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。     

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.     

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.     

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.     

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).     

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     

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.     

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.     

Transformations in soil and availability to plants of15N applied as inorganic fertilizer and legume residues

Summary A pot experiment was conducted to study the transformations of organic and inorganic N in soil and its availability to maize plants. Inorganic N was in the form of¹⁵N labelled ammonium sulphate (As) and¹⁵N labelledSesbania aculeata (Sa), a legume, was used as organic N source. Plants utilized 20% of the N applied as As; presence of Sa reduced the uptake to 14%. Only 5% of the Sa-N was taken up by the plants and As had no effect on the availability of N from Sa. Losses of N from As were found to be 40% which were reduced to 20% in presence of Sa. Losses of N were also observed from Sa which increased in the presence of As. Application of As had no effect on the availability of soil or Sa-N. However, more As-N was transported into microbial biomass and humus components in the presence of Sa.Plants derived almost equal amounts of N from different sourcesi.e., soil, Sa and As. However, more As-N was transported into the shoots whereas the major portion of nitrogen in the roots was derived from Sa.     

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。     

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.     

氮磷营养因子对赤潮异弯藻生长的影响

研究了N、P营养浓度对赤潮异弯藻(Heterosigma akashiwo)生长的影响.结果表明,该藻的生长速率与N、P营养因子浓度的关系符合Monod公式.在NO₃^--N浓度达到7.5 mg·L^-1时,赤潮异弯藻开始生长;浓度为3.75～75 mg·L^-1时,赤潮异弯藻的比生长速率与NO₃^--N浓度成正比关系.N营养充足时,赤潮异弯藻的最大生长速率μ_m-n=0.3475·d^-1,K_s-n=18.91 mg·L^-1.PO₄^--P浓度为0～1.0 mg·L^-1时,赤潮异弯藻的比生长速率与P浓度成正比关系;P营养充足时,赤潮异弯藻的最大生长速率μ_m-p=0.3024·d^-1,K_s-p=0.4086 mg·L^-1.N/P达到25后藻细胞浓度达到最大,表明N/P为25时最适合赤潮异弯藻生长.赤潮异弯藻最适合在N 37.5～225.0 mg·L^-1、P 5.0～50.0 mg·L^-1、N/P=25条件下生长.     

Purification and characterization of calmodulin from rat liver mitochondria

Mitochondrial calmodulin of rat liver was purified and classified. It co-migrated with bovine brain calmodulin in non-denaturing polyacrylamide gel electrophoresis, SDS-polyacrylamide gel electrophoresis and isoelectric focusing. The mitochondrial calmodulin activated Ca²⁺-dependent phosphodiesterase of bovine brain in the presence of Ca²⁺. About 80% of the mitochondrial calmodulin was proved to be of cytosol origin. It was easily detached by washing with buffer containing EGTA. The other 20% was intramitochondrial calmodulin; half of it was in the matrix space, and half in the membrane.     

Uptake by wheat plants and turnover within soil fractions of residual N from leguminous plant material and inorganic fertilizer

Summary The availability and turnover in different soil fractions of residual N from leguminous plant material and inorganic fertilizer was studied in a pot culture experiment using wheat as a test crop. Plants utilized 64% of the residual fertilizer N and 20% of the residual legume N. 50–60% of the N taken up by plants was recovered in grain and 4–8% in roots. After harvesting wheat up to 35% and 38% of the residual legume N and fertilizer N, respectively was found in humic compounds. A loss of humus N derived from legume and fertilizer was found during wheat growth but the unlabelled N increased in this fraction. Biomass contained 6% and 8% of the residual legume and fertilizer N, respectively when both were available. The mineralizable component contained upto 28% of both the residual legume and residual fertilizer N. Only a small percentage of the soil N (3–4%) was observed in biomass whereas the mineralizable component accounted for 7–14% of the soil N. In this fraction legume derived N increased during wheat growth whereas unlabelled N increased in both the mineralizable component and microbial biomass. Some loss of N occurred from residual legume and fertilizer N. Nevertheless, a positive total N balance was observed and was attributed to the addition of unlabelled N in the soil-plant system by N₂ fixation. The gain in N was equivalent to about 38% of the plant available N in the soil amended with leguminous material. The additional N was concentrated mainly in the mineralizable fraction and microbial biomass, although some addition was also noted in humus fractions.     

Structure and function of Fc receptors : Receptors and ligands in intercellular communication: volume 2 Edited by A. Froese and F. Paraskevas Marcell Dekker; New York and Basel, 1983 294 pages. Sw.Fr. 120.00

Plasmalemma vesicles were isolated in a sucrose-containing medium from wheat and oat roots and the net negative surface charge density was determined with 9-aminoacridine fluorescence [Chow, W.S. and Barber, J. (1980) J. Biochem. Biophys. Methods 3, 173-185]. The outer surface of the vesicles (measured in the presence of sucrose) had densities of ? 16 to ? 20 mC·m^?2 and ?29 mC·m^?2 for wheat and oat roots, respectively. The inner surface - presumed to be the cytoplasmic side and calculated from the values measured in the presence and absence of sucrose - was more negative, and its size depended on the salt status of the roots.     

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.     

Inmobilization-remineralization of NO3-N and total N balance during the decomposition of glucose,sucrose and cellulose in soil incubated at different moisture regimes

A laboratory incubation experiment was conducted to study the effect of organic amendment and moisture regimes on the immobilization-remineralization of NO₃-N and total N balance in soil fertilized with KNO₃. Immobilization of NO₃-N was very rapid in soil amended with glucose and sucrose followed by a remineralization of organic N and accumulation of mineral N. Cellulose caused a slow but continued immobilization and did not show net accumulation of mineral N during 8 weeks of incubation. At the end of incubation, a significant increase in total N and organic N content of the soil was observed which is perhaps attributable to the activity of free living N₂ fixers. Although N losses seemed to have occurred at 100% WHC through denitrification in soil amended with glucose and sucrose, main cause of NO₃ elimination was microbial immobilization.     

Enhanced foliar 15N enrichment with increasing nitrogen addition rates: Role of plant species and nitrogen compounds

Determining the abundance of N isotope (δ¹⁵N) in natural environments is a simple but powerful method for providing integrated information on the N cycling dynamics and status in an ecosystem under exogenous N inputs. However, whether the input of different N compounds could differently impact plant growth and their ¹⁵N signatures remains unclear. Here, the response of ¹⁵N signatures and growth of three dominant plants (Leymus chinensis, Carex duriuscula, and Thermopsis lanceolata) to the addition of three N compounds (NH₄HCO₃, urea, and NH₄NO₃) at multiple N addition rates were assessed in a meadow steppe in Inner Mongolia. The three plants showed different initial foliar δ¹⁵N values because of differences in their N acquisition strategies. Particularly, T. lanceolata (N₂-fixing species) showed significantly lower ¹⁵N signatures than L. chinensis (associated with arbuscular mycorrhizal fungi [AMF]) and C. duriuscula (associated with AMF). Moreover, the foliar δ¹⁵N of all three species increased with increasing N addition rates, with a sharp increase above an N addition rate of ~10 g N m⁻² year⁻¹. Foliar δ¹⁵N values were significantly higher when NH₄HCO₃ and urea were added than when NH₄NO₃ was added, suggesting that adding weakly acidifying N compounds could result in a more open N cycle. Overall, our results imply that assessing the N transformation processes in the context of increasing global N deposition necessitates the consideration of N deposition rates, forms of the deposited N compounds, and N utilization strategies of the co-existing plant species in the ecosystem.