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971.
Werner Härdtle Goddert von Oheimb Marion Niemeyer Thomas Niemeyer Thorsten Assmann Hartmut Meyer 《Biogeochemistry》2007,86(2):201-215
Atmospheric nutrient deposition has contributed to widespread changes in sensitive seminatural ecosystems throughout Europe.
For an understanding of underlying processes it is important to quantify input–output flows in relation to ongoing atmospheric
inputs and current management strategies. In this study we quantified losses of N, P, Ca, Mg, and K via leaching in heathland
ecosystems (Lüneburger Heide, NW Germany) as a function of current deposition rates and different management measures (mowing,
prescribed burning, choppering, sod-cutting) which aim to prevent shrub and tree encroachment. Leaching was only moderately
related to atmospheric input rates, indicating that leaching was mostly affected by internal turnover processes. Leaching
significantly increased for most of the nutrients after the application of management measures, particularly in the choppered
and sod-cut plots. However, atmospheric nutrient inputs exceeded leaching outputs for most of the nutrients, even in the plots
subjected to management. Despite high deposition rates (20–25 kg N ha−1 year−1), retention of atmospheric N input ranged between 74% and 92% in the control plots. In the treated plots, N retention decreased
to 59–80%. However, in the study area mean N leaching in the controls has almost doubled since 1980 and currently amounts
to 3.7 kg ha−1 year−1, indicating an early stage of N saturation. Our study provides evidence that leaching did not compensate for atmospheric
nutrient deposition, particularly as regards N. Management, thus, will be an indispensable tool for the maintenance of the
low-nutrient status as a prerequisite for the long-term preservation of heathland ecosystems. 相似文献
972.
Long-term changes in nutrient concentrations of the Changjiang River and principal tributaries 总被引:5,自引:0,他引:5
We present long-term nutrient data on the Changjiang River (Yangtze River) at six hydrological stations and eight principal
tributaries during the period 1958–1985. Three patterns of temporal changes were observed in nitrate
and nitrite : minimal variations in the upper catchment area, rapid increases in the middle watershed towards the end of the 1970s, and
a gradual increase in the lower drainage basin. Prior to the 1970s, the level of throughout the Changjiang River system remained fairly constant. In the 1980s, however, this changed, with the lowest values
in the upper Changjiang changing rapidly to the highest in the middle reaches and then declining slowly but steadily in the
lower courses. Compared to and ammonium and soluble reactive phosphorus (SRP) showed smaller increases or no long-term variations, while dissolved silica (DSi) concentration
generally decreased at most stations. These three patterns of and changes in the Changjiang River system were reflective of the difference in chemical fertilizer use and landscape features
(e.g., slope, soil type and water body area) of the drainage basins of the primary tributaries. The decreases in DSi were
most likely attributed to a reduction in suspended sediment loading due to dam constructions and increasing diatom consumption.
The increase in and with a reduction in DSi concentrations in the Changjiang River could have significant effects on the stoichiometric balance
of nutrients delivered to the East China Sea and the ecosystem in this dynamic region. 相似文献
973.
Takeno S Ohnishi J Komatsu T Masaki T Sen K Ikeda M 《Applied microbiology and biotechnology》2007,75(5):1173-1182
Oxygen limitation is a crucial problem in amino acid fermentation by Corynebacterium glutamicum. Toward this subject, our study was initiated by analysis of the oxygen-requiring properties of C. glutamicum, generally regarded as a strict aerobe. This organism formed colonies on agar plates up to relatively low oxygen concentrations
(0.5% O2), while no visible colonies were formed in the absence of O2. However, in the presence of nitrate (), the organism exhibited limited growth anaerobically with production of nitrite (), indicating that C. glutamicum can use nitrate as a final electron acceptor. Assays of cell extracts from aerobic and hypoxic cultures yielded comparable
nitrate reductase activities, irrespective of nitrate levels. Genome analysis revealed a narK2GHJI cluster potentially relevant to nitrate reductase and transport. Disruptions of narG and narJ abolished the nitrate-dependent anaerobic growth with the loss of nitrate reductase activity. Disruption of the putative
nitrate/nitrite antiporter gene narK2 did not affect the enzyme activity but impaired the anaerobic growth. These indicate that this locus is responsible for nitrate
respiration. Agar piece assays using l-lysine- and l-arginine-producing strains showed that production of both amino acids occurred anaerobically by nitrate respiration, indicating
the potential of C. glutamicum for anaerobic amino acid production. 相似文献
974.
Plants growing in acid soils suffer both phosphorus (P) deficiency and aluminum (Al) toxicity stresses. Selection of genotypes for adaptation to either P deficiency or Al toxicity has sometimes been unsuccessful because these two soil factors often interact. Two experiments were conducted to evaluate eight cowpea genotypes for Al resistance and to study the combined effect of P deficiency and Al toxicity stress on growth, P uptake, and organic acid anion exudation of two genotypes of contrasting Al resistance selected from the first experiment. Relative root inhibition by 30 μM Al ranged from 14% to 60% and differed significantly among the genotypes. Al significantly induced callose formation, particularly in Al-sensitive genotypes. P accumulation was significantly reduced (28% and 95%) by Al application for both the Al-resistant and the Al-sensitive genotypes. Al supply significantly enhanced malate release of root apices of both genotypes. However, the exudation rate was significantly higher in the Al-resistant genotype. P deprivation induced an enhanced malate exudation in the presence of Al only in the Al-resistant genotype IT89KD-391. Citrate exudation rate of the root apices was lower than malate exudation by a factor of about 10, and was primarily enhanced by P deficiency in both genotypes. Al treatment further enhanced citrate exudation in P-sufficient, but not in P-deficient plants. The level of citrate exudation was consistently higher in the Al-resistant genotype IT89KD-391 particularly in presence of Al.It is concluded that the Al-resistant genotype is better adapted to acid Al-toxic and P-deficient soils than the Al-sensitive genotype since both malate and citrate exudation were more enhanced by combined Al and P-deficiency stresses. 相似文献
975.
长期在高浓度CO2环境下生长的植物往往会发生光合适应或下调,即在相同CO2浓度下的光合速率明显低于普通空气中生长的对照。虽然关于这种现象已经有许多研究报告和综述文章,但是它的机理还不很清楚。本文结合作者所在研究组的工作,概述了关于植物光合适应机理研究的新进展,提出除了呼吸作用增强和光合产物超常积累的可能作用以外,二磷酸核酮糖(RuBP)羧化限制和RuBP再生限制可能是导致植物光合适应的主要因素。 相似文献
976.
In comparison with its wild type (WT), the transgenic (TG) rice with silenced OsBP-73 gene had significantly lower plant height, grain number per panicle, and leaf net photosynthetic rate (P
N). Also, the TG rice showed significantly lower chlorophyll (Chl), ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO),
RuBPCO activase, and RuBP contents, photosystem 2 (PS2) photochemical efficiency (Fv/Fm and ΔF/Fm′), apparent quantum yield of carbon assimilation (Φc), carboxylation efficiency (CE), photosynthetic electron transport and photophosphorylation rates as well as sucrose phosphate
synthase activity, but higher intercellular CO2 concentration, sucrose, fructose, and glycerate 3-phosphate contents, and non-photochemical quenching of Chl fluorescence
(NPQ). Thus the decreased P
N in the TG rice leaves is related to both RuBP carboxylation and RuBP regeneration limitations, and the latter is a predominant
limitation to photosynthesis. 相似文献
977.
The Florida Everglades is a naturally oligotrophic hydroscape that has experienced large changes in ecosystem structure and
function as the result of increased anthropogenic phosphorus (P) loading and hydrologic changes. We present whole-ecosystem
models of P cycling for Everglades wetlands with differing hydrology and P enrichment with the goal of synthesizing existing
information into ecosystem P budgets. Budgets were developed for deeper water oligotrophic wet prairie/slough (‘Slough’),
shallower water oligotrophic Cladium jamaicense (‘Cladium’), partially enriched C. jamaicense/Typha spp. mixture (‘Cladium/Typha’), and enriched Typha spp. (‘Typha’) marshes. The majority of ecosystem P was stored in the soil in all four ecosystem types, with the flocculent
detrital organic matter (floc) layer at the bottom of the water column storing the next largest proportion of ecosystem P
pools. However, most P cycling involved ecosystem components in the water column (periphyton, floc, and consumers) in deeper
water, oligotrophic Slough marsh. Fluxes of P associated with macrophytes were more important in the shallower water, oligotrophic
Cladium marsh. The two oligotrophic ecosystem types had similar total ecosystem P stocks and cycling rates, and low rates
of P cycling associated with soils. Phosphorus flux rates cannot be estimated for ecosystem components residing in the water
column in Cladium/Typha or Typha marshes due to insufficient data. Enrichment caused a large increase in the importance of
macrophytes to P cycling in Everglades wetlands. The flux of P from soil to the water column, via roots to live aboveground
tissues to macrophyte detritus, increased from 0.03 and 0.2 g P m−2 yr−1 in oligotrophic Slough and Cladium marsh, respectively, to 1.1 g P m−2 yr−1 in partially enriched Cladium/Typha, and 1.6 g P m−2 yr−1 in enriched Typha marsh. This macrophyte translocation P flux represents a large source of internal eutrophication to surface
waters in P-enriched areas of the Everglades. 相似文献
978.
Hoi-Ping Shi Chi-Mei Lee Wei-Hsien Ma 《World journal of microbiology & biotechnology》2007,23(5):625-632
Polyhydroxyalkanoates (PHAs), intracellular carbon and energy reserve compounds in many bacteria, have been used extensively
in biodegradable plastics. PHA formation is influenced by nutrient limitations and growth conditions. To characterize the
PHA accumulation in a new denitrifying phosphorus-removing bacterium Brachymonas sp. P12, batch experiments were conducted in which the electron acceptor (oxygen or nitrate) was varied and different concentrations
of carbon (acetate), nitrogen (NH4Cl), and phosphorus (KH2PO4) were used. Polyhydroxybutyrate (PHB) was the dominant product during PHA formation when acetate was the sole carbon source.
The PHB content of aerobically growing cells increased from 431 to 636 mg PHB g−1 biomass, but the PHB concentration of an anoxic culture decreased (−218 mg PHB g−1 biomass), when PHB was utilized simultaneously with acetate as an electron donor for anoxic denitrification. The specific
PHB production rate of the carbon-limited batch, 158.2 mg PHB g−1 biomass h−1, was much greater than that of batches with normal or excess carbon. The effects of phosphorus and nitrogen concentrations
on PHB accumulation were clearly less than the effect of carbon concentration. According to the correlation between the specific
PHB production rate and the specific cell growth rate, PHB accumulation by Brachymonas sp. P12 is enhanced by nutrient limitation, is growth-associated, and provides additional energy for the biosynthesis of
non-PHB cell constituents to increase the cell growth rate beyond the usual level. 相似文献
979.
A mutation in NLA, which encodes a RING-type ubiquitin ligase, disrupts the adaptability of Arabidopsis to nitrogen limitation 总被引:3,自引:0,他引:3
Peng M Hannam C Gu H Bi YM Rothstein SJ 《The Plant journal : for cell and molecular biology》2007,50(2):320-337
Abundant nitrogen is required for the optimal growth and development of plants, while numerous biotic and abiotic factors that consume soil nitrogen frequently create a nitrogen limitation growth condition. To cope with this, plants have evolved a suite of adaptive responses to nitrogen limitation. However, the molecular mechanism governing the adaptability of plants to nitrogen limitation is totally unknown because no reported mutant defines this trait. Here we isolated an Arabidopsis mutant, nla (nitrogen limitation adaptation), and identified the NLA gene as an essential component in this molecular mechanism. Supplied with insufficient inorganic nitrogen (nitrate or ammonium), the nla mutant failed to develop the essential adaptive responses to nitrogen limitation, but senesced much earlier and more rapidly than did the wild type. Under other stress conditions including low phosphorus nutrient, drought and high temperature, the nla mutant did not show this early senescence phenotype, but closely resembled the wild type in growth and development. Map-based cloning of NLA revealed that this gene encodes a RING-type ubiquitin ligase, and nla is a deletion mutation which does not code for the RING domain in the NLA protein. The NLA protein is localized to the nuclear speckles, where this protein interacts with the Arabidopsis ubiquitin conjugase 8 (AtUBC8). In the nla mutant, the deletion of the RING domain from NLA altered its subcellular localization, disrupted the interaction between NLA and AtUBC8 and caused the early senescence phenotype induced by low inorganic nitrogen. All the results indicate that NLA is a positive regulator for the development of the adaptability of Arabidopsis to nitrogen limitation. 相似文献
980.
三种水华蓝藻对不同磷浓度生理响应的比较研究 总被引:10,自引:0,他引:10
本实验研究了铜绿微囊藻(Microcystis aeruginosa FACHB469)、水华鱼腥藻(Anabaena flos-aquae FACHB245)和浮游颤藻(Oscillatoria planctonicaFACHB708)对磷浓度变化的生理响应。结果表明,在缺磷条件下,A. flos-aquae对低磷环境的适应能力较强,O. planctonica其次,M. aeruginosa最差;在磷充足条件,微囊藻对磷过量吸收的能力明显高于其他两种蓝藻。三种蓝藻胞外碱性磷酸酶活性(APA)与培养基中磷浓度呈负相关性,其产生碱性磷酸酶(AP)的能力由高至低为:A. flos-aquae>O. planctonica>M. aeruginosa。磷缺陷时A. flos-aquae产生的胞外APA约是M. aeruginosa的10倍,是O. planctonica的5倍。 相似文献