Soil organisms, acids produced

By 1945, Stacey speculated about the possibility of a structural relationship between Pneumococcus capsular polysaccharides and those produced by other organisms. With Miss Schliichterer, he had examined the capsular polysaccharide of Rhizobium radicicolum. This polysaccharide gave a precipitin reaction in high dilution, not only with Type III Pneumococcus antiserum, but also mixed with antisera from other Pneumococcus types. The chemical evidence indicated that the polysaccharide resembled the specific polysaccharides of Types I and II Pneumococcus. A decade later, the acidic capsular polysaccharide from Azoto-bacter chroococcum, a soil organism, was studied. It, too, produced serological cross-reactions with certain pneumococcal specific antisera. Although the molecular structure of the polysaccharide was not established, adequate evidence was accumulated to show a structural relationship to Type III Pneumococcus-specific polysaccharide. This was sufficiently close to account for the Type III serological cross-relationship. 

The role of the secretion from the root apex of organic acids such as citric and malic in the resistance of maize and wheat, respectively, to Al toxicity (81,82) has emerged recently as one with plausibility (83). These studies have been carried out in solution cultures, but how does the suggestion hold up in soil The first and probably greatest difficulty is that the toxic species of Al, probably hydrated Al ", must diffuse to some site in the root apex and stimulate the produc-... 

Microbial activity, which is often stimulated during bioremediation projects, can alter the external pH. For instance, the anaerobic degradation of chlorinated compounds produces organic acids and HC1 and the pH may drop to acidic values if the soil has a low buffering capacity. In this case, control of the external pH will be required in order to maintain biodegradation activity at... 

Dissolved organic molecules have many acidic functions (hydroxol and carbonic groups) to complex trace elements and their compounds to form soluble chelates. This is one of the reasons why solubility and bioavailability of trace elements in the rhizosphere are higher than bulk soils. At the same time, many organic acids also directly dissolve trace elements and their compounds in soils. Plant-produced phytosiderophores facilitate elements, such as Fe and Zn, uptake by plants (Zhang et al., 1991 Romheld, 1991 Hopkins et al., 1998). However, Shenker et al. (2001) did not find significant uptake of the Cd-phytosiderophores complex by plant roots. 

Short-chain acids accumulate.under anoxic conditions/-which favor fermentative metabolism of bacteria. Such phytotoxins nay damage the plant directly or predispose plants to infection by pathogens. However plant residues nay also be used as substrates for beneficial micro-organisms to produce plant nutrients, soil conditioners, and plant protection chemicals. There is scope to promote the beneficial microbial effects against the harmful by soil management and by inoculation. 

The potential of nanipulating soil micro-organisms/ especially for the utilization of crop residues, has been outlined (28). For example, accelerating straw breakdown can reduce the TTme period in which organic acid toxins are produced (29). By inoculating straw... 

Liming an acidic lake is similar to the process many people use to maintain a pH balance in their soil for lawn maintenance. Plants have an optimum pH range in which they strive. Acidic conditions often develop in soils for several reasons. Rain tends to leach away basic ions, weak organic acids develop from the carbon dioxide produced by decaying organic matter, and strong acids, such as nitric acid, can form when ammonium fertilizers oxidize. To neutralize these acids, different forms of lime such as quicklime, CaO, and slaked lime, Ca(OH)2, are used to neutralize the acid and increase the pH of the soil. Table 13.9 shows how much fertilizer is wasted when applied to... 

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