How Does pH Affect Plants? - Paper Example

The Effect of PH on Water Potential of Soil

Water potential of the soil or in other words, soil-water potential refers to the measure of the amount of potential energy per unit volume, weight or mass of the soil water when equaled to that of free and pure water. The PH value of the soil indicates its acidity levels which is essential for the proper growth of plants. The acidity level in the soil affects the distribution of important nutrients, a situation that is causing the balance of physical properties of the soil. High soil nutrients often increase its ability to absorb and retain water, a scenario that increases the potential energy per unit volume, weight or mass of water in the soil.

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Water potential in plants refers to the measurable propensity for water to move from one part of the plant to another; the above process is however influenced by the forces generated by different chemical activities. Water potential enhances the determination the direction and the speed in the movement of water from one cell to the other. PH value greatly influences the water potential in plants, the PH of the plant xylem sap while experiencing diverse environmental conditions, can upsurge by over one unit of PH value. The above increase often results in the rise of ABA concentration within the apoplast contiguous to the stomatal guard cells on the upper part of the leaf epidermis. The increase in concentration within the guard cell increases the osmotic potential thereby causing the stomata to open; transpiration rate therefore increases significantly causing the water to move from one part of the plant to the other. In other words, the above scenario results in high water potential within the plant. The water potential in plants is also activated through the PH changes within the xylem tissues. The PH range from 0 to 5 within the xylem cells results into an increased ions concentration, a situation which increases the osmotic potential or water potential within the xylem tissues. The above effect causes the movement of water from one cell to the other. Therefore, increasing acidity of the cell sap leads to high water potential within the plant.

The Effect of PH on Osmatic Potential of Soil, Plant

Osmotic potential is the potential of water to move from one hypotonic solution to a hypertonic solution. In other words, it is the movement of water from the region of fewer solutes to a region of more solutes across a semi-permeable membrane. A lower PH value in the plant roots increases the osmotic potential a situation that causes water to move from the soil to the plant cells. With the lower PH values within the cell sap, there is an increased acidity which results into high ionization effects; this therefore creates a region of a hypertonic solution, a situation that increases the osmotic potential (In George et al., 2007). When there is a balance in the PH values, in other words, when the PH value of solution from one cell balances the PH value of the other cell, there is low osmotic potential and therefore, there is a low movement of solution from one region to the other. The equilibrium between two different compartments within the plant tissues is achievable when their water potential are the same or equal. Succinctly, by convention, the water potential of distilled water is zero and this becomes more negative as the solution increases. With the increasing acidity of the pure water, there is an equal increase in osmotic pressure from one cell to the other or from the soil to the root hair. Osmotic potential is only observable across the cell membranes, therefore, it is usually evident when water moves from the soil to the plant cells and between the plant cells.

The Effect of PH on Photosynthesis

Photosynthesis is the process by which green plants use simple inorganic substances to synthesize complex organic ones in the presence of radiant energy. The process however, involves the activities of enzymes within the plant cells. These enzymes react well at specific PH levels. For each and every plant, there is the best PH for enzyme operation. When the PH level is too high or too low, the enzymes become denatured and as a result, their reaction may slow down or they may stop working. In the above states, they can no longer support the process of photosynthesis to their full potential. Therefore, as the PH values drift away from the optimum level, the rate of photosynthesis slows down. The graph below indicates the effect of PH on the rate of photosynthesis.

The PH values influence the three pathways of photosynthesis, C3, C4 and CAM. In the C3 pathway, an optimum PH value accelerates the rate of photosynthesis. In C4 Pathway, the Calvin cycle and the light-dependent reactions take place through physical dissociations. The light-dependent reactions occur mesophyll cells. The Carbon IV oxide is fixed within the mesophyll cells in the form of simple 4-carbon organic acid, the process, thus take place under the control of enzymes that possess high affinity for oxygen. The above enzymes work best at the optimum PH levels as indicated in the graph. The optimum PH value ranges from 5.5 to 7.0 which is effective for both C3 and C4 plants. The CAM pathways for fixing Carbon IV oxide is another adaptation that enhances the efficiency of photosynthesis through ensuring that Rubisco encounters a high concentration of Carbon IV Oxide, a situation that decreases photorespiration. In the CAM path too, take place under the influence of enzyme activities. Therefore, the Optimum PH value will facilitate the enzyme reaction in the CAM path.

Effect on Distribution of Plants Based On Photosynthesis Pathway (C3, C4, CAM)

Different plants have different photosynthetic pathways. In C3 plants, the initial step of the Calvin cycle is the fixation of carbon IV oxide to RuBP, close to 85% of the plants across the globe are C3 plants. C3 plants apply more energy in the form of ATP for photorespiration. In C4 plants, the Calvin cycle and the light-dependent reactions are separate. In C4 plants, photorespiration is minimal, and they require less water to carry out photosynthesis, this, therefore, explains their distribution in areas with less water. In C4 plants, there are high PH values within the guard cell to enhance the closing of the stomata, this, in turn, reduces the amount of water loss from the upper mesophyll layer. C3 plants are therefore more distributed across the planet than the C4 plants.

Some plants such as Pineapples and cacti that are well suited to survive in the arid and semi-arid areas apply different water and energy saving pathway known as crassulacean acid metabolism (CAM). The CAM plants separate the light-dependent reactions and the Calvin cycle temporarily. At night, under the optimum PH value, these plants open their stomata through an enzyme controlled reaction. The reaction of the enzymes is triggered by the optimum PH value.

How Plant Can Adapt To High/Low PH

C3 plants often carry out chemical activities through optimum PH values. However, in some cases, they often adapt to high or low PH depending on the environmental conditions. When the soil has high acidity (low PH), the plant cells automatically reduce the concentration of the cell sap so as to generate an osmotic potential between the surrounding environment and the plant tissues. On the other hand, when the soil is alkaline, the plant cell will develop highly concentrated cell sap so as to enhance the osmotic potential. For C4 cells, when the surrounding soil has high acidity, they will tend to reduce the PH levels of the guard cells so as to balance the enzymatic activities. With the regulations of the PH values, these plants are able to survive both in the low or high PH areas. CAM plants with their adaptive features to the arid and semi-arid areas, apply the same mechanism to regulate the PH values of the surrounding environment. The plants automatically reduce the ionization process inside the plant cell, a process that automatically decreases the concentration of the cell sap, in the process, the plants adapt to low or high acidic soils.

Conclusion

Different plant species are adaptable to diverse PH values, they thus survive in soils with different PH ranges. Although high/low PH values may affect the plant growth, diverse plants c3, c4 and CAM are able to adapt to alkalinity and acidity of the soil. With the regulations of the concentration of the cell sap, these plants are able to achieve the optimum PH values that are suitable to the biochemical activities within the cells. In other words, the variation in the PH values within and outside the cell often lead to the development of osmotic pressure as well as the water potential inside the cells, a situation the leads to the movement of water within the plant.