The most productive ecosystems are systems with high temperatures, plenty of water and lots of available soil nitrogen. Table 7l-1 describes the approximate average net primary productivity for a variety of ecosystem types. Average annual Net Primary Productivity of the Earth's major biomes. Although all biological activity in plants is ultimately dependent on received solar radiation, it is obvious that solar radiation alone does not determine primary productivity. All plants require sunlight, carbon dioxide, water, and soil nutrients for photosynthesis.
Photosynthesis is also dependent on temperature, moisture, and nutrient availability.
Most biological metabolic activity takes place within the range 0 to 50 degrees Celsius. There is little activity above or below this range. The optimal temperatures for productivity coincide with 15 to 25 degrees Celsius optimal range of photosynthesis. The graph in the Figure 7l-2 illustrates the relationship between the net primary productivity of forests with annual air temperature. The general relationship between net primary productivity and precipitation for forests of the world is shown in the following Figure 7l-3 .