Effects of 4-amino 1,2,4-triazole, dicyandiamide and encapsulated calcium carbide on nitrification inhibition in a subtropical soil under upland and flooded conditions

 Nitrification inhibition of soil and applied fertilizer N is desirable as the accumulation of nitrates in soils in excess of plant needs leads to enhanced N losses and reduced fertilizer N-use efficiency. In a growth chamber experiment, we studied the effects of two commercial nitrification inhibitors (NIs), 4-amino 1,2,4-triazole (ATC) and dicyandiamide (DCD), and a commonly available and economical material, encapsulated calcium carbide (CaC₂) (ECC) on the nitrification of soil and applied NH₄ ⁺-N in a semiarid subtropical Tolewal sandy loam soil under upland [60% water-filled pore space (WFPS)] and flooded conditions (120% WFPS). Nitrification of the applied 100 mg NH₄ ⁺-N kg^–1 soil under upland conditions was retarded most effectively (93%) by ECC for up to 10 days of incubation, whereas for longer periods, ATC was more effective. After 20 days, only 16% of applied NH₄ ⁺-N was nitrified with ATC as compared to 37% with DCD and 98% with ECC. Under flooded soil conditions, nitrates resulting from nitrification quickly disappeared due to denitrification, resulting in a tremendous loss of fertilizer N (up to 70% of N applied without a NI). Based on four indicators of inhibitor effectiveness, namely, concentration of NH₄ ⁺-N and NO₃ ^–-N, percent nitrification inhibition, ratio of NH₄ ⁺-N/NO₃ ^–-N, and total mineral N, ECC showed the highest relative efficiency throughout the 20-day incubation under flooded soil conditions. At the end of the 20-day incubation, 96%, 58% and 38% of applied NH₄ ⁺-N was still present in the soil where ECC, ATC and DCD were used, respectively. Consequently, nitrification inhibition of applied fertilizer N in both arable crops and flooded rice systems could tremendously minimize N losses and help enhance fertilizer N-use efficiency. These results suggest that for reducing the nitrification rate and resultant N losses in flooded soil systems (e.g. rice lowlands), ECC is more effective than costly commercial NIs. Received: 25 May 2000     

Effects of the urease inhibitor N-(n-butyl)phosphorothioic triamide in low concentrations on ammonia volatilization and evolution of mineral nitrogen

Laboratory incubation experiments were conducted to study the influence of increasing concentrations of N-(n-butyl)phosphorothioic triamide (NBPT) on NH₃ volatilization and rate of urea hydrolysis and evolution of mineral N in Ozzano, Rimini and Carpi soils with different physicochemical characteristics. Low concentrations of NBPT reduced NH₃ losses due to volatilization after urea fertilization and the effectiveness of the inhibitor was related to the soil characteristics (e.g. high concentrations of organic C and sand). After 15 days of incubation, no significant reductions of losses were found for any of the NBPT concentrations employed in Rimini soil. The application of NBPT led to a considerable reduction of the formation of nitrite. This process was completely annulled with the highest dose of NBPT (0.5% w/w_urea) in the Carpi soil after 15 days. In Rimini soil, however, the use of NBPT was less effective in influencing nitrite formation. The use of NBPT favoured accumulation of nitrate proportional to the NBPT concentration employed while it had no influence on the NH _inf4 ^sup+ fixation by 2:1 layer silicates. The data obtained support previous evidence that NBPT is effective in reducing the problems encountered in using urea as fertilizer. However, environmental conditions and soil physicochemical characteristics may have an important influence on the effectiveness of NBPT.     

高效异养硝化细菌的分离筛选及多样性分析

采用生长曲线指导的富集培养法,从生活污水排放渠中分离筛选出高效异养硝化细菌,并对其多样性进行了分析。结果显示,从分离得到的27株异养硝化细菌中筛选出6株高效菌株Ni1-2、Ni1-8、Ni2-5、Ni2-7、Ni3-1和Ni3-4,其48 h氨氮去除率分别为88.9%、76.6%、87.7%、93.1%、99.2%和91.4%;结合菌落形态、革兰氏染色反应、扫描电镜观察和16S r DNA序列分析,发现菌株的种类较为丰富,初步确定Ni1-2和Ni1-8为节杆菌属(Arthrobacter),Ni2-5和Ni3-1为产碱杆菌属(Alcaligenes),Ni2-7为无色杆菌属(Achromobacter),Ni3-4为芽孢杆菌属(Bacillus)。该结果可为高效异养硝化菌的分离筛选及其多样性分析提供参考。     

Colostral Trypsin-Inhibitor Capacity in Different Animal Species

Colostral trypsin-inhibitor capacity was monitored during the first two weeks from parturition. The colostrum of the mare, sow, cow and ewe showed high antitrypsin activity at parturition, decreasing to about one hundredth during the first week. Canine milk remained on a relatively high antitrypsin level, and human milk was poor in antitrypsin from childbirth. The antitrypsin content seems to parallel the known changes in the colostral immunoglobulin levels of different species. The role of antitrypsin in protection of immunoglobulins from proteolytic damage during passive transfer of immunity to the newborn is obvious.     

NO在雏鸡球虫感染过程中的作用

研究以腹腔注射途径给予试验雏鸡cNOS抑制剂L－NAME、L－NA以及iNOS抑制剂L－AG，通过测定血浆NO2^-水平、肠道粘膜NOS活性、雏鸡日增重以及肠道病变计分、肠道组织切片中球虫数量、O.P.G值、异常粪便百分率等指标，研究了NO在雏鸡感染E.tenella或E.acervulina过程中的作用。试验结果表明，在雏鸡感染E.tenella或E.acervulina后，每日连续给予L－AG或L－NAME，不但加重了雏鸡的肠道组织显微病变，而且使肠道组织切片中的球虫数量增多。此外L－AG或L－NAME处理还使感染雏鸡的O.P.G值和肠道病变记分等指标出现不同程度的升高，但与感染对照组的相比未见显著性影响。另外，无论是NO2^-测定结果，还是NOS活性测定结果均表明，3种NOS抑制剂对感染E.acervulina雏鸡体内NO的生成均有较好的抑制作用，其中以L－AG的抑制作用最为理想，L－AG处理组雏鸡血浆NO2^-水平或肠道粘膜NOS活性值均与给予的L－AG剂量之间呈现较好的剂量依赖性递减关系。结果提示，在雏鸡感染球虫过程中，体内大量生成的NO对球虫具有一定的毒性作用。NO可能是在雏鸡E.tenella和E.acervulina感染过程中发挥作用的一种效应分子。     

偏重亚硫酸钠钝化生豆粕胰蛋白酶抑制因子的研究

试验用不同浓度的Ｎａ２Ｓ２Ｏ５处理生豆粕，进行适宜水平研究。结果表明，当生豆粕ＴＩＡ和ＵＡ分别为２９．７２酶活单位和１．９５△ｐＨ时，分别用０．３％、０．４％、０．５％和０．６％ＮａＳ２Ｏ５处理ＲＳＢＭ，ＴＩＡ依次降低了５１．８％、５５．９６％、５９．８３％和５２．０５％，均极显著地低于ＲＳＢＭ（Ｐ＜０．０１）。０．３％Ｎａ２Ｓ２Ｏ５对ＵＡ无影响，其它处理ＵＡ提高约０．０６△ｐＨ。     

Effect of chlorimuron-ethyl on Bradyrhizobium japonicum and its symbiosis with soybean

Possible side-effects of the acetolactate synthase (ALS)-inhibiting herbicide chlorimuron-ethyl on Bradyrhizobium japonicum (Kirchner & Jordan) in pure culture and on inoculated soybean plants growing under controlled conditions were investigated. Growth of B japonicum strain E109 was not affected by this herbicide even when exposed to concentrations 150 times higher than recommended field doses. However, nodulation of soybean plants treated 5 days after emergence with chlorimuron-ethyl at standard application rates was impaired: a 38% decrease in the number of nodules per plant was observed four weeks after treatment. Despite nodule number decrease, no changes in shoot nitrogen content could be detected. Total fresh biomass was diminished by 25% in herbicide-treated plants. Leghemoglobin content in nodules did not vary; nevertheless total nodule protein was diminished by 40% in the herbicide-treated group. ALS activity in different soybean tissues and their relative sensitivity to chlorimuron-ethyl were also investigated. Roots and bacteroids had the greatest specific ALS activities. On a fresh weight basis, the bacteroid fraction displayed the highest ALS activity and was also the most tolerant to in vitro chlorimuron addition: 72% of its activity was retained after including 10 microM chlorimuron-ethyl in the reaction mixture. These results indicate that standard application rates of chlorimuron-ethyl will have limited incidence on B japonicum survival, and effects on nodulation may have little long-term consequences on soybean nitrogen fixation potential. The differences found among soybean tissues not only in intrinsic ALS activity but also in their relative sensitivity to this herbicide suggests that, in leguminous plants living in symbiosis with rhizobia, nodules may contribute to an enhanced tolerance to ALS inhibitors.     

Re-examination of inhibitor resistance conferred by Qo-site mutations in cytochrome b using yeast as a model system

Cytochrome b from yeast (Saccharomyces cerevisiae Meyer ex Hansen) provides a convenient model system for the study of Qo-site inhibitor (QoI) resistance mutations from a variety of organisms. QoI resistance mutations from fungal plant pathogens (G143A and F129L), malaria agent Plasmodium sp (Y279C/S), and Pneumocystis carinii (L275F), an opportunistic pathogenic fungus of man, were introduced into yeast cytochrome b and their effect on the binding of a variety of natural (myxothiazol and stigmatellin) and synthetic (atovaquone, azoxystrobin and pyraclostrobin) inhibitors to the bc1 complex monitored. L275S (from a myxothiazol-resistant yeast) was also re-examined. Stigmatellin binding was relatively unaffected by the introduction of these mutations. Significant increases in resistance were observed for the strobilurin-class inhibitors myxothiazol, azoxystrobin and pyraclostrobin, with the largest increase in resistance conferred by G143A. In contrast, atovaquone binding was most effected by Y279C/S and L275S. Notably, F129L, G143A and L275S had a minor effect on bc1 activity, and so are unlikely to confer significant fitness penalties in vivo. These data are discussed in the light of the atomic structures for myxothiazol- and azoxystrobin-inhibited bovine bc1 which have recently become available. We propose that QoI resistance due to G143A arises from steric hindrance between the inhibitor and cytochrome b, whereas the mechanism of resistance for the other mutations is due to an increase in binding energy between the protein and inhibitor molecule. Site-directed mutagenesis was also used to model selected regions of the mammalian Qo site in yeast cytochrome b in order to further understand the differential efficacy of these QoI in the mammalian and pathogen bc1 complexes.     

Genetic analysis and molecular characterisation of laboratory and field mutants of Botryotinia fuckeliana (Botrytis cinerea) resistant to QoI fungicides

BACKGROUND: QoI fungicides, inhibitors of mitochondrial respiration, are considered to be at high risk of resistance development. In several phytopathogenic fungi, resistance is caused by mutations (most frequently G143A) in the mitochondrial cytochrome b (cytb) gene. The genetic and molecular basis of QoI resistance were investigated in laboratory and field mutants of Botryotinia fuckeliana (de Bary) Whetz. exhibiting in vitro reduced sensitivity to trifloxystrobin. RESULTS: B. fuckeliana mutants highly resistant to trifloxystrobin were obtained in the laboratory by spontaneous mutations in wild‐type strains, or from naturally infected plants on a medium amended with 1–3 mg L^?1 trifloxystrobin and 2 mM salicylhydroxamic acid, an inhibitor of alternative oxidase. No point mutations were detected, either in the complete nucleotide sequences of the cytb gene or in those of the aox and Rieske protein genes of laboratory mutants, whereas all field mutants carried the G143A mutation in the mitochondrial cytb gene. QoI resistance was always maternally inherited in ascospore progeny of sexual crosses of field mutants with sensitive reference strains. CONCLUSIONS: The G143A mutation in cytb gene is confirmed to be responsible for field resistance to QoIs in B. fuckeliana. Maternal inheritance of resistance to QoIs in progeny of sexual crosses confirmed that it is caused by extranuclear genetic determinants. In laboratory mutants the heteroplasmic state of mutated mitochondria could likely hamper the G143A detection, otherwise other gene(s) underlying different mechanisms of resistance could be involved. Copyright © 2012 Society of Chemical Industry