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1.
Soil is often incubated under controlled conditions to assess its capacity to mineralize nitrogen and to define the N mineralization potential (No) by fitting a negative exponential curve to N mineralization data. The specificity of No for a given soil and its relevance in N mineralization studies was examined as part of an overall study of the N mineralization process. Soil mixed with an equal amount of sand was aerobically incubated at 35 °C and leached at specific time intervals. Upon leaching, ammonium and nitrate were measured in the extract.It was found that N mineralization data did not always follow first-order kinetics making it difficult to calculate No. The computed No value was influenced by the shape of the curve, the duration of the incubation experiment and was reciprocally related to the N mineralization constant (kexp). No did not always give an adequate indication of the amount of N mineralized and was not soil specific as the time of sampling largely affected its size. The usefulness of No in the simulation of the N mineralization process with a kexp value valid for all soils was limited and a kexp value specific for each soil was required. A value combining the soil specific No and kexp values and reflecting the amount of N mineralized over one year was proposed as a suitable alternative to the use of No in comparative studies of the N mineralization process. It was concluded that a calculated No could not be used in studies comparing the N mineralization of different soils. In addition, the simulation of the N mineralization required the use of the soil specific kexp and could not be carried out with a kexp valid for all soils. 相似文献
2.
Zhilu Sheng Yongmei Huang Kejian He Narigele Borjigin Hanyue Yang Huiying Chen Engui Li Xia Xu Lei Duan 《Journal of Plant Ecology》2019,12(3):550
Aims
Elevated anthropogenic nitrogen (N) deposition could alter N status in temperate steppe. However, threshold observations of N status change from N limit to N saturation by far are not conclusive in these ecosystems. Research on the natural abundance of15N (δ15N) could greatly help provide integrated information about ecosystem N status. The goal of this study was to investigate the suitability of measurements of δ15N of major ecosystem N pools and several key species, plant15N fractionation, together with key vegetation and soil indicators in response to N fertilization as a tool to identify the N status in a temperate steppe in Inner Mongolia. 相似文献
3.
Molecular dynamics calculations of the adiabatic elastic constants of group III-Nitrides for temperatures ranging from 300 to 900 K have been performed. The results show good agreement with first-principles calculations. The moduli decreased with increasing temperature. The structural properties of zinc-blende GaN, AlN and InN are reported. Good agreement between the calculated and experimental values of the lattice constant, the cohesion energy, and the bulk modulus and its derivative are obtained. 相似文献
4.
E. L. Sisworo D. L. Eskew W. H. Sisworo H. Rasjid H. Kadarusman S. Solahuddin G. Soepardi 《Plant and Soil》1990,128(2):209-220
Field experiments (20 m2 plots) were conducted to compare Azolla and urea as N sources for rice (Oryza sativa L.) in both the wet and dry seasons. Parallel microplot (1 m2) experiments were conducted using 15N. A total of approximately 60 kg N ha-1 was applied as urea, Azolla, or urea plus Azolla. Urea or Azolla applied with equal applications of 30 kg N ha-1 at transplanting (T) and at maximum tillering (MT) were equally effective for increasing rice grain yields in both seasons. Urea at 30 kg N ha-1 at T and Azolla 30 kg N ha-1 at MT was also equally effective. Urea applied by the locally recommended best split (40 kg at T and 20 kg at MT) gave a higher yield in the wet season, but an equal yield in the dry season. The average yield increase was 23% in the wet season, and 95% in the dry season. The proportion of the N taken up by the rice plants which was derived from urea (%NdfU) or Azolla (%NdfAz) was essentially identical for the treatments receiving the same N split. Recovery of 15N in the grain plus straw was also very similar. Positive yield responses to residual N were observed in the succeeding rice crop following both the wet and dry seasons, but the increases were not always statistically significant. Recovery of residual 15N ranged from 5.5 to 8.9% for both crops in succeeding seasons. Residual recovery from the urea applications was significantly higher than from Azolla in the crop succeeding the dry season crop. Azolla was equally effective as urea as an N source for rice production on a per kg N basis. 相似文献
5.
《Biomass》1988,15(4):249-257
An experiment was conducted in the growth chamber to quantify the biomass production, N removal and N2 fixation from a synthetic medium by Chlamydomonas reinhardtii and Anabaena flos-aquae. Nitrogen was supplied at a concentration of 100 mg liter−1 of NO3−−15N and NH4+−15 (3·5 atom %), respectively. After 21 days Chlamydomonas reinhardtii removed an average of 83·8 and 78·7 mg N liter−1 as NO3− and NH4+, respectively. Averages of 0·89 and 0·71 g liter−1 (first batch), 1·63 and 0·95 g liter− (second batch) algal biomass were collected from NO3− and NH4+ media, respectively. Uptake rates of 0·11 mg 15N g−1 algae day−1 from NO3− medium and 0·10 mg 15N g−1 algae day−1 from NH4+ medium were calculated. Algal cells grown in NO3− and NH4+ medium contained 71 and 65 g N kg−1 (first batch), 39 and 58 g N kg−1 (second batch), respectively. Anabaena flos-aquae produced averages of 0·58 and 0·46 g liter−1 (first batch), 0·55 and 0·48 g liter−1 (second batch) after 14 days of growth from NO3− and NH4+ media, respectively. Blue-green algal biomass contained higher N (81–98 g kg−1) than green algae. Isotope dilution method for determining N2 fixation indicated that 55% and 77% of total N of blue-green algae grown in NO3− and NH4+ media, respectively, was derived from the atmosphere. 相似文献
6.
S. Starke C. Cox K.-H. Südekum K. Huber 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2014,184(1):137-147
In our former studies low crude protein (LCP) intake influenced N homeostasis and electrolyte handling in goats. We hypothesised that due to rumino-hepatic nitrogen (N) recycling adaptation of N homeostasis and adjustment of electrolyte handling to LCP intake differs between goats and monogastric animals. Therefore, an experiment similar to that with goats was conducted with rats. Two feeding groups received a diet either containing 20 or 8 % crude protein (as fed basis) for 5 weeks and intake and excretion of N, calcium (Ca) and phosphorus (P) were determined. To detect systemic and endocrine adaptation to LCP intake plasma concentrations of urea, Ca, phosphate (Pi), insulin-like growth factor 1 (IGF-1), 1,25-dihydroxyvitamin D3 (calcitriol), parathyroid hormone (PTH) and cross-linked telopeptide of type I collagen (CTX) were measured. Adjustment of renal electrolyte transport was assessed by detecting protein expression of key proteins of renal Pi transport. All data were compared with the data of the goat experiment. LCP intake decreased plasma urea concentration stronger in goats than in rats. In both species urinary N excretion declined, but faecal N excretion decreased in goats only. Furthermore, in goats urinary Ca excretion decreased, but in rats urinary Ca concentration increased. Decreased plasma IGF-1 and calcitriol concentrations were found in goats only. Thus, renal Ca excretion appears to be a common target in adaptation of electrolyte homeostasis in both species, but is regulated differently. 相似文献
7.
David I. Friedman Gerald S. Wilgus Richard J. Mural 《Journal of molecular biology》1973,81(4):505-516
We report the isolation and characterization of a new mutation in the hybrid phage λimm21. Both genetic and physiological studies demonstrate that this new mutation, N21?1, is similar to N mutations of phage λ. As in the case of the N gene of λ (Niλ), the N21?1 mutation maps immediately to the left of the cI gene and has a pleiotropic effect on the expression of phage functions. Although these studies strongly suggest that phage 21 has an N function, they do not definitely locate the N21?1 mutation within the N21 structural gene.Reported here are studies demonstrating that N21 acts in trans, similar to Nλ, to stimulate the expression of phage functions. N products show an immunity specificity; N21 being only active on phage carrying the immunity region of phage 21, while the nλ is only active on phage carrying the immunity region of λ or phage 434. However, one site of action for Nλ can be rescued from phage 21. We propose that the specificity of an N function is determined by its sites of recognition and that these sites may be different from the sites of N action. 相似文献
8.
Masakazu Uramoto Masayuki Matsuoka J.G. Liehr James A. Mccloskey Kiyoshi Isono 《Bioscience, biotechnology, and biochemistry》2013,77(8):1901-1902
Eclosion hormone was purified 5,000-fold from the extracts of male adult heads of the silkworm, Bombyx mori. The fourteen-step purification procedure consisting of solvent extractions, fractional precipitations and chromatographies afforded a partially purified preparation of eclosion hormone, 1.8 μg of which showed activity in a Bombyx pharate adult. The hormone was inactivated by proteolytic enzymes. The molecular weight of eclosion hormone was estimated to be 8,400 ± 1,000 daltons by gel-filtration on Sephadex G-50. 相似文献
9.
T Matsubara 《Journal of biochemistry》1975,77(3):627-632
The oxidation of cytochromes during the reduction of N2O to N2 by a denitrifying bacterium was studied spectrophotometrically. The reduced b- and c-type cytochromes are partially oxidized when N2O is added to intact cells reduced with lactate under anaerobic conditions. The oxidation of cytochromes is inhibited non-competitively by azide, cyanide, 2,4-dinitrophenol and CuSO4, which inhibit the reduction of N2O to N2. In the presence of each inhibitor at a high concentration, at which the reduction of N2O to N2 is perfectly inhibited, cytochromes are not oxidized by N2O, while when an adequate, low concentration of inhibitor is added, b-type cytochrome is partially oxidized but c-type cytochrome is apparently not oxidized. In cell-free extracts, prepared by the sonic disruption of cells, that have entirely lost their activity in the reduction of N2O to N2, cytochromes are not oxidized by N2O. From the above results, it was concluded that b-type and c-type cytochromes should participate in the electron transport mechanism of the reduction of N2O to N2. 相似文献
10.
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13.
N7-Ethyldeoxyguanosine 5'-triphosphate (N7-Etd-GTP) was synthesized by direct ethylation of dGTP with diethyl sulfate and purified by TLC on cellulose plates at approximately 5% yield. N7-EtdGTP was identified by its uv spectra at pH 1, 7.4, and 13, by its absorbance maxima and minima, and by the lability of the glycosidic bond to acid- and heat-induced cleavage. At pH 7.4, spontaneous cleavage of the glycosidic bond proceeded with a half-life of greater than 48 h. An enzymatic method for placing an N7-ethylguanine in a specific site in DNA was developed using terminal deoxynucleotidyltransferase and the 3' to 5' exonuclease and 5' to 3' polymerase of the Klenow fragment of Escherichia coli DNA polymerase I. The method should be readily adaptable to other modified bases as long as the modification does not occur at a base-pairing site (e.g., 5-methylcytosine, N6-methyladenine, and others). 相似文献
14.
Jason P. Rife Charles S. Cheng Peter B. Moore Scott A. Strobel 《Nucleosides, nucleotides & nucleic acids》2013,32(12):2281-2288
Abstract The phosphoramidites of the naturally occurring modified nucleotides N 2-methylguanosine and N 6,N 6-dimethyladenosine were synthesized and incorporated into short oligoribonucleotides. Described are the syntheses of the phosphoramidites and the procedures used to deprotect oligoribonucleotides in which the O 6 of m2G is protected with a 2-(p-nitrophenyl)ethyl group. 相似文献
15.
Autumnal N storage determines the spring growth,N uptake and N internal cycling of young peach trees
Although N storage determines early spring growth in trees, the usefulness of autumn N supply remains unclear as N uptake
decreases in autumn, but could be restored earlier in spring to compensate for low N cycling. We intended here to evaluate
the effects of autumn N supply on N uptake, storage and cycling, and spring growth. Four levels of N fertilisation were applied
to 1-year-old peach trees, between the end of shoot growth and leaf fall. In spring, N supply was 15N labelled. Organ dry weights and concentrations of 14N, 15N, starch and soluble sugars were evaluated after the first growth flush. Bud development had previously been described in
the same trees by Jordan et al. (Trees-Struct Func 23:235–245, 2009). Fertilisation promoted autumn N uptake, spring N uptake and growth up to a threshold level, since no differences were evidenced
between the three highest N treatments. The variability in tree 14N contents was related to the number of phytomers per tree in autumn, i.e. to tree size. In spring, the depletion of the perennial
structures was independent of treatment, indicating a complete mobilisation of the N stores. Spring growth was related to
the amounts of cycling N, and spring N uptake was in turn proportioned to shoot and fruit growth. The lower N uptake of the
N limited trees was not due to a C shortage since these trees displayed the highest starch concentrations. We conclude that
a moderate autumn fertilisation improved spring growth and fruit production (Jordan et al. in Trees-Struct Func 23:235–245,
2009) and that a deficit of N storage could not be compensated for by an increase in spring N uptake. 相似文献
16.
Effects of nitrate concentration on the denitrification potential of a calcic cambisol and its fractions of N2, N2O and NO 总被引:1,自引:0,他引:1
Rui Wang Qi Feng Tingting Liao Xunhua Zheng Klaus Butterbach-Bahl Wei Zhang Chunyi Jin 《Plant and Soil》2013,363(1-2):175-189
Background and aims
The direct measurement of denitrification dynamics and its product fractions is important for parameterizing process-oriented model(s) for nitrogen cycling in various soils. The aims of this study are to a) directly measure the denitrification potential and the fractions of nitrogenous gases as products of the process in laboratory, b) investigate the effects of the nitrate (NO 3 ? ) concentration on emissions of denitrification gases, and c) test the hypothesis that denitrification can be a major pathway of nitrous oxide (N2O) and nitric oxide (NO) production in calcic cambisols under conditions of simultaneously sufficient supplies of carbon and nitrogen substrates and anaerobiosis as to be found to occur commonly in agricultural lands.Methods
Using the helium atmosphere (with or without oxygen) gas-flow-soil-core technique in laboratory, we directly measured the denitrification potential of a silt clay calcic cambisol and the production of nitrogen gas (N2), N2O and NO during denitrification under the conditions of seven levels of NO 3 ? concentrations (ranging from 10 to 250 mg N kg?1 dry soil) and an almost constant initial dissolved organic carbon concentration (300 mg C kg?1 dry soil).Results
Almost all the soil NO 3 ? was consumed during anaerobic incubation, with 80–88 % of the consumed NO 3 ? recovered by measuring nitrogenous gases. The results showed that the increases in initial NO 3 ? concentrations significantly enhanced the denitrification potential and the emissions of N2 and N2O as products of this process. Despite the wide range of initial NO 3 ? concentrations, the ratios of N2, N2O and NO products to denitrification potential showed much narrower ranges of 51–78 % for N2, 14–36 % for N2O and 5–22 % for NO.Conclusions
These results well support the above hypothesis and provide some parameters for simulating effects of variable soil NO 3 ? concentrations on denitrification process as needed for biogeochemical models. 相似文献17.
Katja Pörtl Sophie Zechmeister-Boltenstern Wolfgang Wanek Per Ambus Torsten W. Berger 《Plant and Soil》2007,295(1-2):79-94
Natural 15N abundance measurements of ecosystem nitrogen (N) pools and 15N pool dilution assays of gross N transformation rates were applied to investigate the potential of δ15N signatures of soil N pools to reflect the dynamics in the forest soil N cycle. Intact soil cores were collected from pure
spruce (Picea abies (L.) Karst.) and mixed spruce-beech (Fagus sylvatica L.) stands on stagnic gleysol in Austria. Soil δ15N values of both forest sites increased with depth to 50 cm, but then decreased below this zone. δ15N values of microbial biomass (mixed stand: 4.7 ± 0.8‰, spruce stand: 5.9 ± 0.9‰) and of dissolved organic N (DON; mixed stand:
5.3 ± 1.7‰, spruce stand: 2.6 ± 3.3‰) were not significantly different; these pools were most enriched in 15N of all soil N pools. Denitrification represented the main N2O-producing process in the mixed forest stand as we detected a significant 15N enrichment of its substrate NO3− (3.6 ± 4.5‰) compared to NH4+ (−4.6 ± 2.6‰) and its product N2O (−11.8 ± 3.2‰). In a 15N-labelling experiment in the spruce stand, nitrification contributed more to N2O production than denitrification. Moreover, in natural abundance measurements the NH4+ pool was slightly 15N-enriched (−0.4 ± 2.0 ‰) compared to NO3− (−3.0 ± 0.6 ‰) and N2O (−2.1 ± 1.1 ‰) in the spruce stand, indicating nitrification and denitrification operated in parallel to produce N2O. The more positive δ15N values of N2O in the spruce stand than in the mixed stand point to extensive microbial N2O reduction in the spruce stand. Combining natural 15N abundance and 15N tracer experiments provided a more complete picture of soil N dynamics than possible with either measurement done separately. 相似文献
18.
Compatible interactions between rhizobia and their leguminous host plant(s) culminate in the formation of a new plant organ, the root nodule. Within this structure, the bacteria reduce N2 to NH3 which is then assimilated by the plant. The formation of a N2-fixing nodule requires a continuous process of two-way signalling and cellular recognition between the prokaryote and the plant. Such a process involves the sequential activation and/or repression of host plant- and bacteria-encoded genes. Finally, functioning of a legume-nodule necessitates not only the adaptation of plant and bacterial carbon, nitrogen and oxygen metabolism to an environment allowing N2-fixation to occur, but also requires a tight co-ordination and integration of these plant and bacterial metabolic processes. 相似文献
19.
Simultaneous quantification of N2, NH3 and N2O emissions from a flooded paddy field under different N fertilization regimes 总被引:1,自引:0,他引:1
Longlong Xia Xiaobo Li Qianqian Ma Shu Kee Lam Benjamin Wolf Ralf Kiese Klaus Butterbach‐Bahl Deli Chen Zhian Li Xiaoyuan Yan 《Global Change Biology》2020,26(4):2292-2303
Gaseous nitrogen (N) emissions, especially emissions of dinitrogen (N2) and ammonia (NH3), have long been considered as the major pathways of N loss from flooded rice paddies. However, no studies have simultaneously evaluated the overall response of gaseous N losses to improved N fertilization practices due to the difficulties to directly measure N2 emissions from paddy soils. We simultaneously quantified emissions of N2 (using membrane inlet mass spectrometry), NH3 and nitrous oxide (N2O) from a flooded paddy field in southern China over an entire rice‐growing season. Our field experiment included three treatments: a control treatment (no N addition) and two N fertilizer (220 kg N/ha) application methods, the traditional surface application of N fertilizer and the incorporation of N fertilizer into the soil. Our results show that over the rice‐growing season, the cumulative gaseous N losses from the surface application treatment accounted for 13.5% (N2), 19.1% (NH3), 0.2% (N2O) and 32.8% (total gaseous N loss) of the applied N fertilizer. Compared with the surface application treatment, the incorporation of N fertilizer into the soil decreased the emissions of NH3, N2 and N2O by 14.2%, 13.3% and 42.5%, respectively. Overall, the incorporation of N fertilizer into the soil significantly reduced the total gaseous N loss by 13.8%, improved the fertilizer N use efficiency by 14.4%, increased the rice yield by 13.9% and reduced the gaseous N loss intensity (gaseous N loss/rice yield) by 24.3%. Our results indicate that the incorporation of N fertilizer into the soil is an effective agricultural management practice in ensuring food security and environmental sustainability in flooded paddy ecosystems. 相似文献
20.
Nitrogen (N) Dynamics in the Mineral Soil of a Central Appalachian Hardwood Forest During a Quarter Century of Whole-Watershed N Additions 总被引:1,自引:0,他引:1
Frank S. Gilliam Christopher A. Walter Mary Beth Adams William T. Peterjohn 《Ecosystems》2018,21(8):1489-1504
The structure and function of terrestrial ecosystems are maintained by processes that vary with temporal and spatial scale. This study examined temporal and spatial patterns of net nitrogen (N) mineralization and nitrification in mineral soil of three watersheds at the Fernow Experimental Forest, WV: 2 untreated watersheds and 1 watershed receiving aerial applications of N over a 25-year period. Soil was sampled to 5 cm from each of seven plots per watershed and placed in two polyethylene bags—one bag brought to the laboratory for extraction/analysis, and the other bag incubated in situ at a 5 cm depth monthly during growing seasons of 1993–1995, 2002, 2005, 2007–2014. Spatial patterns of net N mineralization and nitrification changed in all watersheds, but were especially evident in the treated watershed, with spatial variability changing non-monotonically, increasing then decreasing markedly. These results support a prediction of the N homogeneity hypothesis that increasing N loads will increase spatial homogeneity in N processing. Temporal patterns for net N mineralization and nitrification were similar for all watersheds, with rates increasing about 25–30% from 1993 to 1995, decreasing by more than 50% by 2005, and then increasing significantly to 2014. The best predictor of these synchronous temporal patterns across all watersheds was number of degree days below 19°C, a value similar to published temperature maxima for net rates of N mineralization and nitrification for these soils. The lack of persistent, detectable differences in net nitrification between watersheds is surprising because fertilization has maintained higher stream-water nitrate concentrations than in the reference watersheds. Lack of differences in net nitrification among watersheds suggests that N-enhanced stream-water nitrate following N fertilization may be the result of a reduced biotic demand for nitrate following fertilization with ammonium sulfate. 相似文献