Optimization of Nitrogen Demand in Vegetables by Different Impacts on Autotrophic and Heterotrophic Nitrification

Aims The understanding of the interactions between N transformations and N uptake by plants in greenhouse soils with large N accumulation is still not clear. The aim is to understand the plant- soil interactions (vegetables) on N transformations with respect to N supply. Methods 15N tracing studies were conducted in two greenhouse soils to simultaneously quantify soil gross N transformation and plant N uptake rates using the Ntraceplant tool. Results There were significant feedbacks between vegetable N uptake and soil gross N transformation rates, whether soil N accumulation occurred or not. Plant NO3– uptake rates (UNO3) were higher than the NH4+ uptake rates (UNH4), which is consistent with the NO3–-preference of the vegetable plants studied. While UNH4 was still responsible for 6-49% of total N uptake rates, significantly negative relationships between UNH4 and NH4+ immobilization rate and autotrophic nitrification rate (ONH4) were observed. ONH4 was significantly inhibited in the presence of plants and decreased with time. ONH4 (1.11 mg N kg-1 d-1) was much lower than UNO3 (8.29 mg N kg-1 d-1) in the presence of plants. However, heterotrophic nitrification rate (ONrec), which ranged from 0.10 to 8.11 mg N kg-1 d-1 was significantly stimulated and was responsible for 5-97% of NO3– production in all plant treatments, providing additional NO3– to meet N requirements of plants and microorganisms.Conclusions The management of organic N fertilizers should be improved to stimulate inorganic N production via heterotrophic nitrification in greenhouse cultivation.

Gene expression analysis of Alcaligenes faecalis during induction of heterotrophic nitrification

Alcaligenes faecalis is a heterotrophic nitrifying bacterium that oxidizes ammonia and generates nitrite and nitrate. When A. faecalis was cultivated in a medium containing pyruvate and ammonia as the sole carbon and nitrogen sources, respectively, high concentrations of nitrite accumulated in the medium whose carbon/nitrogen (C/N) ratio was lower than 10 during the exponential growth phase, while the accumulation was not observed in the medium whose C/N ratio was higher than 15. Comparative transcriptome analysis was performed using nitrifying and non-nitrifying cells of A. faecalis cultivated in media whose C/N ratios were 5 and 20, respectively, to evaluate the fluctuations of gene expression during induction of heterotrophic nitrification. Expression levels of genes involved in primary metabolism did not change significantly in the cells at the exponential growth phase under both conditions. We observed a significant increase in the expression levels of four gene clusters: pod cluster containing the gene encoding pyruvic oxime dioxygenase (POD), podh cluster containing the gene encoding a POD homolog (PODh), suf cluster involved in an iron-sulfur cluster biogenesis, and dnf cluster involved in a novel hydroxylamine oxidation pathway in the nitrifying cells. Our results provide valuable insight into the biochemical mechanism of heterotrophic nitrification.

Biochar enhanced the nitrogen removal performance of heterotrophic nitrification-aerobic denitrification strain pseudomonas fluorescent sp. Z03 for insufficient carbon source wastewater under low temperature

In this study, biochar BC400 and BC700 were prepared, characterized and coupled with heterotrophic nitrification-aerobic denitrification (HNAD) strain Z03 for nitrogen removal experiments. The characterization results showed that BC700 has a higher specific surface area and a more complex multilayered pore structure, with increased aromatic condensation and higher crystallinity. BC400 and BC700 both have good redox activity, while BC400 has stronger electron donor capacities and BC700 owns better electron transfer properties. In addition, both BC400 and BC700 contain relatively high levels of dissolved organic carbon (DOC), reaching at 62.95 and 51.617mg/g respectively. BC400/BC700 coupled with strain Z03 can significantly improve the NH4+-N removal performance of low-temperature and low C/N wastewater compared with the control group. At a dosage of 4.0 g/L, the removal rate of NH4+-N reached to 95.16% (BC400 + Z03) and 84.37% (BC700 + Z03) within 72h, respectively. Higher than the sum of adsorption by BC400/BC700 (16.19%/18.85%) and microbial degradation (41.03%). Besides, the BC400 + BC700 + Z03 NH4+-N removal systems provide higher nitrogen removal efficiencies than BC400/BC700 + Z03 nitrogen removal systems. When the dosage (BC400 + BC700, mass ratio 5:1) reaches 3.0g/L, it can achieve more than 90% NH4+-N removal rate within 48h. The reasons for the promotion of biochar on microbial denitrification were analyzed as follows: 1) DOC can provide an additional carbon source for microorganisms; 2) biochar, as a pH buffer, can neutralize the acidity due to nitrification; 3) BC400 and BC700, as materials with good redox activity, may play a role in promoting the activity of electron transfer system and enzyme activity.