Impact of coastal wetland cultivation on microbial biomass, ammonia-oxidizing bacteria, gross N transformation and N2O and NO potential production

A ¹⁵N dilution experiment was carried out to investigate effects of cultivation on the gross N transformation rate in coastal wetland zone. Microbial community composition was estimated by phospholipid fatty acid (PLFA) analysis and abundance of soil ammonia-oxidizing bacteria (AOB) was quantified by real-time polymerase chain reaction (PCR). Soil salinity decreased significantly, while total N increased after coastal wetland was cultivated. Microbial biomass (total PLFA), bacterial biomass, fungal biomass, and actinomycete biomass of the native coastal wetland soils were significantly (p < 0.05) lower than those of the cultivated soils whereas AOB population size also significantly increased after coastal wetland cultivation. Multiple regression analysis showed that total PLFA biomass and soil total N (TN) explained 97% of the variation of gross N mineralization rate in the studied soils (gross mineralization rate = 0.179 total PLFA biomass + 5.828TN − 2.505, n = 16, p < 0.01). Gross nitrification rate increased by increasing the soil AOB population size and gross mineralization rate (M) (gross nitrification rate = 3.39AOB + 0.18 M − 0.075, R ² = 0.98, n = 16, p < 0.01). Management of salt discharge and mineral N fertilization during the cultivation of wetland soils might have changed composition of soil microflora and AOB population size, thus influencing mineralization and nitrification. Probably, the cultivation of coastal wetland soils increased the risk of N losses from soil through nitrate leaching and gas emission (e.g., N₂O and NO).