Aquatic plants and roots?
F. Mattier
Aquatic plants and roots: is soil really necessary in an aquarium?
Submerged aquatic plants often raise the same question among aquarists: do they feed through their roots or directly through the water?
Is a nutrient soil, a technical substrate, or fertilizers necessary for them to develop properly?
In reality, the functioning of aquatic plants is very different from that of terrestrial plants, and many misconceptions still persist. This article offers a simple, scientific, and accessible explanation of the real role of roots in aquatic plants, especially in natural and low-tech aquariums.
How do submerged aquatic plants feed (leaves, roots or water)?
Unlike terrestrial plants, aquatic plants live entirely submerged in their nutrient solution: water. They can therefore absorb the elements they need through all their organs:
- leaves,
- stems,
- and sometimes roots.
They never had to develop barriers against drying out, like the waxy cuticles of terrestrial plants. This lack of specialization explains why nutrient absorption is mostly done directly in the water, via the leaves.
Some terrestrial plants still retain from their aquatic origins a residual capacity for foliar absorption, inherited from their aquatic origins, now used for the supply of trace elements by spraying.
Submerged leaves and emerged leaves: two forms, two functions
In several aquatic species, the emerged parts have a different morphology from the submerged parts. This is notably the case of water milfoil.
Submerged leaves are adapted:
✅ to the direct absorption of nutrients in the water,
✅ to low mechanical resistance,
✅ to constant exposure.
Emergent leaves, on the other hand, can neither feed effectively underwater nor dry out in open air. This duality illustrates the very fine adaptation of aquatic plants to their environment.
Are the roots of aquatic plants indispensable in aquariums?
In plants rooted in a substrate, roots can contribute to nutrition. However, even in this case, their role often remains accessory and rarely vital.
In an aquarium, much of the nutrients present in the soil quickly diffuse into the water by osmotic pressure. Plants can therefore access them directly through their leaves.
Why do we observe so many “roots” in some species?
Anchoring and stability
In many cases, the main function of these organs is not nutritional but mechanical.
Currents, digging fish, or water movements require plants to have minimal anchoring. Without this, they would be continuously displaced, losing their orientation toward the light.
The case of strictly foliar plants
Some aquatic plants feed exclusively through their leaves, notably:
🌱 the Najas.
In these species, 100% of mineral nutrition comes from the water.
Roots or rhizoids: an essential distinction
The white filaments observed in these plants are not true roots in the botanical sense. They are rhizoids:
➡️ lacking specialized root tissues,
➡️ incapable of significant nutrient absorption,
➡️ solely dedicated to anchoring and orientation.
Their role is to keep the plant stable facing the light, avoiding constant readjustment.
Is soil or a nutrient substrate necessary for aquatic plants in aquariums?
In aquariums, many plants can live:
- without soil,
- directly in the water column,
- or with simple neutral sand.
In the absence of strong current, they develop perfectly without a nutrient substrate. The idea that technical soil is indispensable often stems more from marketing than biology.
A coherent and functional low-tech approach
At Aquazolla, only easy and autonomous aquatic plants are selected. This implies:
👍 no CO₂ addition,
👍 no fertilizer,
👍 no technical soil.
In a balanced aquarium, animals naturally produce:
- CO₂ through respiration,
- minerals through their excretions.
Plants consume these elements directly in the water, transforming waste into plant biomass. Adding inputs then disrupts this balance.
Aquatic plants therefore have a central role: purifying the water and transforming waste into greenery, directly in the water column.
FAQ
Do aquatic plants feed through roots or leaves?
In most cases, they feed directly through leaves and stems, absorbing nutrients present in the water.
Is a nutrient substrate mandatory for aquarium plants?
No. Many aquatic plants live very well without a nutrient substrate, especially in low-tech aquariums.
Can aquatic plants be kept without soil?
Yes. Many species can live without soil, directly in the water column.
Are the long white filaments observed true roots?
Often not. These are generally rhizoids, whose function is anchoring and not nutrition.
Do aquatic plants need fertilizer?
In a balanced aquarium, the waste produced by animals is generally sufficient.
To go further
Discovering the interest of structuring plants like Rotala
Knowing how to choose your floating plants
Understanding why the "friend's" plants recover better
Discovering the Sagittaria subulata and its aquatic lawns
In water, everything is simpler.
Aquatic plants use directly what the ecosystem provides them.
Understanding their real functioning allows designing more natural, more stable, and more life-respecting aquariums.
2 comments
Encore un bel article plein d’enseignement.
Article très intéressant pour lequel j’ai toujours été en accord.