Trees, like all plant life, depend entirely on carbon dioxide for their existence and growth. This atmospheric gas serves as a fundamental building block for trees, much as oxygen is essential for human respiration. Without a consistent supply of carbon dioxide, trees would be unable to produce the energy and structural materials they require to survive.
The Photosynthesis Process
Trees utilize carbon dioxide through a biological process called photosynthesis, primarily occurring within their leaves. During photosynthesis, trees convert light energy from the sun, water absorbed from the soil, and carbon dioxide from the air into sugars, their primary food source, and oxygen, a byproduct. This conversion takes place within specialized organelles called chloroplasts, which contain a green pigment called chlorophyll. Chlorophyll absorbs the light energy needed to power these chemical reactions.
Carbon dioxide enters the leaves through regulated pores on their surface called stomata. These stomata also facilitate the release of oxygen and the regulation of water vapor. Within the chloroplasts, the absorbed light energy splits water molecules, and the hydrogen atoms then combine with carbon dioxide to form glucose, a simple sugar. This process fixes atmospheric carbon into an organic compound.
Carbon Dioxide’s Vital Role
Beyond merely being a reactant in photosynthesis, carbon dioxide provides the carbon atoms that form the physical structure of a tree. The glucose produced during photosynthesis is not just for immediate energy; it is converted into more complex organic compounds. These compounds become the tree’s structure, forming its wood, leaves, roots, and bark.
Approximately 50% of a tree’s dry weight is composed of carbon from atmospheric carbon dioxide. Without this influx of carbon, trees cannot synthesize the biomass necessary for their development and expansion. The carbon is stored in various parts of the tree, including about 62% in the trunk, 26% in the roots, and 11% in the branches. This demonstrates how carbon dioxide is for the tree’s physical construction and overall growth.
Atmospheric Carbon Dioxide and Tree Health
The concentration of carbon dioxide in the atmosphere significantly impacts tree health and growth. When CO2 levels are too low, tree growth can be severely hindered. Below approximately 150 parts per million (ppm), many plants struggle to grow and reproduce. Historically, periods of very low CO2 concentrations have reduced plant productivity.
Conversely, increased atmospheric CO2 can enhance tree growth, called the carbon fertilization effect. Elevated CO2 levels can boost photosynthetic rates and improve water use efficiency by reducing stomatal opening. For example, some studies have shown that increasing CO2 from pre-industrial levels to current concentrations has a positive effect on plant biomass accumulation.
However, the benefits of the carbon fertilization effect are limited by other factors. Tree growth also requires sufficient water and other nutrients, particularly nitrogen and phosphorus. If these other resources are scarce, the enhanced growth from higher CO2 may be constrained. While increased CO2 can initially stimulate growth, the long-term response of trees can be limited by these co-factors.