Agricultural systems that receive high or low organic matter (OM) inputs would be expected to differ in soil nitrogen (N) transformation rates and fates of ammonium (NH4 þ) and nitrate (NO3 ). To compare NH4 þ availability, competition between nitrifiers and heterotrophic microorganisms for NH4 þ, and microbial NO3 2 assimilation in an organic vs. a conventional irrigated cropping system in the...

We monitored the water quality and hydrological conditions of a horizontal subsurface constructed wetland (HSSF-CW) in Beijing, China, for two years. We simulated the area-based constant and the temperature coefficient with the first-order kinetic model. We examined the relationships between the nitrogen (N) removal rate, N load, seasonal variations in the N removal rate, and environmental fact...

As a vital beverage crop, tea has been extensively planted in tropical and subtropical regions. Nitrogen (N) levels and forms are closely related to tea quality. Based on different N levels and forms, we studied changes in NO3- and NH4+ fluxes in tea roots utilizing scanning ion-selective electrode technique. Our results showed that under both single and mixed N forms, influx rates of NO3- were...

Nitrobacter winogradskyi Nb-255 is a nitrite-oxidizing bacterium that can grow solely on nitrite (NO2(-)) as a source of energy and nitrogen. In most natural situations, NO2(-) oxidation is coupled closely to ammonium (NH4(+)) oxidation by bacteria and archaea and, conceptually, N. winogradskyi can save energy using NH4(+) to meet its N-biosynthetic requirements. Interestingly, NH4(+) delayed t...

Schoenoplectus maritimus (alkali bulrush) has desirable attributes, such as a short growth habit (height of mature stands < 1.5 m) and annual senescence, for a potential alternative to tall (height > 3 m) emergent macrophytes in shallow constructed treatment wetlands treating ammonium-dominated wastewater. The effects of different ammonium nitrogen (NH4-N) levels on alkali bulrush growth and it...

Ammoniacal nitrogen (ammonia and ammonium) in agricultural wastewaters can promote eutrophication of receiving waters and be potentially toxic to fish and other aquatic life. Zeolites, which are hydrated aluminum-silicate minerals, have an affinity for ammonium ions (NH4"") and are, therefore, potentially useful in removing this contaminant from wastewaters. The major objectives of this study w...

Effects of simulated nitrogen (N) deposition on soil net nitrogen mineralization (NNM) were examined in situ during two growing seasons, using the resin-core technique in the semiarid meadow steppe in Inner Mongolia, China. The aim of this study is to clarify the effect of N levels (0, 10, and 20 kg N ha-1yr-1) and forms (NH4+ and NO3-) on soil mineral N and NNM. Our results showed that N level...

The mechanisms involved in regulating high-affinity ammonium (NH4+) uptake and the expression of the AtAMT1 gene encoding a putative high-affinity NH4+ transporter were investigated in the roots of Arabidopsis thaliana. Under conditions of steady-state nitrogen (N) supply, transcript levels of the AtAMT1 gene and Vmax values for high-affinity 13NH4+ influx were inversely correlated with levels ...