Control of carbon and ammonium ratio for simultaneous nitrification and denitrification in a sequencing batch bioreactor

This study shows how the carbon and nitrogen (C/N) ratio controls the simultaneous occurrence of nitrification and denitrification in a sequencing batch reactor (SBR). Data demonstrated that a low C/N ratio resulted in a rapid carbon deficit, causing an unbalanced simultaneous nitrification–denitrification (SND) process in SBR. When the initial COD/NH₄⁺-N ratio was adjusted to 11.1, the SND-based SBR achieved complete removal of NH₄-N and COD without leaving any NO₂⁻-N in the effluent. The nitrogen removal efficiency decreases gradually with increasing ammonium-loading rate to the SND–SBR system. Altogether, data showed that appropriate controls of carbon and nitrogen input are required to achieve an efficient SND–SBR. An established SND technology can save operation time and energy, and might replace the traditional two-stage biological nitrification and denitrification process.     

Continuous citric acid fermentation by <Emphasis Type="Italic">Candida oleophila</Emphasis> under nitrogen limitation at constant C/N ratio

Summary The central aspect of this work was to investigate the influence of nitrogen feed rate at constant C/N ratio on continuous citric acid fermentation by Candida oleophila ATCC 20177. Medium ammonia nitrogen and glucose concentrations influenced growth and production. Space-time yield (STY) meaning volumetric productivity, biomass specific productivity (BSP), product concentration, product selectivity and citrate/isocitrate ratio increased with increasing residence time (RT). BSP increased in an exponential mode lowering nitrogen feed rates. Highest BSP for citric acid of 0.13 g/(g h) was achieved at lowest NH₄Cl concentration of 1.5 g/l and highest STY (1.2 g/l h) with 3 g NH₄Cl/l at a RT of 25 h. Citric acid 74.2 g/l were produced at 58 h RT and 6 g NH₄Cl/l. Glucose uptake rate seems to be strictly controlled by growth rate of the yeast cells. Optimum nitrogen concentration and adapted C/N ratio are essential for successful continuous citric acid fermentation. The biomass-specific nitrogen feed rate is the most important factor influencing continuous citric acid production by yeasts. Numerous chemostat experiments showed the feasibility of continuous citrate production by yeasts.     

PHOTOSYNTHETIC RESPONSE OF LAKE PLANKTON TO COMBINED NITROGEN ENRICHMENT1

The complex interplay between photosynthesis and the uptake of nitrogen was investigated in samples from five lakes of different size and trophic state. When enriched with ¹⁵NH₄⁺, the photosynthetic rate was often reduced for 4–5 h in samples believed to be nitrogen deficient. This implies that energy was reallocated from photosynthesis to the uptake and assimilation of N. Stimulation in C uptake at low levels of NH₄⁺ enrichment was followed by a progressive decline with further NH₄⁺ enrichment. On other occasions when ambient NH₄⁺ was undetectable, nutrient regeneration by zooplankton supplied a significant fraction of the required nitrogen. At these times and when the plankton had sufficient available N, there usually was no change in photosynthetic rate with either NH₄⁺ or NO₃^?enrichment. Typically, little NO₃^? was taken up and no photosynthetic response was observed. On two occasions, however, the uptake of NO₃^? was significant due to high NO₃^? and low NH₄⁺ levels early in the season. At one of these times there was a reduction in photosynthesis with NO₃^? enrichment. A further complication was observed when photosynthesis decreased with NH₄⁺ enrichment but increased with NO₃^? enrichment despite negligible NO₃^? uptake. These observations illustrate that the complex metabolism of these two nitrogen sources is not fully understood. At optimum light intensity, C:N uptake ratios, even under NH₄⁺ enrichment, are only sufficient to maintain the cellular C:N ratio unless much of the fixed C is respired or excreted. Three observations suggest that photosynthesis and N uptake are not coupled, (i) Photoinhibition of C uptake, but not N uptake was observed when low light adapted populations are exposed to high light conditions, (ii) The light intensity for maximum N uptake was slightly less than that for carbon. (iii) Dark N uptake was always near 50% of the maximum rate in the light whereas the C uptake was near 2% of P_opt. Certainly, there is an interconnection because dark C uptake was enhanced by NH₄⁺ enrichment.     

Simultaneous nitrification and denitrification with different mixed nitrogen loads by a hypothermia aerobic bacterium

Microorganism with simultaneous nitrification and denitrification ability plays a significant role in nitrogen removal process, especially in the eutrophic waters with excessive nitrogen loads. The nitrogen removal capacity of microorganism may suffer from low temperature or nitrite nitrogen source. In this study, a hypothermia aerobic nitrite-denitrifying bacterium, Pseudomonas tolaasii strain Y-11, was selected to determine the simultaneous nitrification and denitrification ability with mixed nitrogen source at 15 °C. The sole nitrogen removal efficiencies of strain Y-11 in simulated wastewater were obtained. After 24 h of incubation at 15 °C, the ammonium nitrogen fell below the detection limit from an initial value of 10.99 mg/L. Approximately 88.0 ± 0.33% of nitrate nitrogen was removed with the initial concentration of 11.78 mg/L and the nitrite nitrogen was not detected with the initial concentration of 10.75 mg/L after 48 h of incubation at 15 °C. Additionally, the simultaneous nitrification and denitrification nitrogen removal ability of P. tolaasii strain Y-11 was evaluated using low concentration of mixed NH₄⁺-N and NO₃^?–N/NO₂^?–N (about 5 mg/L-N each) and high concentration of mixed NH₄⁺–N and NO₃^?–N/NO₂^?–N (about 100 mg/L-N each). There was no nitrite nitrogen accumulation at the time of evaluation. The results demonstrated that P. tolaasii strain Y-11 had higher simultaneous nitrification and denitrification capacity with low concentration of mixed inorganic nitrogen sources and may be applied in low temperature wastewater treatment.     

Effects of ammonium and nitrate nutrition or take-all disease of wheat in pots

Plant debris, naturaiiy infested with the take-all fungus (Ophiobolus graminis), was washed from soil and added to a leached sandy loam, deficient in nitrate nitrogen (NO₃-N) and magnesium. Nutrient solutions containing potassium and phosphorus, with and without magnesium, were added to the amended soil unsupplemented, or with either NO₃-N, ammonium nitrogen (NH₄+-N), or both. Nitrification of NH₄+-N was inhibited by 2–chloro-6–(trichloromethy1)-pyridine (N-Serve). After 38 days at 19°C, fewer plants had take-all with N (75 or 100 mg/kg soil) than without and root systems were most discoloured and had most diseased axes when nutrients were not added. Plants given NH₄+-N developed less take-all when magnesium was present. A comparison of forms of N in the presence of added magnesium showed that take-all was least with a mixture of both forms of N, intermediate with NO₃-N alone and worst with NH₄+-N alone. The most extensive lesions on individual root axes occurred on plants given NH₄+-N. It is suggested that take-all will be least when the amounts and ratio of NH₄+-N and NO₃-N are optimum for the growth of the host.     

The Influence of Nitrogen Nutrition on the Carbohydrate and Nitrogen Status of Emergent Macrophyte Acorus calamus L.

Carbon and nitrogen balance in Acorus calamus, a wetland species colonising littoral zones with a high trophic status, was studied under experimental conditions using water or sand culture with a defined composition of the nutrient solution. Influence of graded level of N (1.86, 7.5 and 18.6 mM) and/or forms of N (NH₄⁺ versus NO ₃^–) on the content of non-structural carbohydrates, free amino acids, total C, and total N was studied in Acorus rhizomes and roots to find possible connection with a reduced growth of Acorus plants under high N and NH₄⁺–N nutrition described in our previous study [Vojtíšková et al., 2004. Hydrobiologia 518: 9–22]. High N availability and pure NH₄⁺–N nutrition affected the C/N balance of rhizome and root systems of Acorus in a similar way. NH₄⁺–N was the only form of N elevated under the high N treatment. The major proportion of the total non-structural carbohydrates (TNC) was starch (91–93% and 51–64% in rhizomes and roots, respectively). The content of starch was significantly and and negatively affected by high N availability (P = 0.001), as well as by NH₄⁺–N nutrition (P=0.001). Amounts of simple soluble carbohydrates (sucrose, glucose, and fructose) were negligible in comparison to starch in rhizomes and branched roots (up to 5% of TNC), while roots without developed lateral roots (unbranched) contained up to 33% of TNC in the form of simple soluble sugars. Moreover, high hexoses/sucrose ratio, low starch/soluble sugars ratio, high content of N, and low C/N ratio support the notion that unbranched roots are metabolically active young roots with tissue differentiation in progress. A high content of free amino acids, typically with dominance of N-rich amino acids (Arg-46%, Gln-8%, Asn-7%), was found simultaneously with a low carbohydrate content under high N supply, which indicates that NH₄⁺ received is effectively incorporated into the organic form by this species. Since the decrease in carbohydrate content was not accompanied by luxurious growth, other possible carbon consuming processes were discussed in relation to NH₄⁺ nutrition. More dramatic changes in total N than C were found under high N availability resulting a shift in C/N ratio in favour of N. Although the shift towards N metabolism was obvious, no serious carbohydrate depletion occurred, which could explain the reduced growth of Acorus plants under high N and sole NH₄⁺–N nutrition described previously.     

Changes in the C/N balance caused by increasing external ammonium concentrations are driven by carbon and energy availabilities during ammonium nutrition in pea plants: the key roles of asparagine synthetase and anaplerotic enzymes

An understanding of the mechanisms underlying ammonium (NH₄⁺) toxicity in plants requires prior knowledge of the metabolic uses for nitrogen (N) and carbon (C). We have recently shown that pea plants grown at high NH₄⁺ concentrations suffer an energy deficiency associated with a disruption of ionic homeostasis. Furthermore, these plants are unable to adequately regulate internal NH₄⁺ levels and the cell‐charge balance associated with cation uptake. Herein we show a role for an extra‐C application in the regulation of C–N metabolism in NH₄⁺‐fed plants. Thus, pea plants (Pisum sativum) were grown at a range of NH₄⁺ concentrations as sole N source, and two light intensities were applied to vary the C supply to the plants. Control plants grown at high NH₄⁺ concentration triggered a toxicity response with the characteristic pattern of C‐starvation conditions. This toxicity response resulted in the redistribution of N from amino acids, mostly asparagine, and lower C/N ratios. The C/N imbalance at high NH₄⁺ concentration under control conditions induced a strong activation of root C metabolism and the upregulation of anaplerotic enzymes to provide C intermediates for the tricarboxylic acid cycle. A high light intensity partially reverted these C‐starvation symptoms by providing higher C availability to the plants. The extra‐C contributed to a lower C4/C5 amino acid ratio while maintaining the relative contents of some minor amino acids involved in key pathways regulating the C/N status of the plants unchanged. C availability can therefore be considered to be a determinant factor in the tolerance/sensitivity mechanisms to NH₄⁺ nutrition in plants.     

Manure composition affects net transformation of nitrogen from dairy manures

The plant available nitrogen (PAN) content of dairy manure is commonly calculated using concentration and availability coefficients for organic nitrogen (N) and ammonium N (NH₄), but the carbon (C) fraction of the manure also influences the availability of N over time. We evaluated the interactive effect of manure C and N from nine dairy manures during a 176 days aerobic incubation. All of the manures had appreciable NH₄ content, and varied widely in fibrous C. The incubation was conducted using sandy loam (coarse-loamy, mixed, frigid, Typic Haplorthod) and silt loam (fine, illitic, non-acid, frigid, Aeric Epiaquepts) soils at 25°C and 60% water-filled pore space. There were clear differences in nitrate (NO₃) accumulation over time, including manures that resulted in net nitrification and net immobilization. For both soils, the rate of nitrification at 7 and 56 days after application, and the amount of NO₃ accumulated at the end of the incubation (176 days) were strongly correlated (r = –0.88) with C: NH₄ and also to the ratio of neutral detergent fiber (NDF):NH₄ (r = –0.90). The addition of manure C also resulted in significant net immobilization, compared to addition of mineral N fertilizer alone. These studies demonstrate that increased understanding of manure C and N interactions may lead to improved prediction of manure PAN.     

Ammonium-nitrogen metabolism and nitrogen fixation in azotobacter vinelandii

The probable effect of increasing levels of ammonium nitrogen on the growth, efficiency of nitrogen fixation, and main cellular constituents of Azotobacter vinelandii was studied under shaking and static culture conditions. The presence of NH₄⁺-N up to 50 mgl^-1 level has no harmful effect on the multiplication as well as the yield efficiency ratio of the tested organism. A. vinelandii was able to fix dinitrogen in the presence of NH₄⁺-N when both nitrogen sources were available in the culturing medium. The efficiency of nitrogen fixation was affected by the initial presence of NH₄⁺-N in the medium, it was quite low at the highest level. The crude protein efficiency ratio was correlated inversely with the initial NH₄⁺-N concentration, whereas the total carbohydrate efficiency ratio as well as the total lipid efficiency ratio were positively correlated with the NH₄⁺-N concentration. The presence of NH₄⁺-N in the culturing medium has no essential influence on the qualitative composition of the amino acids in the Azotobacter cells.     

Asparagine formation in soybean nodules

¹⁵NH₄⁺ and [¹⁵N](amide)-glutamine externally supplied to detached nodules from soybean plants (cv. Tamanishiki) were incorporated within nodule tissues by vacuum infiltration and metabolized to various nitrogen compounds during 60 minutes of incubation time. In the case of ¹⁵NH₄⁺ - feeding, the ¹⁵N abundance ratio was highest in the amide nitrogen of glutamine, followed by glutamate and the amide nitrogen of asparagine. In ¹⁵N content (micrograms excess ¹⁵N), the amide nitrogen of asparagine was most highly enriched after 60 minutes. ¹⁵NH₄⁺ was also appreciably assimilated into alanine.     

Biological role of mycorrhizal fungi on the assimilation and transportation of carbon and nitrogen to Anacamptis palustris and Anacamptis laxiflor

Fungal is a physiological trail and its understanding in the assimilation with the transfer of carbon (C) cum nitrogen (N) or (C/N) to orchid-seedlings have not been determined. Labelled stable isotopes ¹³C and ¹⁵N were used to plan the flow of C and N between orchid plants and mycorrhizal connotations in-terms of bulk transfer for C/N. This study attends to comprehend the mechanism, supporting mycorrhizal fungi which influences on orchid-seedling growth. Determined integration and transfer of C/N from amino acids (AA), ammonium nitrate (NH₄NO₃) and sugar for orchid-plant may lead to understand these mechanisms. This current study tries to estimate the importance of organic compounds as a source for C/N over the inorganic-NH₄NO₃. Generally, after begging of germination and when it is found to be associated to the nutrient resource, organic compound enhance the biomass accumulation of two orchid species. AA significantly increase the mass of ¹³C assimilated by two species. With amino acids the concentration of ¹³C in two species was greater than with NH₄NO₃ and sugar. At another phase, amount of ¹⁵N content shoots was a higher value in Anacamptis laxiflora shoots assimilated substantially additional of ¹⁵N with NH₄NO₃ plus sugar compared with ammonium nitrate only. This study showed that two terrestrial orchids species are reliant on organic compounds as a source of carbon and nitrogen more than inorganic compounds.     

A closeup study of early beech litter decomposition: potential drivers and microbial interactions on a changing substrate

Aims

Litter decomposition and subsequent nutrient release play a major role in forest carbon and nutrient cycling. To elucidate how soluble or bulk nutrient ratios affect the decomposition process of beech (Fagus sylvatica L.) litter, we conducted a microcosm experiment over an 8 week period. Specifically, we investigated leaf-litter from four Austrian forested sites, which varied in elemental composition (C:N:P ratio). Our aim was to gain a mechanistic understanding of early decomposition processes and to determine microbial community changes.

Methods

We measured initial litter chemistry, microbial activity in terms of respiration (CO₂), litter mass loss, microbial biomass C and N (C_mic and N_mic), non purgeable organic carbon (NPOC), total dissolved nitrogen (TDN), NH₄ ⁺, NO₃ ^- and microbial community composition (phospholipid fatty acids – PLFAs).

Results

At the beginning of the experiment microbial biomass increased and pools of inorganic nitrogen (N) decreased, followed by an increase in fungal PLFAs. Sites higher in NPOC:TDN (C:N of non purgeable organic C and total dissolved N), K and Mn showed higher respiration.

Conclusions

The C:N ratio of the dissolved pool, rather than the quantity of N, was the major driver of decomposition rates. We saw dynamic changes in the microbial community from the beginning through the termination of the experiment.     

Nitrogen dynamics of storm runoff in the riparian zone of a forested watershed

The influence of storm runoff processes on stream nitrogen dynamics was investigated in a headwater riparian swamp on the Oak Ridges moraine in southern Ontario. Hydrologic data were combined with analysis of an isotopic tracer (¹⁸0) and nitrogen (NH ₄ ⁺ , NO ₃ ^– ) concentrations in saturation overland flow and stream discharge. Storm runoff was separated into its event and pre-event components using¹⁸O in order to examine the effect of water source on nitrogen chemistry. Laboratory experiments were also used to study nitrogen transformation associated with storm runoff-surface substrate interactions in the swamp. In most storms N0₃-N and NH₄-N concentrations in the initial 3–4 mm throughfall increment were 10–20x and 20–100x higher respectively than stream base flow concentrations. Maximum stream N0₃-N concentrations were < 2x to 6x higher than base flow concentrations and preceded or coincided with peak stream discharge. Storm-to-storm variations in stream N0₃-N behaviour also occurred during the hydrograph recession phase. NH₄-N concentrations attained an initial peak on the rising hydrograph limb, or at peak stream discharge. A second NH₄-N increase occurred during the late recession phase 3–5 h after maximum stream discharge. Inorganic-N concentrations in surface runoff were similar to peak streamflow.The close agreement between observed N0₃-N concentrations and values predicted from a chemical mixing model indicate that stream N0₃-N variations were controlled mainly by the mixture of throughfall and groundwater in surface stormflow from the swamp. Laboratory experiments also indicated that N0₃-N in surface runoff behaved conservatively when mixed with swamp substrates. With the exception of the late hydrograph recession phase, observed stream NH₄-N concentrations were much lower than concentrations predicted by the chemical mixing model. The rapid loss of NH₄-N from mixtures of surface stormflow and swamp substrates in laboratory experiments and the absence of uptake in sterilized substrates indicated that NH₄-N retention in surface storm runoff was due to biotic processes.     

Nitrogen Assimilation in Mycorrhizas : Ammonium Assimilation in the N-Starved Ectomycorrhizal Fungus Cenococcum graniforme

Ammonium assimilation was followed in N-starved mycelia from the ectomycorrhizal Ascomycete Cenococcum graniforme. The evaluation of free amino acid pool levels after the addition of 5 millimolar NH₄⁺ indicated that the absorbed ammonium was assimilated rapidly. Post-feeding nitrogen content of amino acids was very different from the initial values. After 8 hours of NH₄⁺ feeding, glutamine accounted for the largest percentage of free amino acid nitrogen (43%). The addition of 5 millimolar methionine sulfoximine (MSX) to NH₄⁺-fed mycelia caused an inhibition of glutamine accumulation with a corresponding increase in glutamate and alanine levels.

Using ¹⁵N as a tracer, it was found that the greatest initial labeling was into glutamine and glutamate followed by aspartate, alanine, and ornithine. On inhibiting glutamine synthetase using MSX, ¹⁵N enrichment of glutamate, alanine, aspartate, and ornithine continued although labeling of glutamine was quite low. Moreover, the incorporation of ¹⁵N label in insoluble nitrogenous compounds was lower in the presence of MSX. From the composition of free amino acid pools, the ¹⁵N labeling pattern and effects of MSX, NH₄⁺ assimilation in C. graniforme mycelia appears to proceed via glutamate dehydrogenase pathway. This study also demonstrates that glutamine synthesis is an important reaction of ammonia utilization.

     

氨基酸添加对亚热带森林红壤氮素转化的影响

为探究氨基酸氮形态对亚热带土壤氮素含量及转化的影响,选择建瓯市万木林保护区的山地红壤为对象,采用室内培养实验法,通过设计60%和90%WHC两种土壤含水量并添加不同性质氨基酸,测定了土壤中铵态氮、硝态氮、可溶性有机氮的含量和氧化亚氮的释放量,分析了可溶性有机碳、土壤p H值的大小变化及其与氮素的相互关系。结果表明:与对照处理相比,氨基酸添加显著增加了土壤NH_4~+-N含量并使土壤p H值升高,且在一定程度上解除了高含水量(90%WHC)对NH_4~+-N产生的抑制,其中甲硫氨基酸的效果最为明显。酸性、碱性、中性氨基酸对土壤NO_3~--N含量和N_2O释放影响不显著,但甲硫氨基酸可显著抑制土壤硝化从而导致NH_4~+-N的积累,并在培养前期抑制土壤N_2O产生而在培养后期促进N_2O释放,总体上促进N_2O释放。60%WHC的氨基酸添加处理较90%WHC条件下降低土壤可溶性有机氮的幅度更大。氨基酸对土壤氮素转化的影响与带电性关系较小,而可能与其分解产物密切相关。可见,不同性质氨基酸处理对森林土壤氮素含量及转化存在不同程度的影响,且甲硫氨基酸对土壤氮素转化的影响机理值得深入研究。     

Effects of ammonium on the activity and community of methanotrophs in landfill biocover soils

The influence of NH₄⁺ on microbial CH₄ oxidation is still poorly understood in landfill cover soils. In this study, effects of NH₄⁺ addition on the activity and community structure of methanotrophs were investigated in waste biocover soil (WBS) treated by a series of NH₄⁺-N contents (0, 100, 300, 600 and 1200 mg kg⁻¹). The results showed that the addition of NH₄⁺-N ranging from 100 to 300 mg kg⁻¹ could stimulate CH₄ oxidation in the WBS samples at the first stage of activity, while the addition of an NH₄⁺-N content of 600 mg kg⁻¹ had an inhibitory effect on CH₄ oxidation in the first 4 days. The decrease of CH₄ oxidation rate observed in the last stage of activity could be caused by nitrogen limitation and/or exopolymeric substance accumulation. Type I methanotrophs Methylocaldum and Methylobacter, and type II methanotrophs (Methylocystis and Methylosinus) were abundant in the WBS samples. Of these, Methylocaldum was the main methanotroph in the original WBS. With incubation, a higher abundance of Methylobacter was observed in the treatments with NH₄⁺-N contents greater than 300 mg kg⁻¹, which suggested that NH₄⁺-N addition might lead to the dominance of Methylobacter in the WBS samples. Compared to type I methanotrophs, the abundance of type II methanotrophs Methylocystis and/or Methylosinus was lower in the original WBS sample. An increase in the abundance of Methylocystis and/or Methylosinus occurred in the last stage of activity, and was likely due to a nitrogen limitation condition. Redundancy analysis showed that NH₄⁺-N and the C/N ratio had a significant influence on the methanotrophic community in the WBS sample.     

Nitrogen accumulation and distribution in Danthonia richardsonii swards in response to CO2 and nitrogen supply over four years of growth

Nitrogen‐stressed microcosms of the C3 grass Danthonia richardsonii gained nitrogen from the environment when grown under ambient or enriched (359, ‘amb’ or 719 μL L^{? 1}‘enr’, respectively) atmospheric CO₂ concentrations over a 4‐y period. This gain was apparent at all rates of supplied mineral N (2.2, 6.7 or 19.8 g N m^{? 2} y^{? 1}– low‐N, mid‐N or high‐N), although it was small at high‐N. Small losses of N occurred from the microcosm as leachate, while gaseous losses of N were estimated to be between 10% and 25% of applied mineral N. Losses of applied mineral N were slightly lower under CO₂ enrichment only at the highest rate of mineral N supply. Levels of ¹⁵N natural abundance in green leaf (δ¹⁵Ν) of ? 2‰ (amb low‐N) and of below ? 4‰ (enr low‐ & mid‐N) suggest that absorption of atmospheric NH₃ may have been a source of some of the extra N in the low and mid‐N treatments. Biological N₂ fixation, of up to 2 g m^{? 2} y^{? 1} was hypothesized to form the remainder of the environmental N source. Microcosm C:N ratio was higher under CO₂ enrichment. Nitrogen productivity of microcosm carbon gain (g C accumulated g^{? 1} leaf N day^{? 1}) was increased (up to 100%) by CO₂ enrichment at all rates of mineral N supply. Green leaf %N was reduced by CO₂ enrichment, and there was less nitrogen in the green leaf pool under CO₂ enrichment. Less, or the same amount of nitrogen was present in senesced leaf, surface litter and root under CO₂ enrichment while more nitrogen was present in the soil in organic forms, and as NH₄ + at the highest rate of mineral N supply.     

氮素形态及配比对5个种源菘蓝的生物碱类成分和多糖的影响

以5份不同种源的菘蓝为材料,采用田间小区试验,设置不施氮(CK)、硝态氮(NO3--N)、铵态氮(NH4+-N)、NH4+-N/NO3--N=75/25、NH4+-N/NO3--N=50/50、NH4+-N/NO3--N=25/75和酰胺态氮等7个处理,分析比较了不同种源植株的靛蓝、靛玉红和总生物碱含量、(R,S)-告依春及多糖含量等指标的差异,为菘蓝栽培生产中氮素的高效利用提供理论参考。结果表明:氮素处理有利于提高山西运城菘蓝和陕西商洛菘蓝叶内靛蓝含量,以及安徽亳州菘蓝和陕西商洛菘蓝叶内的总生物碱含量;NH4+-N/NO3--N=50/50处理对山西运城菘蓝,以及酰胺态氮处理对山西运城菘蓝和陕西商洛菘蓝叶内生物碱类成分的积累均有促进作用;与对照相比,氮素处理亦能有效地提高甘肃张掖菘蓝和陕西商洛菘蓝根内的(R,S)-告依春及安徽亳州菘蓝根内的多糖含量;安徽阜阳菘蓝(R,S)-告依春含量在任一氮处理下均远远高于其他种质菘蓝。研究表明,不同种源菘蓝对氮素处理的响应存在较大的差异,建议生产中综合考虑菘蓝的来源和需肥规律,采用经济有效的施氮组合,以提高其活性成分含量。     

Modeling the Dynamic Regulation of Nitrogen Fixation in the Cyanobacterium Trichodesmium sp.

A physiological, unbalanced model is presented that explicitly describes growth of the marine cyanobacterium Trichodesmium sp. at the expense of N₂ (diazotrophy). The model involves the dynamics of intracellular reserves of carbon and nitrogen and allows the uncoupling of the metabolism of these elements. The results show the transient dynamics of N₂ fixation when combined nitrogen (NO₃⁻, NH₄⁺) is available and the increased rate of N₂ fixation when combined nitrogen is insufficient to cover the demand. The daily N₂ fixation pattern that emerges from the model agrees with measurements of rates of nitrogenase activity in laboratory cultures of Trichodesmium sp. Model simulations explored the influence of irradiance levels and the length of the light period on fixation activity and cellular carbon and nitrogen stoichiometry. Changes in the cellular C/N ratio resulted from allocations of carbon to different cell compartments as demanded by the growth of the organism. The model shows that carbon availability is a simple and efficient mechanism to regulate the balance of carbon and nitrogen fixed (C/N ratio) in filaments of cells. The lowest C/N ratios were obtained when the light regime closely matched nitrogenase dynamics.     

Temperature sensitivity of soil carbon and nitrogen mineralization: impacts of nitrogen species and land use type

Background and aims

Climate warming, nitrogen (N) deposition and land use change are some of the drivers affecting ecosystem processes such as soil carbon (C) and N dynamics, yet the interactive effects of those drivers on ecosystem processes are poorly understood. This study aimed to understand mechanisms of interactive effects of temperature, form of N deposition and land use type on soil C and N mineralization.

Methods

We studied, in a laboratory incubation experiment, the effects of temperature (15 vs. 25 °C) and species of N deposition (NH₄ ⁺-N vs. NO₃ ^?-N) on soil CO₂ efflux, dissolved organic C (DOC) and N (DON), NH₄ ⁺-N, and NO₃ ^?-N concentrations using intact soil columns collected from adjacent forest and grassland ecosystems in north-central Alberta.

Results

Temperature and land use type interacted to affect soil CO₂ efflux, concentrations of DON, NH₄ ⁺-N and NO₃ ^?-N in most measurement times, with the higher incubation temperature resulted in the higher CO₂ efflux and NH₄ ⁺-N concentrations in forest soils and higher DON and NO₃ ^?-N concentrations in grassland soils. Temperature and land use type affected the cumulative soil CO₂ efflux, and DOC, DON, NH₄ ⁺-N and NO₃ ^?-N concentrations. The form of N added or its interaction with the other two factors did not affect any of the C and N cycling parameters.

Conclusions

Temperature and land use type were dominant factors affecting soil C loss, with the soil C in grassland soils more stable and resistant to temperature changes. The lack of short-term effects of the deposition of different N species on soil C and N mineralization suggest that maybe there was a threshold for the N effect to kick in and long-term experiments should be conducted to further elucidate the species of N deposition effects on soil C and N cycling in the studied systems.