Abstract:

To investigate soil enzyme activities (catalase, invertase and urease) in response to increased nitrogen deposition in the subtropical plantation of Chinese Fir (Cunninghamia lanceolata), a field experiment with 20 m×20 m plots was conducted in a 12-year-old Chinese Fir plantation for 2 years. Nitrogen loadings were designed at 4 levels of 0, 60, 120, 240 kg N ·hm^-2a^-1, referred to N0, N1, N2 and N3, respectively, with 3 replicates in each treatment. In the inner 15 m×15 m of the plot, solution of CO(NH₂)₂ was sprayed on the forest floor each month, and on the margin of the plot between the inner plot and the boundary, nitrogen was fertilized once a year. The results showed that compared to N0 treatment, N1 consistently had a positive effect on activities of soil catalase, invertase and urease, determined both by variations of soil enzyme activities in the center plot area every 10 days after nitrogen treatment and monthly dynamics (July through September) in the buffered zone. However, the effects of N2 and N3 treatments were found to vary with time and soil depth. The activities of these three enzymes decreased significantly with increasing soil depth.

Key words: nitrogen deposition, Chinese Fir plantation, soil enzyme