Nitrogen in soils beneath 18–65 year old stands of subtropical evergreen broad-leaved forests in Laoshan Mountains in Eastern China

Monitoring of soil nitrogen (N) cycling is useful to assess soil quality and to gauge the sustainability of management practices. We studied net N mineralization, nitrification, and soil N availability in the 0–10 cm and 11–30 cm soil horizons in east China during 2006–2007 using an in situ incubation method in four subtropical evergreen broad-leaved forest stands aged 18-, 36-, 48-, and 65-years. The properties of surface soil and forest floor varied between stand age classes. C:N ratios of surface soil and forest floor decreased, whereas soil total N and total organic C, available P, and soil microbial biomass N increased with stand age. The mineral N pool was small for the young stand and large for the older stands. NO 3 − -N was less than 30% in all stands. Net rates of N mineralization and nitrification were higher in old stands than in younger stands, and higher in the 0–10 cm than in the 11–30 cm horizon. The differences were significant between old and young stands ( p < 0.031) and between soil horizons ( p < 0.005). Relative nitrification was somewhat low in all forest stands and declined with stand age. N transformation seemed to be controlled by soil moisture, soil microbial biomass N, and forest floor C:N ratio. Our results demonstrate that analyses of N cycling can provide insight into the effects of management disturbances on forest ecosystems.