Journal of Soils and Sediments - The quality of organic matter influencing sediment nitrate (NO3?) reduction processes in estuarine zones is not well understood. This study aimed to assess... 相似文献
Invasion of an exotic C_4 plant Spartina alterniflora has been shown to increase soil organic carbon(SOC) concentrations in native C_3 plant-dominated coastal wetlands of China. However, little is known about the effects of S. alterniflora invasion on SOC concentrations and fractions in tidal marshes dominated by native C_4 plants. In this study, a field experiment was conducted in a tidal marsh dominated by the native C_4 plant Cyperus malaccensis in the Minjiang River estuary, China. Concentrations of SOC and liable SOC fractions, dissolved organic carbon(DOC), microbial biomass carbon(MBC), and easily oxidizable carbon(EOC),were measured in the top 50-cm soils of the C. malaccensis community, as well as those of three S. alterniflora communities with an invasion duration of 0–4 years(SA-4), 4–8 years(SA-8), and 8–12 years(SA-12), respectively. Results showed that both SOC stocks in the 50-cm soils and mean SOC concentrations in the surface soils(0–10 cm) of the C. malaccensis community increased with the duration of S. alterniflora invasion, whereas SOC concentrations in the 10–50-cm soils decreased slightly during the initial period of S. alterniflora invasion, before increasing again. The pattern of changes in labile SOC fractions(DOC, MBC, and EOC) with invasion duration was generally similar to that of SOC, while the ratios of labile SOC fractions to total SOC(DOC:SOC, MBC:SOC, and EOC:SOC) decreased significantly with the duration of S. alterniflora invasion. The findings of this study suggest that invasion of the exotic C_4 plant S. alterniflora into a marsh dominated by the native C_4 plant C. malaccensis would enhance SOC sequestration owing to the greater amount of biomass and lower proportion of labile SOC fractions present in the S. alterniflora communities. 相似文献
Denitrification and anaerobic ammonia oxidation (anammox) play key roles in nitrogen (N) loss, and nitrification can supply substrates of NO2– and NO3– for denitrification and anammox. Coupled nitrification-denitrification/anammox processes are thus crucial for N removal in coastal ecosystems. This study aims to examine the spatial-temporal variations of ambient, coupled, and uncoupled N removal rates in the coastal sediments off the north East China Sea, and to clarify the controlling factors and microbial mechanisms of coupled nitrification-denitrification/anammox.
Materials and methods
The rates of ambient, coupled, and uncoupled denitrification and anammox in coastal sediments off the north East China Sea were quantified using the continuous-flow experiments combined with 15N isotope pairing technique. The quantitative polymerase chain reaction method was used to determine the abundances of nitrifiers, denitrifiers, and anammox bacteria, with the functional genes of amoA and nirS, and 16S rRNA gene, respectively.
Results and discussion
Ambient denitrification rates varied between 0.43 and 7.39 μmol N m?2 h?1, and ambient anammox rates ranged from 0.05 to 0.62 μmol N m?2 h?1. Coupled nitrification-denitrification was the dominant N removal pathway. The rates and coupling of N removal processes with nitrification varied distinctly between nearshore and offshore sites, which were driven by diverse environmental factors. Redundancy analysis suggested that nitrate and sulfide were important factors controlling the coupled and uncoupled N removal rates, and nitrate was proved to be the key factor influencing the ratio between coupled and uncoupled N removal via an integrated analysis. Abundances of ammonia oxidizing bacteria (AOB) correlated significantly with coupled denitrification rates and abundances of denitrifiers, suggesting the importance of AOB in coupled nitrification-denitrification.
Conclusions
This study investigated the ambient, coupled, and uncoupled denitrification and anammox rates in coastal sediments off the north East China Sea. Nitrate was proved to be the critical factor influencing the ratio between coupled and uncoupled N removal, and AOB may play important role in coupled nitrification-denitrification. These results emphasized that nitrification is crucial for N removal with important implications on N loss in coastal ecosystems.
