Springer Online Journal Archives 1860-2000
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Summary Studies of the effects of different forms of N on urease production in soils amended with organic C showed that although microbial activity, as measured by CO2 production, was stimulated by the addition of NH4 + or NO3 - to C-amended soils (200 μmol glucose-C g−1 soil), urease production was repressed by these forms of N. The addition of L-methionine sulfoximine, an inhibitor of inorganic N assimilation by microorganisms, relieved the NH4 + and NO3 - repression of urease production in C-amended soil. The addition of sodium chlorate, an inhibitor of NO3 - reduction to NH4 + by microorganisms, relieved the NO3 - repression of urease production, but did not eliminate the repression associated with NH4 +. These observations indicate that microbial production of urease in C-amended soils is not directly repressed by NH4 + or NO3 -, but by products formed by microbial assimilation of these forms of N. This conclusion is supported by our finding that the biologically active L-isomers of alanine, arginine, asparagine, aspartate, and glutamine, repressed urease production in C-amended soil, whereas the D-isomers of these amino acids had little or no influence on urease production. This work suggests that urease synthesis by soil microorganisms is controlled by the global N regulon.
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