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Effect of extracellular-enzyme activities on solubilization rate of soil organic nitrogen


Biology & Fertility of Soils 17(1): 32-38
Effect of extracellular-enzyme activities on solubilization rate of soil organic nitrogen
In a sandy soil containing 15N-labeled active (soluble and easily degradable) and non-labelled passive (recalcitrant) fractions of soil organic matter, the rate of net N mineralization (solubilization) was determined during a 55-day incubation at 25 degree C, 63% water-holding capacity and different levels of soil extracellular-enzyme activities. The active fraction of soil N was labelled by preincubation (at 5 degree C and 74% water-holding capacity for 6 months) of soil amended with 15 N-labeled plant material. Increases in the activity of extracellular-enzymes in soil were induced by the addition of glucose and KH-2PO-4 at the beginning of the incubation. The results show that the contents of total soluble N (NO-3--N + NH-4+-N + soluble organic N) were significantly higher in glucose-amended soil compared to the unamended soil. The increases in soluble N in soil amended with 1 and 2 mg glucose g-1 dry soil corresponded to a mean rate of net solubilization of 7.9 +- 1.4 and 18.8 +- 0.7 nmol N g-1 dry soil day-1, respectively. The mean rate of net N solubilization (3.6 +- 1.0 nmol N g-1 dry soil day-1) in unamended soil was significantly lower than those of glucose amended soils. The content of 15N in total soluble N in soil amended with 2 mg glucose, for example, was diluted from 3.11 +- 0.08 atom% before the incubation to 2.77 +- 0.03 atom% after 55 days. This indicates that 89% of soluble-N accumulated in soil by the end of the incubation originated from the active fraction of soil N and the rest, estimated at 11%, originated from the passive fraction. The activities of soluble and total proteases as well as the rate of N solubilization in the soil increased with the application of glucose. The activity of these extracellular enzymes was highly correlated with the rates of net N solubilization. Thus, increases in extracellular-enzyme activities in glucose-amended soils had a priming effect on the solubilization of 15N-labeled active and non-labeled passive fractions of soil organic N. It seems that the activity of extracellular-enzymes expressed in terms of total and soluble protease activities could be a rate-limiting factor in the processes of soil organic N solubilization.

Accession: 002355554

DOI: 10.1007/bf00418669

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