Effects of Heavy Metals on Ammonification, Nitrification and Denitrification in Maize Rhizosphere

The ammonification, nitrification and denitrification in maize rhizosphere of alluvial soils were compared with those in the bulk soil after exposure to different kinds of heavy metals. The addition of cadmium at low levels (2 mg kg-1 and 5 mg kg-1) could stimulate the ammonification and nitrification in the soils, while inhibition influences were found at high levels of Cd addition (10 mg kg-1 and 20 mg kg-1). The relationship between microbial activity and cadmium concentration varied with the kind of microorganisms. The nitrifying bacteria were more sensitive to cadmium pollution than the ammonifying bacteria. When Cd(II), Cu(II) and Cr(VI) were compared at the same addition concentration of 20 mg kg-1 soil, Cd(II) was the most effective inhibitor of ammonification and denitrification among the three investigated heavy metals, and Cr(VI) had the most strong inhibitory influence on the nitrifying bacteria. The microbial activities in rhizosphere were higher than those in the bulk soil for most of the treatments. Cr(VI) proved to be the most effective in enhancing the microbial activities in rhizosphere, and this could be caused by the positive reduction of Cr(VI) to Cr(III) in rhizosphere, and the relatively sufficient existence of organic matter which intensified the adsorption of the metal. It seemed that the rhizosphere had some mitigation effect on heavy metal toxicity.

Elucidation of the last steps of photo-ammonification:analytical method development and mechanism elucidation

The mechanisms underlying the photo-ammonification of nitrogenous organic compounds(NOCs)remain unclear,partly due to the analytical challenges of small NOC intermediates.This study introduced a simple methodology for accurately and simultaneously quantifying multiple small NOCs during ammonification processes.The developed method employed phenyl isothiocyanate as derivatization reagents,followed by high-performance liquid chromatography analysis to measure primary and secondary amines,amides,as well as NH4+over variable photo-ammonification conditions.In our experimental setup,vacuum ultraviolet(VUV)irradiation serves as the controlled reaction environment to simulate harsh photo-ammonification environment.Representative NOCs,including pyridine,N,N-dimethylformamide,and acrylonitrile,were chosen due to their structural diversity and environmental relevance as model NOCs.This method was able to achieve excellent nitrogen mass balance,and revealed that the last steps of photo-ammonification involved oxidation of nitrogen-adjacent carbon to amide followed by the cleavage of N-C bond.This novel method may also help quantitative investigation of nitrogen transformations in different environmental contexts.

Reaction of Ferralsol to Acidifying Effect of Nitrogen Fertilisation

Background: The objective of this study was to determine the short-term effect of urea fertiliser application on soil reactions in a Ferralsol, with particular thrust on P sorption. Methods: Two experiments were conducted for this purpose: 1) a screenhouse pot experiment; and 2) a laboratory P sorption component. The pot (10 litre capacity plastic pots) experiment was conducted at the Makerere University Agricultural Research, Kabanyolo in Uganda, using a Ferralsol. The study comprised of four urea N (46% N) fertiliser treatments, namely, 0, 40, 80 and 120 kg N·ha-1, equivalent to 0, 200, 400 and 600 mg N per pot. A completely randomised design was adopted with three replicates. Urea rates were applied in 50% split doses, one at planting and the other at 19 days after seedling emergence (to simulate farmer practice). This was followed by watering to field capacity using distilled water. Soil samples were taken at three daily intervals until day fourteen;thereafter, soil sampling was at an interval of seven days. The second urea split dose was applied at 21 days followed by soil sampling at an interval of three days till day fourteen. Thereafter, soil was sampled at seven day intervals until the end of experiment. Soil samples were analysed for exchangeable H+, Al3+, NH4+and NO3- ions. The reaction trends of the concentrations of these ions and Bray 1 P were used to structure different response curves representing the instantaneous reactions. As for the laboratory P-sorption study, treatments included the four rates of urea used in the pot experiment (0, 40, 80 and 120 kg N·ha-1) and seven levels of P (2.5, 5, 10, 20, 30, 40 and 50 ppm) as KH2PO4. The setup was incubated under laboratory conditions and soil samples were repeatedly taken at 10 days (after 4 days of urea incubation plus 6 days of P application). The P sorption data were fitted to Langmuir model. Results: The pot experiment revealed an abrupt drop in the concentrations of exchangeable Al3+ and H+ ions (p < 0.05) within the first 6 days after urea application, accompanied by a positive surge in the concentration of NH4+ ions. This phase (6 days) was followed by a rise in the levels of exchangeable Al3+, H+ and NO3- ion concentration, which was inversely mirrored by a drop in the concentration of NH4+ ions. Consequently, the patterns displayed by the soil reactions were delineated into four phases, with Phase 1 (6 days) being characterised by urea hydrolysis reactions of deamination and ammonification, Phase 2 (10 days) being dominated by nitrification and its acidifying properties, Phase 3 being a repeat of Phase 1, both occurring immediately after urea application (within 6 days);and Phase 4 being a repeat of Phase 2. As for the P-sorption study, the effects of urea hydrolysis in a Ferralsol markedly increased soil pH and surprisingly P sorption. The contradictory P sorption behavior, despite the drop in exchange acidity was attributed to presence of divalent calcium in the extraction reagent used. Conclusion: The short term insights obtained in response to urea N application in the Ferralsol, are eye openers to future use of N fertilisers as well as strategic management of the associated acidification process which is often more costly and complicated to manage.

Ecotoxicological effect of zinc oxide nanoparticles on soil microorganisms

The widespread production and use of zinc oxide nanoparticles （ZnO-NPs） in recent years have posed potential threat to the ecosystem. This study aimed to investigate the ecotoxicological effect of ZnO-NPs on soil microorganisms using laboratory microcosm test. Respira- tion, ammonification, dehydrogenase （DH） activity, and fluorescent diacetate hydrolase （FDAH） activity were used as ecotoxicological parameters. The results showed that in the neutral soil treated with 1 mg ZnO-NPs per g soil （fresh, neutral）, ammonification was significantly inhibited during the study period of three months, but the inhibition rate decreased over increasing time. Inhibition in respira- tion was observed in the first month of the test. In various ZnO-NPs treatments （1 rag, 5 rag, and 10 mg ZnO-NPs per g soil）, DH activity and FDAH activity were inhibited during the study period of one month. For both enzyme activities, there were positive dose-response relationships between the concentration of ZnO-NPs and the inhibition rates, but the curves changed over time due to changes of ZnO-NPs toxicity. Soil type affected the toxicity of ZnO- NPs in soil. The toxicity was highest in the acid soil, followed by the neutral soil. The toxicity was relatively low in the alkaline soil. The toxicity was not accounted for by the Zn2＋ released from the ZnO-NPs. Direct interaction of ZnO-NPs with biologic targets might be one of the reasons. The adverse effect of ZnO-NPs on soil micro- organisms in neutral and acid soils is worthy of attention.

Enhancement of Alkene Epoxidation Activity of Titanosilicates by Gas-Phase Ammonia Modification

Novel ammonia-treated titanosilicates have been prepared by heating the samples of Ti-MWW, TS-l and Ti-Beta under pure ammonia gas flow at 673 K for a period of time. The ammonia modification improved their catalytic performance in liquid-phase oxidations. Especially, the catalytic activities of ammonified Ti-MWW, N-Ti-MWW, were enhanced greatly in the epoxidation of 1-hexene with H2O2. The reason that the ammonia treat- ment played such an important role in post-modification of titanosilicate was investigated in details. In comparison to the parent Ti-MWW catalyst, N-Ti-MMW was more robust and produced less coke in oxidation reactions.