Soil Net Nitrogen Mineralization at Different Ecosystem Development Stages after the Year 2000 Eruption on Miyakejima Island

Soil nitrogen (N) mineralization is a central process in the N cycle in terrestrial ecosystems. Previously many studies were conducted on soil N mineralization in terrestrial ecosystems, but those studies remain unclear due to large spatial and temporal variations. In present study soil N mineralization rates were measured in situ by using a resin core technique. The study reports the relationship of these rates with environmental factors at ten sites with various vegetation and soil properties which formed after the latest eruption in year 2000 on a volcanic island, Miyakejima. Miyakejima has diverse ecosystems, from grasslands with little soil organic matter to mature forests. With little damage from the year 2000 eruption, it is suitable for exploration of spatial and temporal variations in soil N mineralization. Annual soil N mineralization rates ranged from 0.9 to 52.5 kg N ha-1 yr-1 and were higher in the presence of the N-fixing vegetation Alnus sieboldiana. Present study data along with other data obtained from insitu observation suggested that soil C/N ratio can be a good indicator of annual soil N mineralization rate, like many previous studies pointed out; however, the relationship between the rate and soil C/N ratio was complicated due to some factors, such as existence of N-fixing vegetation and high sulfur dioxide gas exposure.