Development of the nitrogen cycle in the soils of a coastal dune succession

Abstract

SUMMARY The development of the soil nitrogen cycle in a coastal dune succession (xerosere) on the East Frisian Island Spiekeroog was investigated. In 13 sites of different successional age the nitrogen pools in the topsoil (0–30 cm) and the organic soil layers were determined. The nitrogen mineralization was studied at the sites during the vegetation period in 1987 (38 weeks) and winter 1990-91 (14 weeks). Turnover rates and nitrification rates were calculated. The nitrogen pool of the soil was very low in the first stage of the succession (<100 kg N ha−1 30cm−1) and increased rapidly to more than 1500 kg N ha−1 within approx. 200 years. This accumulation rate was strongly exposition-dependent. Mineralization of nitrogen was low in the young sites (15 kg Nmin ha−1 year−130 cm−1) and increased to more than 100 kg Nmin ha−1 year−1 in sites covered by buckthorn (Hippophae rhamnoides) and in dune forest. Mineralization was also exposition-dependent. The annual nitrogen turnover rate was very high in the young dune sands (up to 18%) and was only 2% in the brown dune sand podsols under Empetrum heathland. Nitrification dropped as well in the course of the dune development from 80–90% to 20% nitrate of total mineral nitrogen production over a year. Some hypotheses on nitrogen accumulation and retention during ecosystem and plant cover development are discussed.