The question of whether a plant can grow without air is fundamentally a question of chemistry and biology. While plants do not require the entire bulk of the atmosphere, they absolutely depend on specific gaseous components for every stage of their life cycle. The true answer depends on separating the common idea of “air” from the specific molecules a plant must acquire to build its structure and power its functions.
The Dual Role of Essential Gases
Plant growth is powered by two distinct, continuous processes that rely on gaseous components. The first is photosynthesis, which demands carbon dioxide (\(\text{CO}_2\)), the foundational building block for all plant mass. Plants draw this gas through tiny pores called stomata, primarily on their leaves, combining it with water and sunlight to synthesize glucose. This glucose provides the carbon skeleton necessary to create cellulose, starches, and other complex organic molecules that form the plant’s structure.
The second process is cellular respiration, which requires oxygen (\(\text{O}_2\)) to convert stored sugar into usable energy. Every living cell in the plant must perform respiration constantly, day and night. Oxygen acts as the final electron acceptor in the cellular machinery, breaking down the glucose to produce Adenosine Triphosphate (ATP), the primary energy currency for growth, nutrient uptake, and repair. Without a continuous supply of oxygen, the plant cannot generate the energy needed to power its metabolism, and growth quickly ceases.
Why Roots Must “Breathe”
The need for oxygen extends below the soil surface, where roots must perform cellular respiration. Since roots are unable to photosynthesize, they rely entirely on oxygen diffusing into the soil from the air above. Healthy soil contains numerous air pockets, providing the necessary aeration for root hairs to absorb oxygen dissolved in the thin film of water surrounding them. This constant oxygen supply fuels the energy-intensive process of absorbing water and mineral nutrients.
When soil becomes waterlogged, the water fills all available air spaces, slowing the diffusion of oxygen by a factor of up to 10,000 compared to air. The roots quickly consume the remaining dissolved oxygen, leading to anaerobic conditions. This lack of oxygen prevents efficient cellular respiration, causing roots to suffocate and leading to root rot, a common cause of plant death from overwatering. Therefore, the soil must be porous enough to constantly replenish the oxygen supply for the roots to remain healthy.
Growing Outside the Open Atmosphere
Plants can thrive without access to the open atmosphere, but only if the specific required gases are provided in an alternate form. Aquatic plants, for instance, obtain both carbon dioxide and oxygen in their dissolved form directly from the surrounding water. They have adapted to rely on the slower diffusion of these gases, with some species even able to utilize bicarbonate as an alternative carbon source when dissolved \(\text{CO}_2\) is scarce.
Hydroponic Systems
In controlled environment agriculture, like hydroponics, plants are grown without soil and often without direct atmospheric exchange. In these systems, oxygen is actively introduced into the nutrient solution using methods like air pumps and air stones. These methods release fine bubbles to maintain high dissolved oxygen levels, often targeted between 8 and 12 milligrams per liter.
Closed Terrariums
A closed terrarium demonstrates a self-sustaining miniature ecosystem where the plants and microorganisms form a closed gas cycle. Plants produce oxygen during the day. Both the plants and decomposing microbes consume that oxygen and release \(\text{CO}_2\) during respiration, ensuring the necessary gas components are continually recycled within the sealed container.