, 58.2 and 78.8 at Cd-1 while 51.0, 78.1, 34.4, 53.1 and 84.4% at Cd-2 with PR, Si, FYM, BI and PR+Si+FYM+BI, respectively compared with respective Cd treatments without any amendment. TFstem/root ranged from 0.47-0.53 at Cd-1 while 0.56-0.81 at Cd-2, TFupper leaf/root 0.14-0.41 at Cd-1 and 0.55-0.81 at Cd-2, TFlower leaf/root 0.22-0.38 at Cd-1 and 0.64-0.84 at Cd-2, while TFachene/root 0.11-0.21 at Cd-1 and 0.11-0.30 at Cd-2 with the addition of different amendments. For BF, maximum reduction was found with PR+Si+FYM+BI followed by Si, Bi, PR and FYM in descending order. However, in the case of TF, no consistent trend was observed (Table 5).

Treatment

BF

TFstem

TFleaf

TFachene

Upper leaf

Lower leaf

Cd-1

1.65a

0.46fg

0.21g

0.23g

0.16

Cd-1+PR

1.03d

0.47fg

0.27f

0.29f

0.19de

Cd-1+Si

0.44g

0.48f

0.21g

0.26fg

0.17e

Cd-1+FYM

0.76e

0.51f

0.40e

0.37ef

0.16ef

Cd-1+ BI

0.69ef

0.53ef

0.41e

0.38ef

0.21d

Cd-1+PR+Si+FYM+BI

0.35gh

0.48f

0.14gh

0.22g

0.11g

Cd-2

0.96d

0.69c

0.48d

0.60c

0.21d

Cd-2+PR

0.47fg

0.81a

0.63bc

0.58cd

0.30a

Cd-2+Si

0.21h

0.80a

0.81a

0.84a

0.23c

Cd-2+FYM

0.63f

0.56e

0.55cd

0.48de

0.11g

Cd-2+ BI

0.45g

0.62d

0.60c

0.64c

0.14f

Cd-2+PR+Si+FYM+BI

0.15h

0.78a

0.74ab

0.79b

0.19de

Table 5: Bioaccumulation and translocation factors of sunflower (Helianthus annuus L.) grown in cadmium contaminated soil by applying different amendments.

Values in a column followed by the same letter are not significantly different at p ≤ 0.05. (Control: No cadmium addition; Cd-1: Cadmium @ 20 mg kg-1; Cd-2: Cadmium @ 40 mg kg-1; PR: Phosphate Rock @ 5g kg-1; Si: Silicon @100 mg kg-1; FYM: Farmyard Manure @ 5% w/w of soil; BI: Bacterial Inoculation).

Growth and yield characteristics

Maximum plant height was found in control which reduced by 25% and 36.64% at Cd-1 and Cd-2, respectively compared with control (Figure 1). Application of different amendments alleviated the deleterious effects of Cd and markedly improved the plant height. At Cd-1, plant height improved by 10.75% with PR, 25.68% with Si, 2.7% with FYM, 23.72% with BI and 29.23% with PR+Si+FYM+BI compared with Cd-1 treated plants without any amendment. At Cd-2, plant height improved by 16.39% with PR, 35.81% with Si, 19.11% with FYM, 33.40% with BI and 46.27% with PR+Si+FYM+BI compared with Cd-2 treated plants without any amendment. The stem girth reduced by 23.8% and 31.7% at Cd-1 and Cd-2, respectively compared with control (Figure 2). However, stem girth increased by 17.1% with PR, 21.4% with Si, 22.0% with FYM, 21.4% with BI and 26.4% with PR+Si+FYM+BI compared with Cd-1 treated plants without any amendment. At Cd-2, stem girth improved by 21.9% with PR, 27.4% with Si, 31.5% with FYM, 32.8% with BI and 37.6% with PR+Si+FYM+BI compared with Cd-2 treated plants without any amendment. Head diameter reduced by 37.7% and 46.5% at Cd-1 and Cd-2, respectively compared with control (Figure 3). Application of different amendments mitigated the deleterious effects of Cd and improved head diameter. At Cd-1, head diameter improved by 25.3% with PR, 42.2% with Si, 32.4% with FYM, 35.5% with BI and 50.0% with PR+Si+FYM+BI compared with Cd-1 treated plants without any amendment. At Cd-2, head diameter improved by 34.7% with PR, 52.8% with Si, 51.5% with FYM, 54.1% with BI and 64.5% with PR+Si+FYM+BI compared with Cd-2 treated plants without any amendment. Maximum head weight of 22.65 g was found in control which reduced by 28.5% and 43.3% at Cd-1 and Cd-2, respectively compared with control (Figure 4). However, head weight improved with the use of different amendments, maximum improvement of 28.7% at Cd-1 and 54.1% at Cd-2 with PR+Si+FYM+BI compared with respective Cd treatment without any amendment. Maximum 100-achene weight of 4.1 g was found in control which reduced by 46.3% and 55.2% at Cd-1 and Cd-2, respectively compared with control (Figure 5). However, 100-achene weight improved by 34.1% with PR, 43.2% with Si, 35.4% with FYM, 38.6% with BI and 65.0% with PR+Si+FYM+BI at Cd-1 compared with Cd-1 treated plants without any amendment. At Cd-2, 100-achene weight improved by 42.9% with PR, 60.8% with Si, 55.4% with FYM, 63.6% with BI and 75% with PR+Si+FYM+BI compared with Cd-2 treated plants without any amendment. Maximum achene yield of 18.20 g plant-1 was found in control treatment which reduced by 43.8% and 52.7% at Cd-1 and Cd-2, respectively compared with control (Figure 6). However, achene yield of sunflower improved by different amendments at both levels of Cd contamination. Maximum improvement in achene yield was 65.8% with PR+Si+FYM+BI followed by 50.7% (Si), 47.7% (BI), 43.0% (FYM) and 35.5% (PR) in descending order at Cd-1 compared with Cd-1 treated plants without any amendment. At Cd-2, achene yield improved by 25.6% with PR, 65.1% with Si, 57.0% with FYM, 47.1% with BI and 76.7% with PR+Si+FYM+BI compared with Cd-2 treated plants without any amendment.

Efficiency of Different Amendments for Ameliorating Cadmium Toxicity in Sunflower

Figure 1: Plant height of sunflower (Helianthus annuus L.) grown in cadmium contaminated soil by applying different amendments. (Control: No cadmium addition; Cd-1: Cadmium @ 20 mg kg-1; Cd-2: Cadmium @ 40 mg kg-1; PR: Phosphate Rock @ 5g kg-1; Si: Silicon @100 mg kg-1; FYM: Farmyard Manure @ 5% w/w of soil; BI: Bacterial Inoculation).

Efficiency of Different Amendments for Ameliorating Cadmium Toxicity in Sunflower

Figure 2: Stem girth of sunflower (Helianthus annuus L.) grown in cadmium contaminated soil by applying different amendments. (Control: No cadmium addition; Cd-1: Cadmium @ 20 mg kg-1; Cd-2: Cadmium @ 40 mg kg-1; PR: Phosphate Rock @ 5g kg-1; Si: Silicon @100 mg kg-1; FYM: Farmyard Manure @ 5% w/w of soil; BI: Bacterial Inoculation).

Efficiency of Different Amendments for the Mitigation of Cadmium Toxicity in Sunflower

Figure 3: Head diameter of sunflower (Helianthus annuus L.) grown in cadmium contaminated soil by applying different amendments. (Control: No cadmium addition; Cd-1: Cadmium @ 20 mg kg-1; Cd-2: Cadmium @ 40 mg kg-1; PR: Phosphate Rock @ 5g kg-1; Si: Silicon @100 mg kg-1; FYM: Farmyard Manure @ 5% w/w of soil; BI: Bacterial Inoculation).

Efficiency of Different Amendments for the Mitigation of Cadmium Toxicity in Sunflower

Figure 4: Head weight of sunflower (Helianthus annuus L.) grown in cadmium contaminated soil by applying different amendments. (Control: No cadmium addition; Cd-1: Cadmium @ 20 mg kg-1; Cd-2: Cadmium @ 40 mg kg-1; PR: Phosphate rock @ 5g kg-1; Si: Silicon @100 mg kg-1; FYM: Farmyard Manure @ 5% w/w of soil; BI: Bacterial Inoculation).

Efficiency of Different Amendments for the Mitigation of Cadmium Toxicity in Sunflower

Figure 5: 100-achene weight of sunflower (Helianthus annuus L.) grown in cadmium contaminated soil by applying different amendments. (Control: No cadmium addition; Cd-1: Cadmium @ 20 mg kg-1; Cd-2: Cadmium @ 40 mg kg-1; PR: Phosphate Rock @ 5g kg-1; Si: Silicon @100 mg kg-1; FYM: Farmyard Manure @ 5% w/w of soil; BI: Bacterial Inoculation).

Efficiency of Different Amendments for the Mitigation of Cadmium Toxicity in Sunflower

Figure 6: Achene yield plant-1 of sunflower (Helianthus annuus L.) grown in cadmium contaminated soil by applying different amendments. (Control: No cadmium addition; Cd-1: Cadmium @ 20 mg kg-1; Cd-2: Cadmium @ 40 mg kg-1; PR: Phosphate Rock @ 5g kg-1; Si: Silicon @100 mg kg-1; FYM: Farmyard Manure @ 5% w/w of soil; BI: Bacterial Inoculation).

Physiological characteristics

Physiological characteristics of sunflower in terms of chlorophyll content, photosynthetic rate, RWC, electrolyte leakage and MDA concentration were significantly (p ≤ 0.05) influenced by Cd, PR, Si, FYM and BI (Table 6). Chlorophyll content declined by 37.2% at Cd-1 and 53.2% at Cd-2 compared with control. However, application of different amendments significantly (p ≤ 0.05) improved chlorophyll content. Results revealed that chlorophyll content improved by 31.6 and 61.6% with PR, 45.9 and 74.0% with Si, 17.3 and 43.8% with FYM, 39.8 and 53.4% with BI, and 51.0 and 79.4% with PR+Si+FYM+BI at Cd-1 and Cd-2, respectively compared with Cd stressed plants without any amendment. Photosynthetic rate declined by 29.2% at Cd-1 and 57.5% at Cd-2 compared with control. However, photosynthetic rate improved by 25.1 and 49.4% with PR, 26.4 and 66.2% with Si, 9.6 and 39.1% with FYM, 16.8 and 58.7% with BI, and 30.5 and 79.4% with PR+Si+FYM+BI at Cd-1 and Cd-2, respectively compared with Cd stressed plants without any amendment. RWC reduced by 14.9 and 22.3% at Cd-1 and Cd-2, respectively compared with control. However, RWC improved by 5.8 and 7.3% with PR, 7.7 and 11.6% with Si, 4.1 and 6.2% with FYM, 8.4 and 10.7% with BI, and 8.6 and 15.3% with PR+Si+FYM+BI at Cd-1 and Cd-2, respectively compared with Cd stressed plants without any amendment. In contrast, electrolyte leakage increased by 23.5 at Cd-1 and 32.4% at Cd-2 compared with control. However, electrolyte leakage reduced by 13.0 and 13.6% with PR, 17.3 and 17.1% with Si, 10.0 and 10.3% with FYM, 13.5 and 16.1% with BI, and 14.9 and 16.2% with PR+Si+FYM+BI at Cd-1 and Cd-2, respectively compared with Cd stressed plants without any amendment. MDA concentration increased by 3.5 times at Cd-1 and 4.6 times at Cd-2 compared with control. Different amendments were significantly (p ≤ 0.05) effective in mitigating oxidative damage as evidenced by reduced MDA. It was found that MDA concentration reduced by 57.5, 66.2, 45.2, 49.8 and 69.7% by PR, Si, FYM, BI and PR+Si+FYM+BI compared with Cd-1 treated plants without any amendment. At Cd-2, MDA reduced by 52.1, 61.6, 40.6, 52.9 and 67.4% by PR, Si, FYM, BI and PR+Si+FYM+BI compared with Cd-2 treated plants without any amendment.

Treatment

Chlorophyll content

(mg kg-1 f.w.)

Photosynthetic rate

mol CO2 m-2 s-1)

RWC (%)

Electrolyte leakage (%)

MDA

(µmol g-1 FW)

Control

1.56a

14.62a

89.10a

66.70h

11.92fg

Cd-1

0.98de

10.36d

75.80ef

82.36bc

53.64b

Cd-1+PR

1.29bc

12.96b

80.22d

71.65f

22.80e

Cd-1+Si

1.43ab

13.10b

81.64cd

68.10gh

18.10ef

Cd-1+FYM

1.15cd

11.36c

78.94de

74.12ef

29.40de

Cd-1+ BI

1.37b

12.10bc

82.20cd

71.20fg

26.90e

Cd-1+PR+

Si+FYM+BI

1.48ab

13.52ab

82.36cd

70.12fg

16.22f

Cd-2

0.73f

6.21fg

69.22gh

88.29a

67.29a

Cd-2+PR

1.18c

9.28de

74.30f

76.24de

32.20d

Cd-2+Si

1.27bc

10.32d

77.28e

73.18ef

25.82e

Cd-2+FYM

1.05d

8.64e

73.52f

79.14cd

39.98cd

Cd-2+ BI

1.12cd

9.86d

76.68e

74.10ef

31.68de

Cd-2+PR+

Si+FYM+BI

1.31bc

11.14cd

79.80d

73.95ef

21.90ef

 Table 6: Physiological characteristics of sunflower (Helianthus annuus L.) grown in cadmium contaminated soil by applying different amendments.

Values in a column followed by the same letter are not significantly different at p ≤ 0.05. (Control: No cadmium addition; Cd-1: Cadmium @ 20 mg kg-1; Cd-2: Cadmium @ 40 mg kg-1; PR: Phosphate Rock @ 5g kg-1; Si: Silicon @100 mg kg-1; FYM: Farmyard Manure @ 5% w/w of soil; BI: Bacterial Inoculation).

Discussion

Cadmium buildup in the environment as the result of natural and anthropogenic activities leads to the contamination of food chain and has become an emerging threat to human health. Among different strategies used to minimize the deleterious effects of Cd on plant growth and development, its immobilization in soil by the use of different amendments may be an efficient, economically viable and environment friendly approach. In present research, various amendments including PR, Si, FYM, BI and their integrated use were evaluated and found that PR+Si+FYM+BI showed supremacy followed by Si, BI, FYM and PR in descending order to reduce Cd concentration in different plant parts. Hamid et al., reported that different organic and inorganic amendments could immobilize metals in soil through adsorption, precipitation, complexation or ion exchange, reducing metal mobility in soil and transfer to plants [68]. Ahumada et al., reported that due to high cation exchange capacity, organic matter made complexes with metals and reduced its movement to plants [69]. Paul and Chaney, found that integrated use of organic and inorganic amendments were more effective in mitigating Cd toxicity compared with their individual application [70]. Hamid et al., also compared the individual and combined application of organic and inorganic amendments to mitigate Cd toxicity in rice-wheat system, and found relatively higher reduction in Cd uptake by plants in case combined application [71]. Wang et al., reported P-induced a marked reduction in metal accumulation by plants via increased metal adsorption, precipitation and complexation [29]. Abd Allah et al., reported that sunflower plants grown in Cd treated soil accumulated more Cd but inoculation with arbuscular mycorrhizal fungi significantly reduced Cd accumulation in plants [72]. Babu and Nagabovanalli, reported a significant reduction in Cd uptake by rice plants grown in Cd contaminated soil when amended with Si compared with Cd treated plants without Si [73]. When comparing the Cd concentration in different plant tissues, maximum retention in roots was attributed to its direct contact with Cd contaminated growth medium. Silva et al., also found the highest Cd in roots of Cassia alata treated with Cd [74].

A marked reduction in BF with different amendments indicated their potential to immobilize Cd in soil and reduced its transfer from soil to plant roots. Si either alone or in combination with other amendments caused highest reduction in BF. Gu et al., reported that Si-enriched amendments could have great potential to reduce metal uptake by plants [75]. However, no amendment could greatly reduce metal translocation from roots to aerial plant parts. This was contrary to earlier studies which reported a marked reduction in metal movement from roots to aerial parts [76]. Cadmium-induced reduction in plant growth and yield characteristics of sunflower in terms of plant height, stem girth, head diameter, head weight, 100-achene weight and achene yield was attributed to a marked decline in physiological attributes such as chlorophyll content, photosynthesis, plant water status while increase in electrolyte leakage and MDA concentration. Mohamed et al., demonstrated that Cd concentration in plant beyond the threshold level interfered with metabolic and physiological processes, leading to a decline in plant growth and development [77]. Piracha et al., also found a great alteration in physiological behavior of sunflower in arsenic-stressed environment due to arsenic effects on root structure, chlorophyll synthesis, photosynthetic apparatus and metabolic activities [78]. However, application of different amendments reversed the damaging effects of Cd on physiological characteristics and improved plant growth and yield. The comparison of the individual effect of different amendments to mitigate Cd toxicity revealed the supremacy of Si over others. Alleviative effects of Si against Cd toxicity might be attributed to metal complexation, regulation of gene expression, scavenging of ROS, improved plant water status, metal compartmentation, changing metal structure, change in pH, improved nutrient use efficiency, and apoplastic barrier [33,35]. Likewise, Haferburg and Kothe, reported that plant associated microbes could protect plants against metal toxicity by complexing metals in soil or plant roots, compartmentation and dilution effect [79]. Ahmad et al., reported that bacterial inoculation could protect plants against Cd toxicity by decreasing electrolyte leakage and MDA while improving plant water status and photosynthetic rate [80]. However, maximum improvement in physiological characteristics, plant growth and yield with integrated use of PR, Si, FYM and BI might be attributed to higher decline in Cd uptake by plants. Hamid et al., reported that combined application of organic and inorganic amendments had higher potential to ameliorate metal toxicity in rice-wheat system [71].

Conclusion

The reduction in growth and yield attributes of sunflower at both levels of Cd contamination was attributed to increased Cd accumulation in plant tissues which increased electrolyte leakage and MDA while decreased plant water status, chlorophyll content and photosynthesis. Maximum Cd retention was found in roots followed by leaves, stems and achenes in descending order. All the tested amendments were effective to reduce Cd accumulation by plants and mitigate the deleterious effects of Cd on plant growth, yield and physiological characteristics of sunflower, with ranking as PR+Si+FYM+BI > Si > BI > PR > FYM. However, these amendments could not markedly reduce Cd transfer from roots to aerial plant parts. Reduction in Cd accumulation in plant tissues, electrolyte leakage, MDA while improvement in chlorophyll content and photosynthesis could be the major mechanisms induced by organic and inorganic amendments for improving sunflower adaptation to Cd contaminated soils.

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