Section 1.5: The Nutrient Cycle

Outcomes

Students will:

  • Interpret the nutrient cycle as a representation of energy flow and the cycling of matter through ecosystems.

  • Recognize some of the elements trees require and use for growth and survival.

  • Understand the factors that influence the nutrient cycle, including climate, location, various forest ecosystems, and potential disturbances.

Key Terms

Compounds / Elements

See content or Module Glossary for definitions

What is the Nutrient Cycle?

The nutrient cycle is the exchange of elements between living and nonliving things. It is nature's recycling system. The nutrient cycle shows how essential nutrients travel through the environment, providing every organism what it needs to live. There are various nutrient cycles (ex: carbon, oxygen/water, nitrogen) but this section will provide an overview of the general process for essential nutrients.

Nutrient Cycle Process

Much like the water cycle, there is no beginning or end to the nutrient cycle process, but this process can be broken down step-by-step.

  • First water and air penetrate the soil causing nutrient-rich litter (leaves and other plant matter) to break down into the soil, releasing nutrients and minerals.

  • The litter is then decomposed and broken down by organisms called decomposers (ex: fungi, algae, earthworms, millipedes, slugs, etc.).

  • The soil stores these nutrients and a certain percentage is absorbed by the tree, leading to plant growth and nutrient-rich leaves.

  • The nutrients also leave from the soil in gaseous form and enter into the atmosphere to then be absorbed by the leaves, restarting the cycle.

As shown in Figure 22, this cycle has been shown for one tree but can be expanded for entire forests.


Figure 22 shows a tree participating in the nutrient cycle. Original image by Pixabay.
Figure 22 shows a tree participating in the nutrient cycle. Original image by Pixabay.

What Elements are Found in the Nutrient Cycle?

Trees and plants need many nutrients in order to thrive. Nutrient availability is strongly influenced by the quantity and quality of litter produced in a forest. There are three elements critical for tree survival and these are carbon, nitrogen, and phosphorus. These elements are the building blocks of all matter but there are also many other elements and compounds that make up nutrients. Elements are the simplest substances found in the world and that make up all matter while compounds refer to something composed of two or more elements. The periodic table below shows the elements commonly found in the nutrient cycle.

  • Trees require large quantities (shown in blue) of elements such as: Hydrogen (H) / Carbon (C) / Oxygen (O) / Nitrogen (N) / Magnesium (Mg) / Phosphorus (P) / Potassium (K) / Calcium (Ca)

  • Trees also use small quantities (shown in red) of elements such as: Boron (B) / Chlorine (Cl) / Manganese (Mn) / Iron (Fe) / Copper (Cu) / Zinc (Zn)

Figure 23 highlights some of the important nutrients trees need on the periodic table. Original image by LeVanHan.
Figure 23 highlights some of the important nutrients trees need on the periodic table. Original image by LeVanHan.

What Factors Influence the Nutrient Cycle?

The nutrient cycle is controlled by the climate, location, and living communities in forest ecosystems. The role of each factor varies from the diversity of forest ecosystems around the world (ex: boreal, temperate, tropical). Even in Canada, we see this diversity among our forest. Each of these forests behave uniquely and respond to environmental conditions differently, storing varying rates of carbon and producing different amounts of nutrient-litter. For example, in tropical forests, there is a low storage rate of carbon and a high amount of litter production while in boreal forests, there is high carbon storage and low litter production.

What Disturbs the Nutrient Cycle?

Fire, harvesting, storms, pests or disease can all affect the nutrient cycle processes. Often, these disturbances are natural and important to the forest ecosystem as some nutrients are added or lost which can have a positive or negative impact.

For example, after a fire, there is a redistribution of nutrients in the forest due to the combination of the following:

  1. Fire burns all live and decomposing plant material.

  2. Ash is distributed by the wind.

  3. Water erodes the surface soil.

  4. Liquid filtering of nutrients through and out of the soil.

The relative importance of these processes varies with each nutrient and is modified by differences in fire intensity, soil characteristics, landscape, climatic patterns, and biotic communities.

It may help to remember the information from this module or refer back to it when you are conducting your data analysis on your tree and soil samples. If you notice a presence of a certain element, recall how nutrients are transported and stored and it may help you understand how the element found its way into the tree you sampled.

References for Section 1.5

Bhatti, J. & Foster, N. (2006) Forest ecosystems: Nutrient cycling. Encyclopedia of Soil Science, 718-721. doi: 10.1081/E-ESS-120001709

Wikipedia. (2019). Nutrient cycle. Retrieved from https://en.wikipedia.org/wiki/Nutrient_cycle