Where is npp the lowest

Some Definitions So far we have not been very precise about our definitions of "production", and we need to make the terms associated with production very clear. Respiration can be further divided into components that reflect the source of the CO 2. This will be discussed more in our lectures on climate change and the global carbon cycle. Note that in these definitions we are concerned only with "primary" and not "secondary" production.

Secondary production is the gain in biomass or reproduction of heterotrophs and decomposers. The rates of secondary production, as we will see in a coming lecture, are very much lower than the rates of primary production. To better understand the relationship between respiration R , and gross and net primary production GPP and NPP , consider the following example.

This is your "gross production" of money, and it is analogous to the gross production of carbon fixed into sugars during photosynthesis. That is the "cost" you pay to keep operating, and it is analogous to the respiration cost that a plant has when their cells use some of the energy fixed in photosynthesis to build new enzymes or chlorophyll to capture light or to get rid of waste products in the cell.

Measuring Primary Production You may already have some idea of how one measures primary production. There are two general approaches: one can measure either a the rate of photosynthesis , or b the rate of increase in plant biomass.

Will they give the same answer? The method used in studies of aquatic primary production illustrates this method well. In the surface waters of lakes and oceans, plants are mainly unicellular algae, and most consumers are microscopic crustaceans and protozoans. Both the producers and consumers are very small, and they are easily contained in a liter of water.

If you put these organisms in a bottle and turn on the lights, you get photosynthesis. If you turn off the lights, you turn off the primary production. However, darkness has no effect on respiration. Remember that cellular respiration is the reverse process from photosynthesis, as follows. When calculating the amount of energy that a plant stores as biomass, which is then available to heterotrophs, we must subtract plant respiration costs from the total primary production.

The general procedure is so simple that primary production of the world's oceans has been mapped in considerable detail, and many of the world's freshwater lakes have also been investigated Figure 3. One takes a series of small glass bottles with stoppers, and half of them are wrapped with some material such as tin foil so that no light penetrates. These are called the "light" and "dark" bottles, respectively.

Figure 3. The bottles are filled with water taken from a particular place and depth; this water contains the tiny plants and animals of the aquatic ecosystem.

The bottles are closed with stoppers to prevent any exchange of gases or organisms with the surrounding water, and then they are suspended for a few hours at the same depth from which the water was originally taken.

Inside the bottles CO 2 is being consumed, and O 2 is being produced, and we can measure the change over time in either one of these gases. For example, the amount of oxygen dissolved in water can be measured easily by chemical titration.

Then, the final value is measured in both the light and dark bottles after a timed duration of incubation. What processes are taking place in each bottle that might alter the original O 2 or CO 2 concentrations? The equations below describe them. In this example we may also have some consumer respiration in both bottles, unless we used a net to sieve out tiny heterotrophs. Now consider the following simple example. It illustrates how we account for changes from the initial oxygen concentrations in the water that occurred during the incubation.

We will assume that our incubation period was 1 hour. The oxygen technique is limited in situations where the primary production is very low. In these situations, the radioactive form of carbon, C 14 14 CO 2 , can be used to monitor carbon uptake and fixation. You can also convert the results between the oxygen and carbon methods by multiplying the oxygen values by 0.

Consider the following example. Suppose we wish to know the primary production of a corn crop. We plant some seeds, and at the end of one year we harvest samples of the entire plants including the roots that were contained in one square meter of area. We dry these to remove any variation in water content, and then weigh them to get the "dry weight".

Thus our measure of primary production would be grams m -2 yr -1 of stems, leaves, roots, flowers and fruits, minus the mass of the seeds that may have blown away. What have we measured? It isn't GPP, because some of the energy produced by photosynthesis went to meet the metabolic needs of the corn plants themselves.

Is it NPP? Well, if we excluded all the consumers such as insects of the corn plant, we would have a measure of NPP. But we assume that some insects and soil arthropods took a share of the plant biomass, and since we did not measure that share, we actually have measured something less than NPP. Note that this is exactly the same situation in the bottle method we described above if small heterotrophs that grazed on algae were included in the bottle, in which case the two methods would measure the same thing.

In recent years it has also become possible to estimate GPP and R in large plants or entire forests using tracers and gas exchange techniques. These measurements now form the basis of our investigations into how primary production affects the carbon dioxide content of our atmosphere. Production, Standing Crop, and Turnover With either of these methods, the primary Production can be expressed as the rate of formation of new material, per unit of earth's surface, per unit of time.

Standing crop , on the other hand, is a measure of the biomass of the system at a single point in time, and is measured as calories or grams per m 2. The difference between production and standing crop is a crucial one, and can be illustrated by the following question. Should a forester, interested in harvesting the greatest yield from a plot, be more interested in the forest's standing crop or its primary production?

Well, the key element to the answer is "TIME". If the forester wants a short term investment i. If instead the forester wants to manage the forest over time sell some trees while growing more each year , then the rate at which the forest produces new biomass is critical. Thus the stock or standing crop of any material divided by the rate of production gives you a measure of time.

Notice how similar really, identical this turnover time is to the residence time that you learned about in earlier lectures. It is really important to consider this element of "time" whenever you are thinking about almost any aspect of an organism or an ecosystem or a problem in sustainability.

Learning about how much of something is happening and how fast it is changing is a critical aspect of understanding the system well enough to make decisions; for example, the decision of the forester above may be driven by economic concerns or by conservation concerns, but the "best" choice for either of those concerns still depends on an understanding of the production, standing crop, and turnover of the forest. This highlights the point made in earlier lectures that to make decisions about sustainability you must understand these basic scientific concepts.

Patterns and Controls of Primary Production in the World's Ecosystems 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 see Figure 4. Figure 4. Net Primary Production per unit area of the world's common ecosystems. If we wish to know the total amount of NPP in the world, we must multiply these values by the area that the various ecosystems occupy. In doing that, we find that now the most productive systems are open oceans, tropical rain forests, savannas, and tropical seasonal forests see Figure 5.

Figure 5. Average world net primary production of various ecosystems. 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 6a and 6b. Overall, 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. Figures 6a and 6b. 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. For example, look at the range of production values Y axis at a temperature value of 10 deg C or at a precipitation value of mm. The scatter or variation in the production 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 low, but the turnover rate can be high see below 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. Summary of Part 1, Primary Production Organisms are characterized as autotrophs and heterotrophs.

Autotrophs produce their own food by fixing energy through photosynthesis or, less commonly, chemosynthesis. Heterotrophs must feed on other organisms to obtain energy. Primary production is the creation of new organic matter by plants and other autotrophs.

It can be described per unit area for individual ecosystems or worldwide. Production also is a rate, measured per time unit, while standing crop biomass is the amount of plant matter at a given point in time. The ratio of standing crop to production is called turnover. The turnover time of a system is important in determining how a system functions.

Production rates can be quantified by a simple method by which oxygen or carbon production is measured. Production can also be quantified by measuring the rate of new biomass accumulation over time. The distinction between gross primary production GPP , net primary production NPP , and net ecosystem production NEP is critical for understanding the energy balance in plants and in whole ecosystems. Production varies among ecosystems, as well as over time within ecosystems.

Rates of production are determined by such factors as climate and nutrient supply. Precipitation is the dominant control worldwide, but nutrient availability often limits primary production in any particular, local system.

The Flow of Energy to Higher Trophic Levels In the section above we examined the creation of organic matter by primary producers.

Without autotrophs, there would be no energy available to all other organisms that lack the capability of fixing light energy. However, the continual loss of energy due to metabolic activity puts limits on how much energy is available to higher trophic levels this is explained by the Second Law of Thermodynamics.

Key Words: Tropical rain forest - biodiversity - layering - tundra - alpine - deserts - global patterns. Tropical rain forests have high NPP and the highest biodiversities of any terrestrial ecosystems. The physical environment favours vast photosynthetic output and high growth rate. In rain forests, plants have constant high levels of water and light at canopy level and the nutrient supply is as high as possible, due to rapid decomposition. Because the light is strong, it is able to sustain several layers of plant growth.

High levels of water allow plants to maintain a constant flow from their roots, bringing up more nutrients.

They can keep stomata open all day to optimise CO 2 uptake without becoming short of water. They can use water to cool down if required. Because the trees have access to a plentiful supply of ground water that builds up in the rainy season, they actually grow better when the rainy skies clear and allow more sunlight to reach the forest. Land Life. EO Explorer. Show All Maps. Net Primary Productivity. Net Radiation. Sea Surface Temperature. Sea Surface Temperature Anomaly.