Abstract The Seeds of Mung bean, wheat, and silver beet were tested in environments of differing salinities to note down if high salinity environments were worse for the seeds. It was found that generally lower concentrations were better for germination then higher concentrations. Despite this, the hypothesis was not completely supported as in wheat and silver beet the second concentration had a higher rate of germination than the control and in all instances the highest concentration had a higher germination rate than the second highest concentration. Introduction
Salinity refers to salt dissolved in a substance such as water or soil. Different plants have differing levels of salt tolerance, due to certain adoptions to specific environments. If a plant is not adapted to high salinity areas, they can be very detrimental to them. This is due to the process of osmosis. Osmosis is the process that occurs when there are differing concentrations between the inside and outside of a cell (Etomica, 2010). The reason that solutions can travel through a cell is due to its cell membrane, which is a semi-permeable, meaning that only some things and not others can pass through it (Purchon, N, 2000).
If there is a higher concentration on the outside of the cell than on the inside of the cell then it is referred to as hypotonic. When this happens, water flows from outside the cell into it, and the cell starts to swell. When the cell swells it is said to be turgid, which means swollen and hard (Etomica, 2010). In plant cells there is a cell wall which prevents these cells from bursting, and when the internal and external pressures become equal the ‘turgor pressure’ prevents the cell from taking in any more water (Etomica, 2010). If the concentration is higher on the inside, however, than it is referred to as hypertonic.
When a cell is in a hypertonic solution, water from the inside of the cell will travel out of the cell (Etomica, 2010). When this happens, the cell is said to be ‘flaccid’, and when this happens the cytoplasm of the cell, which is the organelle of a cell concerned with the storage of water, pulls away from the cell walls in a process known as plasmolysis (Etomica, 2010). If there is an equal concentration on both the inside and outside of the cell than it has reached a ‘dynamic equilibrium’ and is referred to as isotonic, ‘incipient plasmolysis’ occurs .
Incipient means about to be, meaning that it is in-between being turgid and being plasmolysed (Etomica, 2010). If a fully sprouted plant is in an isotonic solution, then a plant droops because it is not turgid enough to hold itself up (Etomica, 2010). High salinity environments can be bad for plants not adapted to them because their cells become flaccid. This is because the concentration of water in a high salinity environment is relatively low, meaning that water diffuses from inside the cell outwards, and eventually can deprive a cell completely from water (Etomica, 2010).
The effects of high salinity environments on plants are an especially large problem in Australia. This is because, over millions of years, salt has been taken from the sea in the form of salt water, and deposited over the Australian landscape in the form of rain (DENR SA, 2010). This salt has stayed even deposited through soil for millions of years due to the native plants living in it, but with the plantation of introduced crops has become a large problem. In deep-rooted, native plants, when rainfall occurs, a large amount of water is taken up through the roots from the soil, resulting in no difference to the environment.
However, with introduced, shallow-rooted plants, less water is taken up through the roots. Because less water is taken up, more water remains, and when the water evaporates from the soil, salt which has been low below ground for millions of years is brought to the surface, surrounding these new plants and depriving them of further water (DENR SA, 2010). This process can be made worse by the irrigation of crops, which result in more water soaking into the soil and thus more water to evaporate and carry salt to the soil’s surface (DENR SA, 2010).
An example of a plant adapted to high salinity environments is the mangrove. The mangrove is a halophilous plant, meaning that it is a plant that grows in saline soils and waters (Conservancy Association, 2010). This gives it an advantage as not many plants can live in these conditions. The mangrove handles these high salinity conditions in a number of methods. The first method is through salt exclusion, which is the process the mangrove uses to prevent salt from entering its roots and therefore stopping it being transported to the plant cells (Conservancy Association, 2010).
Despite this, some salt still gets through to the cells, and there are more methods to deal with it. With mangroves such as the Black Mangrove, salt can be excreted through its tissues, through specific salt glands (Conservancy Association, 2010). Another method is the storage of this salt on the leaves of the plant, in the form of crystals. These leaves then drop to the ground, taking this salt with them (Conservancy Association, 2010). The germination of mangroves is also a process specifically adapted to high salinity conditions.
A mangrove seed begins to develop before it is dropped to the ground from the plant, to improve its chances of survival once it is dropped (Conservancy Association, 2010). As a mangrove is surrounded by water, when a seed drops it will start floating, as the seed coat starts to shed. The speed at which this coat sheds depends on how ideal the conditions are for it, as it will fall off slowly if it is in a high or low salinity environment (Conservancy Association, 2010). The best environment for a mangrove seedling is one of a combination of sea and fresh water.
If the environment has a high temperature then the process is also quickened (Conservancy Association, 2010). Finding the right environment fairly quickly is important as a mangrove seed can only stay alive a few days, before it needs to implant (Conservancy Association, 2010). In this extended experimental investigation, the germination process of the seeds of mung beans, wheat, and silver beet in differing saline environments are tested to see how high salinity environments can affect plants.
Mung beans can grow in both moist and dry environments, and can survive very dry drought conditions if necessary (Jefferson Institute, 2010). Despite this, they are not well adapted to high salinity conditions. Silver beet seeds are also adapted to a wide range of climates, although prefer cool, dry areas to germinate (Primefacts, 2009). Silver beet seeds have some tolerance to saline conditions, but not much tolerance during the germination process (Primefacts, 2009).
There are over a thousand different kinds of wheat, whose seeds once again can survive well in drought-like conditions, but are relatively unadapted to saline environments (Shipard, I, 2009). Ten of each of these seeds will be put into five differing solutions. The solutions consist of a control solution, being a distilled water solution with no salt, a solution of 4. 375g/L of salt, a solution of 8. 75g/L of salt, a solution of 17. 5g/L of salt, and a solution of 35g/L of salt, being the average salinity of sea