Electron transport-linked nitrous oxide synthesis and reduction by Paracoccusdenitrificans monitored with an electrode

The nitrous oxide reductase activity of $\text{Paracoccus}\text{denitrificans}$ can be conveniently measured using an electrochemical method for determining N₂O. Introduction of this procedure has shown that (i) N₂O reductase activity is reversibly inhibited by oxygen; (ii) antimycin strongly inhibits electron flow to N₂O and that the inhibition is bypassed by tetramethyl-p-phenylenediamine; (iii) ascorbate plus tetramethyl-p-phenylenediamine, presumably by donating electrons to cytochrome c, is an effective reductant for nitrous oxide reductase; (iv) in the presence of the nitrous oxide reductase inhibitor, acetylene, N₂O is promptly produced from nitrite, consistent with the product of nitrite reductase being N₂O.     

冬玉米对氮肥的吸收利用和需求

在不同施氮量下 ,研究了冬玉米对氮肥的吸收利用 ,结果表明 :(1 )冬玉米地上各部分中氮的累积随着用氮量的增加而增加 ,花丝期前的吸收量均多于后期 ,但高氮区的前期吸氮比大于低氮区 ;(2 )营养体氮的转移率随施氮量的增加而降低 ,但绝对量依然是高氮处理大于低氮处理 ,其中雄穗的转移率最高 ,叶的转移量最大 ;(3 )氮肥利用率随施氮量的增加而提高 ,但氮的生产力下降。根据试验结果 ,在肥力好的土地上种植冬玉米以 1 80～ 2 70 kg N/hm2比较适宜     

EUF-N fractions in different soils during a vegetation period in pot and field experiments

Summary Mobilization of soil-borne N, N fertilization and N removal by crops influence EUF-NO₃-N contents as well as EUF-N_org contents in the course of a vegetation period. N mobilization alone (no N fertilization) increases the EUF-N_org contents only temporarily (mainly in May and July), while in December they are almost the same as in March (Table 1). The EUF-NO₃ contents, on the contrary, increase during the vegetation period, so that an increment in NO₃ is registered in unplanted pots in December. This increment is larger the higher the EUF-N_org contents are in March (Table 2).N fertilization increases the contents of both EUF-N_org and EUF-NO₃, so that there is an increment in EUF-N_org as well as EUF-NO₃ in December (Table 2). This finding also applies to field experiments under fallow (Figs. 4 and 5). However, in contrast to the pot experiment, the EUF-N contents in the field experiment were only temporarily increased by N mobilization alone. This means that N immobilization had taken place which had not been observed in the pot experiment under stable moisture conditions (Fig. 4 and Table 1).A close correlation between hot-water-soluble N contents and EUF-N_org is found only under uniform management conditions (uniform N-fertilizer rates). Depending on the time of sampling different regression equations are, however, obtained because of changes in EUF-N_org due to N mobilization, whereas the hot-water-soluble N contents hardly show any variations during the vegetation period (Fig. 6 and Table 3).     

Distribution and remobilization of symbiotically fixed nitrogen in soybean (Glycine max)

Partitioning of nitrogen by soybeans ( Glycine max L. Merr. cv. Hodgson) grown in natural conditions was studied by successive exposures of root systems to ¹⁵N₂ and periodical measurements of ¹⁵N distribution. Nitrogen derived from the atmosphere was mainly found in the aerial parts of the plants, and the stage of development exerted a strong influence on the initial ¹⁵N distribution (measured one week after incorporation). Until day 69 after sowing, leaf blades contained 47 to 57% of the fixed N. After that, reproductive structures attracted increasing proportions, 10 to 60% between days 69 and 92. Around day 82, stems and petioles stored up to 30% of the newly fixed N. During pod development and pod filling and until maturity, fixed N was remobilized from vegetative tissues and pod walls to seeds. These transfers first concerned the newly incorporated N, but at maturity 80 to 90% of the total was recovered in the seeds. The high mobility of N originating from the atmosphere as compared to that coming from the soil (vegetative tissues exported only 50% of their total N) seems to indicate that fixed N was at least partially integrated in a special pool. This was certainly the case at the later stage of N₂ fixation, when a large portion of fixed N accumulated in the stems and petioles, probably in the form of storage compounds such as ureides for later transfer to the developing seeds. Further research is needed in order to investigate the nature and role of this pool in the nitrogen nutrition of soybeans.     

Prediction of long-term fertilizer nitrogen requirements of maize in the tropics using a nitrogen balance model

A simple N balance model was used to calculate fertilizer requirement for a target N uptake by maize. Nitrogen uptake from soil sources and target uptake of N with fertilizer N additions were obtained from fertilizer trials in Africa and Latin America. Most experiments had data for only one cropping period, although some from Latin America had data for four to six crops. The transfer coefficient of fertilizer N to the crop was adjusted to realize maximum recovery of fertilizer N under best methods of fertilizer application. The time constants of transfer of soil N to the crop were allowed to vary and were affected mainly by soil texture. Where 4 to 6 cropping periods were available good agreement between actual and predicted fertilizer N requirements was obtained. With this approach long-term fertilizer N requirements for 14 sites were predicted using first cropping period N uptake. This study showed that pools of organic N in more coarse-textured soils were usually smaller and declined more rapidly than in fine-textured soils. Labile organic N pools declined with time under all simulations, but approached equilibrium within 10 croppings seasons. Equilibrium N uptake from the soil organic N pool was predicted to be 31 kg ha^–1 for the more coarse-textured soils and 36 kg ha^–1 for the fine-textured soils. Long-term projections of fertilizer requirements using input data of the field experiments were reasonable, and effects of legume green manures and other amendments could be clearly evaluated.     

P effects on N uptake and remobilization during regrowth of Italian ryegrass (Lolium multiflorum)

The influence of P deficiency on the utilization of two sources of N, mineral N (exogenous N) and reserved N (endogenous N), for regrowth of Italian ryegrass (Lolium multiflorum) was studied. P-sufficient (+P) or P-free (−P) nutrition solution was applied from 7 days before defoliation to 24 days of regrowth and the N flows derived from two different N sources within the plant were quantified by ¹⁵N pulse-chase labeling. Shoot regrowth significantly reduced by 12 days of regrowth, while root growth was more in −P plants. Inorganic P (P_i) concentration was highly reduced by P deprivation more in the stubble and regrowing shoots and less in the roots. At defoliation, P deprivation had induced a higher accumulation for all N compounds in the stubble and for amino acids in the roots. The previously incorporated ¹⁵N in stubble and roots as nitrate and amino acids was much decreased in −P plants especially for the first 6 days of regrowth. Total N content in the regrowing leaves was not significantly different between +P and −P plants, but percentage contribution of remobilized N for total leaf N formation was significantly higher in −P plants (78%) than in +P plants (69%) at 6 days of regrowth. From day 12, the utilization of both endogenous and exogenous N was apparently inhibited in −P plants.     

Simulation of nitrogen assimilation by heterotrophic soil microbial biomass

Assimilation of N by heterotrophic soil microbial biomass is associated with decomposition of organic matter in the soil. The form of N assimilated can be either low molecular weight organic N released from the breakdown of organic matter (direct assimilation), or NH⁺₄ and NO⁻₃ from the soil inorganic N pool, into which mineralized organic N is released (mineralization immobilization turnover). The kinetics of C and N turnover in soil is quantifiable by means of computer simulation models. NCSOIL was constructed to represent the two assimilation schemes. The rate of N assimilation depends on the rate of C assimilation and microbial C/N ratio, thereby rendering it independent of the assimilation scheme. However, if any of the N forms is labeled, a different amount of labeled N assimilation will be simulated by the different schemes. Experimental data on inorganic N and ¹⁵N and on organic ¹⁵N dynamics in soils incubated with ¹⁵N added as NH⁺₄ or organic N were compared with data simulated by different model schemes. Direct assimilation could not account for the amount of ¹⁵N assimilated in any of the experimental treatments. The best fit of the model to experimental data was obtained for the mineralization immobilization turnover scheme when both NH⁺₄ and NO⁻₃ were assimilated, in proportion to their concentration in the soil.     

Localization of Cu and heme a on cytochrome c oxidase polypeptides.

After mild dissociation of cytochrome $\text{c}$ oxidase protomers, and polyacrylamide gel electrophoresis, copper was found predominantly in polypeptides of Bands V (m.w. 12,100) and VII (m.w. 3,400), and heme a predominantly in polypeptides of Bands I (m.w. 35,300) and II (m.w. 21,000). Some copper was found in Band II – III, and heme a in Band V.     

Allometry and morphometrics of clypeal membrane size and shape in Nicrophorus (Coleoptera: Silphidae)

Contests between same‐sex opponents over resources necessary for reproduction, as well interactions used to discern mate quality, often involve exaggerated traits wherein large individuals have disproportionately larger traits. This positive allometric scaling of weapons or signals facilitates communication during social interactions by accentuating body size differences between individuals. Typically, males carry these exaggerated traits, as males must compete over limited female gametes. However, in Nicrophorus beetles both males and females engage in physical contests over the vertebrate carcasses they need to provision and raise offspring. Male and female Nicrophorus beetles have extended clypeal membranes directly above their mandibles, which could serve as signals. We investigated the scaling relationships between clypeal membrane size and shape and body size for five species of North American burying beetle to determine whether clypeal membranes contain exaggerated body size information. We found that clypeal membranes for both sexes of all species scaled positively with body size (slope > 1). Three of the five species also displayed sexual dimorphism in aspects of clypeal membrane size and shape allometry despite lack of dimorphism in body size. In two dimorphic species, small male clypeal membranes were statistically indistinguishable from the female form. We conclude that colored clypeal membranes in Nicrophorus beetles do contain exaggerated body size information. Observed patterns of dimorphism suggest that males sometimes experience stronger selection on marking size and shape, which might be explained by life history differences among species.     

Uptake of ammonium and nitrate ions from acid mist applied to Sitka spruce [Picea sitchensis (Bong.) Carr.] grafts over the course of one growing season

Cloned Sitka spruce grafts were subjected to NH₄NO₃ mist (1 mm day^-1 equivalent) acidified with H₂SO₄, for 4 days a week, from April until November. Three N treatments at pH 5.0 used 0.01 mol m^{-3 15}NH₄ ¹⁵NH₃, 1.6 mol m^{-3 15}NH₄ NO₃ or 1.6 mol m^-3 NH₄ ¹⁵NO₃. At pH 2.5, the treatments were¹⁵NH₄ ¹⁵NO₃,¹⁵NH₄NO₃ and NH₄ ¹⁵NO₃ all at 1.6 mol m^-3. At the end of the growing season,¹⁵N was found in every part of the trees, even when NH₄NO₃ was supplied at 0.01 mol m^-3. It was shown that both and could enter needles to a similar degree and be transported to the roots. No differences between pH treatments or clones could be demonstrated. Entry of labelled N via the roots, in those trees with unprotected compost, was reflected in higher fine root¹⁵N content, but no change in shoot¹⁵N levels. Per cent incorporation expressed as labelled N as a percentage of total N, was generally at its highest in bark, and in older needles in all treatments, values ranging from 5 to 11%. When¹⁵N content was expressed as total content for each tree part on a per tree basis, 25–36% was found in current year needles, with a further 12% in current year bark. The most reproducible data was that for dry weight of tree parts as per cent of the whole tree, where proportions compared closely between treatments and the two clones used. The implications of the results for cuticular transport mechanisms, N storage and internal cycling are discussed.     

华北平原冬小麦/夏玉米轮作体系土壤硝态氮的适宜含量

采用冬小麦季不同施氮处理(夏玉米季不施氮)研究了华北平原冬小麦/夏玉米轮作体系夏玉米季土壤硝态氮的适宜含量.结果表明:在播前土壤无机氮含量较高的条件下,冬小麦季施用150kgN.hm-2即可满足冬小麦/夏玉米两季作物的氮素需求;各氮肥处理在冬小麦季的氮肥施用当季的利用率仅为11%～23%,在夏玉米季氮肥残效利用率则高达30%～52%.当夏玉米播前0～90cm土层硝态氮含量达到82kg.hm-2时,无需施氮即可保证夏玉米十叶期的生长,达到151kg.hm-2时,无需施氮即可保证整个生育期的生长.夏玉米十叶期和收获后0～90cm土层硝态氮含量低于46和65kg.hm-2时,则影响作物正常生长.综合考虑产量和环境效应,冬小麦/夏玉米轮作体系中0～90cm土层硝态氮含量应控制在65～151kg.hm-2之间.     

Yield and crop parameters of wetland rice as influenced by soil and fertilizer nitrogen

Summary The behavior of soil N, fertilizer N and plant N was studied in a greenhouse experiment with 2 plant densities of rice (IR 36) under flooded conditions. Increasing plant density from 25 hills m² to 50 hills m² increased tiller number and panicle number but had no influence on grain yield. The yield of grain was linearly related to N content of the above ground dry matter at harvest (r²=.96) and thus the effect of manipulating the N supply on yield was directly related to N uptake.Mixing of (NH₄)₂SO₄ with the soil volume before transplanting resulted in increases in N in the aboveground dry matter equal to 87% of the applied N. When (NH₄)₂SO₄ was broadcast into the flood water at 4 stages of growth beginning 25 DAT, the corresponding increase was 77% of the applied N. When (NH₄)₂SO₄ was split between shallow mixing before transplanting and a broadcast application of 32 DAT, the corresponding increase was 42%. Thus several applications of fertilizer N increased grain production per unit of applied N.Inorganic N extractable by KCl was a useful but not an infailible guide to the behavior of the soil and fertilizer inorganic N.     

土壤动物与N素循环及对N沉降的响应

以主要的生态过程之一——N循环为对象,论述了土壤动物不仅对凋落物的分解有重要影响,而且在N素矿化和植物对N的吸收过程中也起着重要作用。同时,日益严重的全球变化问题之一——N沉降对土壤动物的多样性及其在生态系统中的功能构成了极大的威胁。另还对土壤动物与N循环研究的方法、土壤动物在N循环过程中的作用机制、热带地区的需求及N沉降下土壤动物的响应作了探讨,并提出,开展大尺度的专类研究及长期定位研究成为下一步研究的需要。     

Effect of visible light on the mitochondrial inner membrane.

Exposure of mitochondria to visible light in the presence of riboflavin resulted in the initial release of respiratory control, followed by inhibition of electron transport and dissolution of structural integrity. Under these conditions, however, cytochrome c oxidase activity remained unchanged. ATPase activity was stimulated initially and remained in this activitated state even under continued illumination. In submitochondrial preparations, both electron transport and ATPase declined as a function of illumination time; cytochrome c oxidase was not sensitive to light. Enzyme inactivation also occurred to a lesser extent in the absence of riboflavin.     

Glucosides of ionone-related compounds in several nicotiana species

The β-glucosides of 3-oxo-α-ionol and 5,6-epoxy-5,6-dihydro-3-hydroxy-β-ionol were isolated from fresh leaves of Nicotiana rustica. Two or more of the glucosides of 3-oxo-α-ionol, 5,6-epoxy-5,6-dihydro-3-hydroxy-β-ionol, 3-hydroxy-β-damascone, blumenol A, 4-(3-hydroxybutylidene)-3,5,5-trimethyl-2-cyclohexenl-one and blumenol C were shown to be present and the amounts measured in N. alata, N. repanda, N. rustica, N. undulata, N. accuminata, N. sylvestris and N. tabacum. No glucosides were detected in N. paniculata.     

Nitrogen fertilization in citrus orchards

Summary The purpose of this review was to evaluate critically the results obtained in citrus nitrogen fertilization experiments in Israel and in other parts of the world, in order to increase our understanding of the processes involved and to improve the recommendations to growers. Mature citrus trees contain 1–2 kg N/tree, 30–60% of which is in the annual parts (leaves and fruits). 30g N is deposited annually in the tree skeleton. Based on these results and on a review of long-term fertilization experiments with citrus from various parts of the world, it was concluded that 200 kg N/ha applied annually is sufficient to sustain good citrus yields and tree development, about half of which is incorporated in the fruits and one-tenth deposited in the tree, the balance being made up by leaching and gaseous losses. Experiments with¹⁵N labeled fertilizer applications showed that the highest N-uptake rate occurred during fruit set and that in winter the uptake was very low. N reserves in the older tissues played an important part in the development of new leaves and flowers in the spring, when the uptake from the soil was still low. It was concluded that the nitrogen contained in the soil organic matter (2 Mg/ha) and in the mature trees (1 Mg/ha) plays an important part in the regulation of N supply to the growing parts of the tree. More N is derived from these parts with low N fertilization than with an abundant supply. The purpose of fertilization is to ensure proper development of the tree, not the current fruit yield. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 1770-E. 1986 series.     

燕麦-绿豆间作效应及氮素转移特性

为探究燕麦(Avena sativa)-绿豆(Phaseolus radiatus)间作效应及氮素转移特性, 在不施氮肥的大田试验条件下, 设置3种种植模式(燕麦单作、绿豆单作和燕麦-绿豆间作), 采用传统挖根法和¹⁵N同位素标记法进行研究。结果表明, 间作系统中燕麦侵袭力强于绿豆, 绿豆生长受到抑制。整个生育期, 间作燕麦地上部干物质积累量比单作增加14.9%-33.1%, 2年成熟期间作燕麦的氮素积累量比单作分别提高53.1%和44.8%; 间作减少了开花结荚期绿豆氮素积累量和根瘤重量, 降低了绿豆的固氮效率, 绿豆的固氮效率2年平均降低23.7%, 生物固氮量平均减少11.66%。间作绿豆向燕麦的氮素转移率2年平均值达31.7%, 氮素转移量为212.16 kg∙hm^-2。燕麦-绿豆间作降低了开花结荚期绿豆的根瘤固氮酶活性和固氮效率, 但绿豆体内氮素转移增加了燕麦对氮素的吸收利用, 实现了地上部与地下部生长的相互调节和促进, 优化了农田生态系统的氮素管理。