Impacts of Spartina alterniflora invasion on abundance and composition of ammonia oxidizers in estuarine sediment

Abstract

Spartina alterniflora widely invades coastal wetland in China and might change nitrification in sediment. Both ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) are involved in nitrification in this environment. The objective of this study was to examine the effect of S. alterniflora invasion on abundance and composition of AOA and AOB. The abundance and composition of AOA, AOB, and total bacteria in the sediments from S. alterniflora-invaded native mangrove vegetated and unvegetated zones at two depths of 0–5 cm (O) and 5–20 cm (R) were investigated using quantitative real-time polymerase chain reaction and denaturing gradient gel electrophoresis. Relationships were also determined between sediment properties and the AOB and AOA population sizes. Compared with native mangrove vegetated zone, the archaeal amoA gene abundance was reduced by 11.3-fold (O) and 46.1-fold (R), but the bacterial amoA gene abundance was increased by 9.8-fold (O) and 1.8-fold (R), respectively, in the S. alterniflora-invaded zone. The AOA abundance was always higher than AOB, especially in the native mangrove zone. Both AOA and AOB population sizes in the upper layer (O) were bigger than those in the deeper layer (R). Little difference was found in the AOB community composition among different zones, while diversity of AOA community was increased by the presence of S. alterniflora. This study demonstrated that the S. alterniflora invasion affects the abundance of both AOA and AOB, but only affects the community composition of AOA in the tidal sediments.