不同无机氮条件下一种硅藻的氮吸收动力学及模型预测分析

针对海水体系中藻类对无机氮源的吸收利用以及氮源之间相互关系,在室内条件下,利用单细胞藻一次性培养的方法,以无机氮源铵态氮(NH+4-N)和硝态氮(NO-3-N)为基础,通过改变氮源的形态及比例,研究了三角褐指藻(Phaeodactylum tricornutum)的生长动力学和氮吸收动力学特征,并通过构建动力学模型对该特征进行拟合。结果表明,同浓度不同形态的无机氮源培养中,三角褐指藻生长无显著差异(P0.05)。分别以NH+4-N和NO-3-N作为唯一氮源时,三角褐指藻能够快速对氮源吸收利用,而两种氮源同时存在时,藻类优先利用NH+4-N,NO-3-N的吸收则受到一定的抑制。同时,所构建的模型较好地预测了藻类的生长动力学和氮吸收动力学趋势。     

The ocean: a natural source of carbon monoxide

The surface waters of the western Atlantic are supersaturated with respect to the partial pressure of carbon monoxide in the atmosphere. Under these conditions, the net transport of carbon monoxide across the air-sea interface must be from the sea into the atmosphere. Thus, the ocean appears to act as a source of carbon monoxide. The ocean may be the largest known natural source of this gas, contributing possibly as much as 5 percent of the amount generated by burning of fuels by man.     

Carbonate compensation depth: relation to carbonate solubility in ocean waters

In situ calcium carbonate saturometry measurements suggest that the intermediate water masses of the central Pacific Ocean are close to saturation with resppect to both calcite and local carbonate sediment. The carbonate compensation depth, located at about 3700 meters in this area, appears to represent a depth above which waters are essentially saturated with respect to calcite and below which waters deviate toward undersaturation with respect to calcite.     

Nitrogen fixation by a blue-green epiphyte on pelagic sargassum

Nitrogen fixation by Dichothrix fucicola, an epiphyte on pelagic Sargassum, was measured in May and June 1972 in the western Sargasso Sea and the Gulf Stream. This is the first report of nitrogen fixation by a heterocyst-bearing blue-green alga in the open ocean, and also the first observation of nitrogen fixation in the genus Dichothrix. Cellular carbon/nitrogen ratios suggested that the Dichothrix was nitrogen-starved. In dense aggregations of Sargassum, such as rafts or windrows, the enrichment of surface seawater with combined nitrogen from nitrogen fixation may be pronounced.     

Age of Canada basin deep waters: a way to estimate primary production for the arctic ocean

An empirical model of carbon flux and (14)C-derived ages of the water in the Canada Basin of the Arctic Ocean as a function of depth was used to estimate the long-term rate of primary production within this region. An estimate can be made because the deep waters of the Canadian Basin are isolated from the world oceans by the Lomonosov Ridge (sill depth about 1500 meters). Below the sill, the age of the water correlates with increased nutrients and oxygen utilization and thus provides a way to model the average flux of organic material into the deep basin over a long time period. The (14)C ages of the deep water in the Canada Basin were about 1000 years, the carbon flux across the 1500-meter isobath was 0.3 gram of carbon per square meter per year, and the total production was 9 to 14 grams of carbon per square meter per year. Such estimates provide a baseline for understanding the role of the Arctic Ocean in global carbon cycling.     

Synthesis of methylphosphonic acid by marine microbes: a source for methane in the aerobic ocean

Relative to the atmosphere, much of the aerobic ocean is supersaturated with methane; however, the source of this important greenhouse gas remains enigmatic. Catabolism of methylphosphonic acid by phosphorus-starved marine microbes, with concomitant release of methane, has been suggested to explain this phenomenon, yet methylphosphonate is not a known natural product, nor has it been detected in natural systems. Further, its synthesis from known natural products would require unknown biochemistry. Here we show that the marine archaeon Nitrosopumilus maritimus encodes a pathway for methylphosphonate biosynthesis and that it produces cell-associated methylphosphonate esters. The abundance of a key gene in this pathway in metagenomic data sets suggests that methylphosphonate biosynthesis is relatively common in marine microbes, providing a plausible explanation for the methane paradox.     

Nitrogen fixation at 92 degrees C by a hydrothermal vent archaeon

A methanogenic archaeon isolated from deep-sea hydrothermal vent fluid was found to reduce N(2) to NH(3) at up to 92 degrees C, which is 28 degrees C higher than the current upper temperature limit of biological nitrogen fixation. The 16S ribosomal RNA gene of the hyperthermophilic nitrogen fixer, designated FS406-22, was 99% similar to that of non-nitrogen fixing Methanocaldococcus jannaschii DSM 2661. At its optimal growth temperature of 90 degrees C, FS406-22 incorporated (15)N(2) and expressed nifH messenger RNA. This increase in the temperature limit of nitrogen fixation could reveal a broader range of conditions for life in the subseafloor biosphere and other nitrogen-limited ecosystems than previously estimated.     

3,4-dihydroxyproline: a new amino acid in diatom cell walls

An analog of proline, 2, 3-cis-3, 4-trans-3, 4-dihydroxy-L-proline, was found in the cell walls of the eight species of diatoms studied and was isolated from the proteinaceous material of the wall of Navicula pelliculosa. The properties of this substance are described; its structure was confirmed by nuclear magnetic resonance spectros-copy.     

施氮后蚯蚓对植物吸氮及微生物固氮的影响

为探讨尿素施用后蚯蚓对植物吸氮量及微生物固氮量的影响,通过盆栽试验,以威廉腔环蚓(Metaphire guillelmi)为试验材料,对比有、无蚯蚓作用下15N标记的尿素施入后植物氮素含量的差异及土壤微生物量的变化过程。结果表明:培养结束后对植物进行取样测定,发现不同处理间植株氮含量并无显著差异,但接种蚯蚓的处理增加了植株生物量,进而导致蚯蚓作用下的植株总吸氮量提高了约30.8%。从分配比例上看,接种蚯蚓显著增加了植物吸收土壤氮的比例,却显著降低了植物吸收肥料氮的比例。在整个试验过程中,两处理的全氮(TN)含量均无显著变化,但土壤中来源于肥料的氮却随着培养的进行逐渐降低,且接种蚯蚓使其下降速度更快。微生物生物量氮(M BN)先下降后上升,且接种蚯蚓处理的MBN含量在试验初期(第5d)与试验末期(第30d)较高,但MBN中固定的肥料氮含量始终低于不接种蚯蚓的对照处理。试验过程中,土壤可溶性有机氮(D ON)的含量先下降后上升,与MBN变化趋势一致。与对照处理相比,接种蚯蚓处理的铵态氮(N H4+-N)含量降低,硝态氮(N O-3-N)含量则差异不显著。综上,蚯蚓可通过调节微生物生物量形成氮素缓冲库,从而促进植株对土壤氮而非尿素氮的吸收。     

Optimized nitrogen application methods to improve nitrogen use efficiency and nodule nitrogen fixation in a maize-soybean relay intercropping system

In China, the abuse of chemical nitrogen(N) fertilizer results in decreasing N use efficiency(NUE), wasting resources and causing serious environmental problems. Cereal-legume intercropping is widely used to enhance crop yield and improve resource use efficiency, especially in Southwest China. To optimize N utilization and increase grain yield, we conducted a two-year field experiment with single-factor randomized block designs of a maize-soybean intercropping system(IMS). Three N rates, NN(no nitrogen application), LN(lower N application: 270 kg N ha–1), and CN(conventional N application: 330 kg N ha–1), and three topdressing distances of LN(LND), e.g., 15 cm(LND1), 30 cm(LND2) and 45 cm(LND3) from maize rows were evaluated. At the beginning seed stage(R5), the leghemoglobin content and nitrogenase activity of LND3 were 1.86 mg plant–1 and 0.14 m L h–1 plant–1, and those of LND1 and LND2 were increased by 31.4 and 24.5%, 6.4 and 32.9% compared with LND3, respectively. The ureide content and N accumulation of soybean organs in LND1 and LND2 were higher than those of LND3. The N uptake, NUE and N agronomy efficiency(NAE) of IMS under CN were 308.3 kg ha–1, 28.5%, and 5.7 kg grain kg–1 N, respectively; however, those of LN were significantly increased by 12.4, 72.5, and 51.6% compared with CN, respectively. The total yield in LND1 and LND2 was increased by 12.3 and 8.3% compared with CN, respectively. Those results suggested that LN with distances of 15–30 cm from the topdressing strip to the maize row was optimal in maize-soybean intercropping. Lower N input with an optimized fertilization location for IMS increased N fixation and N use efficiency without decreasing grain yield.     

Nitrogen source for a detritivore: detritus substrate versus associated microbes

Detritivores have been thought to derive nutrition from microbes associated with detrital particles and not from the nonliving plant substrate. The polychaete Capitella capitata, however, was found to derive a major portion of its nitrogen from the plant substrate when it feeds on detritus derived from seaweed. Microbes play a role as a nitrogen source for this detritivore when it feeds on detritus derived from marsh grass.     

Zonal temperature-anomaly maps of Indian ocean surface waters: modern and ice-age patterns

Maps of sea surface temperature anomalies in the Indian Ocean in modern and ice-age times reveal striking changes in its surface circulation. During the last glacial maximum (18,000 years before the present), the Indian Ocean had colder average zonal surface temperatures, a cooler and less extensive Agulhas Current, a distinct eastern boundary current, and decreased upwelling and a weaker southwest monsoon in its northwestern region.     

Spreading of the ocean floor: new evidence

It is suggested that the entire history of the ocean basins, in terms of oceanfloor spreading,is contained frozen in the oceanic crust. Variations in the intensity and polarity of Earth's magnetic field are considered to be recorded in the remanent magnetism of the igneous rocks as they solidified and cooled through the Curie temperature at the crest of an oceanic ridge, and subsequently spread away from it at a steady rate. The hypothesis is supported by the extreme linearity and continuity of oceanic magnetic anomalies and their symmetry about the axes of ridges. If the proposed reversal time scale for the last 4 million years is combined with the model, computed anomaly profiles show remarkably good agreement with those observed, and one can deduce rates of spreading for all active parts of the midoceanic ridge system for which magnetic profilesor surveys are available. The rates obtained are in exact agreement with those needed to account for continental drift. An exceptionally high rate of spreading (approximately 4.5 cm/year) in the South Pacific enables one to deduce by extrapolation considerable details of the reversal time scale back to 11.5 million years ago. Again, this scale can be applied to other parts of the ridge system. Thus one isled to the suggestion that the crest of the East Pacific Rise in the northeast Pacific has been overridden and modified by the westward drift of North America, with the production of the anomalous width and unique features of the American cordillera in the western United States. The oceanicmagnetic anomalies also indicate that there was a change in derection of crustal spreading in this region during Pliocene time from eastwest to southeast-northwest. A profile from the crest to the boundary of the East Pacific Rise, and the difference between axial-zone and flank anomalies over ridges, suggest increase in the frequency of reversal of Earth's magnetic field, together, possibly, with decrease in its intensity, approximately 25 million years ago. Within the framework of ocean-floor spreading, it is suggested that magnetic anomaliesmay indicate the nature of oceanic fracture zones and distinguish the parts of the ridge system that are actively spreading. Thus data derived during the past year lend remarkable support to thehypothesis that magnetic anomalies may reveal the history of the ocean basins.     

Perception of environmental signals by a marine diatom

Diatoms are a key component of marine ecosystems and are extremely important for the biogeochemical cycling of silica and as contributors to global fixed carbon. However, the answers to fundamental questions such as what diatoms can sense in their environment, how they respond to external signals, and what factors control their life strategies are largely unknown. We generated transgenic diatom cells containing the calcium-sensitive photoprotein aequorin to determine whether changes in calcium homeostasis are used to respond to relevant environmental stimuli. Our results reveal sensing systems for detecting and responding to fluid motion (shear stress), osmotic stress, and iron, a key nutrient that controls diatom abundance in the ocean.     

Quantitative imaging of nitrogen fixation by individual bacteria within animal cells

Biological nitrogen fixation, the conversion of atmospheric nitrogen to ammonia for biosynthesis, is exclusively performed by a few bacteria and archaea. Despite the essential importance of biological nitrogen fixation, it has been impossible to quantify the incorporation of nitrogen by individual bacteria or to map the fate of fixed nitrogen in host cells. In this study, with multi-isotope imaging mass spectrometry we directly imaged and measured nitrogen fixation by individual bacteria within eukaryotic host cells and demonstrated that fixed nitrogen is used for host metabolism. This approach introduces a powerful way to study microbes and global nutrient cycles.     

Suppression of nitrogen fixation by blue-green algae in a eutrophic lake with trace additions of copper

Nitrogen fixation by blue-green algae in highly eutrophic Clear Lake, California, was severely inhibited by trace amounts of copper. The chelation capacity of the lake is probably saturated by indigenous copper. Additions were only 1/200 of those normally used in algal control. Since nitrogen fixation provides half of the lake's annual nitrogen budget, economical eutrophication control appears possible.     

Assessment of nitrogen losses to the environment with a Nitrogen Trading Tool (NTT)

Nitrogen (N) losses from agriculture often contribute to reduced air, groundwater, and surface water quality. The minimization of these N losses is desirable from an environmental standpoint, and a recent interest in discounted reductions of agricultural N losses that might apply to a project downstream from an agricultural area has resulted in the concept of N credits and associated N trading. To help quantify management-induced reductions in N losses at the farm field level (essential components of a Nitrogen Trading Tool), we defined a Nitrogen Trading Tool difference in reactive N losses (NTT-DNL_reac) as the comparison between a baseline and new management scenarios. We used a newly released Windows XP version of the Nitrogen Losses and Environmental Assessment Package (NLEAP) simulation model with Geographic Information System (GIS) capabilities (NLEAP-GIS) to assess no-till systems from a humid North Atlantic US site, manure management from a Midwestern US site, and irrigated cropland from an arid Western US site. The new NTT-DNL_reac can be used to identify the best scenario that shows the greatest potential to maximize field-level savings in reactive N for environmental conservation and potential N credits to trade. A positive NTT-DNL_reac means that the new N management practice increases the savings in reactive N with potential to trade these savings as N credits. A negative number means that there is no savings in reactive N and no N available to trade. The new NLEAP-GIS can be used to quickly identify the best scenario that shows the greatest potential to maximize field-level savings in reactive N for environmental conservation and earning N credits for trade.     

接种根瘤菌对豆科绿肥的固氮效果研究

对豆科绿肥接种根瘤菌能显著提高豆科绿肥的固氮作用,提高土壤的肥力水平,增加土壤微生物,增加豆科绿肥的年固氮量,提高豆科绿肥与禾本科牧草的鲜草产量和品质,从而提高豆科绿肥的利用率。