Ecology: the Biology of Interactions. 3.06. Ecosystem Production and Its Measurement

Ukrainian language (latest version) / Russian language (updates stopped)

3.05. Ecological Balance

D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 3. Biogeocenology and Ecology of Communities

3.07. Productivity of Different Biomes

3.06. Ecosystem Production and Its Measurement Humans are one of many consumer species inhabiting Earth. Their existence requires organic matter produced by plants. As humanity grew, it repeatedly faced food shortages. Now that it has become a global force, a natural question arises: how much total organic matter, potentially usable by humans, is produced on our planet? From 1964 to 1974, coordinated data collection on ecosystem productivity and the factors influencing it was conducted worldwide within the framework of the UN's International Biological Programme. To this day, these results form the basis of our knowledge about the natural resources Earth possesses. First, we need to define the basic concepts used in studying ecosystem productivity. Biomass is the total mass of all organisms in a community or a separate population, measured in units of wet or dry mass per unit area or volume of the environment. Biomass includes the bodies of organisms entirely, even if some of their parts are dead, such as wood. The aggregate of dead parts of living organisms constitutes necromass, the dead mass within organisms (note the etymological paradox: necromass is part of biomass!). The proportion of necromass is particularly large in forests. Production is the amount of reproduced biomass per unit area (or volume) per unit time (as well as this biomass itself). Primary production is distinguished—the amount of organic matter produced by autotrophs (producers), and secondary production—the production of heterotrophs (consumers and decomposers). Various methods for measuring ecosystem productivity have been developed. Since the formation and decomposition of organic matter are closely linked to gas exchange (during the formation of organic matter in the most common forms of photosynthesis, carbon dioxide is absorbed and oxygen is released), by measuring the content of these gases, one can estimate production! Which gas's content is better to measure: oxygen or carbon dioxide? The answer will differ for aquatic and terrestrial ecosystems. The fact is that it is more accurate to measure changes in the amount of the gas that is present in smaller quantities under the given conditions. There is relatively a lot of oxygen in the air and little carbon dioxide, so the production of terrestrial ecosystems is usually estimated by CO2. In water, the situation is the opposite: carbon dioxide dissolves very well in it, and oxygen is often scarce. Therefore, the productivity of aquatic ecosystems is determined by measuring changes in oxygen concentration. How is this done? You will better understand the basic principle if you try to guess the essence of one of the simplest methods—the dark and light bottle method. From a boat, during daylight hours, a weight is lowered to a certain depth, to which a pair of bottles is attached: one transparent and the other dark, opaque. Using a special device, the stoppers are pulled from these bottles at a certain depth. The bottles are filled with water characteristic of that depth, along with the phytoplankton and zooplankton organisms contained in that water. Additionally, a sample of this water is brought to the surface, and the oxygen content is determined. Let's denote the initial oxygen concentration as C0. The dark and light bottles filled with water are left at depth for a certain time (e.g., 1 hour), then brought to the surface, and the oxygen concentration is immediately determined. This yields two more values: Cb—the oxygen concentration in the dark bottle after being kept at depth for a standard time, and Cw—the oxygen concentration in the light bottle after the same holding time. Task. Indicate how, knowing C0, Cb, and Cw, to determine the respiration rate and production of the plankton community. To make it easier for you to find the answer to this question, consider why the difference in oxygen content between the dark and light bottles appears only during daylight hours. The method described here for determining ecosystem productivity is far from the only one. Many methods for measuring productivity are based on the use of "labeled" atoms (radioactive isotopes of common biogens). The chlorophyll method is based on the fact that approximately a constant amount of primary production corresponds to one molecule of chlorophyll. All biomass is collected from a certain area, chlorophyll is extracted from it, and its amount is measured. The productivity of a given territory can be estimated even by measuring from a satellite the spectral composition of light that fell on it and reflected from it! The fact is that chlorophyll is characterized by a well-known absorption spectrum, and by the difference between the light that entered the ecosystem and left it, one can measure what portion of the radiation was absorbed by chlorophyll.

3.05. Ecological Balance

D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 3. Biogeocenology and Ecology of Communities

3.07. Productivity of Different Biomes