关键词: 氮沉降, 杉木人工林, 凋落物, 养分归还量

Abstract:

This field experiment was conducted in a 12-year-old Chinese fir plantation. Four levels of nitrogen, that is N0 (0 kg N ·hm^-2a^-1), N1(60 kg N ·hm^-2a^-1), N2 (120 kg N · hm^-2a^-1) and N3 (240 kg N ·hm^-2a^-1), were annually added with three replicates in each level. After seccessive two-years additions of the nitrogen, the annual litterfall production was estimated to be 1 164.10, 1 147.30 and 2 599.50 kg ·hm^-2 , respectively for N1, N2 and N3 treatments, compared with 976.47 kg ·hm^-2 for the control (N0), indicating that the low-to-medium N loads (N1 and N2) increased litterfall amount significantly, while high levels of N deposition (N3) decreased the quantities to some extents. The concentrations of C and N in fallen leaves increased with the increasing nitrogen deposition, but C/N ratios decreased gradually from 65.55 (N0) to 65.38 (N1), 61.77 (N2), and 53.77 (N3). The annual C flux through litterfall to the forest floor was estimated at 474.70, 544.07, 538.55 and 474.02 kg ·hm^-2, and the annual N at 7.21, 8.56, 9.03 and 9.04 4 kg ·hm^-2, and the P at 1.17, 1.24, 1.32 and 1.09 g ·hm^-2; respectively, for the above four treatments (N0, N1, N2 and N3). The annual N flux responded positively to the increased nitrogen loads, C and P fluxes were promoted by N1 and N2 treatments, but inhibited by N3.

Key words: nitrogen deposition, Chinese fir plantation, litterfall, nutrient flux