Effect Of Salinity On Growth Of Plant

Plants and germinating seeds both get their share of salt and other mineral from the water and the soil around them. Plants endure a set level of salinity to germinate which is what we will be finding out as which is the optimum level for them to germinate. Soil salinity cause severe problems in the agriculture sector worldwide. And different levels on salinity affect plants in different ways and hinder their growth in different ways.

Like the 2 major stress under salt conditions for plants are ionic and osmotic. On land salinity caused by drought are the most severe ones and in water the water bodies close to seawater face the highest salinity. Seedlings being the most  in respiration cause of water stress and reduction in photosynthesis. Level salinity around the globe can cause destruction of local ecosystems. As salinity can cause issues to young plants like imbalance in osmotic potential leading to poor water uptake, or by toxic ions on the embryo viability, which reduce shoot growth. As the salt effects cell division and enlargement in the growing point. Research conducted on which plant seeds land or water are more tolerable to salt is still fresh, though relative importance of osmotic and ionic effects on early halophyte growth is still incomplete as the seeds acquired are usually pre- germinated under non saline conditions.  Thus, its tuff to say wheatear halophytes are more tolerant to salty conditions as it totally depends on the species.

In our present study, I will use NaCl as experimental salt and the young seedlings after measuring the shoot length will be harvested keeping in mind ethical issues.

In my childhood days, I used to visit the garden near my house with my grandparents. This has become a habit which I tend to follow almost every time in their absence as well. As the Coronavirus hit the world, the daily routine of every human being got disrupted thereby forcing us to self-quarantine to meet the needs of the situation. After few months, when the restrictions were lifted to a certain level, I visited the nearby garden and realised that some plants died due to air sprays that were used to purify the surrounding air of any germ particles. It broke my heart when I realised that once a deep green leaf has turned into pale yellow. It made me think that whether the air purifying sprays  Which contained sodium hypochlorite affected the salinity of the soil or not. Now we all know that plants requires sodium which acts a micronutrient for its growth. So, the plants must grow to a considerable height but in this case they al dried up, developed a pale-yellow colouration and eventually died. Then it made me think that whether an increase in the percentage of soil salinity inhibits the growth of plant or not and therefore I decided to carry on with this investigation.

How does the growth of of moong beans (vigna radiata), measured in terms of maximum shoot height in cm depends on the percentage composition of the salt solution in which it is germinated and grown?

Sodium mainly acts a micronutrient in plant growth and also affects the cell division and hormonal discharge of the plant body. Traces of sodium are very much essential for the plant growth. Halophytes are plants that mainly prefer soil having high content of sodium chloride for their growth. Water also plays an important role in plant growth. It affects the turgidity of the plant and due to the turgor pressure and cell enlargement it affects the plant growth. All the important nutrients that are beneficial for the plant growth are mainly provided by the water intake by the plant. Dissolved sugar and other nutrients are transported by the water. plants require an optimum level of saline soil for the plant growth. Salinity affects the osmotic pressure around the root hair cells which indirectly affects the water uptake of the plant resulting which if not executed properly will lead to the dehydration of the plant. Thus, soil salinity plays a vital role in the growth of a plant.

Moong beans were chosen for this experiment as they are easily available and cost-effective. The seeds of moong beans do not require any particular temperature or atmospheric conditions for its growth. The growth happens naturally under toom conditions and makes the experiment feasible.

6 petri dishes were taken. 7 seeds of moong beans plant were taken in each petri dish. For the control observation, the petri dish was filled with tap water and for the other petri dishes, salt solution was used where the salt concentration varied from 1% to 5%. The seeds were allowed to germinate by keeping them under room temperature and near a source of light (preferably sunlight) and the vertical shoot height was measured using a thread for a period of 7 days.

In the article “Effects of salinity and sodicity on plant growth” published in the journal “Annual review of Phytopathology”, it was concluded that soil salinity affects the pH of the soil and therefore has a negative impact on the plant growth. The correlation constant was found to be -0.0124 further suggesting a negative impact of the soil salinity in the plant growth.

The maximum shoot height (in cm) does not depend on the percentage concentration of the salt solution in which it is grown. In case, any correlation is found that is because of experimental errors or random outcomes.

The maximum shoot height (in cm) does depends on the percentage concentration of the salt solution in which it is grown.

A) Preparation of NaCl salt solution (1% NaCl salt solution)

• 1.00 gm of sodium chloride crystals were taken by measuring it with a mass balance in a beaker.
• 100 gm of tap water was measured by a measuring cylinder and added to the beaker.
• The beaker was shaken and allowed to rest for some time.
• The same procedure was repeated for 2.00%, 3.00%, 4.00% and 5.00% NaCl solutions using 2.00 g, 3.00 g, 4.00 g and 5.00 g salt.

B) Preparation of the seeds for the experiment:

• 20 cc of the salt solution prepared was transferred to the petri dish by using a graduated pipette.
• 7 moong beans seeds were kept in the petri dish.
• The petri dish was kept near the window.
• After 24 hours the height of the germinating plant was measured using a thread and ruler.
• This process was continued for the next seven days.
• The same process was repeated in case of other concentrations of salt solution (2.00,3.00,4.00,5.00 % of NaCl solution).
• For control, (0.00% salt solution), tap water was used.

All ethical issues were kept in mind, and no solutions above 5% were taken to avoid serious damage to the plants. Solution was added to the cotton and not the soil to prevent contamination of the nearby plants.

• Safety gloves and safety masks were used.
• Any sort of edible items were not allowed inside the laboratory.
• The work-station was kept clean and organized.

Sample calculation

Mean =\(\frac{(0.80+0.81+0.69+0.80+0.81+0.80+0.69)}{7}\)= 0.77

Standard deviation =

\(\frac{(0.77-0.80)^2+(0.77-0.81)^2+(0.77-0.69)^2+(0.77-0.80)^2+(0.77-0.81)^2+(0.77-0.80)^2+(0.77-0.69)^2}{7}\)=0.05

The above graph depicts the comparison of daily measurement of average shoot height in cm against % of concentration of salt solution. The graph drawn above is a scattered plot which has the mean shoot height in ± 0.05 cm in the Y-axis and number of days in the X-axis. This graph is indicating how the shoot height of the plant is changing as the number of days are increasing. It is clearly evident from the graph that irrespective of the percentage composition of the salt solution that has been used, the mean shoot height is increasing as the number of days are increasing. So more the number of days the plant is allowed to grow, the shoot height is also more. However, it is also clearly visible that the mean shoot height for the control i.e., 0.00% of salt concentration. All the experimental data values in the graph are following a linear trendline and the equation of the linear trendline has also been displayed in the graph. The gradient of the trendline will indicate how fast is the growth of the shoot height with respect to days. The gradients of the straight lines are compared and it can be further concluded that the gradient is maximum for 0.00% salt concentration which is 0.2657 and minimum for 5.00% salt concentration which is 0.1714. Thus, it can also be claimed that as the percentage composition of the salt in the solution is increasing, the increase in the mean shoot height with respect to the number of days happening at a slower rate. Thus, we can conclude that the mean shoot height increases with the number of days for all the cases. However, the increase is maximum in case of control which is 0.00% of salt solution and minimum in case of 5.00% of salt solution.

Sample calculation

For 1.00 %,

percentage decrease = \(\frac{Value\ for\ control \ (0.00\ \%)-Value\ at 1.00\ \% }{Value\ for \ control \ (0.00\ \%)}\)× 100

=\(\frac{2.23-1.83}{2.23}\)× 100=17.94

The graph plotted above (Graph 2) is showing how the maximum shoot height changes with the percentage composition of the salt solution in which the seeds are grown. The maximum shoot height in cm is plotted along the Y-axis as it is the dependent variable while the percentage composition of the salt solution is plotted along the X- axis as it is the independent variable. The graph clearly shows as the percentage composition of the salt solution increases from 0.00% to 5.00%, the maximum shoot height of the plant is decreasing from 2.23 ± 0.05 cm to 1.20 ± 0.05cm. This clearly shows as the percentage composition of the salt solution is increasing, the maximum shoot height is continuously decreasing. The value of R² is also displayed in the graph that also shows there is correlation between the two variables and the correlation is negative in nature. The data follows a linear trendline.

The equation of the trendline:

y=-0.196x + 2.0767

y represents the maximum shoot height achieved by the plant and x represents the percentage of salt solution used. The graph allows us to conclude that the salt solution or increase in the number in the percentage of salt solution has a negative effect on the mean height achieved by the plant.

A Pearson correlation test was carried out to understand the correlation between the maximum shoot height achieved and percentage of the salt solution used. The formula used is stated below:

\(r=\frac{\sum(x_i-\underline{x})(y_i-\underline{y})}{\sqrt{\sum(x_i-\underline{x})^2(y_i-\underline{y})^2}}\)

\(r=\frac{7.710×(-0.04)}{\sqrt{12.1323×2438}}\)=-0.1793

The value of the Pearson Correlation Constant is -0.1793 which is close to -1 i.e., a negative value and therefore indicates that the correlation between the maximum shoot height and the percentage composition of the salt solution is negative in nature and therefore concludes that increase in the salt concentration has a negative impact on the maximum shoot height.

The graphs plotted above (Graph 1 and graph 2) indicates that the increase in the percentage composition of the salt solution has a negative impact on the growth of the plant. To understand the scientific justification, we need to focus on the mechanism of how root hair cells absorb water from the soil. The root hair cells absorb water from the soil by a process known as osmosis. Osmosis is an example of active transport and it always happens along the concentration gradient across a semipermeable membrane i.e., here from soil to the root hair cells.

The water molecules travel across a semipermeable membrane from a region of higher concentration to lower concentration of solvent molecules. As the percentage of salt in the solution increases, the solution becomes more concentrated and the osmotic pressure in the water layer of the soil decreases which makes the water in the soil hypotonic as compared to water within the root hair cells. This causes water from the root hair cells to travel across the semipermeable membrane and come into soil solution. This makes the cell rigid in nature and loses its water content which is an inhibitory factor for the growth of the plant. Moreover, increase in the salt concentration reverses the direction of water flow from the soil to the root hair cells to root hair cells to the soil layer along the concentration gradient. This not only reduces the water content of the plant but it also decreases the amount of nutrients
that the plant extracts from the soil. Both of these factors combined inhibits the growth of the plant.

How does the maximum shoot height in cm of moong beans (vigna radiata) depends on the percentage composition of the salt solution in which it is germinating and grown?

• The percentage composition of the salt solution has a negative impact on the maximum shoot height of the plant.
• As the percentage concentration of the salt solution increases from 0.00% to 5.00%, the maximum shoot height decreases from 2.23 ± 0.05 cm to 1.20 ± 0.05 cm.
• As the day progressed, the maximum shoot height increased but the rate of increment varied as the concentration was changed from 1.00% to 5.00% of NaCl solution.
• The graph plotted (percentage composition of NaCl vs maximum shoot height) indicated that as the percentage composition of the salt solution increases, the slope or the gradient of the graph decreases indicating the decrease in the rate of growth of the shoot. The gradients of the straight lines are compared and it can be further concluded that the gradient is maximum for 0.00% salt concentration which is 0.2657 and minimum for 5.00% salt concentration which is 0.1714. Thus, it can also be claimed that as the percentage composition of the salt in the solution is increasing, the increase in the mean shoot height with respect to the number of days happening at a slower rate.
• Pearson's correlation constant was found to be -0.1793 indicating that a negative correlation exists between the percentage composition of NaCl solution and maximum shoot height.
• The value of R² equals 0.9083 indicating the value was accurate and precise.
• Thus, the null hypothesis has been rejected and the alternate hypothesis has been accepted.
• As the percentage of salt concentration increases, the water becomes more saline and thus the water molecules begins to move from the root hair cells to the outer layer across the semi-permeable membrane and reduces the supply of both water and micro nutrients to the plant. This in turn inhibits the activation and functioning of all the enzymes that are necessary during the germination and growth of plant. These micro nutrients acts as a co-factor for most of the enzymes. Thus, lack of availability of the nutrients will be an inhibitory factor for the growth of the plant.

• The intensity of the sunlight falling on the petri dishes could not be controlled which may cause fluctuations affecting plant growth. Although all the petri dishes were kept near the window to ensure that all the plants receive the same amount of sunlight.
• The use of tap water, could have affected in addition of a few salts and sediments.
• No control over  sunlight and temperature Though same batch was taken the geneic differnces due to  genetic recombination would be inherent in sexually reproducing plants and some inherent genetic differences were inevitable.

• All ethical and environmental considerations were taken into consideration.
• Multiple readings have been considered to optimize the random error.
• Data has been collected and processed coherently to arrive at a valid conclusion.
• The growth of the shoot height was calculated day-wise which indicated the rate of growth along with the data for the maximum shoot height. Thus, the investigation not only outline the effect of salinity on the maximum shoot height but it also allows us to understand the rate at which the plant is grown.
• Tap water could have been replaced with distilled water, to avoid the mixing of naturally present sediments. However tap water was used to replicate natural conditions.
• Growth was measured with a thread end points were marked and then a scale was used to measure the length this avoided error in measurements as the shoots were curved depending upon the direction of light.

A comparison of halophytes and mesophytes. Knowing that salt causes growth inhibition and affects crops in arid regions I wish to investigate what can I add to soil in order to neutralise the salinity and thus save destruction of crops in arid regions. A comparison between genetically modified moong seeds and ordinary moong seeds to see the effect on growth.

The experiment performed determines the effect of salinity on the maximum shoot height of the plant. The experiment can be extended further to determine:

• Dependence of the root height of the plant on salinity.
• Dependence of the number of leaves formed on  salinity
• Dependence of the percentage of seeds germinated on salinity.

The same procedure can be followed to conduct this investigation. The salt solutions can be used to germinate the seeds and grow the plant. Following this, the root height can be measured using a thread and then a ruler. The number of leaves can also be counted. The percentage of seeds germinated can be determined by using the formula:

Percentage of seeds germinated = \(\frac{number\ of \ seeds\ germinated }{total\ number\ of\ seeds \ germinated}\)× 100

• Staverman, A. J. "The theory of measurement of osmotic pressure." Recueil des Travaux Chimiques des Pays‐Bas 70.4 (1951): 344-352.
• Hall, David Oakley, and J. Coombs. Techniques in bioproductivity and photosynthesis. Pergamon press, 1982.