Let the Water Do the Work

Let the Water Do the Work

I want to take you into the invisible world within your aquaponics system’s water.

To do that, we need to take a step back and understand a little bit about plant biology.

Elodea leaf that was placed in a 20% sugar solution. The inside of the cell is shrinking, and the gap between the cell membrane and the cell wall has increased [Plasmolysis « Botany Blog. (n.d.). Retrieved from http://botany.thismia.com/2010/02/24/plasmolysis/]

Let’s start with a close-up view of a plant cell.

The environment within the cell is crowded with all the parts that allow it to function. We’re not going to dive too deep, but I do want us to take notice of the cell wall and membrane. The cell membrane enclosing this soup of life is selective, so it only allows specific small molecules and ions such as water, oxygen, carbon dioxide, nitrogen (N), phosphorous (P), and potassium (K) in and out. Luckily, the plant has evolved to know what to let in and what to exclude.

When we observe plant cells, we must remember that the cell membrane moves freely, swelling and contracting when the cell gains and loses water. On the other hand, the cell wall is rigid.


Water uptake by roots [Capon, B (2007). Botany for Gardeners. Portland, OR: Timberland Press Inc.]

If we zoom out to the root, you’ll see the root’s wall is made up of cells. These cells are like rigid boxes full of slime balloons. Depending on the amount of water and the composition of the water around the plant, the balloons will expand or contract within these boxes. For instance, if you place the plants in water from the ocean, the balloons will shrink significantly. If you put the plants in distilled water the balloons will swell.

But remember, the box never changes its shape, which keeps the balloons from getting so big that they pop.

Great, so now we understand that the wall of a root is composed of cells that act like balloons inside of boxes.

Has anyone ever heard you shouldn’t overwater your plants, or they’ll drown? Does anyone know why? Does anyone know why that doesn’t happen in aquaponics?

As we already talked about, the problem is not excess water around the plant’s roots, since water moves back and forth between the balloon as if it were skipping rope over the cell membrane. What is a problem, is that the water is not moving around the plant’s roots. The cell uses up all of the surrounding water’s oxygen, causing a lack of oxygen that drowns the cell due to stagnant water. Unlike the plants leaves that receive sufficient levels of oxygen from photosynthesis, the plants roots require access to oxygen. However, the levels of available oxygen in stagnant water decline by 60% in an hour and 95% in a day. With aquaponics, the water is always moving and is oxygenated continuously in each section of the system. This allows plants to thrive with their roots submerged in water.

Okay, so we have a wall of balloons inside of boxes, the cells, that allow water and nutrients to exchange into and out of the root continually, let’s explore a level further.

If the water and nutrients get past the wall of balloons in boxes, how does it get to the leaves and the fruits—the whole reason we grow the plant? This happens because the plant has a vascular system, just like the blood vessels in our bodies. Though you may say to me, hey a plant does not have a heart, how does the water move?

Pathway of water across a root [Capon, B (2007). Botany for Gardeners. Portland, OR: Timberland Press Inc.]

You’ve probably noticed when it rains, any raindrops that come close together merge into a larger raindrop—or even a puddle. This is a perfect example of how water prefers to stay next to water. This self-attraction is why the entire vascular system of a plant stays filled with water.

Ok, so what?

We have water surrounding the root and all through the vascular system of the plant, but I still haven’t told you how the water moves.

To do that I want you to think about being outside on a nice sunny day. Maybe you start to sweat a little; well guess what, plants also sweat through structures in the leaves called stomatas.

If a plant is sweating through its stomata that water has to come from somewhere, right? It’s pulled through the vasculature, which draws water from the roots, which pulls water from the soil. 95% of the water that plants need is because it evaporates from their leaves in transpiration.

Why does this matter?

We know that when we sweat, it helps to cool us. Plants are the same. The water that evaporates from the leaves during transpiration serves to cool the leaves. To increase the cooling of your plants you need to increase the air flow and decrease the humidity.

How much water are we talking about doing all this work?

During a season of growth, a single tomato plant can transpire 34 gallons, whereas a corn plant can transpire 54 gallons. What is great about an aquaponics system over a traditional soil garden is that the system automatically refills the water that is lost instead of you going out into the field to replace the water lost through transpiration.

The pathway of water through a plant [Capon, B (2007). Botany for Gardeners. Portland, OR: Timberland Press Inc.]

You now understand the fundamentals of nutrient and water flow through plants. We learned that:

  • Water moves into a cell to try to reduce the concentration of material in that cell
  • Cells will not explode when submerged in water. Therefore, the concern is not water submersion, but the plant’s access to oxygen.
  • Aquaponics automates the labor of growing plants and lets the water do the work.
  • The environment around the leaves pulls water along with disolved nutrients through the plant from the roots during a process called transpiration.
  • Transpiration helps keep your plants cool. This helps to keep your plants from wilting and allows them to function optimally, producing food for you and your family.
  • Aquaponics ensures that the plants have access to the nutrients they need in an optimal environment for them to function.

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