Colchicine after-effects on the absorption and utilisation of phosphates and nitrates by mycelial felts of Cunninghamella sp.

Summary Colchicine at 5 and 10 p.p.m. increased both phosphorus uptake and incorporation into organic forms (nucleoproteins or other simpler organophosphorus compounds). Continuous supply of colchicine at 20 p.p.m., almost checked phosphorus uptake during the second 24 hours of the experiment.The absorbed nitrates were utilised through the classical reduction steps. It appears also that colchicine had an inhibitory effect on the nitrite reductase that increased by increasing the concentration of the drug. Continuous supply of colchicine at its highest concentration (20 p.p.m.) checked completely the protein building during the second 24 hours of the experiment, though nitrate absorption continued; a phenomenon that caused the accumulation, in the tissue medium systems, of large amounts of peptide nitrogen.The mechanism of nitrate reduction as affected by colchicine treatment was fully discussed.     

The effects of nutrient limitation and stream discharge on the epilithic microbial community in an oligotrophic Arctic stream

Nutrient limitation of epilithic microbial activity is modified by stream discharge and drainage from the tundra surrounding the Kuparuk River, Alaska, USA. During 1984, after three weeks of whole stream enrichment with phosphorus, autotrophic activity per unit biomass had increased in the enriched section of the stream suggesting that phosphorus availability was limiting productivity. In contrast, after three weeks of phosphorus enrichment during 1985, heterotrophic and autotrophic activity was similar in the control and enriched sections of the stream. However, when ammonia or nitrate and phosphorus were added to an in situ bioassay chamber for two weeks, higher community biomass and heterotrophic activity resulted. Ten days later biomass significantly dropped in the unenriched section. Nitrate levels over this period increased four fold concomitantly with decreased stream discharge. Apparently during 1985, nitrogen was limiting epilithic microbial community in the phosphorus enriched section of the Kuparuk River. The significant negative relationship between nitrate concentration and stream discharge observed during 1984 supported the trends seen in 1985. These data suggest that nutrient concentrations which limit epilithic microbial activity and biomass are regulated by the stream discharge and drainage from the surrounding tundra.     

氮和磷浓度对中肋骨条藻和锥状斯氏藻种间竞争的影响

采用室内单养和混养方法, 设置不同的氮、磷营养条件, 研究了氮、磷对中肋骨条藻(Skeletonema costatum)和锥状斯氏藻(Scrippsiella trochoidea)种间竞争的影响。结果表明: 混养时各氮和磷浓度下均呈现培养初期中肋骨条藻为优势种、培养后期锥状斯氏藻为优势种的变化趋势, 但随着氮、磷浓度的升高, 中肋骨条藻作为优势种的时间延长; 与单养时相比, 混养中两种微藻的最大密度受到不同程度的抑制, 表现出氮、磷浓度越高, 受抑制的程度越大的特征, 且与锥状斯氏藻相比, 中肋骨条藻的最大密度受到抑制的程度更大。混养时两种微藻均是在氮、磷浓度最高时, 抑制起始点出现时间最长, 随着氮、磷浓度的降低, 抑制起始点出现时间缩短; 各氮、磷浓度条件下, 锥状斯氏藻对中肋骨条藻的竞争抑制参数明显高于中肋骨条藻对锥状斯氏藻的竞争抑制参数, 当氮浓度为512 μmol·L^-1、磷浓度为2 μmol·L ^-1时, 竞争结果是锥状斯氏藻获胜; 其余氮、磷浓度条件下为两种微藻不稳定共存。     

Optimization of arsenic phytoremediation using Eichhornia crassipes

This study aimed to evaluate the pH, phosphate, and nitrate in the process of arsenic absorption by Eichhornia crassipes (water hyacinth), using the surface response methodology, in order to optimize the process. The plants were exposed to a concentration of arsenic of 0.5 mg L^?1 (NaAsO₂) over a period of 10 days. The results indicated optimal levels for the absorption of arsenic by E. crassipes at pH equal to 7.5, absence of phosphate, and minimum nitrate level of 0.0887 mmol L^?1. For the tested concentration, E. crassipes was able to accumulate 498.4 mg kg^?1 of As (dry base) in its plant tissue and to reduce 83% of the initial concentration present in the aqueous medium where it was cultivated. The concentration of phosphorus in solution linearly increased the phosphorus content in the plants and negatively influenced the absorption of arsenic. The concentration of 0.5 mg L^?1 of As did not significantly affect the relative growth rate (RGR) and the tolerance index (TI). 94% of As (III) initially solubilized in water was converted by the end of the experiment period into As (V). The water hyacinth was important in the phytoremediation of arsenic when cultivated under optimal conditions for its removal.     

Nitrate, Ammonium and Kinetin Effects on Growth and Enzyme Activities of Paul's Scarlet Rose Callus

Factorial experiments using the three variables nitrate, ammonium, and kinetin at six different concentrations each (nitrate 4.64 to 215 mM; ammonium 2.15 to 100 mM; and kinetin 0.1 to 4.64 mg/l) were set up to measure the effects of each of these factors, and their interactions, on the fresh weight, protein, and enzyme activities of callus of Paul's Scarlet Rose. Optimum fresh weight values were obtained with nitrate at 46.4 mM. Ammonium inhibited growth at concentrations above 2.15 mM, and kinetin had no significant effect. Significant interaction between nitrate and ammonium effects on growth was found. Kinetin did not interact significantly with either nitrate or ammonium to influence the fresh weight. The specific activity of glutamate dehydrogenase (NAD) in the aminating reaction increased with increasing ammonium concentrations to 21.5; at higher concentrations the activity remained high. Glutamine synthetase specific activity was constant over a large range of nitrate and ammonium concentrations, increasing only when nitrate went from 46.4 to 100 mM. Glutamine synthetase was sensitive to the nitrate: ammonium interaction. Specific activity decreased at progressively higher ammonium levels when nitrate concentration increased. No glutamate synthase activity was detected at optimal nitrate concentrations.     

NITRATE AND PHOSPHATE UPTAKE INTERACTIONS IN A MARINE PRYMNESIOPHYTE1

The short- and long-term uptake of nitrate and phosphate ions, and their interactions, were studied as functions of the preconditioning of Pavlova lutheri (Droop) Green. Populations were preconditioned in continuous culture at a variety of growth rates and N:P supply ratios. The maximum uptake rates cell^?1 for nitrate and phosphate were of similar magnitudes, in spite of the forty-fold smaller requirement for phosphorus. Short-term phosphate uptake was independent of the nitrate concentration, but the short-term nitrate uptake rate was reduced in the presence of phosphate. The severity of inhibition of nitrate uptake by phosphate was positively correlated with the preconditioning N:P supply ratio and the preconditioning growth rate. In response to large additions of nutrients, P. lutheri was able to increase its phosphorus content sixty-fold, but was only able to take up enough nitrate to double its nitrogen content. The high rate of phosphate uptake relative to its requirement, the inhibition of nitrate uptake by phosphate, and the large capacity for phosphorus storage relative to its requirement, all of which were observed even under N limitation, may imply that even where nitrogen is limiting there can be interspecific competition for available phosphate.     

Nitrogen and Phosphorus in a Stretch of the Guadalupe River,Texas, with Five Main-Stream Impoundments by

Nitrogen and phosphorus were studied in a 168-km stretch of the Guadalupe River that had five main-stream impoundments. Flow through the study area was controlled by releases from these five reservoirs and from Canyon Reservoir, a deep-storage reservoir, located 30 km upstream. Parameters measured monthly on a diel basis at 16 stations were nitrate nitrogen, nitrite nitrogen, ammonia nitrogen, Kjeldahl nitrogen, inorganic phosphate phosphorus, organic phosphate phosphorus, and total phosphate phosphorus.Inorganic nitrogen concentrations observed in this study were as high or higher than that previously reported for other bodies of water. Nitrate nitrogen entered the study area in relatively high concentrations from Comal Springs which was a major source of water for the Guadalupe River. Water from Canyon Reservoir, the other major source of water, was relatively low in nitrate nitrogen. The concentration of nitrate nitrogen was, therefore, dependent in part upon the portion of the total river flow originating from the two sources. Increased discharge from Canyon Reservoir and utilization by plants in areas of high chlorophyll a resulted in low nitrate-nitrogen levels. Retention of water in reservoirs reduced the concentration of nitrate nitrogen due to increased utilization by plants in areas of low flow. Nitrate nitrogen, in general, reached seasonal minima in summer and maxima in winter. Nitrite nitrogen showed considerable variation with no meaningful pattern except that higher concentrations occurred in association with high chlorophyll a and high Kjeldahl nitrogen, regions and periods of low river flow, and large phytoplankton populations. There was no increase in concentration of any form of nitrogen in the vicinity of sewage outfalls and no downstream accrual.Phosphorus levels in the study area were as high or higher than those reported in studies of other bodies of water. Sewage treatment plants at New Braunfels and Seguin, Texas, were major sources of phosphorus to the Guadelupe River. Total phosphate phosphorus was determined to be the most critical phosphate parameter in assessing eutrophication. Seasonally, it ranged from a winter high to a summer low. Concentrations were highest immediately below sewage outfalls and decreased as water progressed downstream. Inorganic-phosphate-phosphorus concentrations showed no clear seasonal trend but were clearly associated with sewage outfalls. Since large standing crops of phytoplankton were observed in areas of low inorganic phosphate phosphorus, it was not considered to limit photosynthesis. Total organic phosphate phosphorus varied seasonally, with high concentrations occurring during the spring and low concentrations in the fall. Total organic phosphate phosphorus showed no correlation with sewage outfalls, but was correlated to a degree with total Kjeldahl nitrogen and chlorophyll a. No consistent pattern of diel fluctuations was evident for any phosphorus or nitrogen compounds analyzed.     

Effect of colchicine on the carbohydrate metabolism of mycelial felts of cunninghamella Sp.

Summary An experiment is reported in which 5 days old Cunninghamella spec. mats were incubated at 25°C over Richard's medium alone or together with colchicine. The results show that, up to 20 p.p.m., colchicine had no effect on dry weight and soluble sugar content of the fungal mats but caused an acceleration in the rate of sugar absorption and utilisation and polysaccharide accumulation especially the glucosans. 10 p.p.m. concentration further induced an increase in CO₂ production and synthesis of mononucleotides and nucleoproteins as indicated by excessive accumulation of conjugated pentoses and the pentosan fraction of polysaccharides.     

Hydrocarbon production from secondarily treated piggery wastewater by the green alga Botryococcus braunii

A laboratory study was conducted on the removal of nitrogen and phosphorus from piggery wastewater during growth of Botryococcus braunii UTEX 572, together with measurements of hydrocarbon formation by the alga. The influence was tested of the initial nitrogen and phosphorus concentration on the optimum concentration range for a culture in secondarily treated piggery wastewater. A high cell density (> 7 g L^–1 d. wt) was obtained with 510 mg L^–1 NO₃-N. Growth increased with nitrogen concentration at the basal phosphorus concentration (14 mg P L^–1). The growth rate was nearly independent ( = 0.027 0.030 h^–1) of the initial phosphate concentration, except under conditions of phosphate deficiency ( = 0.019 h^–1). B. braunii grew well in piggery wastewater pretreated by a membrane bioreactor (MBR) with acidogenic fermentation. A dry cell weight of 8.5 mgL^–1 and hydrocarbon level of 0.95 gL^–1 were obtained, and nitrate was removed at a rate of 620 mg NL^–1. These results indicate that pretreated piggery wastewater provides a good culture medium for the growth and hydrocarbon production by B. braunii.     

Enclosure Experiments with Low-dose Additions of Phosphorus and Nitrogen in the Acidified Lake Njupfatet,Central Sweden

Experiments involving low-dose additions of phosphate, ammonium, nitrate and ADP, one by one and in combination, were performed in small (350 litre) in-situ enclosures in a moderately acid (pH 5.4) lake. Before manipulation, all large filter-feeding animals were removed by filtration. Phytoplankton responded to the nutrient additions only when both phosphorus and nitrogen were added, thus indicating a close balance between phosphorus and nitrogen limitation in the system. Variation of the inorganic nitrogen-source resulted in species-specific responses by phytoplankton. With ammonium as the nitrogen source Merismopedia tenuissima was favoured, regardless of whether this species was dominant in the phytoplankton community at the beginning of the experiment or not. With nitrate as nitrogen source Peridinium inconspicuum, which was never particularly common at the beginning of the experiments, was favoured. No other species of phytoplankton present in the bags was able to outcompete these two species as long as inorganic nutrients were added. With ADP as phosphorus source together with nitrate, a third species, Dictyosphaerium cf. botrytella, was favoured and reached dominance. The zooplankton community remaining in the bags, dominated by rotifers and calanoid nauplii, did not respond to the fertilization-induced increases in the total biomass of phytoplankton.     

AN EXPERIMENTAL ASSESSMENT OF THE EFFECTS OF NUTRIENT ENHANCEMENT ON THE INTERTIDAL KELP HEDOPHYLLUM SESSILE (LAMINARIALES,PHAEOPHYCEAE)1

We tested whether experimentally enhancing nutrients around the kelp Hedophyllum sessile would increase growth, tissue nitrogen, or allocation to phenolic compounds. Packets of time‐released fertilizer were anchored adjacent to fronds in the field, and algae were monitored for several months. Although fertilizer packets increased the concentration of ammonium, nitrate, and phosphorus adjacent to treatment algae by an order of magnitude, there was little evidence that this increased frond growth or size. Hedophyllum individuals showed no tendency to alter allocation patterns in response to nutrient addition. Tissue carbon and nitrogen was unchanged by the nutrient manipulation; most H. sessile had tissue nitrogen concentrations in excess of 2.0% of dry mass. Additionally, the concentration of phloroglucinol equivalents was also unaffected by the presence of increased water column nutrients. Although nutrient concentrations in the water column surrounding the study site show relatively high mean values for ammonium, nitrate, and phosphorus, they are characterized by high spatial and temporal variation. Nonetheless, these data suggest that this intertidal kelp is not limited by nitrogen or phosphorus in wave‐exposed areas in the northeast Pacific Ocean.     

Effects of phosphorus and nitrogen enrichment on the yield of some strains of Stigeoclonium Kütz. (Chlorophyceae)

SUMMARY.

• 1 The combined effect of nitrate and phosphate concentrations on the yields of five selected strains of Stigeoclonium is demonstrated in a synthetic medium as well as in natural waters.
• 2 Increase of yield after addition of one nutrient depends on the concentration of the other. A graphic growth model based on the experiments in synthetic medium is presented, which allows prediction of yields at different combinations of nitrate and phosphorus concentrations.
• 3 In general, yields in natural waters before and after addition of nitrate and/or phosphate agree with the model. In some cases, other limiting factors appear to be involved.
• 4 The possible effects of nitrogen and phosphorus limitation on the phosphorus and nitrogen metabolism of the alga are discussed.
• 5 Neither an exponential model (Baule-Mitscherlich) nor a hyperbolic model adequately describe the interaction demonstrated between nitrogen and phosphorus limitation.

     

Interaction of ascorbic acid and colchicine with sucrose utilization byCunninghamella elegans

The stimulating effect of ascorbic acid, administered to colchicine-treated mycelia ofCunninghamella elegans, on respiration, keto acid production and carbohydrate accumulation was lower than the highly increased rate of sugar absorption. Furthermore, the increasing ascorbic acid concentration in colchicine media favoured lower carbohydrate accumulation, keto acid production, carbon dioxide output and highly stimulated the utilization of the absorbed sugars for the formation of non-carbohydrate compounds. In addition, the vitamin seemed to counteract the inhibitory effects of colchicine on nucleoprotein and soluble nucleotide synthesis by colchicine-treated mycelia particularly when the drug was administered at high levels.     

The loss of submerged plants with eutrophication I. Experimental design, water chemistry, aquatic plant and phytoplankton biomass in experiments carried out in ponds in the Norfolk Broadland

SUMMARY. 1 During eutrophication of shallow lakes, communities of submerged plants are often replaced by dense phytoplankton populations, but the mechanism by which this occurs is obscure though often assumed to involve shading. 2. This paper introduces a series investigating this change and describes a system of experimental ponds which were variously fertilized with nitrogen and phosphorus, had fish added or removed, and had their submerged aquatic plants cleared or left intact. 3. Fertilization with phosphate and ammonium nitrate in quantities effectively greater than those in a series of lakes in the adjacent Norfolk Broads, which have lost their submerged plants, did not displace the plant populations. 4. Total phosphorus and soluble reactive phosphorus concentrations in the water did not increase much with increasing loading in the presence of submerged plants but did so if the plants were manually cleared. Ammonium and nitrate concentrations were kept low, despite large additions in both plant dominated and manually cleared ponds. 5. In the absence of fish there were modest increases in chlorophyll a concentrations with phosphorus loading in the presence or absence of submerged plants. The concentrations achieved, however, were much lower than anticipated probably because of grazing by large-bodied Cladocera. 6. Ponds dominated by plants continued to have low phytoplankton populations even when fish were stocked. Low fish survival in these ponds permitted grazing zooplankters to flourish. In ponds cleared of plants, however, there were significant relationships between cholorophyll a concentration with Daphnia biomass (inverse) and log stock of potentially zooplanktivorous fish (positive). There was a significant relationship between chlorophyll a and total phosphorus concentrations in the plant and cleared ponds in 1982 but only in the plant ponds in 1983. In all cases the phytoplankton communities were dominated by small, often flagellated, organisms.     

Effects of pruning on the concentration of macronutrients in Colophospermum mopane leaves

Despite the nutritional value of Colophospermum mopane leaves to browser's diets, there is limited knowledge on the effect of browsers on the concentration of macronutrients in mopane leaves. A field experiment was conducted in Musina Nature Reserve, Limpopo Province, South Africa to determine the effect of pruning, a proxy for browsing, on the concentration of macronutrients in mopane leaves. Samples were analysed for calcium (Ca), potassium (K), nitrogen (N), phosphorus (P), sulphur (S), chlorine (Cl), magnesium (Mg), nitrate (NO₃), sodium (Na), protein and fibre, using inductively coupled plasma atomic emission spectrometry techniques. The effect of pruning on the monthly concentration of macronutrients was tested using a two‐tailed t test: two‐sample assuming equal variance. The seasonal and annual effect of pruning on the concentration of macronutrients was tested using a one‐way ANOVA. Results showed that the amount of Ca, K, N, P, S, Cl, Na, protein and fibre increased during leaf flush in October and then declined as the leaves matured and aged. However, the concentration of Mg and NO₃ increased when the leaves reached maturity in June, particularly during senescence stage, and declined thereafter. The concentration of macronutrients between the control and pruned trees was statistically insignificant for most samples.     

Reassessment of the in vivo Assay for Nitrate Reductase in Leaves

The in vivo assay procedure for nitrate reductase and its dependence on the concentration of nitrate and other ions were examined. It was found that high ion concentrations led to an increased release of nitrite to the reaction media which could be interpreted as a stimulated nitrate reductase activity. This phenomenon is not an osmotic effect, since equivalent concentrations of mannitol did not lead to identical results. The effect of ions on the enhanced nitrite production was attributed to changes in cell membrane permeability rather than to a supply of substrate. This conclusion is based on several findings: (a) in in vitro assays, the rate of nitrite production was not affected by ion concentrations: (b) the stimulation of nitrite production was obtained by various ions and not only by nitrate; (c) pretreatment of alfalfa leaves with nitrate did not increase the NO₂^? release rate to the external solution; and (d) nitrate and nitrite export from leaf discs to the solution was stimulated even in discs which were enzymatically inactive. Calcium ions in the presence of KNO₃ inhibited the enhanced nitrite production, probably due to alteration of membrane stability. The effect of ions on the rate of nitrite production was reversible and the high rate of nitrite production was reduced to the control rate when discs were transferred to a solution of low concentration.     

Détection à l'aide d'un bio-essai (Selenastrum capricornutum) des répercussions d'un rejet minier sur l'environnement aquatique: toxicité ou enrichissement en substance essentielle?

Physical and chemical studies and algal bioassays were conducted to assess the repercussions on waterways receiving the treated effluent wastes of an iron ore mining operation located in north-eastern Quebec, Canada.In the area directly below waste input, conductivity, turbidity, suspended solids, nitrite + nitrate nitrogen and phosphorus levels, as well as algal growth potential generally displayed higher values than elsewhere. With these parameters only, however, no perceptible mining impact on two major receiving waterways (aux Pékans and Moisie rivers) could be shown, except for nitrite + nitrate nitrogen values in the aux Pékans River.The presence of heavy metals did not result in any toxic effects as indicated by bioassays conducted with S. capricornutum. These tests when carried out on samples collected during low water levels, spiked with nitrogen + phosphorus, as well as with modified AAP medium, clearly indicated the contribution of the mining wastes to the enrichment of the receiving waters. This effect was linked to essential element other than nitrogen or phosphorus. For samples collected during high water levels, it is suspected that the increased presence of organic matter interferes by complexation of trace metals.Cautious interpretation of results is therefore recommended when using algal bioassays in order to distinguish between effects of growth-limiting essential element and the presence of toxic substances.

     

Influence of soil fertility on the growth and metabolism of wheat under salt stress

Fertilizer induced improvement of growth and yield of wheat (Triticum aestivum L. cv. Kalyan Sona), under salinity stress, was associated with an increase in the concentrations of nitrogen, phosphorus and potassium and a decrease in the level of chloride in the tissue. The concentration of chloride in grains was also reduced under high fertility as compared to low fertility condition. Results reveal that under both normal and saline conditions, nutritional improvement leads to higher chlorophyll concentration and increased efficiency of enzymes like nitrate reductase, ATPase, alkaline pyrophosphatase and amylase in the leaves. This imparts importance to fertilizer application under saline conditions.     

An experimental investigation of phytoplankton nutrient limitation in two contrasting low arctic lakes

We investigated whether phytoplankton communities in two lakes in SW Greenland were phosphorus or nitrogen limited. The study lakes have contrasting water chemistry (mean conductivities differ ten fold) and are located near Kangerlussuaq, SW Greenland (~67°N, 51°W). A microcosm nutrient enrichment experiment was performed in June 2003 to determine whether nitrate or phosphate addition stimulated phytoplankton growth. Samples were analysed for species composition, biomass, and alkaline phosphatase activity (APA). Initially, both lakes had extremely low total phosphorus but high total nitrogen concentrations and high APA, suggesting that the phytoplankton were phosphorus limited prior to the start of the experiment. The phytoplankton composition and biomass (mainly Ochromonas spp.) responded to phosphate but not to nitrate addition. In both lakes, chlorophyll a increased significantly when phosphate was added. Furthermore, APA was significantly lower in the two lakes when phosphate was added compared to the control and the nitrogen addition treatment. The dominance of mixotrophic phytoplankton and high DOC values suggest that these lakes may be regulated by microbial loop processes.     

The effects of different external nitrate concentrations on growth of Phaseolus vulgaris cv. Seafarer at chilling temperatures

The effects of different applied nitrate concentrations (1 to 50 mol m³) on growth of Phaseolus vulgaris cv. Seafarer at temperatures around 15°C was examined. Total plant dry weight and carbon content decreased sharply with increased applied nitrate 1 to 10 mol m^-3 then decreased slightly with further increases in applied N. Total plant reduced -N content increased sharply with increased applied nitrate concentration from 1 to 5 mol m^-3, changed little with increased applied nitrate from 5 to 25 mol m^-3, then increased when applied nitrate was increased from 25 to 50 mol m^-3. Nitrate concentration in all tissues increased sharply with applied nitrate increased from 1 to 10 mol m³ and showed a further increase at 50 mol m³ applied nitrate. Fresh weight to dry weight ratio for all leaves and specific leaf area for all secondary leaves increased sharply with applied nitrate concentration from 1 to 5 mol m^-3 then decreased with applied nitrate 25 to 50 mol m³ Secondary leaf chlorophyll concentration decreased sharply when applied nitrate increased from 1 to 5 mol m^-3 but increased with applied nitrate from 25 to 50 mol m^-3. Initially, the rate of leaf extension was greater at 20 mol m^-3 applied nitrate than 1 mol m^-3 applied nitrate. It is proposed that decreased growth with increased applied nitrate in the range 1 to 10 mol m^-3 is due to increased leaf damage caused by a greater rate of leaf expansion.