Producers plants take in CO 2 , and synthesize sucrose and starch through photosynthesis. As these carbon compounds are ingested by herbivores and carnivores, the carbons are transferred to a higher trophic level.
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At each stage, part of the carbons returns to the atmosphere or water as CO 2 through respiration and degradation of dead bodies Figure Recent increase in the CO 2 concentration of the atmosphere caused by massive combustion of fossil fuels such as coal and oil is an issue of ongoing concern. Table Flow of energy through ecosystem decreases at each trophic level. In ecosystems, the speed at which producers fix CO2 into organic compounds is referred to as the primary production rate of an ecosystem [in kcal or J per area per time].
It consists of the gross production rate and net production rate. The gross production rate represents the speed at which energy is fixed by the producers, whereas the net production rate is calculated by subtracting the respiration rate from the total production rate, and is used for new growth, storage of material, and seed production.
However, most organisms cannot use nitrogen gas N 2 directly—only nitrogen-fixing bacteria can convert N 2 into ammonium through biological nitrogen fixation 2. Nitrogen-fixing bacteria consist of those that live symbiotically with leguminous plants by forming root nodules, those that live in tissue spaces of various plants and in the soil of rhizospheres, and those that live independently.
Ammonia is incorporated into biological material by nitrogen assimilation 3 , and is then converted to ammonium salts through bacterial activity and decomposition, and discharged into the soil or seawater. Part of the ammonium salts are turned into nitrates by nitrifying bacteria.
The nitrates and ammonium salts are consumed by producers such as plants, to produce biological molecules such as proteins through nitrogen assimilation. Primary consumers then consume the producers and use these proteins as their nitrogen source. Animals metabolize and excrete the nitrogen in the biological molecules as ammonium salts, urea, and uric acid. The nitrogen included in excreted matter, undigested matter in the feces, or dead bodies are eventually converted to ammonium salts and nitrates by the decomposers, and discharged into the soil or seawater.
Part of the nitrates are then converted to N 2 O, and even N 2 , by denitrifying bacteria and returned to the atmosphere. This nitrogen cycle of the ecosystem is summarized in Figure Furthermore, nitrogen oxides generated by automotive engines and through electricity discharged by lightning eventually mix with rain to become nitrates, which fall on the earth as acid rain. Soluble phosphates are cycled in the food web.
Possible external sources of phosphorous from outside the food web include: 1 igneous apatite and fossil bone of corpses of ancient organisms; and 2 phosphates from guano deposits originating from excreta of seabird colonies. These external phosphates are linked to the cycling of phosphates in the ecosystem Figure Recently, blue-green algae growing in swamps and red tides occurring in inner bays have become a problem.
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Outbreaks of blue-green algae genus Cyanobacterium and red tides e. Environmental policies to prevent this situation are increasingly important, as eutrophication becomes progressively more conspicuous.
The application of organic fertilizers increased the organic carbon content of the soil and thereby increasing the microbial counts and microbial biomass carbon. Volatiles of Artemisia annua L. How to cite this article: N. Dkhar, Journal of Agronomy, 9: DOI: Full Name:.
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