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Morpho-physiological Response of Gliricidia Sepium to Seawater-induced Salt Stress

M. A. Rahman
Department of Agroforestry & Environment, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur 1706, Bangladesh

A. K. Das
Department of Agroforestry & Environment, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur 1706, Bangladesh

S. R. Saha
Department of Agroforestry & Environment, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur 1706, Bangladesh

M. M. Uddin
Department of Crop Botany, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur 1706, Bangladesh

M. M. Rahman
Department of Agroforestry & Environment, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur 1706, Bangladesh

Abstract/ Executive Summary:

Soil degradation due to the contamination of excessive saline water has been threatening soil health vis a vis plant productivity worldwide. Gliricidia sepium, a fertilizer tree, has come into limelight in recent decades in Bangladesh due to its potency in improving soil fertility. However, study on its suitability in coastal areas alongside identifying the salt-endurance limit is still lacking. Therefore, morpho-physiological attributes of G. sepium under seawater-induced different levels of salt stress were analyzed in a pot experiment from March to May 2018 to gain an insight into its salt-adaptive mechanisms. Results revealed that seawater-induced salinity negatively affected the growth-related attributes, such as plant height, fresh weight of shoots, dry weights of shoots and roots, and leaf area. The reduction of growth was coincided with reductions in photosynthetic pigments and relative water content. Interestingly, salt tolerance index was not decreased in parallel with increasing dosages of seawater, indicating the salt tolerance capacity of G. sepium. Furthermore, enhanced accumulation of proline increased the osmoprotective capacity of G. sepium in order to overcome the salt-induced osmotic stress. The results of the present study concluded that G. sepium might be suitable for growing in the salt prone areas ranging 20 – 40 dSm^-1.

Keywords: Fertilizer, Growth parameters, Malondialdehyde, Proline, Photosynthetic pigments, Soil salinity, Salt tolerance index

Location: Department of Agroforestry and Environment, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur

Start Date: 00-03-2018

End Date: 00-05-2018

Program Area: Farming System

Commodity: Gliricidia

Objectives:

The present study was aimed to determine the salt tolerance limits as well as appraise the effect of seawater induced salt stress on the morpho-physiological features of G. sepium plants.

Methodology:

Study location, plant materials and growth conditions- A pot experiment was conducted at the research field of the Department of Agroforestry and Environment, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Bangladesh (24° 09` N; 90° 26` E) for a period of 3 months (March to May 2018). The study site is 8.2 m above the sea level and characterized by a sub- tropical climate with hot summer and mild winter. The minimum and maximum temperatures of the research area were fluctuated between 17 to 23°C and 28 to 39°C, respectively, during the experimental period. Healthy G. sepium seeds were surface-sterilized in 5% (v/v) sodium hypochlorite solution containing 0.2% (v/v) Tween-20 for 30 min followed by five times washed with distilled water (dH₂O). Subsequently, the surface- sterilized seeds were incubated in dH₂O at 26°C in the dark for 24 h. The seeds were then transferred to small polythene bags containing 200 g of soils. Twenty-four days old G. sepium seedlings of uniform size were transplanted into each pot (23 cm in height and 28 cm in diameter). The pots were previously filled with sandy loam soil mixture that was prepared by mixing oven-dried soil and cow dung at the ratio of 4:1 (in weight basis). However, the soils used was also treated with formaldehyde (2.5 mL added in 100 mL of water) via spraying at the rate of 3.6-4.2 L of solution per m³ of soils to curtail the probability of developing soil-borne diseases. Subsequently, mix thoroughly and kept the soil covered for 24 h. After removing odor of formaldehyde, the soils were used to fill the pots. In addition to cow dung, one liter of liquid fertilizer containing 1% of-urea, triple super phosphate and potassium sulphate was applied once to each pot on 20 days old-transplanted seedlings. Treatments composition- After transplanting the seedlings into pots, the plants were irrigated with tap water for 6 days for adaptation before being exposed to seawater- induced salt stress. Seawater collected from southern coastal area (Cox’s Bazar sea beach) of Bangladesh (electrical conductivity of 69.6 dS m^- ¹, and Na⁺, K⁺, Ca²⁺ and Mg²⁺ concentrations of 578.70, 20.38, 19.90 and 66.08 mmol L^-1, respectively) was diluted with tap water to formulate different levels of salt treatments (20, 40 and 60 dS m^-1) and the tap water was used as control treatment. For imposing salt stress, the uniformly grown plants were irrigated with the diluted seawater (300 mL) every day for a period of 90 days. The control plants were irrigated with tap water. Root and shoot samples were harvested at 90^th days of salt treatments for determining various morpho-physiological and biochemical parameters of G. sepium. Determination of growth parameters- Plant height and leaf area were measured with a linear scale and following the equation of Carleton and Foote (1965), respectively. For determining biomasses of shoots and roots, plants were carefully uprooted at day 90^th of salt stress imposition and washed with distilled water to remove adherent soil. Fresh weights (FWs) of shoots, dry weights (DWs) of shoots and roots were measured following the method described by Mostofa et al., (2015). Salt tolerance index (STI) was calculated following the formula of Rahman et al. (2017). Determination of leaf relative water content, chlorophyll contents- The fresh, turgid and dry weights of the leaves were used to determine leaf relative water content (RWC) according to the formula described by Rahman et al., (2017). Chlorophyll (Chl) and carotenoids (Car) contents of freshly collected leaf samples were determined using 80% acetone as previously described by Misratia et al., (2013). Contents of proline- The levels of proline (Pro) in shoots were determined following the methods described by Bates et al., (1973). Electrolyte leakage and lipid peroxidation- Electrolyte leakage (EL) and the content of lipid peroxidation product [malondialdehyde (MDA)] in shoots were determined according to Lutts et al., (1996) and Tayebimeigooni et al., (2012), respectively. Statistical analysis- The data were subjected to a one-way analysis of variance (ANOVA), following randomized block design and different letters indicate significant differences among treatments at P<0.05, according to least significant difference test (LSD) using Statistix 10 package. Data presented are means ± standard errors (SEs) of three biological replications (n=3) for each treatment.

Source of Information: The Agriculturists 2019; 17(1-2) 66-75

Article Link (Online Journal): DOI: https://doi.org/10.3329/agric.v17i1-2.44697

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Our findings concluded that exposure of G. sepium plants to seawater-induced salinity adversely affects the performance of the whole plant, particularly by inhibiting growth and development. Nevertheless, the adapted stress tolerance mechanisms of G. sepium at a salinity range of 20 – 40 dsm^-1 could be attributed to (1) maintained higher dry biomass, (2) maintained optimum water status in terms of elevated RWC, (3) abundance of primary photosynthetic pigment Chl a over accessory pigment Chl b to sustain favourable photosynthetic rate, and (4) accumulation of osmolyte like Pro to maintain osmoprotectant capacity under salt-stress. Nevertheless, we postulated that established plants of this species might be tolerant to salt stress higher than the level used in this study because seedlings are more sensitive to high soluble salt levels than established plants.

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