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The organic materials produced by plants, such as leaves, roots, seeds, and stalks. In some cases, microbial and animal metabolic wastes are also considered biomass. The term “biomass” is intended to refer to materials that do not directly go into foods or consumer products but may have alternative industrial uses. Common sources of biomass are (1) agricultural wastes, such as corn stalks, straw, seed hulls, sugarcane leavings, bagasse, nutshells, and manure from cattle, poultry, and hogs; (2) wood materials, such as wood or bark, sawdust, timber slash, and mill scrap; (3) municipal waste, such as waste paper and yard clippings; and (4) energy crops, such as poplars, willows, switchgrass, alfalfa, prairie bluestem, corn (starch), and soybean (oil). See Biological productivity
Biomass is a complex mixture of organic materials, such as carbohydrates, fats, and proteins, along with small amounts of minerals, such as sodium, phosphorus, calcium, and iron. The main components of plant biomass are carbohydrates (approximately 75%, dry weight) and lignin (approximately 25%), which can vary with plant type. The carbohydrates are mainly cellulose or hemicellulose fibers, which impart strength to the plant structure, and lignin, which holds the fibers together. Some plants also store starch (another carbohydrate polymer) and fats as sources of energy, mainly in seeds and roots (such as corn, soybeans, and potatoes).
A major advantage of using biomass as a source of fuels or chemicals is its renewability. Utilizing sunlight energy in photosynthesis, plants metabolize atmospheric carbon dioxide to synthesize biomass. An estimated 140 billion metric tons of biomass are produced annually.
Major limitations of solid biomass fuels are difficulty of handling and lack of portability for mobile engines. To address these issues, research is being conducted to convert solid biomass into liquid and gaseous fuels. Both biological means (fermentation) and chemical means (pyrolysis, gasification) can be used to produce fluid biomass fuels. For example, methane gas is produced in China for local energy needs by anaerobic microbial digestion of human and animal wastes. Ethanol for automotive fuels is currently produced from starch biomass in a two-step process: starch is enzymatically hydrolyzed into glucose; then yeast is used to convert the glucose into ethanol. About 1.5 billion gallons of ethanol are produced from starch each year in the United States.
the total mass of individuals of a single species, group of species, or community as a whole per unit of surface or volume of habitat. It is one of the most important ecological terms. The biomass is generally expressed in mass of wet or dry substance (g/m2, kg per hectare (ha), g/m3, or other measures) or in units proportional to it (mass of carbon or nitrogen of body organic matter, among others).
The plant biomass is called the phytomass and the animal biomass the zoomass. The quantitative correlations of the masses of organisms with different types of nutrition, the dominance of individual species, and so on are judged from the biomass of the individual components of a biocenosis, its distribution in space (for example, from the vertical tiers of forest biocenoses, from the depths or from different soils in bodies of water), and from its seasonal changes. In terrestrial communities (such as forest, steppe, or tundra), the plant biomass greatly exceeds the biomass of herbivorous animals which, in turn, is greater than the biomass of predators (the so-called biomass pyramid).
Plants in an aquatic environment consist mostly of unicellular phytoplankton algae. The phytoplankton biomass is small, often smaller than the biomass of the animals that feed on it. This situation is possible because of the intensive metabolic rate and photosynthesis of unicellular algae, which ensure a high rate of phytoplankton increase. The annual phytoplankton production in the most productive waters is no less than the annual production of forests whose biomass per unit of surface is thousands of times larger. Meadow steppes produce a larger annual increase in biomass than do coniferous forests: with an average phytomass of 23 metric tons/ha their annual production is 10 tons/ha, whereas in coniferous forests with a phytomass of 200 tons/ha the annual production is 6 tons/ha. Small mammalian populations have high growth and reproduction rates, and with an equal biomass their production is higher than that of large mammals. Thus, to evaluate the role of a species or group of species in the cycle of matter and in the biological productivity of a community or ecosystem, one must know not only the biomass of a particular component but also the relative rate of its increase, or the time required for it to be completely renewed. The latter varies in different organisms from many years for trees to several hours or even minutes for bacteria and protozoans under favorable growing conditions.
The biomass is largest in forests (500 tons/ha or more in tropical forests, about 300 tons/ha in broad-leaved forests of the temperate zones). Among the heterotrophic organisms feeding on plants, the microorganisms—bacteria, fungi, actinomycetes, and others—have the largest biomass. Their biomass in productive forests is several tons per hectare. The soil fauna (such as earthworms, insect larvae, nematodes, myriapods, and ticks) account for a large part of the total animal biomass in the temperate zone. This fauna amounts to hundreds of kg/ha in the forest zone, mainly produced by earthworms (300 to 900 kg/ha). The average biomass of vertebrate animals is 20 kg/ha or more, but it often ranges from 3 to 10 kg/ha.
In the hydrosphere, bottom animals (benthos) and large sessile algae in the littoral and sublittoral zones of the seas produce the largest biomass. For example, the biomass of beds of marine algae amounts to several kg/m2. The biomass of bottom animals is also large in some places (on oyster and mussel banks). The biomass of benthos, like that of plankton, decreases rapidly with depth. On most of the ocean bottom the average benthos biomass is several tenths or even hundredths of a g/m2. Phytoplankton and zooplankton in low-productive seawaters do not exceed several dozens mg/m3 or tenths of a g/m2. In highly productive regions, which, incidentally, make up a small fraction of the total area of the ocean, the zooplankton biomass is 10 g/m2, whereas the phytoplankton biomass is 100 g/m2 or more at the time of its maximum development. Lakes differ markedly in plankton and benthos biomass. In moderately productive lakes, both the phytoplankton and zooplankton biomass is usually 1 to 2 g/m3 or several dozenths g/m2. The zoobenthos biomass is often smaller than the zooplankton biomass; it is 10 to 30 g/m2 in the more productive lakes, that is, 100 to 300 kg/ha. The fish biomass in moderately and highly productive lakes is about 75 to 150 kg/ha.
The patterns of geographic distribution and production of the biomass are under intensive study in order to find a solution to the problem of the rational use of biological productivity and to protect the earth’s biosphere.
V. I. Vernadskii in his teaching on the biosphere and geological role of living nature concentrated on determining the total biomass of all the forms of life on earth. The amount can be judged only by crude estimates that will have to be refined by further study. The biomass of forests is the largest; the total wood supply is about 300 billion tons of dry substance. Among the terrestrial animals, the biomass of soil organisms is close to half a billion tons of dry substance, while the total biomass of all the other land animals is one to two orders of magnitude lower. According to the calculations of the Soviet hydrobiologist V. G. Bogorov, the total biomass of all marine plants is 1.7 billion tons and that of animals 32.5 billion tons of wet substance or, in round numbers, 0.3 and 6 billion tons of dry substance, respectively. The total biomass of bacteria and other microorganisms has not yet been determined, but it will undoubtedly be substantial and in terrestrial biocenoses exceed that of animals.
REFERENCESZenkevich, L. A. Biologiia morei SSSR. Moscow, 1963.
Rodin, L. E., and N. I. Bazilevich. Dinamika organicheskogo veshchestva i biologicheskii krugovorot zol’nykh elementov i azota ν osnovnykh tipakh rastitel’nosti zemnogo shara. Moscow-Leningrad, 1965.
Duvigneaud, P., and M. Tanghe. Biosfera i mesto ν nei cheloveka. Moscow, 1968. (Translated from French.)
G. G. VINBERG and IU. I. CHERNOV