AimsTo improve our understanding of N cycle development during primary succession after glacial retreat, we (i) assessed the role of biological N-2 fixation, (ii) determined gross ammonification rates to identify the onset of mineralization, (iii) quantified the retention of (NH4+)-N-15 and (NO3-)-N-15 in various ecosystem compartments to evaluate the accumulation of deposited N and (iv) followed the (NH4+)-N-15 label into the soil NO3- pool to explore the development of nitrification along the subtropical alpine Hailuogou glacial retreat chronosequence, SW China. MethodsWe measured N stocks and delta N-15 values in the dominant tree species, organic layer and 0-10 cm of the mineral soil and quantified N turnover rates and accumulation via N-15 tracer experiments. ResultsN accumulated in the ecosystem at a fast mean rate of 4.5 +/- 1.0 g m(-2) yr(-1) favored by an initially near-neutral soil pH value. The delta N-15 values of the vegetation started near 0 parts per thousand and decreased to a range of -2.7 to -4.4 parts per thousand in 127 years. Gross ammonification rates were initially low but increased with ecosystem age from 0.025 to 50.6 mg kg(-1) d(-1) N, matching those of mature (sub)tropical forests. The maximum accumulation of deposited N shifted from the bryophyte via the shrub layer to the soil organic layer. The (NH4+)-N-15 label hardly appeared in the NO3- pool reflecting little nitrification. ConclusionsStrong initial biological N-2 fixation and retention of deposited N was succeeded by a tight N cycling between soil and vegetation at the older sites within approximately 120 yr.