3. Nutrient Recycling in Ecosystems

Examining the three categories of organisms present in every ecosystem, we can discern the two major features underlying its sustainability; it recycles of all its essential chemical nutrients. (elements: carbon C, nitrogen N, phosphorous P, and others). And it runs entirely on solar energy which is nonpolluting and everlasting in terms of any human perspective. 

We will examine each of these in more detail.  

Nutrient recycling

The following video illustrates the manner of recycling in some detail:

Emphasize that all non-photosynthetic organisms carry on respiration as their only source of energy. In doing so they degrade biomass to carbon dioxide, water, and the other raw chemical nutrients. Carbon dioxide is released to the air, where it may travel anywhere about the earth before it is reabsorbed by plants elsewhere, in photosynthesis. Other chemicals are released in water solution such as urine. Released to the soil they may be reabsorbed by plant roots to repeat the cycle. (The many stages of the nitrogen cycle are not necessary to memorize at this stage, but do note the key roles played by bacteria and fungi.)

Note that carbon reserves, as they come from and return to carbon dioxide in the air, cannot help but be replenished and recycled. Other elements recycle on location. For example, phosphorus (P) absorbed by roots must be retuned to the same soil/locaton to be reabsorbed and recycled.