Aquatic microfauna alter larval food resources and affect development and biomass of West Nile and Saint Louis encephalitis vector Culex nigripalpus (Diptera: Culicidae)

Ciliate protists and rotifers are ubiquitous in aquatic habitats and can comprise a significant portion of the microbial food resources available to larval mosquitoes, often showing substantial declines in abundance in the presence of mosquito larvae. This top‐down regulation of protists is reported to be strong for mosquitoes inhabiting small aquatic containers such as pitcher plants or tree holes, but the nature of these interactions with larval mosquitoes developing in other aquatic habitats is poorly understood. We examined the effects of these two microbial groups on lower trophic level microbial food resources, such as bacteria, small flagellates, and organic particles, in the water column, and on Culex larval development and adult production. In three independent laboratory experiments using two microeukaryote species (one ciliate protist and one rotifer) acquired from field larval mosquito habitats and cultured in the laboratory, we determined the effects of Culex nigripalpus larval grazing on water column microbial dynamics, while simultaneously monitoring larval growth and development. The results revealed previously unknown interactions that were different from the top‐down regulation of microbial groups by mosquito larvae in other systems. Both ciliates and rotifers, singly or in combination, altered other microbial populations and inhibited mosquito growth. It is likely that these microeukaryotes, instead of serving as food resources, competed with early instar mosquito larvae for microbes such as small flagellates and bacteria in a density‐dependent manner. These findings help our understanding of the basic larval biology of Culex mosquitoes, variation in mosquito production among various larval habitats, and may have implications for existing vector control strategies and for developing novel microbial‐based control methods.     

Reduced major minerals and increased minor nutrients improve micropropagation in three apple cultivars

Mineral nutrient medium requirements for propagation of in vitro shoots of apple (Malus domestica Borkh) ‘Golden Delicious’, ‘Maksat’, and ‘Voskhod’ were studied using response surface methodology (RSM). The mineral nutritional factors evaluated were based on Murashige and Skoog (MS) mineral nutrients (NH₄NO₃, KNO₃, CaCl₂, KH₂PO₄, MgSO₄, and minor nutrients), with concentrations ranging from 0.5 to 3.0× the MS concentrations. Nine plant growth qualities were evaluated. The most significant factors were NH₄NO₃ at 0.5 to 1.0× MS, and minor nutrients at 2.0× MS. Most of the other factors were optimal at 0.5×. The quality rating was highest when minor nutrients were 2.0× MS, and most other nutrients were standard concentrations or lower. Increased KH₂PO₄ and minor nutrients were the most significant for improved multiplication, and higher KNO₃ for shoot length. Optimized media were developed for each cultivar based on these models. The cultivars were grown on the three individual optimized media, a general medium based on the three optimizations, and MS. The optimized medium for each cultivar was significantly better for shoot quality and shoot length of each cultivar than MS, but the generalized medium of minors at 2.0× and NH₄NO₃, CaCl₂, and MgSO₄ at 0.5× MS, was significantly better for two of the three cultivars and not significantly different for the third. The next step to develop a final optimized medium will require the evaluation of the minor nutrients, determination of optimal concentrations of each, and screening a wide range of Malus germplasm on the finalized medium.

     

Growth and physiological characteristics of wasabi plantlets cultured by photoautotrophic micropropagation at different temperatures

Iranian seedless barberry is a very recalcitrant species in in vitro culture which does not show appropriate growth on standard culture media. Response surface methodology was employed to evaluate the effects of changing macronutrients concentrations on establishment and proliferation phases. KNO₃ and NH₄NO₃ macronutrients at 0.3 to 1.5?×?MS medium levels and CaCl₂, MgSO₄ and KH₂PO₄ macronutrients in a range of 0.5 to 1.5?×?MS medium concentrations were tested in a response surface design with 30 treatments. Many significant interactions were found among the macronutrients. High concentrations of KNO₃, NH₄NO₃ and CaCl₂ improved the growth rate in the establishment phase. The growth rate in media containing high KNO₃ and low CaCl₂ was high. Reduced concentrations of CaCl₂ and KNO₃ decreased hyperhydricity. The greatest hyperhydricity was induced when both NH₄NO₃ and CaCl₂ were used at 1.5?×?MS level. The number of hooked leaves decreased as KH₂PO₄ increased and MgSO₄ reduced. In the proliferation phase, there were many significant interactions among the macronutrients. Increased concentration of NH₄NO₃ and reduced concentration of KH₂PO₄ improved the growth rate. Proliferation rate increased in media containing high concentration of KNO₃ and low to moderate concentrations of NH₄NO₃. The greatest production of new tissues and organs was seen in media with high KNO₃ and moderate to high CaCl₂. High concentration of NH₄NO₃ and low concentration of KH₂PO₄ also increased production of new tissues and organs. No shoot apical meristem was seen when CaCl₂ level was high and KNO₃ level was low. Formation of shoot apical meristem required high KH₂PO₄ concentration and low CaCl₂ concentration. Finally, low concentration of KNO₃ and low to moderate concentrations of NH₄NO₃ increased phenol exudation.

     

Use of RSM and CHAID data mining algorithm for predicting mineral nutrition of hazelnut

Defining optimal mineral-salt concentrations for in vitro plant development is challenging, due to the many chemical interactions in growth media and genotype variability among plants. Statistical approaches that are easier to interpret are needed to make optimization processes practical. Response Surface Methodology (RSM) and the Chi-Squared Automatic Interaction Detection (CHAID) data mining algorithm were used to analyze the growth of shoots in a hazelnut tissue-culture medium optimization experiment. Driver and Kuniyuki Walnut medium (DKW) salts (NH₄NO₃, Ca(NO₃)₂·4H₂O, CaCl₂·2H₂O, MgSO₄·7H₂O, KH₂PO₄ and K₂SO₄) were varied from 0.5× to 3× DKW concentrations with 42 combinations in a IV-optimal design. Shoot quality, shoot length, multiplication and callus formation were evaluated and analyzed using the two methods. Both analyses indicated that NH₄NO₃ was a predominant nutrient factor. RSM projected that low NH₄NO₃ and high KH₂PO₄ concentrations were significant for quality, shoot length, multiplication and callus formation in some of the hazelnut genotypes. CHAID analysis indicated that NH₄NO₃ at ≤1.701× DKW and KH₂PO₄ at >2.012× DKW were the most critical factors for shoot quality. NH₄NO₃ at ≤0.5× DKW and Ca(NO₃)₂ at ≤1.725× DKW were essential for good multiplication. RSM results were genotype dependent while CHAID included genotype as a factor in the analysis, allowing development of a common medium rather than several genotype specific media. Overall, CHAID results were more specific and easier to interpret than RSM graphs. The optimal growth medium for Corylus avellana L. cultivars should include: 0.5× NH₄NO₃, 3× KH₂PO₄, 1.5× Ca(NO₃)₂.     

Nestedness patterns of container-dwelling mosquitoes: effects of larval habitat within variable terrestrial matrices

Distributions of mosquito larvae likely are a consequence of multiple factors, although two commonly studied factors (quality of the larval environment and the terrestrial matrix in which these habitats reside) have rarely and simultaneously been varied in the field to understand distributions of larvae. We monitored aquatic containers of two leaf detritus levels within a forest, prairie, and industrial habitat across five months to understand the temporal and spatial colonization of aquatic invertebrates in Northcentral Illinois, USA. Data were collected monthly on mosquito populations and the composition of other invertebrates colonizing containers. Overall, six species of mosquitoes colonized containers, with Culex restuans and Aedes triseriatus having the highest relative abundances. There were strong seasonal abundance patterns for these two mosquito species, with the dominant species changing over time in the forest habitat. The responses of other mosquito taxa were more variable, with abundances reflective of either the terrestrial matrix or larval habitat quality. High detritus containers supported the highest abundances of most species encountered, regardless of habitat. Non-mosquito taxa were less common numerically, but analyses suggested that some taxa, such as syrphid larvae, often co-occurred with mosquitoes. Nested subset analysis indicated communities were strongly nested, and that both habitat type and detritus level were important in explaining nested patterns of aquatic invertebrates. Our data show that both the larval habitat and the surrounding terrestrial matrix shape patterns of container mosquitoes, and that other container invertebrates vary in similar ways as mosquitoes. Handling editor: K. Martens     

九龙江河口区养虾塘沉积物-水界面营养盐交换通量特征

通过对九龙江河口区陆基养虾塘水样和沉积物样品采集分析及结合室内模拟实验,探讨了虾塘在不同养殖阶段沉积物-水界面营养盐通量时间变化特征及其主要影响因素。虾塘沉积物向上覆水体释放NO_x~--N(NO_2~--N和NO_3~--N)、NH_4~+-N和PO_4~(3-)-P能力均呈现随养殖时间推移而降低的特征。沉积物在养殖中期和后期分别呈现对上覆水体NO_x~--N和PO_4~(3-)-P的吸收现象,但总体表现为释放(平均通量分别为(1.87±1.15)、(1.58±0.52)mg m~(-2)h~(-1)和(1.22±0.62)mg m~(-2)h~(-1))。沉积物-水界面溶解无机氮交换以NH_4~+-N为主(沉积物平均释放通量为(46.18±13.82)mg m~(-2)h~(-1))。沉积物间隙水与上覆水间的营养盐浓度差(梯度)及温度对上述交换通量的时间动态特征具有重要调控作用。研究结果表明养殖初期或中期沉积物较高的无机氮(尤其是NO_2~--N和NH_4~+-N)释放是养殖塘水质恶化的一个极具潜力的污染内源,可能会对虾的健康生长产生负面效应,控制沉积物无机氮释放是养虾塘养殖初期和中期重要的日常管理活动之一。     

On trends in nutrient concentration in the northern Wadden Sea of Sylt

The mean values on hydrographical parameters in the Wadden Sea of Sylt taken weekly over a period of seven years (1975, 1976 and 1984 to 1988) were compared in order to detect trends in concentrations of nutrients or plankton. An increase in NO₂, NO₃, PO₄ and Si could be found in summer. NH₄ showed a negative trend. Corresponding with the rising nutrient-level, Chlorophyll-a and pH show a positive trend. Salinity decreased significantly. Changes in NH₄ and NO₂ were correlated with rainfall. Presented at the VI International Wadden Sea Symposium (Biologische Anstalt Helgoland, Wattenmeerstation Sylt, D-2282 List, FRG, 1–4 November 1988)     

Growth and Major Nutrient Concentrations in Brassica campestris Supplied with Different NH4^＋/NO3 Ratios

In the present study, we investigated whether growth and main nutrient ion concentrations of cabbage （Brassica campestris L.） could be increased when plants were subjected to different NH4^＋/NO3- ratios. Cabbage seedlings were grown in a greenhouse in nutrient solutions with five NH4^＋/NO3- ratios （1：0; 0.75：0.25; 0.5：0.5; 0.25：0.75; and 0：1）. The results showed that cabbage growth was reduced by 87% when the proportion of NH4^＋-N in the nutrient solution was more than 75% compared with a ratio NH4^＋/NO3- of 0.5：0.5 35 d after transplanting, suggesting a possible toxicity due to the accumulation of a large amount of free ammonia in the leaves. When the NH4＋/NO3- ratio was 0.5：0.5, fresh seedling weight, root length, and H2PO4- （P）, K^＋, Ca^2＋, and Mg^2＋ concentrations were all higher than those in plants grown under other NH4^＋/NO3- ratios. The nitrate concentration in the leaves was the lowest in plants grown at 0.5： 0.5 NH4^＋/NO3-. The present results indicate that an appropriate NH4^＋/NO3- ratio improves the absorption of other nutrients and maintains a suitable proportion of N assimilation and storage that should benefit plant growth and the quality of cabbage as a vegetable.     

Daily Patterns under the Life Cycle of a Maize Crop

Together with photosynthesis, transpiration and respiration, the daily uptake of NO₃^?, NH₄⁺, H₂PO₄^?, K⁺, Ca²⁺, Mg²⁺, SO₄^2?, the root respiration, root volume increase and root excretions have been studied by daily measurements during the growth period of whole maize plants (Zea mays L. cv. INRA F7 × F2) raised until complete maturity on nutrient solution. The uptake patterns show a maximum absorption of NO₃^?, K⁺ and Ca²⁺ during the vegetative growth phase. The absorption of these ions declines during maturation while that of H₂PO₄^? reaches a maximum. Root respiration and particularly the uptake of NO₃^? and K⁺ are well correlated with the rate of root growth. Root excretion is more notable in young plants than in the old. It represents less than 0.2% of the net assimilation of adult plants.     

Effects of macro elements and nitrogen source on adventitious root growth and ginsenoside production in ginseng (Panax ginseng C. A. Meyer)

We investigated the effects on ginseng adventitious root growth and ginsenoside production when macro-element concentrations and nitrogen source were manipulated in the culture media. Biomass growth was greatest in the medium supplemented with 0.5-strength NH₄PO₃, whereas ginsenoside accumulation was highest (9.90 mg g^-1 DW) in the absence of NH₄PO₃. At levels of 1.0-strength KNO₃, root growth was maximum, but a 2.0 strength of KNO₃ led to the greatest ginsenoside content (9.85 mg g^-l). High concentrations of MgSO₄ were most favorable for both root growth and ginsenoside accumulation (up to 8.89 mg g^-1 DW). Root growth and ginsenoside content also increased in proportion to the concentration of CaCI₂ in the medium, with the greatest accumulation of ginsenoside (8.91 mg g^-1 DW) occurring at a 2.0 strength. The NH₄/NO₃ ^-- ratio also influenced adventitious root growth and ginsenoside production; both parameters were greater when the NO₃ ^- concentration was higher than that of NH₄ ⁺. Maximum root growth was achieved at an NH₄ ⁺/NO₃ ^- ratio of 7.19/18.50, while ginsenoside production was greatest (83.37 mg L^-1) when NO₃ ^- was used as the sole N source.     

Nitrogen metabolism of Spirodela oligorrhiza

Summary Spirodela oligorrhiza grown in axenic culture was able to use either ammonium, nitrate, or nitrite as sole source of nitrogen, although the morphology of the plants was affected. Plants utilizing ammonium contained higher levels of NH₄, arginine, asparagine and glutamine than did those utilizing NO₃, whereas concentrations of other amino acids were similar.The utilization of NH₄ inhibited that of NO₃ by inhibiting, at least partially, NO₃ uptake, and by inhibiting almost completely the reduction of NO₃ to NO₂. NO₂ also inhibited the utilization of NO₃. NH₄ and NO₂ were taken up and assimilated simultaneously when they were supplied together in the medium.     

British Container Breeding Mosquitoes: The Impact of Urbanisation and Climate Change on Community Composition and Phenology

The proliferation of artificial container habitats in urban areas has benefitted urban adaptable mosquito species globally. In areas where mosquitoes transmit viruses and parasites, it can promote vector population productivity and fuel mosquito-borne disease outbreaks. In Britain, storage of water in garden water butts is increasing, potentially expanding mosquito larval habitats and influencing population dynamics and mosquito-human contact. Here we show that the community composition, abundance and phenology of mosquitoes breeding in experimental water butt containers were influenced by urbanisation. Mosquitoes in urban containers were less species-rich but present in significantly higher densities (100.4±21.3) per container than those in rural containers (77.7±15.1). Urban containers were dominated by Culex pipiens (a potential vector of West Nile Virus [WNV]) and appear to be increasingly exploited by Anopheles plumbeus (a human-biting potential WNV and malaria vector). Culex phenology was influenced by urban land use type, with peaks in larval abundances occurring earlier in urban than rural containers. Among other factors, this was associated with an urban heat island effect which raised urban air and water temperatures by 0.9°C and 1.2°C respectively. Further increases in domestic water storage, particularly in urban areas, in combination with climate changes will likely alter mosquito population dynamics in the UK.     

Bacterial microbiota assemblage in Aedes albopictus mosquitoes and its impacts on larval development

Interactions between bacterial microbiota and mosquitoes play an important role in mosquitoes’ capacity to transmit pathogens. However, microbiota assemblages within mosquitoes and the impact of microbiota in environments on mosquito development and survival remain unclear. This study examined microbiota assemblages and the effects of aquatic environment microbiota on the larval development of the Aedes albopictus mosquito, an important dengue virus vector. Life table studies have found that reducing bacterial load in natural aquatic habitats through water filtering and treatment with antibiotics significantly reduced the larva‐to‐adult emergence rate. This finding was consistent in two types of larval habitats examined—discarded tires and flowerpots, suggesting that bacteria play a crucial role in larval development. Pyrosequencing of the bacterial 16S rRNA gene was used to determine the diversity of bacterial communities in larval habitats and the resulting numbers of mosquitoes under both laboratory and field conditions. The microbiota profiling identified common shared bacteria among samples from different years; further studies are needed to determine whether these bacteria represent a core microbiota. The highest microbiota diversity was found in aquatic habitats, followed by mosquito larvae, and the lowest in adult mosquitoes. Mosquito larvae ingested their bacterial microbiota and nutrients from aquatic habitats of high microbiota diversity. Taken together, the results support the observation that Ae. albopictus larvae are able to utilize diverse bacteria from aquatic habitats and that live bacteria from aquatic habitats play an important role in larval mosquito development and survival. These findings provide new insights into bacteria's role in mosquito larval ecology.     

胶州湾夏秋季大气湿沉降中的营养盐及其入海的生态效应

为揭示大气湿沉降对胶州湾营养盐的输送通量及其生态效应,分别于2015年6—8月(夏季)、9—11月(秋季)采集胶州湾降水样品,测定了降水中不同形态N、P、Si的浓度。结果表明,降水中不同形态营养盐的浓度变化较大,且均与降水量呈负相关关系,其中NH4-N和NO3-N的浓度较高,溶解有机氮(DON)占溶解态总氮(DTN)含量的25.9%,而NO_2-N,PO_4-P和SiO_3-Si的浓度均很低。溶解无机氮(DIN)、DON、PO_4-P以及SiO_3-Si的湿沉降通量分别为141.7、61.87、0.35 mmol m~(-2)a~(-1)和0.12 mmol m~(-2)a~(-1)。受降水量和营养物质来源制约,各项营养盐湿沉降通量时间变化显著。农业活动导致的无机氮排放构成了胶州湾湿沉降DIN的主要来源。大气湿沉降DIN、DON、PO_4-P和SiO_3-Si分别占胶州湾总输入负荷的9.04%、10.24%、0.57%和0.17%,湿沉降输入的PO_4-P在夏、秋季分别可以支持0.575 mgC m~2d~(-1)和1.42 mg C m~2d~(-1)的新生产力;雨水中DIN/P比值高达1 617,突发性强降雨带来的营养盐输入会加剧表层水体的P限制和Si限制,对胶州湾浮游植物群落结构和粒级结构产生重要影响。大气湿沉降是胶州湾生源要素生物地球化学过程的重要一环,对营养物质收支的贡献及可能引发的生态效应不容忽视。     

Effects of pH,phosphate and ammonia on the rate of uptake of nitrate and ammonia by freshwater phytoplankton

The effect of phosphate (PO₄ ⁺³) and pH in regulating nitrate (NO₃) and ammonia (NH₃ ⁺) uptake by phytoplankton was investigated in two Oklahoma lakes using ¹⁵N tracers. Addition of PO₄ ⁺³ above ambient concentrations had a negligible effect on the rate of uptake of NO₃ ^– or NH₃ ⁺. Manipulation of pH of lake water had little effect on uptake of either NO₃ ^– or NH₃ ⁺. A correlation analysis suggested that NO₃ ^– is not used by phytoplankton when NH₃ ⁺ concentrations exceed about 210 µg NH₃ ⁺-N(1)^–1.     

Effects of different N-sources on growth,nutritional status,chlorophyll content,and photosynthetic parameters of shoots of the apple rootstock MM 106 cultured <Emphasis Type="Italic">in vitro</Emphasis>

The effects of five different N-sources (KNO₃ + NH₄NO₃ = control, KNO₃, NH₄NO₃, NH₄H₂PO₄, L-alanine) on growth, nutritional status, chlorophyll (Chl) content, and photosynthetic parameters of the apple rootstock MM 106 shoots cultured in vitro were investigated. In comparison to all the other treatments, control explants grown on a MS medium containing KNO₃ + NH₄NO₃ had the highest fresh mass, Chl content, net photosynthetic rate, transpiration rate, and stomatal conductance.     

Relationships between the kinetics of NH4+ and NO3− absorption and growth in the cultivated tomato (Lycopersicon esculentum Mill, cv T-5)

Tomato growth was examined in solution culture under constant pH and low levels of NH₄⁺ or NO₃^?. There were five nitrogen treatments: 20 mmoles m^?3 NH₄⁺, 50 mmoles m^?3 NO₃^?, 100 mmoles m^?3 NH₄⁺ 200 mmoles m^?3 NO₃^?, and 20 mmoles m^?3 NH₄₊+ 50 mmoles m^?3 NO₃^?. The lower concentrations (20 mmoles m^?3 NH₄⁺ and 50 mmoles m^?3 NO₃^?) were near the apparent K_m for net NH₄⁺ and NO₃^? uptake; the higher concentrations (100 mmoles m^?3 NH₄⁺ and 200 mmoles m^?3 NO₃^?) were near levels at which the net uptake of NH₄⁺ or NO₃^? saturate. Although organic nitrogen contents for the higher NO₃^? and the NH₄⁺+ NO₃^? treatments were 22.2–30.3% greater than those for the lower NO₃^? treatment, relative growth rates were initially only 10–15% faster. After 24 d, relative growth rates were similar among those treatments. These results indicate that growth may be only slightly nitrogen limited when NH₄⁺ or NO₃^? concentrations are held constant over the root surface at near the apparent K_m concentration. Relative growth rates for the two NH₄⁺ treatments were much higher than have been previously reported for tomatoes growing with NH₄⁺ as the sole nitrogen source. Initial growth rates under NH₄⁺ nutrition did not differ significantly (P≥ 0.05) from those under NO₃^? or under combined NH₄⁺+ NO₃^?. Growth rates slowed after 10–15 d for the NH₄⁺ treatments, whereas they remained more constant for the NO₃^? and mixed NH₄⁺+ NO₃^? treatments over the entire observation period of 24–33 d. The decline in growth rate under NH₄⁺ nutrition may have resulted from a reduction in Ca²⁺, K⁺, and/or Mg²⁺ absorption.     

INORGANIC NITROGEN NUTRITION OF THE SEEDLINGS OF THE ORCHID,CATTLEYA

When grown in vitro in a medium containing NH₄NO₃ as the sole source of nitrogen, seeds ro the orchid, Cattleya (C. labiata ‘Wonder’ X C. labiata ‘Treasure'), germinated readily and proceeded to form small plantlets. Development of the embryos was accompanied by an increase in their total nitrogen and a decline in the percent dry weight. Growth responses of the seedlings in other ammonium salts like (NH₄)₂SO₄, (NH₄)₂HPO₄, NH₄Cl, ammonium acetate and ammonium oxalate were similar to that in NH₄NO₃. However, when grown in a medium containing NaNO₃, development of the seedlings was drastically inhibited; KNO₃, Ca(NO₃)₂, KNO₂ and NaNO₂ also were poor nitrogen sources. Attempts to grow the seedlings in NaNO₃ by changing the pH or by addition of kinetin, molybdenum or ascorbic acid as supplements were completely unsuccessful. When seedlings growing in NH₄NO₃ for varying periods were transferred to NaNO₃, it was found that those plants allowed to grow for 60 or more days in NH₄NO₃ could resume normal growth thereafter in NaNO₃. Determination of the nitrate reductase activity in seedlings of different ages grown in NaNO₃, after NH₄NO₃, showed that the ability of the seedlings to assimilate inorganic nitrogen was paralleled by the appearance of the enzyme.     

NITROGEN UPTAKE BY FUCUS SPIRALIS (PHAEOPHYCEAE)1,2

Ammoniun, nitrate and nitrite update by Fucus spiralis L. from the Massachusetts coast was examined. Uptake of all appeared to follow saturation type nutrient uptake kinetics, with uptake often restricted at ambient nutrient concentrations. Although only relatively large difference in K₈ values could be easily distinguished, K₈ values for NO_3? and NH₄₊ were generally similar and low compared with NO_2?. There was also some suggestion that K₈ was reduced at lower temperatures. At 15 C. V_max for light and dark uptake for both NH₄+ and NO_3?, and light uptake of N0_2? were similar, suggesting comparable potential use at higher concentrations. Ammonium and NO_3?uptake decreased at lower temperatures giving Q_ro values of 1.8 and 1.6, respectively, between 5 and 15°C. Nitrate and NH₄+ were taken up together and high levels of NH₄+ did not inhibit NO_3? uptake. Light did not affect uptake of either but did stimulate NO_2? uptake. Ammonium and NO_3? uptake were highest in apical frond and whole young plants, and lowest in slower growing, older frond and stipe. On a relative basis. NO_3?, NH₄₊ and NO_2? were estimated to have contributed ca. 59, 39 and 2% respectively, to the yearly N uptake by apical frond. During winter, NO_3? would provide ca. twice the N to F. spiralis as would, NH₄+. From summer to early fall, when NO_3? levels are lower, NO_3? and NH₄+ would be used in comparable amounts.     

Optimization and elucidation of interactions between ammonium, nitrate and phosphate inCentella asiatica cell culture using response surface methodology

The effects of macronutrients (NO₃ ⁻, NH₄ ⁺ and PO₄ ³⁻) on cell growth and triterpenoids production inCentella asiatica cell suspension cultures were analyzed using the Box-Behnken response surface model experimental design. In screening and optimization experiments, PO₄ ³⁻ as a single factor significantly influenced cell growth where increasing the phosphate level from 0.1 to 2.4 or 2.6 mM, elevated cell growth from 3.9 to 14–16 g/L. The optimum values predicted from the response surface model are 5.05 mM NH₄ ⁺, 15.0 mM NO₃ ⁻ and 2.6 mM PO₄ ³⁻, yielding 16.0 g/L cell dry weight with 99% fitness to the experimental data. While the NH₄ ⁺-NO₃ ⁻ interaction influenced cell growth positively in the optimization experiment, NH₄ ⁺ and NO₃ ⁻ as single factors; and interactions of NO₃ ⁻-PO₄ ³⁻, NH₄ ⁺-PO₄ ³⁻ and NH₄ ⁺-NO₃ ⁻ were all negative in the screening experiment. Cell growth and the final pH level were positively affected by PO₄ ³⁻, but negatively affected by NH₄ ⁺ and NH₄ ⁺-PO₄ ³⁻ interactions. The different effects of factors and their interactions on cell growth and final pH are influenced by a broad or narrow range of macronutrient concentrations. The productions of triterpenoids however were lower than 4 mg/g cell dry weight.