Background: The Hailuogou Glacier in the Gongga Mountain region (SW China), on the southeastern edge of the Tibetan Plateau, is well known for its low-elevation modern glaciers. Since the end of the Little Ice Age (LIA), the Hailuogou Glacier has retreated continuously due to global warming, primary vegetation succession and soil chronosequence have developed in this retreat area. The retreated area of Hailuogou Glacier has not been strongly disturbed by human activities, thus it is an ideal models for exploring the biological colonization of nitrogen in the primary successional stages of ecosystem. The nosZ gene encodes the catalytic center of nitrous oxide reductase and is an ideal molecular marker in studying the variation in the denitrifying bacterial community.
Methods: Soil properties as well as abundance and composition of the denitrifying bacterial community were determined via chemical analysis, quantitative polymerase chain reaction (qPCR), and terminal restriction fragment length polymorphism (T-RFLP), respectively. The relationships between the nosZ denitrifying bacterial community and soil properties were determined using redundancy analysis (RDA). Soil properties, potential denitrify activity (PDA), and the nitrous oxide reductase gene (nosZ)-denitrifying bacterial communities significantly differed among successional stages.
Results: Soil properties, potential denitrify activity (PDA), and the nitrous oxide reductase gene (nosZ)-denitrifying bacterial communities significantly differed among successional stages. Soil pH in the topsoil decreased from 8.42 to 7.19 in the course of primary succession, while soil organic carbon (SOC) and total nitrogen (TN) gradually increased with primary succession. Available phosphorus (AP) and available potassium (AK), as well as potential denitrify activity (PDA), increased gradually and peaked at the 40-year-old site. The abundance of the nosZ denitrifying bacterial community followed a similar trend. The variation in the denitrifying community composition was complex; Mesorhizobium dominated the soil in the early successional stages (0-20 years) and in the mature phase (60 years), with a relative abundance greater than 55%. Brachybacterium was increased in the 40-year-old site, with a relative abundance of 62.74%, while Azospirillum dominated the early successional stages (0-20 years). Redundancy analysis (RDA) showed that the nosZ denitrifying bacterial community correlated with soil available phosphorus and available potassium levels (P < 0.01).