Shin-ichi Tokuda

Involvement of Two Plasmids in Fenitrothion Degradation by Burkholderia sp. Strain NF100

ABSTRACT A bacterium capable of utilizing fenitrothion (O,O-dimethylO-4-nitro-m-tolyl phosphorothioate) as a sole carbon source was isolated from fenitrothion-treated soil. This bacterium was characterized taxonomically as being a member of the genus Burkholderia and was designated strain NF100. NF100 first hydrolyzed an organophosphate bond of fenitrothion, forming 3-methyl-4-nitrophenol, which was further metabolized to methylhydroquinone. The ability to degrade fenitrothion was found to be encoded on two plasmids, pNF1 and pNF2.

Nitrous Oxide Flux from a Tea Field Amended with a Large Amount of Nitrogen Fertilizer and Soil Environmental Factors Controlling the Flux(Environment)

Abstract Nitrous oxide (N2O) is one of the main greenhouse gases, and accurate estimation of the N2O flux from fertilized arable land is required. It is known that acidic tea field soil displays a higher N2O production activity than neutral arable soil and that tea fields could be a major source of N2O. Therefore, N2O fluxes from four plots (Std, 2N, 2Ca and −Ca plots) in a tea field that had been subjected to different conditions of fertilizer management were measured using the closed chamber method over a period of two years, and the relationships between the N2O flux and soil environmental factors were analyzed. The amounts of nitrogen fertilizer and liming material (dolomite) applied to the Std plot were 600 kg N ha−1 y−1 and 1,500 kg ha−1 y−1, respectively. The amount of nitrogen fertilizer applied to the 2N plot was two-times larger than that applied to the Std plot and corresponded to the conventionallevel in Japanese tea fields. The soil was acidified due to heavy nitrogen fertilization in the 2N plot. The 2Ca plot was amended with two-times the amount of liming material of the Std plot and in the −Ca plot no liming material was applied. There were significant differences among the N2O fluxes from the plots, and the highest value of N2O flux was 8.785 mg N m−2 h−1 in the 2N plot. Annual emission rate and emission factor of N2O in the 2N plot were 25.22 kg N2O-N ha−1 and 2.10%, respectively. Both long-term heavy nitrogen fertilization and subsequent soil acidification possibly enhanced the N2O flux from the tea field. The N2O flux from the tea field showed temporal variations, namely the N2O flux was relatively low from December to March possibly due to the low soil temperature and it increased gradually after March as the soil temperature increased over 10°C. The N2O flux reached the first major peak in July, decreased transiently in August presumably due to the drying of soil, increased again and reached the second peak in September or October, and then decreased after November. Multiple linear regression analysis of the relationships between the N2O flux and soil environmental factors indicated that the N2O production activity was significantly related to the N2O flux from the tea field. The N2O production activity showed temporal variations corresponding to the temporal variations of the N2O flux.

Nitrous oxide emission potential of 21 acidic tea field soils in Japan

Abstract The nitrous oxide (N2O) emission potential of 21 acidic tea field soils in Japan was evaluated using a laboratory incubation method. The range of pH values of the soils was 6.26–2.96, and 17 of the 21 soils were strongly acidified below pH 5.0 due to long-term heavy application of nitrogen fertilizer. The N20 emission potential ranged from 0.001 to 1.463 µg N2O-N g-1 d-1. There was a negative exponential relationship between the soil pH value and N2O emission potential. The application of more than 1,000 kg N ha-1 y-1 of nitrogen fertilizer significantly enhanced the N2O emission potential of acidic tea field soils.

Nitrous oxide production from strongly acid tea field soils

Abstract Nitrous oxide (N2O) production from acid (pH 3.60) tea field soil under aerobic conditions was studied in a laboratory experiment. A large amount of N2O (53 μ N g−1 soil 14 d−1) was produced under aerobic conditions when ammonium and nitrate were added to the soil. It was assumed that the high N2O production was an inherent property of the soil because soil pre-treatments (e.g., air-drying) did not affect it. A 15N tracer study indicated that N 2 was not produced from the acid tea field soil. N2O was produced during biological reactions, and the contribution of N2O production during chemical reactions to the whole N2O production was negligible. Nitrapyrin (2-chloro-6-(trichloromethyl)- pyridine) and acetylene (0.1 Pa), which are selective nitrification inhibitors, slightly reduced N2O production. These results indicate that denitrification is the main process of N2O production in acid tea field soil. The levels of N2O production from four tea field soils collected from the same area were compared. The results showed that a large amount of N2O is likely to be produced from a soil with a pH value below about 3.60 and to which a large amount of nitrogen fertilizer (more than 1,000 kg N ha1−1 y1−1) had been added.

Soil microbial biomass and fluorescein diacetate hydrolytic activity in Japanese acidic tea field soils

Abstract The soil microbial biomass (SME) content and fluorescein diacetate (FDA) hydrolytic activity in 21 acidic tea field soils in Japan were determined. SM 3 content in the tea field soils was quantitatively similar to that in 13 arable soils with neutral soil pH previously reported. However, the ratio of the SMB content to organic matter content in the tea field soils classified as red-yellow soil, brown forest soil, and lithosol was clearly lower than that in the neutral arable soils classified as non-volcanic ash soil. FDA hydrolytic activity in the tea field soils was higher than the activity in various soils with neutral soil pH and showed a negative relationship with the soil pH.

Comparison of the Effects of Phenylhydrazine Hydrochloride and Dicyandiamide on Ammonia-Oxidizing Bacteria and Archaea in Andosols

Dicyandiamide, a routinely used commercial nitrification inhibitor (NI), inhibits ammonia oxidation catalyzed by ammonia monooxygenase (AMO). Phenylhydrazine hydrochloride has shown considerable potential for the development of next-generation NIs targeting hydroxylamine dehydrogenase (HAO). The effects of the AMO inhibitor and the HAO inhibitor on ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) present in agricultural soils have not been compared thus far. In the present study, the effects of the two inhibitors on soil nitrification and the abundance of AOA and AOB as well as their community structure were investigated in a soil microcosm using quantitative polymerase chain reaction and pyrosequencing. The net nitrification rates and the growth of AOA and AOB in this soil microcosm were inhibited by both NIs. Both NIs had limited effect on the community structure of AOB and no effect on that of AOA in this soil microcosm. The effects of phenylhydrazine hydrochloride were similar to those of dicyandiamide. These results indicated that organohydrazine-based NIs have potential for the development of next-generation NIs targeting HAO in the future.