Effects of concentration,incubation temperature,and repeated applications on degradation kinetics of dicyandiamide (DCD) in model experiments with a silt loam soil

Summary The kinetics of dicyandiamide (DCD) decomposition were studied (at 80% water-holding capacity) in pretreated and non-pretreated soils, using model experiments. DCD was added in different concentrations (6.7, 16.7, and 33.3 g DCD-N g^–1 dry soil) and incubated at various temperatures (10°, 20°, and 30°C). Additionally, DCD decomposition was examined in sterile soil (with or without Fe₂O₃) after inoculation with a DCD-enrichment culture. In the sterile variant, (30°C)the applied dicyandiamide concentration remained constant, even after 36 days. In the sterilized and reinoculated variant, DCD disappeared within 7 days. Addition of Fe₂O₃ powder to the sterilized soil had no effect on DCD degradation. In the pretreated soils, DCD mineralization started immediately at all temperatures and concentrations without a lag phase. A temperature increase of 10°C doubled the mineralization rate. The mineralization rates were independent of the initial concentrations. In the non-pretreated soils (except at 30°C with 16.7 and 33.3 g DCD-N g^–1 dry soil) DCD decreased only after a short (30°C) or a long (10°C) lag phase. These results suggest that an inducible metabolic degradation occurred, following zeroorder kinetics.     

抗盐小麦突变体的诱变筛选及其抗盐性的比较

Ｘ射线辐照前用修复抑制剂咖啡因预处理或辐照后热处理诱变冬小麦萌发种子，Ｘ射线剂量８．６Ｇｙ，剂量率２．１５Ｇｙ／ｍｉｎ。在不同浓度的ＮａＣｌ溶液中进行抗盐突变体的筛选。３个原始品种的诱变处理对比实验表明，相对于单纯的Ｘ射线２，Ｘ射线分别与咖啡因以及热复合处理，能够显提高小麦萌发１．９％ＮａＣｌ溶液中生长１５天的苗存活率。将在１．９％ＮａＣｌ溶液中生长１５天存活的小植株移植到人工气候室中加代繁殖。     

脲酶/硝化抑制剂在土壤N转化过程中的作用

综述了脲酶抑制剂/硝化抑制剂对土壤氮的转化过程:尿素水解过程、硝化过程、硝酸盐淋溶过程、反硝化过程、微生物固持过程、N矿化过程及气体挥发过程的影响和抑制剂的作用机理,并提出今后研究的发展方向,为今后如何施用抑制剂来提高土壤中氮素利用率和减少环境污染提供一定的参考价值。     

Effects of N sources and methane concentrations on methane uptake potential of a typical coniferous forest and its adjacent orchard soil

After removal of the above-ground plant debris three different soil layers were taken from a typical coniferous forest and its adjacent orchard in Numata City, Japan. The potentials of soil CH₄ uptake at two initial CH₄ concentrations were studied under aerobic conditions in the laboratory, along with inhibition of soil CH₄ oxidation by urea-N or KNO₃-N addition. Due to long-term N inputs, the CH₄ uptake of the upper mineral layer of the orchard soil was 25.4% and 87.7% lower than that of the surface forest soil at 2.4 and 12.6 l l^–1 CH₄, respectively. Methane uptake of the forest soil decreased with increasing soil depths at two CH₄ levels. However, maximal CH₄-consuming activity occurred in the 9- to 23-cm depth of the orchard soil at 12.6 l l^–1 methane. Nitrogen additions in the form of KNO₃ or urea at the rate of 200 g N g^–1 soil substantially reduced soil CH₄ uptake in the upper and sub-surface mineral layers at both sites, except that the addition of KNO₃-N had no apparent inhibitory effect on the CH₄ uptake in the 9- to 23-cm depth of the orchard soil. A strong inhibitory effect of NO₃^– addition on the CH₄ uptake, in contrast to NH₄⁺, occurred in the surface forest soil. The use of KNO₃-N, as compared to urea or urea plus a nitrification inhibitor (dicyandiamide), resulted in a lower potential to cause inhibition of CH₄ oxidation in the 0- to 23-cm depth of the orchard soil.     

The effect of precipitation and application rate on dicyandiamide persistence and efficiency in two Irish grassland soils

The nitrification inhibitor dicyandiamide (DCD) has had variable success in reducing nitrate () leaching and nitrous oxide (N₂O) emissions from soils receiving nitrogen (N) fertilizers. Factors such as soil type, temperature and moisture have been linked to the variable efficacy of DCD. As DCD is water soluble, it can be leached from the rooting zone where it is intended to inhibit nitrification. Intact soil columns (15 cm diameter by 35 cm long) were taken from luvic gleysol and haplic cambisol grassland sites and placed in growth chambers. DCD was applied at 15 or 30 kg DCD/ha, with high or low precipitation. Leaching of DCD, mineral N and the residual soil DCD concentrations were determined over 8 weeks high precipitation increased DCD in leachate and decreased recovery in soil. A soil × DCD rate interaction was detected for the DCD unaccounted (proxy for degraded DCD). In the cambisol, degradation of DCD was high (circa 81%) and unaffected by DCD rate. In contrast, DCD degradation in the gleysol was lower and differentially affected by rate, 67 and 46% for the 15 and 30 kg/ha treatments, respectively. Variation in DCD degradation rates between soils may be related to differences in organic matter content and associated microbiological activity. Variable degradation rates of DCD in soil, unrelated to temperature or moisture, may contribute to changing DCD efficacy. Soil properties should be considered when tailoring DCD strategies for improving nitrogen use efficiency and crop yields, through the reduction of reactive nitrogen loss.     

小分子植物病毒抑制物质研究进展

论述了小分子病毒抑制物的结构及对病毒的抑制机理 ,讨论了植物病毒抑制剂研究中存在的问题及研究前景     

烘烤过程多酚氧化酶抑制剂对烤烟多酚的影响

 选用4种多酚氧化酶抑制剂处理备烤烟叶,与对照进行烘烤比较试验。通过对烤后烤烟样品总酚、绿原酸、芸香苷含量及烘烤前鲜烟匀浆中多酚氧化酶活性的检测。比较结果显示：常规烘烤条件下4种抑制剂对烤烟多酚含量无明显影响;在不当的烘烤条件下,4种处理样品的多酚含量明显高于对照,其中对烤烟多酚降解抑制作用最强的是NaDiCa,聚乙烯吡咯烷酮相对弱些但无异味,它们可能是防止不当烘烤导致烟叶褐变的有效抑制剂。鲜活烤烟匀浆中4种抑制剂对多酚氧化酶活性抑制作用由强到弱依次为NaDiCa,聚乙烯吡咯烷酮,EDTA和硫脲。匀浆酶活性检测结果与整叶烘烤处理后烤烟样品总酚含量高低顺序不完全一致,可能是不同抑制剂在烟叶组织中渗透性不一致引起,值得进一步研究。     

野生二粒小麦α-淀粉酶抑制因子编码基因序列分析

对3份野生二粒小麦(Triticum dicoccoides)材料的抗虫24 kDaα-淀粉酶抑制因子编码基因进行分离克隆,得到72个24 kDaα-淀粉酶抑制因子基因,并进行序列分析。结果发现,α-淀粉酶抑制因子在野生二粒小麦中以多拷贝形式存在,经卡方检验初步推断野生二粒小麦中的α-淀粉酶抑制因子成熟蛋白编码基因序列变异类型在供试材料间无显著差异。序列分析表明,24 kDaα-淀粉酶抑制因子成熟蛋白编码基因序列无论在野生二粒小麦种内还是与小麦属的其他物种之间,都具有很高的一致性,说明该基因在进化过程中十分保守。     

硝酸银诱导的大豆子叶中大豆Kunitz胰蛋白酶抑制剂的研究

采用二维电泳技术对硝酸银诱导的大豆子叶微粒体膜蛋白进行分离,利用四极杆-飞行时间串联质谱,对仅存在于诱导样品而不存在于对照样品中的蛋白质点进行氨基酸序列测定和分析,以期研究硝酸银处理对大豆子叶微粒体蛋白质的影响。结果显示:硝酸银可以诱导大豆Kunitz胰蛋白酶抑制剂(SKTI)的产生,在诱导处理的子叶中大量存在其成熟形式,也存在其5 kDa小亚基,小亚基含有“GIGTIISSPER”和“FIAEGNPLR”氨基酸序列。该研究结果为SKTI的深入研究提供了实践依据,并为其分离纯化提供了简便途径,从而有利于对其更多性质的进一步研究。     

噻嗪酮对褐飞虱作用方式及其田间应用研究

在室内以不同生测方法测定了噻嗪酮对褐飞虱若虫的毒力,结果表明:噻嗪酮对褐飞虱若虫的活性主要是触杀作用;噻嗪酮也具有一定的内吸作用,但难以由叶片渗透转移到叶鞘部位起杀虫作用。在田间试验中,噻嗪酮对褐飞虱和白背飞虱的防治效果明显高于叶蝉散和甲胺磷,以每亩2.5～5克有效成份的剂量在褐飞虱大发生代前一代的若虫中期施用,既有效控制了当代飞虱,又压低了大发生代飞虱的数量。在田间试验中,噻嗪酮对稻田蜘蛛的数量影响很小。