To elucidate temporal N mineralization patterns, soil samples were amended with cellulose in combination with inorganic (NH₄) or organic (protein) N.  We hypothesized that extracellular enzyme activity is directly linked to the availability of C and N. Nitrogen addition were held equal, while different amounts of cellulose were added to achieve C to N ratios of 10, 25 and 40 to 1.

During the first month, protein degradation resulted in increased protease activity, CO₂ evolution and mineral N in solution. Cellulose degradation could be associated with increases in CO₂ evolution, exocellulase activity and a depletion of the mineral N pool except in treatments with a low C to N ratio. In general, extracellular enzyme activity was a function of substrate availability, the sum of protease and cellulase activity being significantly related to CO₂ evolution. In addition, the protease to cellulase ratio was related to changes in the mineral N pool.  A high protease to cellulase ratio resulted in net N mineralization, whereas a low ratio lead to N immobilization.

After one month, enzyme activity decreased in tandem with CO₂ evolution. However, the protease activity remained relatively stable. Its level was dependent on the C to N ratio of the original substrates added. High C to N ratio substrates lead to higher sustained protease activity. The results indicate the  pattern of enzyme expression is related to initial substrate quality.