Soil nitrogen mineralization in a wind-disturbed area on Changbai Mountain after 30 years of vegetation restoration

Abstract

Wind-disturbed (1986) and undisturbed primary forest areas (controls) on Changbai Mountain (China) were studied to compare levels of soil nitrogen mineralization. Soil samples were collected at 0–10cm (topsoil) and 10–20cm (subsoil) depths from the vegetation zones of a broadleaf Korean pine forest (BKPF), spruce-fir forest (SFF), and an Erman's birch forest (EBF) at different altitudes. Nitrogen status and mineralization characteristics were studied in the soil samples from a wind-disturbed area where vegetation cover has been restored after 30years of regrowth. Soil organic carbon (SOC) and total nitrogen (TN) contents in the topsoil layer of the three vegetation types were significantly higher than in the subsoil layer. SOC and TN contents in the topsoil layer increased, and soil C/N ratio significantly decreased with increasing altitude. No significant differences in SOC, TN or pH were detected in the wind-disturbed and control area soils of BKPF and EBF. SOC and TN levels in the subsoil layer of SFF were significantly higher in wind-disturbed than in control areas. The topsoil C/N ratios of BKPF and SFF were significantly higher in the control area vs. the wind-disturbed area. After 21d incubation, inorganic nitrogen contents (ammonium nitrogen NH4+-N and nitrate nitrogen NO3−-N) in the soils of BKPF, SFF and EBF increased in both the wind-disturbed and control areas. Ammonium nitrogen (NH4+-N) was the primary inorganic form of nitrogen. The changes in the amount of NH4+-N formed from ammonification contributed to the 57.1–76.2% total amount of nitrogen mineralized (net nitrogen mineralization) and the net nitrogen mineralization rate. The nitrogen mineralization process was mainly the result of net ammonification. Correlation analysis on the soil nitrogen mineralization rate and chemical properties showed that the ammonification rate had strong positive correlation with SOC and the C/N ratio. Nitrification rate was highly correlated with SOC and TN contents, as well as soil pH. Net nitrogen mineralization rate was significantly correlated with SOC and TN contents, C/N ratio, and soil pH. Multiple comparisons analysis of variance (ANOVA) demonstrated that soil nitrogen mineralization was greatly influenced by vegetation type, soil depth, and wind disturbance in the forest soils at different altitudes. Net ammonification and net nitrogen mineralization were significantly affected by wind disturbance. The vegetation cover has undergone restoration for nearly 30years in the wind-disturbed area on Changbai Mountain, but our data demonstrate that differences in soil quality between primary forest and wind-disturbed areas remain significant due to the different vegetation types.