Increasing deamination reactions in soil with pyridoxal-5'-phosphate

Abstract

Amino acid N accounts for ca 30–45% of the total soil N content and represents a potentially-available nutrient source for plant growth. Previous investigations have demonstrated that amino acid deamination in soil is catalyzed by pyridoxal-5'-phosphate (PLP) in the absence of any enzyme. Batch experiments using soils managed under different land uses and tillage regimes were conducted in which 3 g soil was amended with 1.9 or 9.6mM PLP and 19.2 mM NaN 3 and kept at 35 C for 24 h. Maximum NH + 4-N production (2.7 mg kg −1 soil) occurred in Melton soil previously managed as pasture. Comparison of Palouse soil previously managed under conventional, minimum or no-tillage regimes showed no differences in NH 4 +-N production with tillage and relatively little NH + 4-N production as a result of substrate limitations. In a second set of experiments, soil columns containing a 40 g soil-sand mixture (1:1. w:w) were maintained for 29 weeks at a water potential of −0.08 MPa. Soil columns were incubated without organic matter addition, or were amended with l g wheat straw or alfalfa. PLP or pyridoxine (Pd) addition to the columns at weeks 2 and 14 resulted in the detection of increased inorganic N in the leachate most likely as a result of PLP or Pd mineralization. Amounts of inorganic N produced by PLP- and Pd-treated soils never exceeded N produced by soils treated with an equivalent amount of N in the form of NH 4Cl. Inorganic N produced in the leachate of PLP- or Pd-amended soil columns also never exceeded N expected as a result of PLP and Pd mineralization. PLP does not appear to be a useful soil amendment to catalytically increase inorganic N production from the organic N pool.