Deficiencies and Toxicity
An inadequate amount of a nutrient is a deficiency. Deficiencies can be due to a number of causes including inadequacy in nutrient intake called dietary deficiency, or conditions that interfere with the utilization of a nutrient within an organism. Some of the conditions that can interfere with nutrient utilization include problems with nutrient absorption, substances that cause a greater than normal need for a nutrient, conditions that cause nutrient destruction, and conditions that cause greater nutrient excretion.
Nutrient toxicity occurs when an excess of a nutrient does harm to an organism.
In plants five types of deficiency or toxicity symptoms are common:
- Chlorosis - which is the yellowing of plant tissue caused by a shortage of chlorophyll synthesis.
- Necrosis - which is the death of plant tissue.
- Accumulation of anthocyanin - which produces a purple or reddish colorization of foliage and/or stems.
- Lack of new growth.
- Stunting or reduced growth - where new growth is stunted or reduced.
Oversupply of plant nutrients in the environment can cause excessive plant and algae growth. Eutrophication, as this process is called, may cause imbalances in population numbers and other nutrients that can be harmful to certain species. For example, an algal bloom can deplete the oxygen available for fish to breathe. Causes include water pollution from sewage or runoff from farms (carrying excess agricultural fertilizer). Nitrogen and phosphorus are most commonly the limiting factor in growth, and thus the most likely to trigger eutrophication when introduced artificially.
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