2.1 study site
This study site was located in the Heping town (119°91’N, 30°79’E), changxing County, Zhejiang Province, China. This area was characterized as a subtropical monsoon climate, and the mean annual temperature and precipitation are 15.6℃ and 1309 mm, respectively. Soil parent material was siltstone. The stand density of the intensively managed Moso bamboo forests was 3000 stem ha-1. Because of the rapid regeneration and growth of bamboo, plants more than 5 years old were selectively harvested every 2 years to obtain wood and achieve uniform stem density among the forest sites studied. Accordingly, a reasonable chronosequence of Moso bamboo forests was established with different durations (years) under intensive management even though the bamboo forests studied are uneven-aged. Inorganic fertilizers were applied at a rate of 600 Kg ha-1 of compound fertilizer (N : P2O5 : K2O = 15:15:15) every September. The annual organic manure input were about 5.25 t ha-1 from piggery was applied every June annually.
2.2 Experimental design and soil sampling
Before soil sampling, we conducted a strict investigation and evaluation of each plot to confirm it met the criteria for the chronosequence of intensive management. Ultimately, a chronosequence of moso bamboo plantations with different ages was established to represent 4 different stand ages: 6 year (IM6), 10 years (IM10), 15 years (IM15) and 20 years (IM20), respectively, each with three replicates. Additionally, three extensively-managed Moso bamboo forests without fertilization or weeding located adjacent to the IM stands were considered as controls (CK). Due to having similar site conditions, including elevation, soil type, slope gradient and soil texture, we considered the study plots of represent a completely randomized design. Within each of the stands, a 10 m × 10 m plot was established, and thus 15 plots were established for the present study. All bamboo forests in the study were randomly selected within an area of about 6 km2.
The soil samples used in this study were collected from five soil cores (0-20 cm and 20-40 cm depth) of each plot taken approximately 30 cm away from the plants; these were mixed to provide one composite sample for each layer for a total of 30 samples. Any mulch layer present was avoided during soil sampling. All the soil samples were placed on ice for transporting to the laboratory where they were sieved (2 mm) to homogenize the sample and remove visible roots and plant fragments. After sieving, a portion of each soil sample was used to analyze for physicochemical properties and another portion was stored immediately at -80℃ for soil DNA extraction.