Effect of Alternate Bearing Phenomenon and Boron Foliar Application on Nitrogen-15 Uptake,Translocation and Distribution in Mango Tree(cv.Zebda)

The objectives of this investigation are to study nitrogen uptake,translocation,accumulation and distribution in mango tree organs using labeled nitrogen(^(15)N)and to understand the mechanism of boron action in increasing fruit yield in the off-year.A field experiment was conducted using fifteen-year-old mango trees(cv.Zebda)grown at Al Malak Valley Farm,El-Sharkeya Governorate-Egypt.Treatments included the application of(^(15)NH4)2SO4,“in the on-year”,at a rate of 50 g nitrogen/tree through the stem injection technique.While boron was sprayed on the same trees“in the off-year”at the following rates:0.0(control),250 and 500 mg·L^(-1).The authors hypothesize that boron and nitrogen act synergistically to increase mango fruit yield in the off-year.Results indicated that the highest ^(15)N uptake and accumulation in the on and off-years was observed in the upper(young leaves).When boron was applied at 250 mg·L^(-1),in the off-year,the upper(young leaves)recorded the highest ^(15)N uptake and accumulation(%^(15)Ndff=13.93)relative to the other two leaf categories and those of the on-year.In the on-year fruit accumulated higher ^(15)N than leaf or bud.In the off-year,bud exhibited the highest ^(15)N accumulation without boron application,while leaves exhibited the highest ^(15)N with boron application.The highest%^(15)Ndff in all tree organs was observed at 250 mg·L^(-1) boron rate.Boron increased nitrogen uptake,translocation and accumulation in mango tree organs.A synergistic relationship was observed between boron and nitrogen which led to an increase in fruit yield in the off-year.

Nitrate and Ammonium Leaching in Variable-and Permanent-Charge Paddy Soils

A variable-charge （VC） and a permanent-charge paddy soil （PC） were selected to study nitrate-N （NO3^--N） and ammonium-N （NH4^＋-N） leaching with N isotopes for one consecutive year. An irrigation and intermittent drainage pattern was adopted to mimic natural occurrence of rainfall during the upland crop season and drainage management during the flooded rice season. Treatments to each soil type were no-N controls （CK）, ^15N-labeled （NH4）2SO4 （NS）, and milk vetch （NV） applied at a rate equivalent to 238 kg N ha^-1 to unplanted lysimeters, totaling six treatments in triplicates. Results indicated that the soil type dominated N leaching characteristics. In the case of PC, NO3^--N accounted for 78% of the total leached inorganic N; NS was prone to leach three times more than the NV, being 8.2% and 2.4% of added ^15N respectively; and 〉 85% of leached NO3-N came from of the total inorganic N in leachate. Moreover, NH4^＋-N native N in the soil. In the case of VC, NH4^＋-N made up to 92% leaching was detected throughout the whole incubation, and was particularly high during the flooded season. NO3^--N leaching in VC occurred later at a lower rate compared to that in PC. The findings of this study indicate that NO3^--N leaching during the drained season in permanent-charge paddy soils and NH4^＋-N leaching in variable-charge soils deserve more attention for regional environmental control.

有机无机肥料配施对棉田氮素去向影响的研究

在等N、P、K条件下,应用15N示踪的方法研究了盆栽条件下不同肥料结构对棉花的生物学效应及N素去向的影响。所得主要结果如下:(1)与单施化肥相比,绿肥+沼肥+化肥配施有利于N向生殖器官转移,增产效果较好,绿肥+化肥配施效果次之。(2)有机无机配施吸收的土壤N和肥料N明显大于单施化肥。棉株生育前期对土壤N的依赖性较高,后期对肥料N的依赖性较高,不同时期施N对各器官的贡献率也说明重施化肥做花铃肥的重要性。(3)有机无机肥配施肥料N在土壤中的残留量为单施化肥的1.57～3.31倍,而损失量后者为前者的1.21～2.57倍,其生态效益十分明显。

不同肥料结构对棉田氮素去向的研究

在等氮、磷、钾条件下，应用^15N示黥的方法研究了盆栽条件下不同肥料结构对棉花的生物学效应度氮素去向的影响。所得主要蛄果如下：（1）与单施化肥相比，绿肥＋沼肥＋化肥配施有利于氮向生殖器官转移，增产效果较好，绿肥＋化肥配施效果次之。（2）有机无机肥配施吸收的土壤氮和肥料氮明显大于单施化肥。棉株生育前期对土壤氮的依赖性较高。后期对肥料氮的依赖性较高，不同时期施氮对各器官的贡献率也说明重施化肥作花铃肥的重要性。（3）有机无机肥配施肥料氯在土壤中的残留量为单施化肥的1．48-1．67和3．12-3．52倍。而损失量后者为前者的1．18-1．24和2．51-2．62倍,其生态效益十分明显。

Distribution and Fate of Anthropogenic Nitrogen in the Calamagrostis angustifolia Wetland Ecosystem of Sanjiang Plain, Northeast China

Wetlands are important for the protection of water quality of rivers and lakes, especially those adjacent to agricultural landscapes, by intercepting and removing nutrients in runoff. In this study, the ^15N tracer technique was applied to study the distribution and fate of anthropogenic nitrogen （^15N-fertilizer） in Calamagrostis angustifolia Kom wetland plant-soil microcosms to identify the main ecological effects of it. ^15NH4^15NO3 solution （14.93 mg N/L, 20.28 at.% ^15N） was added to each microcosm of the first group, which was approximate to the current nitrogen concentration （CNC） of farm drainage, and 29.86 mg NIL ^15NH4^15NO3 solution was added to another group, which was approximate to the double nitrogen concentration （DNC） of farm drainage, while no nitrogen （NN） was added to the third group. The results suggest that the input of anthropogenic nitrogen has positive effects on the biomass and total nitrogen content of plant, and the positive effects will be elevated as the increase of its input amount. The increase of ^15N-fertilizer can also elevate its amounts and proportions in plant nitrogen. Soil nitrogen is still the main source of plant nitrogen, but its proportion will be reduced as the increase of ^15 N-fertilizer. The study of the fate of ^15N-fertilizer indicates that, in CNC treatment, only a small proportion is water-dissolved （0,13 ± 0.20%）, a considerable proportion is soil-immobilized （17.02 ± 8.62%）, or plant-assimilated （23.70 ± 0.92%）, and most is lost by gaseous forms （59.15 ± 8.35%）. While in DNC treatment, about 0.09 ± 0.15% is water-dissolved, 15.33 ± 7.46% is soil-immobilized, 23.55±2.86% is plant-assimilated, and 61.01±5.59% is lost by gaseous forms. The double input of anthropogenic nitrogen can not elevate the proportions of plant-assimilation, soil-immobilization and water-dissolution, but it can enhance the gaseous losses.

Pseudomonas mendocina LYX:A novel aerobic bacterium with advantage of removing nitrate high effectively by assimilation and dissimilation simultaneously

The problem of nitrate accumulation in aerobic tank and total nitrogen excessive discharge in effluent was very common in traditional livestock and poultry farming wastewater treatment systems owing to the lengthy process flow and low process control level.A strain LYX of aerobic bacterium was isolated from the activated sludge of a wastewater treatment system in a pig farm,which could remove nitrate effectively in aerobic tank and was identified Pseudomonas mendocina by 16S rRNA sequencing.Under the condition of nitrate as the sole nitrogen source,this strain removed over 90%of NO_(3)^(−)-N with an initial concentration of 110 mg/L under aerobic conditions within 48 hours.Among them,37.9%of NO_(3)^(−)-N was assimilated into Bio-N,about 51.9%was reduced to gaseous nitrogen and less than 0.5%of nitrogen was replaced by NO_(3)^(−)-N and NH_(4)^(+)-N,9.7%NO_(3)^(−)-N remained in the effluent at the end.At the same time,four key genes(napA,nirK,norB and nosZ)related to nitrate nitrogen removal were expressed during the denitrification process of P.mendocina LYX,in which the transcription level of the indicator genes of this aerobic denitrifying bacterium(napA)was the highest.In addition,it was found with the 15N tracer technique that inoculation of this strain on sludge increased the amount of nitrogen loss from 9.26 nmol N/(g·h)to 23.835 nmol N/(g·h).Therefore,P.medocina LYX is a potential bioagent for advanced nitrogen removal by assimilating and reducing nitrate simultaneously in aerobic tanks.