When is a substance limiting nutrient?

Answer 1

A nutrient is considered "limiting" when it is in low enough quantities to prevent organisms from surviving. Organisms need several different types of nutrients to survive, but to illustrate the point, I will simplify it to three basic elements, carbon, nitrogen, and phosphorus. Consider a hypothetical plant that needs 10g of carbon, 20g of nitrogen, and 2 grams of phosphorus in the soil to grow. If the soil contains 10g of all three, then nitrogen would be limiting and would prevent the plant from growing, despite having 500% of the required phosphorus. You could add all the carbon and phosphorus you wanted and it wouldn't help. If you add 10g of nitrogen to the soil however, you will see plant growth.

There are two impacts to the concept of supplying a "limiting nutrient" to an ecosystem. The first is negative, when a nutrient that is currently limiting algal growth (usually nitrogen or phosphorus) is added to a body of water, you get an algal bloom or red tide. The second impact can be positive if an ecosystem is missing something it needs to flourish, then adding that nutrient would be necessary to maintain that ecosystem. I have a vague memory of a small amount of a non-consumable micronutrient (possibly manganese) being added to a barren field resulting in abundant herbacious growth. (Anyone else know specifics? I can't remember the exact study.) This "positive" concept can also be seen in agriculture a where a farmer would add the necessary nutrients as fertilizer to his crops. Of course too much fertilizer can cause the negative aspect I talked about earlier if this fertilizer runs off into waterways and causes the algal blooms .

Answer 2

A nutrient is considered "limiting" when it is in low enough quantities to prevent organisms from surviving. Organisms need several different types of nutrients to survive, but to illustrate the point, I will simplify it to three basic elements, carbon, nitrogen, and phosphorus. Consider a hypothetical plant that needs 10g of carbon, 20g of nitrogen, and 2 grams of phosphorus in the soil to grow. If the soil contains 10g of all three, then nitrogen would be limiting and would prevent the plant from growing, despite having 500% of the required phosphorus. You could add all the carbon and phosphorus you wanted and it wouldn't help. If you add 10g of nitrogen to the soil however, you will see plant growth.

There are two impacts to the concept of supplying a "limiting nutrient" to an ecosystem. The first is negative, when a nutrient that is currently limiting algal growth (usually nitrogen or phosphorus) is added to a body of water, you get an algal bloom or red tide. The second impact can be positive if an ecosystem is missing something it needs to flourish, then adding that nutrient would be necessary to maintain that ecosystem. I have a vague memory of a small amount of a non-consumable micronutrient (possibly manganese) being added to a barren field resulting in abundant herbacious growth. (Anyone else know specifics? I can't remember the exact study.) This "positive" concept can also be seen in agriculture a where a farmer would add the necessary nutrients as fertilizer to his crops. Of course too much fertilizer can cause the negative aspect I talked about earlier if this fertilizer runs off into waterways and causes the algal blooms .