[KNOW-HOW] Absorption of Excessive Nutrients by the Law of the Minimum
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Excessive nitrogen and phosphorus in the aquarium need to be removed by such
measures as water change to avoid algae infestation. When the aquatic plants
are not yet blooming, they are unable to absorb such excessive amounts.
However, once the aquatic plants have grown healthily and densely, nitrogen and
phosphorus are hardly detected even without frequent water changes. Even if fish
are present in the tank and fed adequately everyday, the level of these
nutrients is extremely low as long as the aquatic plants are dense enough.
This shows that aquatic plants have excellent water purification ability. In
order to promote this ability, we should understand how aquatic plants absorb
nutrients and then apply the acquired knowledge effectively. Unlike terrestrial
plants that absorb water and nutrients from their roots, aquatic plants can
absorb nutrients through their surface including leaves and stems. Aquatic
plants havedeveloped this characteristic so that they are able to absorb
nutrient salts dissolved in water in an environment where they are always
immersed in the water. Among the aquatic plants, Cryptocoryne and Echinodorus
are the species that actively absorb nutrients from the roots, while stem
plants absorb nutrients more from the leaf surface. For stem plants, the
roots are merely an organ to anchor the plant body to the substrate.
Epiphytic plants such as ferns, moss and Anubias also absorb nutrients
directly from the water. Therefore for these plants, the immediate effect
of nutrient supplementation can be expected by directly adding liquid
fertilizer to the water.
Nevertheless, not all the liquid fertilizers are effective. For example,
if liquid fertilizer designed for terrestrial plants is added directly to a
tank, the tank will soon be covered with algae. Meanwhile the aquarium with
fish has a tendency to experience excessive nitrogen and phosphorus but lack
of potassium and trace elements. There is a widely known principle called
"The Law of the Minimum" which states that the growth of a plant is limited
by the particular nutrient least available in relation to the total
requirements of the plant. This principle also applies to aquatic plants in an
aquarium tank and, if this Law of the Minimum is applied in reverse, more
amounts of excessive nutrients will be absorbed by supplementing the nutrients
that are lacking.
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