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What are the patterns and controls of Primary Production in the World's Ecosystems?

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The world's ecosystems vary tremendously in productivity, as illustrated in the following figures. In terms of NPP per unit area, the most productive systems are estuaries, swamps and marshes, tropical rain forests, and temperate rain forests.
What accounts for these differences in production per unit area? Basically, the answer is that climate and nutrients control primary productivity. Areas that are warm and wet generally are more productive (see Figures 5.5 a and b) the amount of water available limits land primary production on our world, in part due to the large areas of desert found on certain continents.
Agricultural crops are especially productive due to "artificial" subsidies of water and fertilizers, as well as the control of pests.
Even though temperature and especially precipitation are related to production, you will notice a large degree of "scatter" around the line of best fit drawn in the graphs above. This scatter or variation is due in part to other aspects of particular (local) systems, such as their nutrient availability or their turnover rates. For example, grasslands can have a relatively high rate of primary production occurring during a brief growing season, yet the standing crop biomass is never very great. This is indicative of a high turnover rate. In a forest, on the other hand, the standing crop biomass of above-ground wood and below-ground roots is large. Each year's production of new plant matter is a small-fraction of total standing crop, and so the turnover of forest biomass is much lower. .
Another good example is seen in the oceans, where most of the primary production is concentrated in microscopic algae. Algae have short life cycles, multiply rapidly, do not generate much biomass relative to their numbers, and are eaten rapidly, by herbivores. At any given point in time, then, the standing crop of algae in an ocean is likely to be low: but the turnover rate can be high. We have now examined the first step in the flow of energy through ecosystems: the conversion of energy by primary producers into a form that is usable by heterotrophs, as well as by producers themselves. In the next lecture we will examine how this energy moves through the rest of the ecosystem, providing fuel for life at higher trophic levels.

francis1897 answered the question on February 27, 2023 at 12:29

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What are the patterns and controls of Primary Production in the World's Ecosystems?

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