For most organisms, optimum growth occurs over a temperature range rather than at a fixed temperature. The associations existing between different soil microorganisms, whether of a symbiotic or antagonistic nature, influence the activities of microorganisms in the soil. Hydrogen Ion Concentration 4. Soil composition is a physical factor determined by the relative amounts of sand, silt, and clay in the soil (the soil texture), as well as by the organic-matter content. Sometimes it also changes the nutritional requirement. If micro­organisms from an acid such as acetic acid in a medium buffered with phosphate, a part of the basic salt (K2HPO4) is converted to the weakly acidic salt. Factors Affecting Soil Formation. Incorrect: Some soils may have various colored horizons due to wind deposited material, or being formed under lakes or oceans, but they would not have organic matter accumulation on the surface. Since microbial activity and growth are manifestations of enzymatic reactions, their rates of growth are, temperature-dependent. Most animals probably do not eat either type of plant. 18.34 illustrates the effect of temperature on the rate of to bacterial species. The fate of amino acids in the cell is also decided by pH. This can be as simple as the burning of a small candle or the combustion of small amount of alcohol to use up some of the free oxygen. Rainfall is usually the limiting factor for microbial biomass in southern Australia (figure 2). (iii)Facultative anaerobes can grow both in the presence and the absence of free oxygen. The maximum growth temperature is the highest temperature at which growth occurs. These differences reflect the normal habits and habitats of the organisms. Question 9: What causes the coniferous forest soil to develop quicker than the grassland soil‏? There are some exceptions to this generalization. Many plant and soil micro-organisms, especially Actinomucetes, prefer relatively alkaline conditions. Fig. Factors Affecting Growth of Bacteria. The successful cultivation of micro-organisms in the laboratory is based upon two basic principles; nutritional requirement to prepare a suitable nutrient medium, and appropriate physical conditions to obtain maximum growth. Scientists attribute soil formation to the following factors: Parent material, climate, biota (organisms), topography and time. Carbonates cannot be used in media exposed to air, because the release of CO2 is rapidly swept away, causing the medium to become extremely alkaline. However, studies on soil and microbial biomass stoichiometry in forests are rare. Wind has not blown away the forest litter, but it has not blown away the grassland litter either, because the plant canopy (tops of plants) force wind up and above the soil surface. Each micro-organism can grow only within a growth temperature range characteristic of the species. Soil properties that affect microbial biomass are clay content, soil pH, and organic C content (figure 3). The effects of biochar on soil microbial and enzyme activities are integrally linked to the potential of biochar in achieving these benefits. Molecular oxygen is relatively insoluble in water, and so must be continuously made available to aerobic micro-organisms. Many culture media contain amphoteric substances such as peptones. Soil texture can also affect the soil nutrient status and water content, thus affecting the living environment and metabolic activity of microorganisms [31–32]. FACTORS AFFECTING SOIL MICROBIAL FUEL CELLS 335 power. Bacteria are normally classified into three broad groups, psychrophiles, mesophiles, and thermophiles (Table 18.4). Soil depth and other factors also influence microbe abundance. Minimum growth temperature is difficult to determine precisely, because of an increase in generation time. Looks Good! Organisms such as Aerobacter aero genes, which can form acetyl methyl-carbinol from glucose, will do so only below pH 6.0. Facultative thermophiles grow both at 37°C and 55°C. If man disturbed the forest soil, it definitely would not look like the photo. At an acid reaction they are decarboxylated to the corresponding amines, whereas at alkaline reaction they are delaminated to an acid. Soil and microbial biomass stoichiometry plays an important role in understanding nutrient cycling in terrestrial ecosystems. Which of the following factors does not affect soil formation. The present atmosphere of the earth contains about 20 per cent (V/V) oxygen. This also influences the structure and texture of the soil. Temperature 2. Soil factors affecting herbicide persistence include soil composition, soil chemistry, and microbial activity. Figure 2:Microbial biomass carbon over a year from a soil near Meckering, Western Australia. Among the edaphic parameters, pH is the factor that most strongly influences soil bacterial communities. Correct: The accumulation of organic matter in the forest soil surface is due to the acidic nature of the needles inhibiting microbial attack and breakdown. Microbial growth and activities are strongly affected by the pH of the medium. Figure 4 also illustrates that humus content decreases with soil depth. The temperature relationships of a micro-organism are usually described by the three cardinal temperatures, the minimum, optimum, and maximum temperatures of growth. The extent to which a medium should or may be buffered depends on its intended purpose, and is limited by the buffering capacity of the compounds used. This makes sense, because humus is derived from decaying plant material which originates at or near the soil surface. 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