COMPARATIVE EFFECTS OF SOIL ORGANIC-MATTER FRACTIONS ON PHOSPHATASE-ACTIVITIES IN WHEAT ROOTS

Soil organic matter was obtained from two agricultural soils using alkali extraction followed by acidification to produce humic and fulvic acids which were further fractionated by adsorption and gel chromatography. All the products inhibited the activity of phosphatase prepared from wheat roots, but to different extents. Humic acids produced a greater inhibition of enzyme activity than either the fulvic acids or water extracts of soil. Aspergillin, from Aspergillus niger, had a similar C, H and N content to humic acid and produced a similar inhibition of phosphatase activity. The inhibitions produced by corresponding fractions derived from the two soils were slightly different, but the trends between similar fractions from different soils were comparable. The lower mol. wt. components of humic acid inhibited phosphatase activity to a greater extent than higher mot. wt. fractions. Although fulvic acid comprised only low mol. wt. components it was less effective in inhibiting enzyme activity than those components of comparable mol. wt. present in the corresponding humic acid. Synthetic polymaleic acid, produced an inhibition of phosphatase activity similar to that caused by fulvic acid. © 1979 Martinus Nijhoff, The Hague.