Constraining the conditions conducive to dissimilatory nitrate reduction to ammonium in temperate arable soils

Here we offer the first assessment of conditions conducive to dissimilatory nitrate reduction to ammonium (DNRA) in temperate arable soils, through an examination of the potential for this process to occur in a range of soils of contrasting characteristics. NH₄¹⁵NO₃ (6.2 g N m⁻², 25 atom % excess ¹⁵N) was applied, and recovery of ¹⁵N in the pool taken as indicative of occurrence of DNRA. Up to 5% of applied ¹⁵N was recovered in the pool 2 d after addition of N, glucose (44.6 g C m⁻²) and l-cysteine (7.7 g m⁻², 0.9 g N m⁻², 2.3 g C m⁻²). concentrations were positively correlated with soil pH, ratio, bulk density, sand content and concentration, but negatively correlated with soil C and organic N content. Our results demonstrate the potential for DNRA to contribute to N cycling in temperate arable soils, but its detection and significance is likely to depend on the provision of a low molecular weight C source.     

农作制度对黑河中游沙质土壤硝态氮积累及作物产量的影响

为研究沙地农田不同土壤耕作、覆盖方式和轮作对作物产量、土壤硝态氮含量及积累的影响,在黑河中游边缘绿洲典型沙地进行农田定位试验。试验结果表明,在沙地农田生态系统,相对传统的三耕两耱的耕作方式,减少秋耕对玉米和大豆产量没有显著影响;相对于地膜覆盖处理,麦秆覆盖处理使玉米减产11.3%～18.8%,使大豆产量增加6%;不同处理0～40cm土壤硝态氮积累量存在显著差异,作物收获后传统耕作处理土壤硝态氮的平均积累量比少耕处理低8.5%～22.7%,覆膜处理比覆麦秆处理低7.0%～8.8%,玉米连作处理比玉米-大豆轮作处理高54.9%。分析结果表明,减少秋耕、麦秆代替地膜覆盖均有利于土壤硝态氮在作物根系集中层的积累,玉米大豆轮作对土壤硝态氮积累和淋失的影响仍需进一步研究;该试验研究的继续深入将对维持绿洲农田环境的健康和提高沙地农田生态系统生产力提供重要的理论依据。     

北运河流域典型区污灌条件下氮素渗漏模拟及灌溉模式优选

为了揭示北运河流域农田氮素的渗漏迁移特征,为该流域水资源总体规划和非点源污染综合整治提供指导,以北运河流域武清区为研究对象,采用改进的SWAT模型对16种不同灌溉模式下农田氮素的渗漏特征进行模拟分析。结果显示,随着污灌次数的增加,氮素渗漏量也相应增加,但3次以下污灌,其变化不明显。在污灌次数相同,且连续污灌或者污灌间隔...     

Na_2CO_3胁迫对碱地风毛菊苗期叶片和根系氮代谢的影响

对碱地风毛菊苗期以Na2CO3进行胁迫处理,浓度为0、30、60、90、120、150和180 mmol/L,测定了盐胁迫下叶片和根系氮代谢过程的可溶性蛋白、硝酸还原酶、硝态氮及谷氨酰胺合成酶等指标。结果表明:在Na2CO3胁迫下,碱地风毛菊叶片和根系可溶性蛋白含量均在120 mmol/L处理下达到最大值,为6.76和6.75 mg/g.FW,且与对照差异显著(P<0.05);随Na2CO3浓度增大,叶片的硝酸还原酶活性下降,根系的先下降后升高,根系硝态氮含量先增加后下降,叶片谷氨酰胺合成酶活性变化不明显,与对照差异不显著,根系的呈上升趋势,与对照差异显著(P<0.05)。     

白菜NRT2基因的克隆及表达模式分析

 以白菜（Brassica campestris ssp. chinensis Makino）品种‘苏州青’为试材,采用RT-PCR技术,获得1个高亲和硝酸盐转运蛋白基因（NRT2）的cDNA序列,全长1 593 bp,推断其编码530个氨基酸,命名为BcNRT2。序列分析表明：BcNRT2基因与甘蓝型油菜BnNRT2基因和拟南芥AtNRT2.1基因核苷酸序列的相似性分别为98%和90%,氨基酸序列的相似性分别为99%和95%,表明植物中NRT2基因保守度较高。实时定量PCR表达分析表明,BcNRT2在白菜根部的表达量最高,为诱导型表达。低浓度NO^₃-（0.2 mmol · L^-1 KNO₃）处理0.5 h后其表达量迅速上升,BcNRT2可能为NO₃^-感受器。高浓度NO₃^-（20 mmol · L^-1 KNO₃）处理后其表达量更高,持续时间较长,可能是受到低亲和硝酸盐转运蛋白NRT1.1的调控而产生的高水平响应。原生质体的瞬时表达显示,BcNRT2蛋白位于细胞膜上。     

甘蔗硝酸还原酶活性与氮素营养的关系

对福引79-9、福引82-41和闽糖70-611三个品种分别施以不同量的氮肥后,各品种的+1叶硝酸还原酶活性(NRA)与+3叶含氮量的变化规律极其相似,不施氮处理的+1叶NRA和+3叶含氮量随蔗株株龄的增长而持续下降;施氮处理在施肥后几天,+1叶NRA和+3叶含氮量逐渐上升至最高峰,以后则随株龄的增长而下降。从施氮后+1叶NRA和+3叶含氮量出现最高峰起,各时期的+1叶NRA和+3叶含氮量的高低顺序(除闽糖70-611 9月11日Nl的+3叶含氮量略高于N2外)为施氮多的处理>施氮少的处理>不施氮的处理。3个品种3种施氨水平下的+1叶NRA与+3叶含氮量均呈极显著正相关。可见,+1叶NRA与+3叶含氨量一样能反映出蔗株的氮素营养状况。但+1叶NRA因品种和株龄而有很大变化,不适用于氮素营养诊断。     

Molybdenum Uptake and Nitrate Reductase Activity in Sorghum (Sorghum bicolor L. Moench). Evidence for Heterosis

The absorption of Mo by the roots and. transport to the shoot of intact seedlings of a sorghum hybrid and its parent cultivars were measured for 3 h from 10 to 100 μmol ammonium molybdate. The patterns of absorption revealed hybrid vigour and the hybrid followed the patterns of the male- parent 168. Studies on the effects of different amounts of Mo on the nitrate reductase activity also showed the occurrence of hybrid vigour in the- hybrid CSH-7.     

Field Investigation of Controlling Acid Mine Drainage Using Alkaline Paper Mill Waste

To verify in situ laboratory test results for the control of acid mine drainage using alkaline paper mill waste, five demonstration cells were built on the Ascot mine site in Sherbrooke (Québec, Canada). A monitoring program was set up to record temperature, leached water quality, oxygen concentration and electrical conductivity.Monitoring results showed that mixing mine residueswith alkaline paper mill waste and covering mine residues with paper mill waste allows an efficient control of acid mine drainage. The paper mill waste cover generates an alkaline front which results in metal precipitation as hydroxides. Also, an increase in pH results in an inhibitionof bacterial catalytic activity. Chemical analyses conducted on the collecting water shows a high reduction of leachingmetals to under ground water. Moreover, a significant reduction of diffusion of oxygen to the mine residue is observed.     

The Effect of Seeding Rate and Nitrogen Fertilization on Barley Yield and Yield Components in a Cool Maritime Climate

Soil and climatic conditions in Newfoundland are on the margins of agricultural capability, and almost all feed grain is imported. The overall objective of this work was to develop guidelines for the production of barley in Newfoundland, with the goal of establishing modern cropping recommendations. We conducted a 4-year study near St. John's to examine the effect of seeding rate and topdress ammonium nitrate (N) fertilization rate on Chapais six-row barley ( Hordeum vulgare L.) yield components and grain yield. Increasing seeding rate from 200 to 380 seeds m^–2 did not alter grain yield in any year. Increasing topdress fertilization from 0 to 60 kg N ha^–1 increased spike density m^–2 at harvest, resulting in linear increases in grain yield in all years. Highest N rates had greatest lodging in two years. Based on our results, agronomic recommendations for eastern Newfoundland now include barley seeding rates of 250 ± 50 seeds m^–2, with topdress applications up to at least 30 kg N ha^–1.     

Nitrogen cycling in organic farming systems with rotational grass–clover and arable crops

Organic farming is considered an effective means of reducing nitrogen losses compared with more intensive conventional farming systems. However, under certain conditions, organic farming may also be susceptible to large nitrogen (N) losses. This is especially the case for organic dairy farms on sandy soils that use grazed grass–clover in rotation with cereals. A study was conducted on two commercial organic farms on sand and loamy sand soils in Denmark. On each farm, a 3‐year‐old grass–clover field was selected. Half of the field was ploughed the first year and the other half was ploughed the following year. Spring barley (Hordeum vulgare L.) was sown after ploughing in spring. Measurements showed moderate N leaching during the pasture period (9–64 kg N ha^?1 year^?1) but large amounts of leaching in the first (63–216 kg N ha^?1) and second (61–235 kg N ha^?1) year after ploughing. There was a small yield response to manure application on the sandy soil in both the first and second year after ploughing. To investigate the underlying processes affecting the residual effects of pasture and N leaching, the dynamic whole farm model farm assessment tool (FASSET) was used to simulate the treatments on both farms. The simulations agreed with the observed barley N‐uptake. However, for the sandy soil, the simulation of nitrate leaching and mineral nitrogen in the soil deviated considerably from the measurements. Three scenarios with changes in model parameters were constructed to investigate this discrepancy. These scenarios suggested that the organic matter turnover model should include an intermediate pool with a half‐life of about 2–3 years. There might also be a need to include effects of soil disturbance (tillage) on the soil organic matter turnover.