The concentration of plant available soil nitrogen (nitrate and ammonium) was measured in the CSPs to quantify and qualify changes in the course of secondary forest succession. Soil mineral N was determined in five to six soil layers in four season: at peak growth in summer, at the time of leaf shedding in autumn, during the peak of the dry season in winter and at the time of bud burst in spring by standard soil analysis protocols (extraction with 1M KCl solution). Ammonium and nitrate concentrations were measured with a Flow Injection Analyzer (FIA) and results are presented as plant available ammonium and nitrate on a dry weight basis.

Soil samples were collected in 10 cm depth-increments in the mineral soil (A- and B-horizon) up to a depth of 50 cm. Samples per depth were pooled from 4 cores taken in the four corners of the central plot. 5 g of field moist soil per sample were extracted the same day with 50 ml of 1M KCl solution. Ammonium and nitrate concentrations were measured with a Flow Injection Analyzer (FIA) and results are presented as plant available NH4+ and NO3- on a dry weight basis. To determine net N mineralization plastic tubes were driven into the soil next to the first sampling location in each of the four corners of the central plot. Tubes were closed with a lid and remained in the soil for an incubation period of 14 days. Aeration is possible through two holes in the upper part of the tube. Plant uptake is avoided and the samples remained subject to natural diurnal temperature fluxes. After the incubation period the soil core was analyzed as described before. In the summer 08 campaign incubated soil from the four corners of the central plot were analyzed separately. Whereas in the autumn 08 campaign the incubated soil was pooled from the samples taken in the four corners of the central plot to receive one sample per soil depth (0-5, 5-10cm). The extractable amount of nitrate and ammonium minus the preincubation quantities provides an estimate of net ammonification and net nitrification. ---- Mineral nitrogen was determined in the following soil layers: Summer 08: : 0-10, 10-20, 20-30, 30-40, 40-50 cm; incubated soil core: 0-10 cm Autumn 08, Spring 09, Winter 10: 0-5, 5-10, 10-20, 20-30, 30-40, 40-50cm, incubated soil core: 0-5, 5-10 cm

CSPs, Gutianshan National Nature Reserve 29°08'-29°17'N 118°02'-118°11'E

2008-2010

No organism sampled, soil samples