Protein synthesis is fundamental in all living organisms, including plants. It involves the construction of proteins from amino acids, which are the building blocks of proteins. The synthesis of proteins is essential for the proper functioning of plants and is involved in various processes such as growth, development, and response to environmental stimuli.
Ammonium and nitrate are two forms of nitrogen that plants commonly use as a nitrogen source for protein synthesis. Nitrogen is an essential element for plants and is required for synthesizing amino acids. Ammonium and nitrate are the two most common forms of nitrogen taken up by plants, and the balance between these two forms can have significant effects on protein synthesis in plants.
According to Marschner’s Mineral Nutrition of Higher Plants, plants adapted to acidic mediums (calcifuge species) or that have a low redox potential (e.g., wetlands) prefer ammonium. In contrast, plants adapted to calcareous, high-pH mediums prefer nitrate. However, a combination of ammonium and nitrate is required to obtain maximum growth rates and plant yields.
For most plants, the ratio of ammonium to nitrate can range between 1-3:10. For plants like rice, which have developed in acidic soils and wetlands, the plant tends to prefer closer to 30% of its total nitrogen demand to come in the form of ammonium. In contrast, plants like lettuce prefer more than 10-15% of the total nitrogen input from ammonium. Exact percentages can vary depending on several factors, including the specific plant species, the environmental conditions, and the availability of other nutrients.
Effect on Energy Use Efficiency:
Nitrate is reduced to nitrite by nitrate reductase enzymes in the plant cell wall and this process requires energy. The nitrite is then converted to ammonium by the enzyme nitrite reductase, which also requires energy. The ammonium can then be incorporated into amino acids through protein synthesis. In contrast, ammonium is directly incorporated into amino acids without further reduction. This can make the conversion of ammonium into amino acids more energy-efficient compared to the conversion of nitrate.
The amount of energy that a plant can save by using ammonium instead of nitrate as a nitrogen source can vary depending on several factors, including the specific plant species, the environmental conditions, and the availability of other nutrients, with some estimates being as high as 16x more energy required to utilize nitrate vs. ammonium. It is also important to note that the energy requirements for nitrate reduction can be reduced in some cases by the presence of other nutrients, such as sulfur and phosphorus. These nutrients can help support the activities of the enzymes involved in nitrate reduction, leading to more efficient energy use.
The preference for ammonium relative to nitrate increases strongly with decreasing temperatures, and below 5°C uptake of ammonium can still proceed, while that of nitrate ceases.
Compared with ammonium, nitrate has the advantage of allowing a more flexible distribution of assimilation between roots and shoots and can be stored in higher amounts than ammonium in the vacuoles.
Ammonium supply may reduce rhizosphere pH through a net excretion of protons, whereas nitrate supply may increase rhizosphere pH through a net uptake of protons from the rhizosphere.
In nitrate-fed plants, reproductive growth may be delayed due to excessive concentrations of cytokinins. Under such circumstances, the provision of ammonium may induce flowering.
Management of ammonium-to-nitrate ratios can play a significant role in the health and development of a plant. The rootzone’s ratio depends on environmental factors (ORP, pH, EC, Temp, DO); the ratio required for plant growth is largely affected by plant evolution, as determined by the specific plant species, the environmental conditions, and the availability of other nutrients. Fish health considerations must be considered when integrating this ratio’s role in the management of an aquaponic system.
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