Primary Production

Abstract

For survival and growth, living organisms must obtain energy and minerals from their environment and must synthesize organic matter. The synthesis of organic matter through photosynthesis by green plants in an ecosystem is called the primary production of that ecosystem. The total amount of organic matter produced by photosynthesis is called gross production (Pg). Green plants consume some photosynthate in respiration (r), the remainder being incorporated into the body of the plant. This we call net production (Pn). So,

$$\text{Pg}\,\text{ = }\,\text{Pn}\,\text{ + }\,\text{r}\,\, \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots$$

(1.1)

$$\text{or}\,\,\,\,\text{Pn}\,\text{ = }\,\text{Pg}\,\text{ - }\,\text{r}\,\,\, \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots$$

(1.2)

The values of Pg and Pn are usually expressed as dry weight in which case they are often called dry matter production. For forest ecosystems it is general practice to use years and hectares as the units of time and area, respectively. We can either determine net production by measuring gross production and respiration or we can determine gross production by measuring net production and respiration.