Nitrifying bacteria change ammonium (NH4+) to nitrite (NO2-) then to nitrate (NO3-) – a preferred form of nitrogen for grasses and most row crops. When leaves or roots from the host plant decompose, soil nitrogen increases in the surrounding area. The plant supplies simple carbon compounds to the bacteria, and the bacteria convert nitrogen (N2) from air into a form the plant host can use. Visible nodules are created where bacteria infect a growing root hair. Nitrogen-fixing bacteria form symbiotic associations with the roots of legumes like clover and lupine, and trees such as alder and locust. In a diverse bacterial community, many organisms will compete with disease-causing organisms in roots and on aboveground surfaces of plants. Stable aggregates improve water infiltration and the soil’s water-holding ability. Some bacteria affect water movement by producing substances that help bind soil particles into small aggregates (those with diameters of 1/10,000-1/100 of an inch or 2-200µm). Some of these species are important to nitrogen cycling and degradation of pollutants.īacteria from all four groups perform important services related to water dynamics, nutrient cycling, and disease suppression. A fourth group, called lithotrophs or chemoautotrophs, obtains its energy from compounds of nitrogen, sulfur, iron or hydrogen instead of from carbon compounds. Bacterial pathogens include Xymomonas and Erwinia species, and species of Agrobacterium that cause gall formation in plants. The third group of bacteria is the pathogens. The most well-known of these are the nitrogen-fixing bacteria. Decomposers are especially important in immobilizing, or retaining, nutrients in their cells, thus preventing the loss of nutrients, such as nitrogen, from the rooting zone.Ī second group of bacteria are the mutualists that form partnerships with plants. A number of decomposers can break down pesticides and pollutants in soil. By this process, bacteria convert energy in soil organic matter into forms useful to the rest of the organisms in the soil food web. Most are decomposers that consume simple carbon compounds, such as root exudates and fresh plant litter. P lease contact the Soil and Water Conservation Society at for assistance with copyrighted (credited) images.īacteria fall into four functional groups. Reprinted with the permission of Cambridge University Press.
Please contact the Soil and Water Conservation Society at for assistance with copyrighted (credited) images.īacteria dot the surface of strands of fungal hyphae.Ĭredit: R. Holmes, Oregon State University, Corvallis. That is as much mass as two cows per acre.Ī ton of microscopic bacteria may be active in each acre of soil.Ĭredit: Michael T. A teaspoon of productive soil generally contains between 100 million and 1 billion bacteria. What bacteria lack in size, they make up in numbers. Bacteria are tiny, one-celled organisms – generally 4/100,000 of an inch wide (1 µm) and somewhat longer in length.
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