Objective  The distribution characteristics of soil microbial biomass carbon (SMBC) were explored in hydro-fluctuation belt at different altitudes during the drying period of the Xiaolangdi Reservoir, so as to provide a theoretical basis for the study of soil carbon cycle in the reservoir area and the reconstruction of damaged vegetation system in the hydro-fluctuation belt.

  Method  Using the method of location test, the SMBC contents and habitat factors of the hydro-fluctuation belt at the control elevation (275 m) and three flooded altitudes (265, 255 and 245 m) during the drying period of Xiaolangdi Reservoir area were monitored and analyzed.

  Result  The results showed that the variation range of SMBC contents in the surface layer of the hydro-fluctuation belt in Xiaolangdi Reservoir area was 29.25-204.97 mg kg⁻¹, and the average value was 112.81 mg kg⁻¹. Compared with the control altitude, the SMBC contents in the middle and short-term flooding altitudes (265 and 255 m) increased significantly (P < 0.05), while the SMBC contents in the long-term flooding altitude (245 m) decreased significantly (P < 0.05). After the hydro-fluctuation belt area dried, the contents of SMBC generally showed a downward trend with time, and the decline was more obvious in the early stage and was gentle in the later stage. The variation laws of SMBC content among different soil layers in the hydro-fluctuation belt were similar, and their difference were mainly reflected in the change of SMBC content, which was shown as upper soil layer (0-10 cm) > lower soil layer (10-20 cm). There were significant correlation between SMBC contents and soil moisture content, temperature, soil organic carbon (SOC) and total nitrogen (P < 0.05), but there were no significant correlation with soil clay content and total phosphorus. At the same altitude, the SMBC contents of herbaceous vegetation in the hydro-fluctuation belt were significantly higher than that of shrub, and the SMBC contents of mixed vegetation type were significantly higher than that of single vegetation type, which were manifested as herb mixed > single herb, and shrub herb mixed > shrub.

  Conclusion  The distribution characteristics of SMBC contents in hydro-fluctuation belt of Xiaolangdi Reservoir area are significant difference in different scales of altitude, time and soil layer, and SMBC responds significantly to the changes of soil physical and chemical properties and vegetation types. Therefore, according to the soil environmental conditions, the restoration method of mixed planting of different vegetation should be considered in the restoration and reconstruction of the damaged vegetation system in the hydro-fluctuation belt of Xiaolangdi Reservoir area.