Experiments to show the factors required in photosynthesis (2) ..
Phosphorus in the soil
The total phosphorus content of soils is generally high. However, only a fraction of it is available directly to the plant and the majority is adsorbed to the soil.
Phosphate dynamics in soils
The availability of phosphorus can be categorised as follows:
~ Orthophosphate in the form of H2PO4- and HPO42-.
~ P fraction which has been adsorbed onto oxides and hydroxides of iron or aluminium as well as clay mineral.
~ calcium-, magnesium-, potassium-, sodium- and ammonium phosphate depending on the concentration of cations in the soil solution.
~ easily soluble organically bound phosphorus.
~ calcium-, iron- and aluminium phosphate (inorganic)
Effect of pH on P availability:
The availability of phosphorus in the soil depends largely on the pH value. The greatest mobilisation occurs at a pH value between 6 and 7. The danger of phosphorus fixation is greater with an increasing soil pH. However, the availability can be improved at a relatively high pH (7.5-8) through addition of organic matter and at a high pH (>8) from addition of S or gypsum.
Increasing acidity of the soil results in the development of aluminium and iron phosphate. The availability of phosphorus can be improved by liming of the soil.
Effect of phosphorus fertilisation on the soil:
Soil fertility status
The fraction of phosphorus that is easily taken up from the soil solution is the important fraction for plant nutrition. Analysing soil for its plant available nutrients is a useful tool in calculating fertiliser requirements. Most countries have a scale of available P in soils and different crops require different P levels according to the responsiveness of that crop to P. It is important that P is neither limiting nor in excess since an excess of P not only increases the risk of leaching into the environment but also can cause problems with micronutrient availability.
Phosphorus in the plant
P is mainly taken up from the soil solution in the orthophosphorus form by the root hairs. These hairs are also able to solubilise a proportion of the unstable phosphate fraction through the excretion of acids. Therefore, a well developed root system is essential for the uptake of phosphorus.
Phosphorus is irreplaceable as a main nutrient for the plant. It is the constituent part of many plant compounds and affects the entire plant metabolism.
Functions of phosphorus in the plant:
Phosphorus deficiency symptoms
its replacement by photosynthesis
Function: Sodium is not an essential element for plants but can be used in small quantities, similar to micronutrients, to aid in metabolism and synthesis of chlorophyll. In some plants, it can be used as a partial replacement for potassium and aids in the opening and closing of stomates, which helps regulate internal water balance. Chloride is needed in small quantities and aids in plant metabolism, photosynthesis, osmosis (movement of water in and out of plant cells) and ionic balance within the cell.
Germinating mung seeds will undergo photosynthesis when exposed to light and have water ( which is a product of the reaction that occurs with the potassium hydroxide and carbon dioxide that removes the carbon dioxide from the system).