Submitted to: Soil Microbiology: Environmental and Agricultural Perspectives
Publication Type: Book / Chapter
Publication Acceptance Date: 4/29/1997
Publication Date: N/A
Interpretive Summary: There are two broad groups of algae that live in the soil; those with subcellular organization and the ones that lack such organization. The latter are commonly called blue-green algae. The algae with subcellular organization are very similar to higher plants. The blue green algae, however, are more comparable to bacteria. Algae use sunlight for energy, and in that respect they all are similar to the higher plants. Some of the blue-green algae can use, or fix, atmospheric nitrogen. This enables them to grow in areas that have poor soils, or colonize land that has been disturbed. Many soil algae have the ability to form spores or resting cells that allow them to withstand harsh environments. The algae are most plentiful in the upper soil layers where some light can enter. In addition to light, their populations are also influenced by soil temperature and soil moisture. Their mineral requirements, including carbon dioxide, are similar to those of higher plants. Soil algae may be attacked and eaten by many of the animals that live in the soil. Some algae may form associations with fungi, for example lichens, or higher plants. Algae are common pioneers on bare soil and contribute to soil development and soil quality. In some areas, such as deserts, they produce significant amounts of organic matter. Some of the complex compounds that they secrete into soil bind particles together to form aggregates, thereby promoting good soil structure. In the future, certain soil algae, especially those that can utilize atmospheric nitrogen, may be managed for biofertilizers. However, to date, this potential has not fully realized.
Technical Abstract: There are two broad groups of algae; eukaryotic algae and prokaryotic cyanobacteria (formerly known as blue-green algae). On a subcellular level, the eukaryotic algae are morphologically and physiologically similar to higher plants. The cyanobacteria, with the exception of their photosynthetic arrangement, are more comparable to bacteria. Algae are photoautotrophs, and their system of photosynthesis generally resembles that of the higher plants. Some prokaryotic cyanobacteria also can fix Nitrogen. Many soil algae have the ability to form spores or resting cells that allow them to withstand harsh environments. Algae are most abundant in the upper soil layers where light can penetrate (photic zone). In addition to light, their populations are affected by soil acidity, temperature and especially moisture. As photoautotrophs, they do not require reduced C for growth; however, Carbon dioxide or dissolved carbonate is essential. Their requirements for macro- and micronutrients are similar to those of higher plants. As primary producers, they are subject to predation by many protozoa, nematodes and soil insects. Some algae form associations with higher plants. For example, lichens are symbiotic associations formed by algae or cyanobacteria with several types of fungi. Algae are common pioneers on bare soil and contribute to soil development. In ecosystems such as deserts, they produce ecologically significant amounts of organic matter. The polysaccharides they exude into soil bind particles together to form aggregates, thereby promoting soil structure. In the future, certain soil algae, especially the Nitrogen-fixing cyanobacteria, may be managed for biofertilizers; however, to date, this potential has not fully realized.