8 



Nutrients 



NUTRIENTS AND THE ENVIRONMENT 



A student once wrote in an ecology paper: "For all organisms nutri- 

 tion is par excellence"— his way of stating that nutrients are a crucially 

 important ecological influence! Indeed, all living things are de- 

 pendent upon the environment for the supply of energy and of 

 the materials necessary for their nutrition. Green plants use sun- 

 light as a source of energy and synthesize carbohydrates from water 

 and carbon dioxide, obtained as discussed in earlier chapters. To 

 produce living tissue other materials must also be present— particu- 

 larly protein. Plants build their own proteins from carbohydrates, 

 nitrogen compounds, and other inorganic substances. These simple 

 inorganic building materials constitute the nutrients of the green plant. 



Colorless plants and animals must have ready-made organic com- 

 pounds for their nutrition, and they feed upon material which is, or 

 recently has been, part of another living organism. Energy is ob- 

 tained by the oxidation of this organic food. Nutrients for green 

 plants are thus obtained from the supply of inorganic substances in 

 the environment, whereas nutrients for animals and colorless plants 

 are represented by the organic matter derived from other organisms. 



Nutrition is obviously and necessarily a reciprocal process. The 

 availability of nutrients in the environment influences the growth and 

 distribution of animals and plants, and the activities of living or- 

 ganisms profoundly change the abundance of nutrient materials. 

 The oxidative metabolism of the living organism and the oxidative de- 

 composition of all plant and animal tissues after death result in the 

 return to the environment not only of water and carbon dioxide but 

 also of inorganic materials that can serve again as nutrients for green 

 plants. These relationships are indicated in the following scheme 

 which might be thought of as the "equation of all outdoors": 



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