Table 1.
Initial ecosystem characteristics at the experimental sites.
Table 2.
Initial chemistry of the investigated litter substrates.
Table 3.
Mean annual precipitation (mm) and wet N deposition rates (kg N ha–1 year–1) in Yucheng and Hongya counties, Sichuan Province, China.
Figure 1.
Percentages of substrate mass remaining in each of the different N treatments.
Error bars represent the standard deviations of the means (n = 3). Lv_BD, Lv_BL, Lv_EG, Lv_NA and Lv_PA indicate leaf litter at the BD, BL, EG, NA and PA sites, respectively; St_NA and St_PA indicate sheath litter at the NA and PA sites, respectively; Tg_EG, Tg_NA and Tg_PA indicate twig litter at the EG, NA and PA sites, respectively. Asterisks (*) indicate significant difference between the control and at least one N treatment (α = 0.05). Two distinct stages were observed for most of the litter substrates (initial rapid decomposition rate followed by a slower rate) separated by dashed lines.
Figure 2.
Annual decomposition rates (k) of substrates in the control and N-addition plots.
Lv_BD, Lv_BL, Lv_EG, Lv_NA and Lv_PA indicate leaf litter at the BD, BL, EG, NA and PA sites, respectively; St_NA and St_PA indicate sheath litter at the NA and PA sites, respectively; Tg_EG, Tg_NA and Tg_PA indicate twig litter at the EG, NA and PA sites, respectively. Error bars represent the standard deviations of the means (n = 3). Different letters denote significant differences in k values among N treatments within each substrate (one-way ANOVA, n = 3).
Figure 3.
Relationships between the of initial chemical properties of substrates and their annual decomposition rates (k).
Lv_BD, Lv_BL, Lv_EG, Lv_NA and Lv_PA indicate leaf litter at the BD, BL, EG, NA and PA sites, respectively; St_NA and St_PA indicate sheath litter at the NA and PA sites, respectively; Tg_EG, Tg_NA and Tg_PA indicate twig litter at the EG, NA and PA sites, respectively. Error bars represent the standard deviations of the means (n = 3).
Figure 4.
Percentage of residual lignin in each substrate in different N treatments.
Lv_BD, Lv_BL, Lv_EG, Lv_NA and Lv_PA indicate leaf litter at the BD, BL, EG, NA and PA sites, respectively; St_NA, St_PA indicate sheath litter at the NA and PA sites, respectively; Tg_EG, Tg_NA and Tg_PA indicate twig litter at the EG, NA and PA sites, respectively. Error bars represent the standard deviations of the means (n = 3). Asterisks (*) indicates significant differences between the control and at least one N treatment (α = 0.05).
Figure 5.
Relationships between residual lignin and substrate mass after a period of decomposition.
Lv_BD, Lv_BL, Lv_EG, Lv_NA and Lv_PA indicate leaf litter at the BD, BL, EG, NA and PA sites, respectively; St_NA and St_PA indicate sheath litter at the NA and PA sites, respectively; Tg_EG, Tg_NA and Tg_PA indicate twig litter at the EG, NA and PA sites, respectively. Error bars represent the standard deviations of the means (n = 3).
Figure 6.
Percentage of nitrogen remaining in each substrate in different N treatments.
Lv_BD, Lv_BL, Lv_EG, Lv_NA and Lv_PA indicate leaf litter at the BD, BL, EG, NA and PA sites, respectively; St_NA and St_PA indicate sheath litter at the NA and PA sites, respectively; Tg_EG, Tg_NA and Tg_PA indicate twig litter at the EG, NA and PA sites, respectively. Error bars represent the standard deviations of the means (n = 3). Asterisks (*) indicates significant difference between the control and at least one N treatment (α = 0.05).