Space gardener: comparing plant root growth

Growing plants in space has generated much interest among space agencies because of its benefits for long-duration space missions and for future human exploration of other planets. Growing plants in space will provide a sustainable food source, help lower carbon dioxide levels, assist in the water recycling process and improve the mental health of astronauts. But in order to successfully grow plants in space, it is important to understand how plant roots grow, both on Earth where there is gravity, and in space where there is microgravity (i.e. very little gravity).

One major challenge of plant growth in space is that in microgravity, water and nutrients don't flow through soil. This affects the behaviour of plant roots, whose job is to absorb nutrients and water for the plant.

The purpose of this experiment is to demonstrate how the nutrient density of soil changes the size and shape of plant roots.

You will need

• Six identical plants at an infant stage in their growth (note: you can grow them yourself using seeds or pits from fruits, vegetables or dried beans).
• Six identical containers for holding soil and the plant. Consider using empty margarine or yogurt containers. (Using a permanent marker, write "nutrient-rich soil" on three of the containers, and "regular soil" on the other three containers.)
• Enough regular soil to fill three containers.
• Enough nutrient-rich soil to fill three containers (soil to which you added manure or fertilizer; for quantities, follow the label instructions).
• Water.

Procedure

1. Place three of the plants into containers with nutrient-rich soil, and place the other three plants into containers with regular soil. (Before you do so, examine the roots of all the plants. You can even take a photo!)
2. Divide the six plants into three pairs. Each pair must have one plant in nutrient-rich soil and one plant in regular soil.
3. Place the first pair in direct sunlight, the second pair in a spot where there is good indoor lighting, and the third pair in a spot where the lighting is low.
4. Allow the plants to grow for several days. Be sure to water them daily. (Rate and amount of growth varies depending on the type of plant.)
5. Carefully remove the plants from their containers and observe the roots. Did they get bigger? What's the difference in root size between the plants?
6. Optional: Use a scale to weigh each set of roots. Produce an average weight for the roots that grew in nutrient-rich soil, and an average weight for the roots that grew in regular soil. Take note of the difference between the two average weights.

How it works

What makes a root grow? You might think that gravity has a major influence because roots always grow downwards. However, roots actually grow to cover more area in the soil and absorb more nutrients. That means that in the microgravity environment of space, the roots would change in size and direction to absorb more nutrients. Roots that have easy access to nutrients don't increase very much in size, and the rest of the plant grows to compensate for the lack of root growth. (Did you notice that when you looked at the roots of your plants in nutrient-rich soil?)

With that in mind, what do you think should be done differently in space to allow plants to grow? Should different types of soil be used, or perhaps deeper or larger containers to give the roots more space to grow? Or maybe more nutrients and various types of lighting would help plants grow?

Currently, the Vegetable Production System (Veggie) on the ISS uses an enclosed system to provide light and nutrients and to control environmental factors like temperature and humidity. Veggie uses plant pillows that are packed with nutrients and allow the plants to grow properly.

After this experiment, do some reading and watch some videos about plant growth in space. Perhaps your work will one day make you the first gardener on the Moon!