What do plants use directly from the atmosphere

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As part of these life processes, nitrogen is transformed from one chemical form to another. The transformations that nitrogen undergoes as it moves between the atmosphere, the land and living things make up the nitrogen cycle. There are three ways nitrogen can be fixed to be useful for living things:. Plants take up nitrogen compounds through their roots. Animals obtain these compounds when they eat the plants.

When plants and animals die or when animals excrete wastes, the nitrogen compounds in the organic matter re-enter the soil where they are broken down by microorganisms, known as decomposers.

This decomposition produces ammonia, which can then go through the nitrification process. Nitrifying bacteria in the soil convert ammonia into nitrite NO 2 - and then into nitrate NO 3 -.

This process is called nitrification. Compounds such as nitrate, nitrite, ammonia and ammonium can be taken up from soils by plants and then used in the formation of plant and animal proteins. Denitrification completes the nitrogen cycle by converting nitrate NO 3 - back to gaseous nitrogen N 2. Denitrifying bacteria are the agents of this process. These bacteria use nitrate instead of oxygen when obtaining energy, releasing nitrogen gas to the atmosphere.

Agriculture may be responsible for about half the nitrogen fixation on Earth through fertilisers and the cultivation of nitrogen-fixing crops. Herridge, D. Global inputs of biological nitrogen fixation in agricultural systems. Plant Soil , Hubbell, D. Biological Nitrogen Fixation. Napoli, C. Ultrastructure of Rhizobium-induced infection threads in clover root hairs. Applied and Environmental Microbiology 30 , National Research Council. Biological Nitrogen Fixation: Research Challenges. Postgate, J.

The Fundamentals of Nitrogen Fixation. Stephan, M. Volume I, eds. Vance, C. Symbiotic nitrogen fixation and phosphorus acquisition. Plant nutrition in a world of declining renewable resouces. Plant Physiology , Van Rhyn, P.

The Rhizobium-plant symbiosis. Microbiological Reviews 59 , Vadakattu, G. Free-living bacteria lift soil nitrogen supply. Farming Ahead , 40 Vitousek, P. Human alteration of the global nitrogen cycle: sources and consequences. Ecological Applications 7 , CO;2 Vlassak, K. Introduction to the Basic Drivers of Climate. Terrestrial Biomes. Coral Reefs. Energy Economics in Ecosystems. Biodiversity and Ecosystem Stability. Ecosystems Ecology Introduction.

Factors Affecting Global Climate. Rivers and Streams: Life in Flowing Water. The Conservation of Mass. The Ecology of Carrion Decomposition. Causes and Consequences of Biodiversity Declines. Earth's Ferrous Wheel.

Alternative Stable States. Recharge Variability in Semi-Arid Climates. Secondary Production. Food Web: Concept and Applications. Terrestrial Primary Production: Fuel for Life. Citation: Wagner, S. Nature Education Knowledge 3 10 Aa Aa Aa. Figure 1. Nitrogen-fixing organisms found in agricultural and natural systems. The Process. Figure 2. True-color image of Mississippi River sediment deposition into the Gulf of Mexico. Figure 3. Nitrogen Fixation by Free-Living Heterotrophs. Many heterotrophic bacteria live in the soil and fix significant levels of nitrogen without the direct interaction with other organisms.

Examples of this type of nitrogen-fixing bacteria include species of Azotobacter , Bacillus , Clostridium , and Klebsiella. As previously noted, these organisms must find their own source of energy, typically by oxidizing organic molecules released by other organisms or from decomposition. There are some free-living organisms that have chemolithotrophic capabilities and can thereby utilize inorganic compounds as a source of energy.