Observe: Trees Help to Cycle Nutrients

Water is not the only thing that trees help to recycle.  Nutrients are chemicals that plants and animals need to grow and live. Trees have important roles in the nitrogen cycle and the phosphorus cycle.

Study the Cycles diagrams below. Note the roles of trees in each simplified cycle.

• As part of the nitrogen and phosphorus cycle, trees absorb nitrates and phosphates, which are used to help make the parts of the tree.

Nitrogen makes up about 78% of our atmosphere. However, this is mostly not usable by animals and plants. Plants and animals could not live without nitrogen. It is an important part of amino acids, proteins, and even our DNA which makes up our cells. About 3% of our body weight is nitrogen.

When nitrogen is found in the soil, bacteria change its state so it can be used by plants. Plants use it to make chlorophyll which helps make their food and energy. Animals then get their nitrogen from the plants. Wastes and decaying plant material return nitrogen to the soil.

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Phosphorus is found in rocks. When it rains, phosphurus moves from rocks to soils and oceans. If phosphorus runs into the ocean, it can no longer be used by trees, humans, and animals.

If however, the phosphates return to the soil, for example when plants die, they can be reused by trees. One other way phosphates disappear is when crops are taken away from the soil in farming so that over many years the soil runs out of phosphorus compounds. Fertilizer must be added to renew the soil.