1.0 Background:
A breakthrough scientific experiment conducted by ‘Carnegie Science’ found that soil salinity considerably affects the growth rate in plants. The experiment found how plants create Abscisic Acid as a stress hormone when the endodermis is exposed to drought or saline environments. “The endodermis also acts as a guard, with Abscisic Acid, to prevent a plant from growing in dangerous environments.” (Science, 2017)
As a consequence of these exposures, the plants osmotically adjust to the environment where the endodermis in the plants act as a filter for substances within the soil which limit the absorption of harmful and nontoxic substances such as magnesium and potassium, thereby inhibiting the production of chlorophyll and growth of the plant. An excessive presence of salt within soils will result in dehydration and imbalances within the plant cells causing them to become flaccid and inhibiting the growth of the plant. (Science, 2017)
Another scientific experiment conducted by the American Journal of Botany (Houle, 2017) also found that salinity reduces substrate water potential, which consequently restricts water and nutrient absorption by plants; ‘salinity may also cause ionic imbalance and toxicity.’ Due to substrate salinity fluctuation through growing seasons, a plant exposed to varying salinity levels, at various stages of development, can potentially have significant consequences on the dynamics of a population.
2.0 Hypothesis:
A prognosis of the experiment predicts that; plants given a higher concentration of saline water will become flaccid and die as a result of dehydration. The plants given a lower salt concentration will not die but will show signs of dehydration due to the presence of salinity. The plants’ water uptake will be restricted due to the presence of salt thereby dehydrating the plant.
During the experiment it is also predicted that the photosynthesis in subjects with higher saline content will decrease as the plants begin to wilt and change leaf color, meaning oxygen content will be lower as a result of decreased oxygen production from photosynthesis (Hudson, 2017). Carbon Dioxide is also predicted to increase as the plants use stored glucose to produce energy without undertaking photosynthesis due to the unavailability of water, thereby increasing the production of carbon dioxide in the plants with saline soil. This may result in dehydration of some plants as the stored glucose will eventually be exhausted if relied upon.
3.0 Risk assessment:
Chance of occurring: 1 – 5, 1 is low and 5 is the highest
Seriousness/severity: 1-5, 1 not a serious injury and 5 is a very serious injury
| Risk: | Chance of occurring | Seriousness/severity | Management |
|
Glass breakage |
1 |
1-2 | Insure that glass is held with care and wear enclosed shoes to prevent injuries to feet. |
| Potting mix (inhalation of micro-organisms) |
3 |
1 | Wash hands with soap to avoid contamination and ingesting micro-organisms.
|
| Cutting hands and or other people
With Stanley knife |
1 |
4-5 | Take care when cutting bottles with Stanley knives and avoid at all times, cutting towards self. |
4.0 Equipment/materials:
- Weight Scales
- Pots
- Sunflower seeds (organic)
- Potting mix
- Glass Beaker
- Water
- Salt (sodium chloride)
- Vernier Co2 sensor
- Vernier O2 sensor
- Temperature sensor
- Vernier Data logger pro
- transparent Plastic container (airtight)
- blue tack
- Duct tape
- Stanley knife
- Dust mask – prevention of microorganism inhalation
- Gloves
- Adequate size ice-cream container enough to fit 4 pots within it – growing plants
- A computer for logging data
- USB – transferation/storage of data
5.0 Procedure:
- Cut four bottles in half and fill all halves with ‘Rocky point potting mix’ – ‘eco potting mix,’ with the top half of the bottles, cut tops off enough for oxygen sensor to fit within bottles (see below diagram).
- Cut a circular hole enough for a carbon dioxide sensor to fit within the bottle. (see below diagram)
- Plant seeds in the potting mix deep enough to induce germination
- Water plants with 100ml of water individually each day until day 7 ensuring all plants germinate at a similar rate (more than 4 plants can be planted to eliminate any dissimilar plants which could affect the data such as a more developed plant)
- After 7 days of watering each plant, on day 7 pour 100ml of solution (varying saline concentrations (see appendix B)) into each subject recording which subject receives the specified amount of saline water by labeling the subject as seen in appendix D.
- Following step 5; re-join two parts of bottles, ideally matching counterparts, with masking tape to seal bottles following masking tape for the other openings and any false readings.
- On day 8, 9 and 10, make sure all openings on the bottle are sealed and air tight with tape when not measuring data and remove tape when collecting data whilst using blue tack to seal the containers and openings around the perimeter of the gas sensors.
- Use your USB to transfer data recorded on the Vernier Data Logger pro onto your chosen computer for analysis.
- Observe any visual changes and record results by the use of a Vernier data logger, Carbon dioxide sensor, oxygen sensor, and a computer for information storage.
Note: insure that tape is firmly placed on the openings of the bottles to prevent any false data collection when plants are not being monitored.
6.0 Results and Discussion:
Observed results:
It was observed that subject A, as expected, had no visible signs of dehydration or wilting over the period of the experiment and remained turgid. (See Appendix D)
Subject B with 10 grams of salt did not show any indications of decay, however, the plant was experiencing plasmolysis within the plants’ cells on day one and remained in the same position for the rest of the experiment, this was due to the loss of turgidity within the plant resulting in a flaccid appearance. (See Appendix E)
Subject C, at 20g of salt, showed signs of flaccidity on day one, and on day 2 the plant had the beginning indications of decay where on day 3 most of the plant was decayed as seen in subject C. This was a result of the plant being surrounded by a hypertonic solution and the cells being hypotonic in the plant eventually showed signs of flaccidity. (See Appendix F)
Subject D with 30g of salt was flaccid after day 1 and was showing signs of decay on day one. By day 3 Subject was clearly decayed with no indication of life or chlorophyll in the leaves of the plant. (See Appendix G)
This Graph shows that the temperature varied for all subjects respective of the day, meaning all subjects were exposed to approximately the same temperature for the duration of the experiment.
Graph 2: Carbon Dioxide
This graph shows that on day 1, carbon dioxide for Sample A – which had not been given saline water – was expectedly high and lowered progressively each day, this shows that the process of photosynthesis was not disrupted.
Subject B, with 10g of salt per 100ml H2O, shows that carbon dioxide levels were low during the commencement of the experiment, rising to 1168ppm and then falling to 664ppm. This indicates that salt did have an effect on the plant, possibly altering the photosynthetic process and thus, using more carbon dioxide to sustain the plant’s energy requirements. Following this decrease on day 2, the plant appears to have been using oxygen to produce energy which resulted in an increase in carbon dioxide. The decrease of carbon dioxide for the following day indicates that the plant was able to resume a normal photosynthetic process by using carbon dioxide and water to produce glucose oxygen and energy.
Subject C, with 20g of salt per 100ml of water, shows that an intense amount of carbon dioxide was required by the plant on the first day to endure the amount of salt in the soil, which resulted in a deficit of carbon dioxide where the plant needed to respire, as it would at night, by using oxygen and glucose made during the day to produce usable energy. The plant cannot, however, indefinitely use oxygen to produce energy because it will eventually exhaust the amount of glucose which was produced and stored throughout the day – which it is unable to do due to the cellular imbalance of water caused by the salt. The plant also uses most energy for extracting usable water, this limits the process of photosynthesis due to the increased amount of energy used to extract water from the soil. This can also be seen in plants where some functioning is impaired or reversed due to the concentration of saline, which impedes the development of the plants and in some cases results in the death of a plant depending on its saline tolerance.
Subject D, with 30g of salt/100ml of water, had similar results compared to subject C as the salt created an imbalance in the cells of the plant, which were hypertonic to the solution, and thus resulted eventually in dehydration. This shows that the plant used oxygen to sustain its energy requirements and this resulted in an overall increase in carbon dioxide – which is a by-product in plant respiration.
Graph 3: Oxygen
This graph shows that in subject A, oxygen has gradually increased over the duration of the experiment, meaning the plants’ photosynthetic process was not impaired and was functioning normally – which is expected as no saline solution was added to this subject.
It is seen that in subject B, the plant was producing oxygen as normal, until day 3, where the saline solution is suspected to have affected the plants’ normal photosynthetic process, which resulted in the use of oxygen to produce usable energy for the plant.
Samples C and D show similar results compared to subject B, which indicates that salinity in the soil results in an eventual change in the production of energy by the use of oxygen and glucose. The store of glucose will eventually be exhausted as plants produce glucose. In respiration, however, plants do not produce glucose and therefore it will deplete if relied upon, eventually, the plant will be unable to sustain itself and will be dehydrated due to the imbalance created by the addition of saline water.
7.0 Conclusion:
It was found after an analysis of the experiment, that salt does affect the functioning of plants with a quantity of less than 20g salt/100ml water and greater than 10g salt/100ml water. Salt also impairs the plants’ photosynthetic rate, and therefore its growth, by creating an imbalance in the cells of the plant being hypertonic to the solution or the saline soil.
It is important to note that, some plants are more salt-tolerant than others, which is corroborated by Paul Arnold In ‘how does salt affect plant growth?’ (Lim, 2011) Also, varying stages of development in plants can largely influence the effect of salinity on the plant being tested. It is, therefore, recommended that the plants in the experiment are of identical height and also not dissimilar in appearance which could result in false data collection.
The hypothesis correctly predicted that plants with higher saline concentration will die and become flaccid as a result of dehydration, due to the saltwater being a hypertonic solution compared to plant cells, water within the plant cells will osmotically diffuse out of the cells in order to reduce the concentration of salinity, thus reducing the turgor pressure inside the cells. This is corroborated by a ‘Socratic’ scientist – answering the question “What will happen if we watered plants with salt water?”
(Socratic, 2017). Plants with lower saline concentration did not die, but did show signs of flaccidity and dehydration.
Plants try to recover as much water as possible when salt is present, meaning when the osmotic gradient is too high the plants use less energy for making leaves formation and flowering; as a result, their growth can be inhibited (Lim, 2011).
The presence of salinity in the soil near the roots of the plant made the uptake of water by the plants restricted as some plants were unable to tolerate the amount of salt in the soil and, as a result, the plants given higher saline concentration have died. Photosynthesis in the plants was correctly predicted to decrease with the addition of saline water, which exhibited the direct symptoms of increased flaccidity resulting in the plants either decaying or having an impaired photosynthetic functioning resulting in underdevelopment. Oxygen content in the air was also correctly predicted to lower, due to decreased oxygen consumption from a reversed photosynthetic cycle.
8.0 Bibliography:
Science, 2017
Science, C. (2017). Breakthrough: How salt stops plant growth | Carnegie Institution for Science. Carnegiescience.edu. Available at: https://carnegiescience.edu/news/breakthrough-how-salt-stops-plant-growth [Accessed 5 Jun. 2017].
Hudson, 2017
Hudson, A. (2017). How Does Salinity Affect Plant Growth and What Can Be Done?. Available at: http://earthwiseharmony.com/GARDENS/EH-How-Does-Salinity-Affect-Plant-Growth-and-What-Can-Be-Done.html [Accessed 5 Jun. 2017].
Houle, 2017
Houle, G., Morel, L., Reynolds, C. and Siegel, J. (2017). The effect of salinity on different developmental stages of an endemic annual plant, Aster laurentianus (Asteraceae). Available at: http://www.amjbot.org/content/88/1/62.long [Accessed 5 Jun. 2017].
Lim, 2011
Bevs Lim., (2011).“What Is The Effect Of Saltwater On Plant Growth”. Bright Hub. Available at: http://www.brighthub.com/environment/science-environmental/articles/89127.aspx [Accessed; 17 June 2017]
Socratic, 2017
Socratic., (2017) “What will happen if we watered the plants with salt water?”. Available at: https://socratic.org/questions/what-will-happen-if-we-watered-the-plants-with-salt-water [Accessed; 17 June, 2017]
