Impact of periodical flooding-drying on nitrification and ammonia oxidizers in hydro-fluctuation belt of the Three Gorges Reservoir

Abstract:

[Objective] This study was aimed to elucidate the effect of periodic flooding-drying to ecological processes of ammonia oxidizers in the hydro-fluctuation belt of the Three Gorges Reservoir. [Methods] Soil samples were collected at thee altitudes in regions of Wanzhou, Fengdu and Changshou, representing 8, 5 and 0 times floodingdrying management, respectively. Soil physiochemical properties were analyzed and microcosms were constructed to monitor nitrification activity by fertilizing soils with ammonium substrate. Real-time PCR was used to quantify the population size of ammonia-oxidizing archaea (AOA) and bacteria (AOB). DGGE fingerprints and clone libraries were conducted to study the shift of AOA and AOB compositions in nitrifying soils. [Results] Among the physiochemical characteristics of the soils, soil organic matter and total phosphates increased along with cycle increasing. After incubation for 13 days, the net nitrification rates of the samples with 8 cycles exceeded those with 5 cycles. The quantities of both AOA and AOB have increased during the incubation. Phylogenetic analysis showed that AOA were placed within the soil group 1.1b and soil group 1.1a, while bacterial ammonia oxidizers were closely related to Nitrosospira and Cluster 0. [Conclusion] Periodical flooding-drying increased soil organic matter, enhanced soil nitrification activity and likely played important roles in shaping community structures of soil ammonia oxidizers.

Key words:Three Gorges Reservoir;periodic flooding-drying;nitrification;ammonia-oxidizing archaea;ammoniaoxidizing bacteria