Glucose-induced nitrate assimilation in prairie and cultivated soils

Abstract

Native prairie and grassland soils are known to accumulate little inorganic N; however, N0₃ ⁻ is constantly being formed and re-immobilized. This suggests that microorganisms in prairie soils would be highly efficient in the assimilation of N0₃ ⁻ and would regularly have the assimilatory N0₃ ⁻ reductase (ANR) enzyme in an induced and active state. Aerated slurries and static systems prepared from prairie and cultivated soils amended with glucose and N0₃ ⁻ were observed for changes in N0₃ ⁻ concentration with time. Nitrate assimilation in the presence of glucose occurred more rapidly in cultivated than in prairie soils from the same soil map unit. Nitrate assimilation rates were not affected by inoculation of prairie soil with cultivated soil. It has been reported that the addition of glucose and NO₃ ⁻ to soils results in increased peptidase activity and a release of free amino acids. Mixing, sieving, and slurrying of prairie soils followed by treatment with glucose and NO₃ ⁻ may release free amino acids and other ANR inhibitors into the prairie soil slurries. Prairie soils had higher concentrations of soluble amino-N than cultivated soils with or without glucose and N0₃ ⁻ additions. Prairie soils also had greater concentrations of total Kjeldahl N and readily hydrolyzed amino acids than corresponding cultivated soils.