Dynamic changes in soil microbial miomass carbon, nitrogen and phosphorus of Taxodium distichum and Salix matsudana plantation in the hydro-fluctuation belt of the Three Gorges Reservoir Region

The operation of the Three Gorges Dam Reservoir（TGDR） on the Yangtze River, China, has formed a hydro-fluctuation belt with an annual water level change of 30 m, spanning an area of 350 km2. This has led to a decline in plant community within the hydro-fluctuation belt. Revegetation is an eco-friendly method that can be used to restore the ecological integrity of the hydro-fluctuation zone of the TGDR. This method also facilitates the proper maintenance of the functions and services of riparian ecosystem. Therefore, in this study, revegetation of the hydro-fluctuation belt of the Three Gorges Reservoir（TGR） of China was carried out in the Ruxi River basin in Gonghe Village of Shibao Township, Zhong County, Chongqing Municipality of China. The changes in soil fertility and quality were evaluated by assessing the content of soil microbial biomass carbon（SMBC）, soil microbial biomass nitrogen（SMBN）, and soil microbial biomass phosphorus（SMBP）. Soil samples were collected from plots of previously planted T. distichum and S. matsudana woodland in Zhong County of the TGR in June 2016（T1）, September 2016（T2）, June 2017（T3）, and September 2017（T4） at elevations between 165 and 175 m above sea level. The results showed the following.:（1） Under the conditions of flooding（T2-T3）, the soil microbial biomass was low. The soil microbial biomass increased significantly after the restorative growth of T. distichum and S. matsudana during the period of drawdown（T1-T2 and T3-T4）, indicating that artificial vegetation restoration has a positive effect on soil microbial recovery.（2） The SMBC/SOC and SMBN/TN of T. distichum and S. matsudana woodland were significantly higher than those of unplanted soil, indicating that the soil turnover rate was faster in the artificial vegetation restoration soil. However, the phosphorus level in the soil of T. distichum varied significantly, which necessitates further evaluation of phosphorus migration within soil.（3） The soil microbial biomass significantly correlated with the soil organic C and total N, but it negatively correlated with the soil pH. Overall, the revegetation of T. distichum and S. matsudana increased soil microbial biomass, and also enhanced the soil quality of the hydro-fluctuation belt. The results of this study further validate artificial revegetation as a suitable method for ecosystem restoration.