Estimation of cytoplasmic nitrate and its electrochemical potential in barley roots using 13NO3 and compartmental analysis

13NO3 was used to determine the intracellular compartmentation of NO3 in barley roots (Hordeum vulgare cv. Klondike), followed by a thermodynamic analysis of nitrate transport.Plants were grown in one-tenth Johnson's medium with 1 mol m3 NO3 (NO3-grown plants) or 1 mol m3 NH4NO3 (NH4NO3-grown plants).The cytoplasmic concentrations of NO3 in roots were only approx. 3-6 mol m3 (half-time for exchange approx. 21 s) in both NO3 and NH4NO3 plants. These pool sizes are consistent with published nitrate microelectrode data, but not with previous compartmental analyses.The electrochemical potential gradient for nitrate across the plasmalemma was +26 +/-1 kJ mol1 in both NO3- and NH4NO3-grown plants, indicating active uptake of nitrate. At an external pH of 6, the plasmalemma electrochemical potential for protons would be approx. -29 +/- 4 kJ mol1. If the cytoplasmic pH was 7.3 +/- 0.2, then 2H+/1NO3 cotransport, or a primary ATP-driven pump (2NO3/1ATP), are both thermodynamically possible. NO3 is also actively transported across the tonoplast (approx. +6 to 7 kJ mol1).     

Root-zone acidity and nitrogen source affects Typha latifolia L. growth and uptake kinetics of ammonium and nitrate

The NH(4)(+) and NO(3)(-) uptake kinetics by Typha latifolia L. were studied after prolonged hydroponics growth at constant pH 3.5, 5.0, 6.5 or 7.0 and with NH(4)(+) or NO(3)(-) as the sole N-source. In addition, the effects of pH and N source on H(+) extrusion and adenine nucleotide content were examined. Typha latifolia was able to grow with both N sources at near neutral pH levels, but the plants had higher relative growth rates, higher tissue concentrations of the major nutrients, higher contents of adenine nucleotides, and higher affinity for uptake of inorganic nitrogen when grown on NH(4)(+). Growth almost completely stopped at pH 3.5, irrespective of N source, probably as a consequence of pH effects on plasma membrane integrity and H(+) influx into the root cells. Tissue concentrations of the major nutrients and adenine nucleotides were severely reduced at low pH, and the uptake capacity for inorganic nitrogen was low, and more so for NO(3)(-)-fed than for NH(4)(+)-fed plants. The maximum uptake rate, V(max), was highest for NH(4)(+) at pH 6.5 (30.9 micro mol h(-1) g(-1) root dry weight) and for NO(3)(-) at pH 5.0 (31.7 micro mol h(-1) g(-1) root dry weight), and less than 10% of these values at pH 3.5. The affinity for uptake as estimated by the half saturation constant, K((1/2)), was lowest at low pH for NH(4)(+) and at high pH for NO(3)(-). The changes in V(max) and K((1/2)) were thus consistent with the theory of increasing competition between cations and H(+) at low pH and between anions and OH(-) at high pH. C(min) was independent of pH, but slightly higher for NO(3)(-) than for NH(4)(+) (C(min)(NH(4)(+)) approximately 0.8 mmol m(-3); C(min)(NO(3)(-)) approximately 2.8 mmol m(-3)). The growth inhibition at low pH was probably due to a reduced nutrient uptake and a consequential limitation of growth by nutrient stress. Typha latifolia seems to be well adapted to growth in wetland soils where NH(4)(+) is the prevailing nitrogen compound, but very low pH levels around the roots are very stressful for the plant. The common occurrence of T. latifolia in very acidic areas is probably only possible because of the plant's ability to modify pH-conditions in the rhizosphere.     

Characterization of wet and dry deposition in the downwind of industrial sources in a dry tropical area

An atmospheric deposition study was conducted in the downwind of Shaktinagar Thermal Power Plant (STPP), Renusagar Thermal Power Plant (RTPP), and Anpara Thermal Power Plant (ATPP), at Singrauli region, Uttar Pradesh (UP), India to characterize dry and wet deposition in relation to different pollution loading. During the study period, dry and wet depositions and levels of gaseous pollutants (SO2 and NO2) were estimated across the sites. Dry deposition was collected on a monthly basis and wet deposition on an event basis. Depositions were analyzed for pH, nitrate (NO3-), ammonium (NH4+), and sulphate (SO4(2-)) contents. Dry deposition rate both collected as clearfall and throughfall varied between 0.15 to 2.28 and 0.33 to 3.48 g m(-2) day(-1), respectively, at control and maximally polluted sites. The pH of dry deposition varied from 5.81 to 6.89 during winter and 6.09 to 7.02 during summer across the sites. During the rainy season, the mean pH of clear wet deposition varied from 6.56 to 7.04 and throughfall varied from 6.81 to 7.22. The concentrations of NO2 and SO2 pollutants were highest during the winter season. Mean SO2 concentrations varied from 18 to 75 g m(-3) at control and differently polluted sites during the winter season. The variation in NO2 concentrations did not show a pattern similar to that of SO2. The highest NO2 concentration during the winter season was 50 g m(-3), observed near RTPP. NO2 concentration did not show much variation among different sites, suggesting that the sources of NO2 emission are evenly distributed along the sites. The concentrations of NH4+, NO3-, and SO4(2-) ions in dry deposition were found to be higher in summer as compared to the winter season. In dry deposition (clearfall) the concentrations of NH4+, NO3-, and SO4(2-) varied from 0.13 to 1.0, 0.81 to 1.95, and 0.82 to 3.27 mg l(-1), respectively, during winter. In wet deposition (clearfall), the above varied from 0.14 to 0.74, 0.81 to 1.82, and 0.67 to 2.70 mg l(-1), respectively. The study clearly showed that both dry and wet depositions varied between the sites and season, suggesting significant impact of industrial activities in modifying the atmospheric input. The nonacidic deposition suggests that there is no threat of acidification of the receiving ecosystem at present.     

In situ monitoring of the ambient air around the chloroprene rubber industrial plant using the Tradescantia-stamen-hair mutation assay.

The city of Yerevan, the capital of Armenia, has been one of the heavily polluted cities since the earlier USSR era. A Chloroprene Rubber Industrial Plant has been the major contributor of air pollution in this city. The first attempt has been undertaken to detect the mutagenic effect of the ambient air around this industrial complex using the Tradescantia-stamen-hair-mutation (Trad-SHM) assay. Tradescantia clone 02 was used for this study. Pots of Tradescantia plants were exposed to ambient air in 10 different locations around the industrial establishment during the months of May and June, 1991 and 1992. Three series of in situ monitoring experiments were carried out. In the first series, sites numbers 1 through 4 were located in the industrial complex, and the second series, sites numbers 5 through 7 were located 1.0-1.3 km away from the Rubber Plant and the third series, sites numbers 8 though 10 were situated 1.5 km from the chemical plant and the monitoring plants were elevated at 5, 13, and 32 m above ground. A control group of plants were grown in a greenhouse about 13 km away from the polluted air from the chemical plant. Results of these two consecutive year's study show significantly elevated high levels of pink mutation events (PME) over the control at sites 1, 2, and 4 in the first series of the study. Positive responses were observed at all sites in the second series of the study. Only site 8 (June 1991) in the third series of the study was significantly higher in PME over the control.     

Growth, nitrogen uptake, and metabolism in two semiarid shrubs grown at ambient and elevated atmospheric CO2 concentrations: effects of nitrogen supply and source

The effect of differences in nitrogen (N) availability and source on growth and nitrogen metabolism at different atmospheric CO(2) concentrations in Prosopis glandulosa and Prosopis flexuosa (native to semiarid regions of North and South America, respectively) was examined. Total biomass, allocation, N uptake, and metabolites (e.g., free NO(3)(-), soluble proteins, organic acids) were measured in seedlings grown in controlled environment chambers for 48 d at ambient (350 ppm) and elevated (650 ppm) CO(2) and fertilized with high (8.0 mmol/L) or low (0.8 mmol/L) N (N(level)), supplied at either 1 : 1 or 3 : 1 NO(3)(-) : NH(4)(+) ratios (N(source)). Responses to elevated CO(2) depended on both N(level) and N(source), with the largest effects evident at high N(level). A high NO(3)(-) : NH(4)(+) ratio stimulated growth responses to elevated CO(2) in both species when N was limiting and increased the responses of P. flexuosa at high N(level). Significant differences in N uptake and metabolites were found between species. Seedlings of both species are highly responsive to N availability and will benefit from increases in CO(2), provided that a high proportion of NO(3)- to NH(4)-N is present in the soil solution. This enhancement, in combination with responses that increase N acquisition and increases in water use efficiency typically found at elevated CO(2), may indicate that these semiarid species will be better able to cope with both nutrient and water deficits as CO(2) levels rise.     

Individual exposure to NO2 in relation to spatial and temporal exposure indices in Stockholm, Sweden: the INDEX study

Epidemiology studies of health effects from air pollution, as well as impact assessments, typically rely on ambient monitoring data or modelled residential levels. The relationship between these and personal exposure is not clear. To investigate personal exposure to NO(2) and its relationship with other exposure metrics and time-activity patterns in a randomly selected sample of healthy working adults (20-59 years) living and working in Stockholm. Personal exposure to NO(2) was measured with diffusive samplers in sample of 247 individuals. The 7-day average personal exposure was 14.3 μg/m(3) and 12.5 μg/m(3) for the study population and the inhabitants of Stockholm County, respectively. The personal exposure was significantly lower than the urban background level (20.3 μg/m(3)). In the univariate analyses the most influential determinants of individual exposure were long-term high-resolution dispersion-modelled levels of NO(2) outdoors at home and work, and concurrent NO(2) levels measured at a rural location, difference between those measured at an urban background and rural location and difference between those measured in busy street and at an urban background location, explaining 20, 16, 1, 2 and 4% (R(2)) of the 7-day personal NO(2) variation, respectively. A regression model including these variables explained 38% of the variation in personal NO(2) exposure. We found a small improvement by adding time-activity variables to the latter model (R(2)?=?0.44). The results adds credibility primarily to long-term epidemiology studies that utilise long-term indices of NO(2) exposure at home or work, but also indicates that such studies may still suffer from exposure misclassification and dilution of any true effects. In contrast, urban background levels of NO(2) are poorly related to individual exposure.     

Dissimilatory Reduction of NO(2) to NH(4) and N(2)O by a Soil Citrobacter sp

Dissimilatory reduction of NO(2) to N(2)O and NH(4) by a soil Citrobacter sp. was studied in an attempt to elucidate the physiological and ecological significance of N(2)O production by this mechanism. In batch cultures with defined media, NO(2) reduction to NH(4) was favored by high glucose and low NO(3) concentrations. Nitrous oxide production was greatest at high glucose and intermediate NO(3) concentrations. With succinate as the energy source, little or no NO(2) was reduced to NH(4) but N(2)O was produced. Resting cell suspensions reduced NO(2) simultaneously to N(2)O and free extracellular NH(4). Chloramphenicol prevented the induction of N(2)O-producing activity. The K(m) for NO(2) reduction to N(2)O was estimated to be 0.9 mM NO(2), yet the apparent K(m) for overall NO(2) reduction was considerably lower, no greater than 0.04 mM NO(2). Activities for N(2)O and NH(4) production increased markedly after depletion of NO(3) from the media. Amendment with NO(3) inhibited N(2)O and NH(4) production by molybdate-grown cells but not by tungstate-grown cells. Sulfite inhibited production of NH(4) but not of N(2)O. In a related experiment, three Escherichia coli mutants lacking NADH-dependent nitrite reductase produced N(2)O at rates equal to the wild type. These observations suggest that N(2)O is produced enzymatically but not by the same enzyme system responsible for dissimilatory reduction of NO(2) to NH(4).     

Anaerobic ammonia oxidation in the presence of nitrogen oxides (NO(x)) by two different lithotrophs

The anaerobic ammonia-oxidizing activity of the planctomycete Candidatus "Brocadia anammoxidans" was not inhibited by NO concentrations up to 600 ppm and NO2 concentrations up to 100 ppm. B. anammoxidans was able to convert (detoxify) NO, which might explain the high NO tolerance of this organism. In the presence of NO2, the specific ammonia oxidation activity of B. anammoxidans increased, and Nitrosomonas-like microorganisms recovered an NO2-dependent anaerobic ammonia oxidation activity. Addition of NO2 to a mixed population of B. anammoxidans and Nitrosomonas induced simultaneous specific anaerobic ammonia oxidation activities of up to 5.5 mmol of NH4+ g of protein(-1) h(-1) by B. anammoxidans and up to 1.5 mmol of NH4+ g of protein(-1) h(-1) by Nitrosomonas. The stoichiometry of the converted N compounds (NO2-/NH3 ratio) and the microbial community structure were strongly influenced by NO2. The combined activity of B. anammoxidans and Nitrosomonas-like ammonia oxidizers might be of relevance in natural environments and for technical applications.     

Effect of turning regime and seasonal weather conditions on nitrogen and phosphorus losses during aerobic composting of cattle manure

Cattle manure from stock bedded on straw was aerobically composted under ambient conditions, turning with either a tractor-mounted front-end loader or a rear discharge manure spreader. Three composting experiments, each of approximately four months duration, were conducted to investigate the effect of turning regime and seasonal weather conditions on nitrogen and phosphorus losses during aerobic composting of cattle manure. Manure stacks of 12-15 m(3) initial volume were constructed in separate 5 x 5 m concrete compartments. Experiment 1 (January-April 1999) compared manure heaps turned once (T1) or three times (T3) using a front-end loader with an unturned static (S) control manure stack. Experiment 2 (June-September 1999) compared the same treatments as Experiment 1. Experiment 3 (September-December 1999) compared T1 and T3 turning regimes using a front end loader with turning by a rear-discharge spreader (TR1 and TR1T2) for more effective aeration of the manure. Turning took place at 6 weeks for the one turn treatments, and after 2, 6 and 10 weeks for the three turn treatments. Leachate losses were dominated by NH(4)-N during the first three weeks of composting, after which time NH4-N and NO3-N concentrations in leachates were approximately the same, in the range 0-20 mg N l(-1). The concentrations of both NH4-N and NO3-N in leachate were higher after turning. Molybdate-reactive P concentrations in leachate tended not to be significantly influenced by turning regime. Gaseous losses of NH3 and N2O rose quickly during the initial phases of composting, peaking at 152 g N t(-1) d(-1) for the T3 treatment. Mean NH3 emission rate (25-252 g N t(-1) d(-1)) for the first two weeks of Experiment 2 conducted during the period June-September were an order of magnitude greater (1-10 g N t(-1) d(-1)) than Experiment 3, conducted during the colder, wetter autumn period (September-December). Nitrous oxide emission rates ranged between 1-14 g N t(-1) d(-1) and showed little influence of turning regime. Total N and P concentrations in turned (T) and static (S) manure were elevated at the end of all experiments, due to loss of dry matter. Mean total N losses were 30.4% (T1) and 36.8% (T3) and total P losses 28.2% (T1) and 27.4% (T3).     

Controls over nitric oxide and ammonia emissions from Mojave Desert soils

Emissions of reactive N compounds produced during terrestrial N cycling can be an important N loss pathway from ecosystems. Most measurements of this process focus on NO and N(2)O efflux; however, in alkaline soils such as those in the Mojave Desert, NH(3) production can be an important component of N gas loss. We investigated patterns of NO and NH(3) emissions in the Mojave Desert and identified seasonal changes in temperature, precipitation and spatial heterogeneity in soil nutrients as primary controllers of soil efflux. Across all seasons, NH(3) dominated reactive N gas emissions with fluxes ranging from 0.9 to 10 ng N m(-2) s(-1) as compared to NO fluxes of 0.08-1.9 ng N m(-2) s(-1). Fluxes were higher in April and July than in October; however, a fall precipitation event yielded large increases in both NO and NH(3) efflux. To explore the mechanisms driving field observations, we combined NO and NH(3) soil flux measurements with laboratory manipulations of temperature, water and nutrient conditions. These experiments showed a large transient NH(3) pulse (~70-100 ng N m(-2) s(-1)) following water addition, presumably driven by an increase in soil NH(4) (+) concentrations. This was followed by an increase in NO production, with maximum NO flux rates of 34 ng N m(-2) s(-1). Our study suggests that immediately following water addition NH(3) volatilization proceeds at high rates due to the absence of microbial competition for NH(4) (+); during this period N gas loss is insensitive to changes in temperature and soil nutrients. Subsequently, NO emission increases and rates of both NO and NH(3) emission are sensitive to temperature and nutrient constraints on microbial activity. Addition of labile C reduces gaseous N losses, presumably by increasing microbial immobilization, whereas addition of NO(3) (-) stimulates NO and NH(3) efflux.     

Leaf-atmosphere NH(3) exchange of white clover (Trifolium repens L.) in relation to mineral N nutrition and symbiotic N(2) fixation.

Plant-atmosphere NH(3) exchange was studied in white clover (Trifolium repens L. cv. Seminole) growing in nutrient solution containing 0 (N(2) based), 0.5 (low N) or 4.5 (high N) mM NO(3)(-). The aim was to show whether the NH(3) exchange potential is influenced by the proportion of N(2) fixation relative to NO(3)(-) supply. During the treatment, inhibition of N(2) fixation by NO(3)(-) was followed by in situ determination of total nitrogenase activity (TNA), and stomatal NH(3) compensation points (chi(NH(3))) were calculated on the basis of apoplastic NH4(+) concentration ([NH4(+)]) and pH. Whole-plant NH(3) exchange, transpiration and net CO(2) exchange were continuously recorded with a controlled cuvette system. Although shoot total N concentration increased with the level of mineral N application, tissue and apoplastic [NH4(+)] as well as chi(NH(3)) were equal in the three treatments. In NH(3)-free air, net NH(3) emission rates of <1 nmol m(-2) s(-1) were observed in both high-N and N(2)-based plants. When plants were supplied with air containing 40 nmol mol(-1) NH(3), the resulting net NH(3) uptake was higher in plants which acquired N exclusively from symbiotic N(2) fixation, compared to NO(3)(-) grown plants. The results indicate that symbiotic N(2) fixation and mineral N acquisition in white clover are balanced with respect to the NH4(+) pool leading to equal chi(NH(3)) in plants growing with or without NO(3)(-). At atmospheric NH(3) concentrations exceeding chi(NH(3)), the NH(3) uptake rate is controlled by the N demand of the plants.     

响应面法优化黑曲霉产异淀粉酶的培养条件

在液态发酵条件下,采用单因素实验确定了Aspergillus niger PZ331产异淀粉酶的最适碳源和氮源,分别为蔗糖和硝酸铵。在上述基础上利用Plackett-Burman设计对影响产异淀粉酶的因素进行评价,并筛选出硝酸铵、接种量、培养温度3个主要因素;继而利用响应面设计优化了最佳硝酸铵浓度、接种量和培养温度。最终确定了最优培养条件为：蔗糖10 g/L,硝酸铵10 g/L,磷酸氢二钾3 g/L,硫酸亚铁0.01 g/L,硫酸镁1 g/L,起始p H值4.2;接种量2%（孢子浓度为107cfu/m L）,30℃培养72 h,酶活达137.3μ/m L;比基础培养基的提高了1.71倍左右。     

Nitrate supply affects ammonium transport in canola roots

Plants may suffer from ammonium (NH4+) toxicity when NH4+ is the sole nitrogen source. Nitrate (NO3-) is known to alleviate NH4+ toxicity, but the mechanisms are unknown. This study has evaluated possible mechanisms of NO3- alleviation of NH4+ toxicity in canola (Brassica napus L.). Dynamics of net fluxes of NH4+, H+, K+ and Ca2+ were assessed, using a non-invasive microelectrode (MIFE) technique, in plants having different NO3- supplies, after single or several subsequent increases in external NH4Cl concentration. After an increase in external NH4Cl without NO3-, NH4+ net fluxes demonstrated three distinct stages: release (tau1), return to uptake (tau2), and a decrease in uptake rate (tau3). The presence of NO3- in the bathing medium prevented the tau1 release and also resulted in slower activation of the tau3 stage. Net fluxes of Ca2+ were in the opposite direction to NH4+ net fluxes, regardless of NO3- supply. In contrast, H+ and K+ net fluxes and change in external pH were not correlated with NH4+ net fluxes. It is concluded that (i) NO3- primarily affects the NH4+ low-affinity influx system; and (ii) NH4+ transport is inversely linked to Ca2+ net flux.     

Evidence for a relationship between malate metabolism and activity of 1-sinapoylglucose: L-malate sinapoyltransferase in radish (Raphanus sativus L.) cotyledons

The control of malate metabolism and stimulation of 1-sinapolyglucose: L-malate sinapoyltransferase (SMT) activity in radish (Raphanus sativus L. var. sativus) cotyledons has been studied. The light-induced and nitrate-dependent activity of SMT catalyzes the formation of O-sinapoly-L-malate via 1-O-sinapoyl--D-glucose. When dark-grown radish seedlings, cultivated in quartz sand with nutrient solution containing NO ₃ ^- as the sole N source, were treated with light, SMT activity increased concomitantly with free malate in the cotyledons. This light effect was suppressed in seedlings grown in a culture medium which contained in addition to NO ₃ ^- also NH ₄ ⁺ . However, treatment with methionine sulfoximine neutralized this ammonium effect, resulting again in both rapid accumulation of malate and rapid increase in SMT activity. When seedlings grown on NO ₃ ^- nitrogen were subsequently supplied with NH ₄ ⁺ nitrogen, the accumulated level of L-malate rapidly dropped and the SMT increase ceased. The enzyme activity decreased later on, reaching the low activity level of plants which were grown permanently on NO ₃ ^- /NH ₄ ⁺ -nitrogen. An external supply (vacuum infiltration) of malate to excised cotyledons and intact seedings, grown on NO ₃ ^- /NH ₄ ⁺ -nitrogen medium, specifically promoted a dose-dependent increase in the activity of SMT. In summary these results provide evidence indicating that the SMT activity in cotyledons of Raphanus sativus might be related to the metabolism of malic acid.Abbreviation MSO L-methionine sulfoximine - SinGlc 1-O-sinapoyl--D-glucose - SinMal O-sinapoyl-L-malate - SMT 1-O-sinapoyl--D-glucose:L-malate sinapolytransferase     

Effects of Nitrate Availability and the Presence of Glyceria maxima on the Composition and Activity of the Dissimilatory Nitrate-Reducing Bacterial Community

The effects of nitrate availability and the presence of Glyceria maxima on the composition and activity of the dissimilatory nitrate-reducing bacterial community were studied in the laboratory. Four different concentrations of NO(inf3)(sup-), 0, 533, 1434, and 2,905 (mu)g of NO(inf3)(sup-)-N g of dry sediment(sup-1), were added to pots containing freshwater sediment, and the pots were then incubated for a period of 69 days. Upon harvest, NH(inf4)(sup+) was not detectable in sediment that received 0 or 533 (mu)g of NO(inf3)(sup-)-N g of dry sediment(sup-1). Nitrate concentrations in these pots ranged from 0 to 8 (mu)g of NO(inf3)(sup-)-N g of dry sediment(sup-1) at harvest. In pots that received 1,434 or 2,905 (mu)g of NO(inf3)(sup-)-N g of dry sediment(sup-1), final concentrations varied between 10 and 48 (mu)g of NH(inf4)(sup+)-N g of dry sediment(sup-1) and between 200 and 1,600 (mu)g of NO(inf3)(sup-)-N g of dry sediment(sup-1), respectively. Higher input levels of NO(inf3)(sup-) resulted in increased numbers of potential nitrate-reducing bacteria and higher potential nitrate-reducing activity in the rhizosphere. In sediment samples from the rhizosphere, the contribution of denitrification to the potential nitrate-reducing capacity varied from 8% under NO(inf3)(sup-)-limiting conditions to 58% when NO(inf3)(sup-) was in ample supply. In bulk sediment with excess NO(inf3)(sup-), this percentage was 44%. The nitrate-reducing community consisted almost entirely of NO(inf2)(sup-)-accumulating or NH(inf4)(sup+)-producing gram-positive species when NO(inf3)(sup-) was not added to the sediment. The addition of NO(inf3)(sup-) resulted in an increase of denitrifying Pseudomonas and Moraxella strains. The factor controlling the composition of the nitrate-reducing community when NO(inf3)(sup-) is limited is the presence of G. maxima. In sediment with excess NO(inf3)(sup-), nitrate availability determines the composition of the nitrate-reducing community.     

Settleability and kinetics of a nitrifying sludge in a sequencing batch reactor

A physiological study of a nitrifying sludge was carried out in a sequencing batch reactor (SBR). Pseudo steady-state nitrification conditions were obtained with an ammonium removal efficiency of 99% +/- 1% and 98% +/- 2% conversion of NH4+-N to NO3 - -N. The rate of biomass production was negligible (1.3 +/- 0.1 mg microbial protein-N.L(-1).d(-1)). The sludge presented good settling properties with sludge volume index values lower than 20 mL.g(-1) and an exopolymeric protein/carbohydrate ratio of 0.53 +/- 0.34. Kinetic results indicated that the nitrifying behavior of the sludge changed with the number of cycles. After 22 cycles, a decrease in the specific rate of NO3- -N production coupled with an increase in the NO2- -N accumulation were observed. These results showed that the activity of the nitrite oxidizing bacteria decreased at a longer operation time. Ammonia oxidizing bacteria were found to exhibit the best stability. After 4 months of operation, the specific rates of NH4+-N consumption and NO3- -N production were 1.72 NH4+-N per microbial protein-N per hour (g.g(-1).h(-1)) and 0.54 NO3- -N per microbial protein-N per hour (g.g(-1).h(-1)), respectively.     

First respiration estimates of cold-seep vesicomyid bivalves from in situ total oxygen uptake measurements

Vesicomyid bivalves are one of the most abundant symbiont-bearing species inhabiting deep-sea reducing ecosystems. Nevertheless, except for the hydrothermal vent clam Calyptogena magnifica, their metabolic rates have not been documented, and only assessed with ex situ experiments. In this study, gathering benthic chamber measurements and biomass estimation, we give the first in situ assessment of the respiration rate of these bivalves. The giant pockmark Regab, located at 3160m depth along the Congo-Angola margin, is a cold-seep site characterised by dense assemblages of two species of vesicomyids: Christineconcha regab and Laubiericoncha chuni with high dominance of C. regab. Two sites with dense aggregates of vesicomyids were selected to measure total oxygen uptake (TOU), and methane fluxes using IFREMER's benthic chamber CALMAR deployed by the ROV Quest 4000 (MARUM). Photographs were taken and bivalves were sampled using blade corers to estimate density and biomass. Total oxygen uptake was higher at Site 2 compared to Site 1 (respectively 492 mmol.m(-2).d(-1) and 332 mmol.m(-2).d(-1)). However, given vesicomyid densities and biomass, mean oxygen consumption rates were similar at both sites (1.9 to 2.5 μmol.g total dry mass(-1).h(-1) at the Site 1 and 1.8 to 2.3 μmol.g total dry mass(-1).h(-1) at Site 2). These respiration rates are higher than published ex situ estimates for cold-seep or hydrothermal vent bivalves. Although methane fluxes at the base of sulphide production were clearly higher at Site 2 (14.6 mmol.m(-2).d(-1)) than at Site 1 (0.3 mmol.m(-2).d(-1)), they do not seem to influence the respiration rates of these bivalves associated to sulphide-oxidizing symbionts.     

大气O_3浓度升高对麦季土壤和植株氮磷钾的影响

以江都稻/麦轮作系统O3-FACE(ozone-free air concentration enrichment)为试验平台,研究了高浓度O3(比周围大气高50%)对麦季土壤和植株N、P、K含量的影响。结果表明:在小麦整个生长期,高浓度O3处理下,土壤NH4+-N、NO3--N和速效K含量分别降低了5.7%、3.6%和3.0%,土壤速效P含量提高了26.3%(P<0.05)。经高浓度O3处理后,小麦植株在拔节期体内K含量增加了28.4%(P<0.01);成熟期小麦植株各器官内N含量均降低,麦粒中P和K含量分别增加了6.5%和4.2%;指出大气O3浓度升高在整个小麦生长期内会促进小麦植株对N、K的吸收,同时提高小麦籽粒中K、P的含量,但降低了成熟期小麦植株N含量。     

低氧对高原鼠兔和大鼠血液NO 与ET-1的影响

将Wistar大鼠暴露于3 780 m低氧环境,分别于24 h、2 wk及3 wk后采用酶联免疫法和硝酸还原酶法测定血液中的ET~(-1)和NO的含量,计算NO/ET~(-1)值,并与高原鼠兔比较,探讨低氧条件下大鼠与高原鼠兔血液中NO与ET~(-1)含量的变化趋势。结果表明,低氧24 h后,大鼠血液中NO和ET~(-1)的含量显著高于同海拔的高原鼠兔(P<0·01),而NO/ET~(-1)值无显著差异(P>0·05)。随着大鼠在高海拔停留时间的延长,血液中NO含量呈减少趋势,而ET~(-1)则有上升趋势,二者呈显著的负相关(r2=0·2416,P<0·01)。高原鼠兔NO/ET~(-1)值约为大鼠低氧2 wk和3 wk的2倍(P<0·01)。说明不同低氧暴露时间,高原鼠兔和大鼠的NO、ET~(-1)及NO/ET~(-1)值有显著差异,提示NO/ET~(-1)值可以作为有机体是否适应高原低氧环境的一个指标。     

Biodegradation of monohalogenated alkanes by soil NH(3)-oxidizing bacteria

Although cooxidative biodegradation of monohalogenated hydrocarbons has been well studied in the model NH₃-oxidizing bacterium, Nitrosomonas europaea, virtually no information exists about cooxidation of these compounds by native populations of NH₃-oxidizing bacteria. To address this subject, nitrifying activity was stimulated to 125–400 nmol NO₃ ^– produced g^–1 soil h^–1 by first incubating a Ca(OH)₂-amended, silt loam soil (pH 7.0±0.2) at field capacity (270 g H₂O kg^–1 soil) with 10 μmol NH₄ ⁺ g^–1 soil for 14 days, followed by another 10 days of incubation in a shaken slurry (2:1 water:soil, v/w) with periodic pH adjustment and maintenance of 10 mM NH₄ ⁺. These slurries actively degraded both methyl bromide (MeBr) and ethyl chloride (EtCl) at maximum rates of 20–30 nmol ml^–1 h^–1 that could be sustained for approximately 12 h. Although the MeBr degradation rates were linear for the first 10–12 h of incubation, they could not be sustained regardless of NH₄ ⁺ level and declined to zero over 20 h of incubation. The transformation capacity of the slurry enrichments (~1 μmol MeBr ml^–1 soil slurry) was similar to the value measured previously in cell suspensions of N. europaea with similar NH₃-oxidizing activity. Several MeBr-degrading characteristics of the nitrifying enrichments were found to be similar to those documented in the literature for MeBr-degrading methanotrophs and facultatively methylotrophic bacteria. Electronic Publication