Trees do not “eat” in the way humans or animals consume food for sustenance. As autotrophs, or self-feeders, trees produce their own energy-rich compounds internally, utilizing simple external inputs from the environment. This process requires a continuous supply of light energy, atmospheric gases, and dissolved minerals to build the complex structures that constitute a tree.
The Primary Energy Source: Sunlight and Carbon Dioxide
A tree’s true “food” is the sugar it manufactures through photosynthesis, a biological conversion that takes place primarily in the leaves. This mechanism is powered by sunlight, which provides the necessary energy to drive the chemical reaction. Specialized green pigment molecules called chlorophyll, housed within the leaves’ cells, capture this light energy.
The light energy converts two simple raw materials—carbon dioxide (CO2) and water (H2O)—into glucose, a type of sugar, and oxygen (O2). Carbon dioxide is absorbed directly from the air through tiny, adjustable pores on the leaf surface called stomata. This atmospheric carbon forms the backbone of the glucose molecule, which is the tree’s energy storage and building block.
The resulting glucose molecules are transported throughout the tree to fuel cellular respiration and create structural materials like cellulose and lignin. This sugar production accounts for the vast majority of the tree’s dry mass. The oxygen produced as a byproduct is released back into the atmosphere through the stomata.
Essential Elements Absorbed from the Soil
While photosynthesis creates the tree’s energy source, the physical structure and internal chemistry require elements absorbed through the root system. Water is the primary input absorbed from the soil, serving as a reactant in photosynthesis and as the solvent that transports all other nutrients. Water also maintains turgor pressure, which provides rigidity to non-woody tissues, keeping leaves and small stems upright.
Trees require relatively large quantities of specific mineral elements, known as macronutrients, to support robust growth. Nitrogen (N) is a major component of chlorophyll and proteins, making it necessary for leaf growth and the photosynthetic process. Phosphorus (P) is involved in energy transfer and storage within the tree’s cells and is important for strong root development.
Potassium (K) helps regulate the opening and closing of the stomata, controlling water loss and CO2 intake. Macronutrients, such as calcium and magnesium, are absorbed by the roots as dissolved ions suspended in the soil water. The tree also requires micronutrients, including Iron (Fe) and Zinc (Zn), which are needed in smaller amounts but are necessary for enzyme function and chlorophyll formation.
Partnerships That Aid Nutrition
The acquisition of soil-bound nutrients is significantly enhanced by specialized biological relationships between the tree and soil microorganisms. Mycorrhizal fungi form a symbiotic partnership with the tree’s roots, creating a vast network of fungal filaments called hyphae. These hyphae extend far beyond the reach of the tree’s own roots, effectively increasing the surface area for absorption of water and minerals.
In this mutual exchange, the fungi are highly efficient at scavenging for certain nutrients, particularly phosphorus and nitrogen, which they deliver to the tree’s root cells. In return, the tree provides the fungi with a steady supply of sugars—the glucose produced during photosynthesis—that the fungi cannot create themselves.
Other microorganisms, such as nitrogen-fixing bacteria, also play a direct role by converting atmospheric nitrogen gas into forms like ammonia that are usable by the tree, especially in the case of certain host plants. This microbial collaboration allows the tree to maximize its nutrient intake from the soil environment.