Trees produce oxygen as a byproduct of growth, leading to the common belief that they do not require it for survival. This is a misunderstanding of plant biology, as trees are complex organisms composed of living cells that need a constant energy supply. Like nearly all life forms, trees require oxygen to power their metabolic processes and sustain life.
Why Trees Require Oxygen
The need for oxygen in trees is rooted in aerobic cellular respiration, the mechanism that converts stored food into usable energy. Photosynthesis creates glucose, a form of stored chemical energy, but this energy cannot be directly used for growth, repair, or maintenance. Respiration acts as the energy-releasing step, breaking down glucose molecules in the presence of oxygen.
This biochemical breakdown occurs primarily within mitochondria inside the plant cells. Oxygen acts as the final electron acceptor in the final stage of respiration. This allows the process to efficiently generate adenosine triphosphate (ATP), the universal energy currency of the cell. Without oxygen to accept these electrons, the energy pathway shuts down, preventing the tree from generating energy for its basic functions.
How Trees Absorb Oxygen
Trees employ multiple pathways to absorb the oxygen necessary for respiration, with the needs of different parts of the plant varying. The root system is the most demanding area for gas exchange, acquiring oxygen directly from the soil. Roots absorb this oxygen from the tiny air pockets, or pores, found between soil particles, which then diffuse into the root hairs and epidermal cells.
The above-ground parts of the tree also take in oxygen from the atmosphere. Leaves absorb oxygen through their stomata, which are small, regulated pores on the surface, though they are primarily known for taking in carbon dioxide. The woody tissues of the trunk and branches possess specialized, slightly raised pores called lenticels. These lenticels break up the impermeable bark layer, allowing for the slow diffusion of oxygen into the living cells beneath the bark to sustain respiration.
The Difference Between Respiration and Photosynthesis
Confusion about a tree’s need for oxygen stems from the dual nature of its gas exchange processes: photosynthesis and respiration. Photosynthesis is the process of energy storage, using light energy to convert carbon dioxide and water into glucose (sugar) and releasing oxygen as a byproduct. This process is limited to the green parts of the plant, such as the leaves, and only occurs during daylight hours when sunlight is available.
Respiration is the opposite, serving as the process of energy release. It combines oxygen with stored glucose to produce ATP, with carbon dioxide and water as waste products. Unlike photosynthesis, respiration happens continuously, 24 hours a day, in every living cell of the tree, from the root tip to the highest leaf. While photosynthesis generates the fuel, respiration consumes the sugar and requires oxygen to unlock the energy, allowing the tree to grow and repair itself even when the sun is down.
What Happens When Oxygen is Unavailable
When a tree’s oxygen supply is restricted, the plant shifts its energy generation from efficient aerobic respiration to anaerobic respiration, or fermentation. This deprivation commonly occurs in the root zone due to waterlogged soil or excessive soil compaction, which eliminate air pockets. When soil pores fill with water, oxygen diffusion slows, and the oxygen is quickly consumed by the roots and surrounding soil microbes.
Anaerobic respiration generates only a fraction of the ATP that aerobic respiration does, which is insufficient for long-term survival and growth. This emergency process produces toxic metabolic byproducts, primarily ethanol, acetaldehyde, and lactate, which accumulate within the root cells. The buildup of these compounds acts as a poison, damaging the root membranes and cellular machinery. This ultimately leads to the death of the root system and the decline of the entire tree.