Effects Of Glucose And Rhizodeposits (With Or Without Cysteine-S) On Immobilized-S-35, Microbial Biomass-S-35 And Arylsulphatase Activity In A Calcareous And An Acid Brown Soil

Our aim was to study the effects of C (as glucose and artificial rhizodeposits) on S immobilization, in relation to microbial biomass-S and soil arylsulphatase (ARS) activity, in contrasting soils (a calcareous and an acid brown soil). The glucose-C and artificial rhizodeposit-C with or without cysteine were added at six rates (0, 100, 200, 400, 600 and 800 mg kg(-1) soil) to the two soils and then incubated with (Na2SO4)-S-35 for 1 week prior to analysis. The percentages of S-35 immobilized increased when C as glucose and rhizodeposit (without cysteine) were added to both soils. With cysteine-containing rhizodeposit, the percentages of S-35 immobilized remained relatively stable (23.5% to 29.9%) in the calcareous soil, but decreased in the acid brown soil (52.7% to 31.5%). For both soils, cysteine-containing rhizodeposit additions showed no significant correlation between immobilized-S-35 and microbial biomass-S-35, suggesting that microorganisms immobilized cysteine-S preferentially instead of S-35 from the tracer ((Na2SO4)-S-35). In the calcareous soil, a positive and significant correlation was found between ARS activity and microbial biomass-S-35 (r = 0.85, P < 0.05) when glucose was added. We also saw this correlation in the acid brown soil when rhizodeposit-C without cysteine was added (r = 0.90, P < 0.05). Accordingly, the results showed the presence of extracellular arylsulphatase activity of 48.7 mg p-nitrophenol kg(-1) soil hour(-1) in the calcareous soil and of 27.0 mg p-nitrophenol kg(-1) soil hour(-1) in the acid brown soil.