Growth of Salvinia molesta as affected by water temperature and nutrition II. Effects of phosphorus level

The growth of Salvinia molesta D.S. Mitchell, as affected by phosphorus supply and water temperature, was studied in a greenhouse using controlled water temperature baths at 16, 19 and 22°C. For significant responses to the phosphorus treatments to be obtained it was found necessary to use P-deficient plant propagules (containing <0.01% P on a dry matter basis). For these plants the highest relative growth rate and dry matter production occurred at 22°C when they received 10.01 mg PO₄P l^?1, but this was not significantly different from that of plants receiving 1.01 mg PO₄-P l^?1. Over a period of 21 days for plants receiving 0.02 mg PO₄ l^?1 the biomass increased 4-fold at 19°C and 6-fold at 22°C. In contrast, for plants receiving 10.01 mg PO₄-P l^?1 biomass was increased 20-fold at 19°C and 32-fold at 22°C. At the latter temperature, when receiving 60.01 mg PO₄-P l^?1, plants concentrated up to 1.3% of phosphorus on a dry matter basis, suggesting a possible use as a biological filter and purifier of contaminated waters.     

Productivity and nutrient uptake of water hyacinth,Eichhornia crassipes I. Effect of nitrogen source

Water hyacinth,Eichhornia crassipes, growth and nutrient uptake rates, as influenced by different N sources and N transformations, were measured using microcosm aquaculture systems. Net productivity was highest in the system receiving equal amounts of NH₄ ⁺ and NO₃ ^- (at 10 mg N 1^-1 each) and decreased in the order of NO₃ ^-, NH₄ ⁺, urea (added at 20 mg N 1^-1 each), and methane digestor effluent (at 6 mg N 1^-1). During the first 7-wk study (average ambient air temperature was 26–28°C), biomass yields were in the range of 19–53 g dry wt m^-2 day^-1, while between the 8th and 12th wk (average ambient air temperature was 16–22°C), biomass yields were in the range of 10–33 g dry wt m^-2 day^-1. In the systems with either NH₄ ⁺ or NO₃ ^-, or both added in equal proportions, about 14–20% of the total yield was contributed by roots, whereas in the system with urea and digestor effluent, roots contributed about 23 and 44% of the total yield, respectively. Nitrogen and P uptake per unit area followed trends similar to biomass yields. Nitrogen uptake rates were in the range of 533–2, 161 mg N m^-2 day^-1 for the systems receiving NH₄ ⁺, NO₃ ^-, and urea, while uptake rates were in the range of 124–602 mg N m^-2 day^-1 for the system receiving methane digestor effluent. Phosphorus uptake rates were found to be in the range of 59–542 mg P m^-2 day^-1. Under the most favorable conditions, maximum recorded biomass yield was 53 g dry wt m^-2 day^-1, with N and P removal rate of 2,161 mg N m^-2 day^-1 and 542 mg P m^-2 day^-1, indicating the potential of water hyacinth to produce large amounts of biomass which can be potentially used as a feedstock to produce methane.     

Withanolide A production from Withania somnifera hairy root cultures with improved growth by altering the concentrations of macro elements and nitrogen source in the medium

Withania somnifera is an important medicinal plant that contains withanolides as bioactive compounds. We have investigated the effects of macroelements and nitrogen source in hairy roots of W. somnifera with the aim of optimizing the production of biomass and withanolide A content. The effects of the macroelements NH₄NO₃, KNO₃, CaCl₂, MgSO₄ and KH₂PO₄ at concentrations of 0, 0.5, 1.0, 1.5 and 2.0× strengths and of nitrogen source [NH₄ ⁺/NO₃ ^? (0.00/18.80, 7.19/18.80, 14.38/18.80, 21.57/18.80, 28.75/18.80, 14.38/0.00, 14.38/9.40, 14.38/18.80, 14.38/28.20 and 14.38/37.60 mM)] in Murashige and Skoog medium were evaluated for biomass and withanolide A production. The highest accumulation of biomass (139.42 g l^?1 FW and 13.11 g l^?1 DW) was recorded in the medium with 2.0× concentration of KH₂PO₄, and the highest production of withanolide A was recorded with 2.0× KNO₃ (15.27 mg g^?1 DW). The NH₄ ⁺/NO₃ ^? ratio also influenced root growth and withanolide A production, with both parameters being larger when the NO₃ ^? concentration was higher than that of NH₄ ⁺. Maximum biomass growth (148.17 g l^?1 FW and 14.79 g l^?1 DW) was achieved at NH₄ ⁺/NO₃ ^? ratio of 14.38/37.60 mM, while withanolide A production was greatest (14.68 mg g^?1 DW) when the NH₄ ⁺/NO₃ ^? ratio was 0.00/18.80 mM. The results are useful for the large scale cultivation of Withania hairy root culture for the production of withanolide A.     

Inorganic nitrogen uptake kinetics of sugarcane (Saccharum spp.) varieties under in vitro conditions with varying N supply

An in vitro system was established for the characterisation of inorganic nitrogen uptake by sugarcane plantlets of variety NCo376. After multiplication and rooting, plantlets (0.27–0.3 g fresh mass) were placed on N-free medium for 4 days, and then supplied with 2–20 mM N as NO₃ ^?-N only, NH₄ ⁺-N only or NO₃ ^?-N + NH₄ ⁺-N (as 1:1). With few exceptions, on all the tested N media, the in vitro plants always had a higher V_max for NH₄ ⁺-N (28.69–66.51 μmol g^?1 h^?1) than for NO₃ ^?-N uptake (10.24–30.19 μmol g^?1 h^?1) and the K_m indicated a higher affinity for NO₃ ^?-N (0.02–7.38 mM) than for NH₄ ⁺-N (0.06–9.15 mM). When N was applied as 4 and 20 mM to varieties N12, N19 and N36, the interaction between variety, N form and concentration resulted in differences in the V_max and K_m. The high N-use efficient varieties (N12 and N19), as determined in previous pot and field trials, behaved similarly under all tested conditions and displayed a lower V_max and K_m than the low N-use efficient ones (NCo376 and N36). Based on this finding, it was suggested that the N-use efficient designation (from pot and field trials) may not be ascribed solely to N uptake. Assessment of the relative preference index (RPI) for NO₃ ^?-N and NH₄ ⁺-N uptake revealed that, at present, the RPI has no application in sugarcane due to its preferential uptake of NH₄ ⁺-N.     

Effect of influent substrate ratio on anammox granular sludge: performance and kinetics

Effect of influent substrate ratio on anammox process was studied in sequencing batch reactor. Operating temperature was fixed at 35 ± 1 °C. Influent pH and hydraulic retention time were 7.5 and 6 h, respectively. When influent NO₂ ^?-N/NH₄ ⁺-N was no more than 2.0, total nitrogen removal rate (TNRR) increased whereas NH₄ ⁺-N removal rate stabilized at 0.32 kg/(m³ d). ΔNO₂ ^?-N/ΔNH₄ ⁺-N increased with enhancing NO₂ ^?-N/NH₄ ⁺-N. When NO₂ ^?-N/NH₄ ⁺-N was 4.5, ΔNO₂ ^?-N/ΔNH₄ ⁺-N was 1.98, which was much higher than theoretical value (1.32). The IC₅₀ of NO₂ ^?-N was 289 mg/L and anammox activity was inhibited at high NO₂ ^?-N/NH₄ ⁺-N ratio. With regard to influent NH₄ ⁺-N/NO₂ ^?-N, the maximum NH₄ ⁺-N removal rate was 0.36 kg/(m³ d), which occurred at the ratio of 4.0. Anammox activity was inhibited when influent NH₄ ⁺-N/NO₂ ^?-N was higher than 5.0. With influent NO₃ ^?-N/NH₄ ⁺-N of 2.5–6.5, NH₄ ⁺-N removal rate and NRR were stabilized at 0.33 and 0.40 kg/(m³ d), respectively. When the ratio was higher than 6.5, nitrogen removal would be worsened. The inhibitory threshold concentration of NO₂ ^?-N was lower than NH₄ ⁺-N and NO₃ ^?-N. Anammox bacteria were more sensitive to NO₂ ^?-N than NH₄ ⁺-N and NO₃ ^?-N. TNRR would be enhanced with increasing nitrogen loading rate, but sludge floatation occurred at high nitrogen loading shock. The Han-Levenspiel could be applied to simulate nitrogen removal resulting from NO₂ ^?-N inhibition.     

Absorption of nitrate and ammonium ions by Lolium perenne from flowing solution cultures at low root temperatures

Lolium perenne L. cv. 23 (perennial ryegrass) plants were grown in flowing solution culture and acclimatized over 49 d to low root temperature (5°C) prior to treatment at root temperatures of 3, 5, 7 and 9°C for 41 d with common air temperature of 20/15°C day/night and solution pH 5·0. The effects of root temperature on growth, uptake and assimilation of N were compared with N supplied as either NH₄ or NO3 at 10 mmol m^?3. At any given temperature, the relative growth rate (RGR) of roots exceeded that of shoots, thus the root fraction (Rf) increased with time. These effects were found in plants grown with the two N sources. Plants grown at 3 and 5°C had very high dry matter contents as reflected by the fresh weight: freeze-dried weight ratio. This ratio increased sharply, especially in roots at 7 and 9°C. Expressed on a fresh weight basis, there was no major effect of root temperature on the [N] of plants receiving NHJ but at any given temperature, the [N] in plants grown with NHJ was significantly greater than in those grown with NO₃. The specific absorption rate (SAR) of NH⁺₄ was greater at all temperatures than SAR-NO₃. In plants grown with NH⁺, 3–5% of the total N was recovered as NH⁺₄, whereas in those grown with NO^?₃ the unassimilated NO^?₃ rose sharply between 7 and 9°C to become 14 and 28% of the total N in shoots and roots, respectively. The greater assimilation of NH⁺₄ lead to concentrations of insoluble reduced N (= protein) which were 125 and 20% greater, in roots and shoots, respectively, than in NO^?₃-grown plants. Plants grown with NH⁺₄ had very much greater glutamine and asparagine concentrations in both roots and shoots, although other amino acids were more similar in Concentration to those in NO^?₃ grown plants. It is concluded that slow growth at low root temperature is not caused by restriction of the absorption or assimilation of either NH⁺₄ or NO^?₃. The additional residual N (protein) in NH⁺₄ grown plants may serve as a labile store of N which could support growth when external N supply becomes deficient.     

Decay rates and nitrogen dynamics of decomposing watercress (Nasturtium officinale R.Br.)

We examined the decomposition of watercress in the laboratory at 10° and 20 °C, and in the field. Rates varied from 0.058 g g^?1 day^?1 in the laboratory to 0.115 g g^?1 day^?1 in the field. There was a rapid generation of particles of size <500 µm. It is thought that washout of these from the litterbags in the field accounted for high field decomposition rate. Formation of dissolved nitrogen compounds during decomposition followed a time series from NH _inf4 ^sup+ to NO _in2 ^sup? to NO _inf3 ^sup? withdissolved organic nitrogen accumulating at the end of decomposition. Ammonification rates were 480 and 657 g NH₄-N g^?1 (dry wt) day^?1 and nitrification rates on the decomposing tissue were 640 and 571 µg NO₃-N g^?1 (dry wt) day^?1 at 10° and 20 °C respectively. Fifty-six per cent of the initial plant N was regenerated as NO₃-N 21% as DON and 25% remained as refractory particulate N.     

The effect of nutrient concentrations,nutrient ratios and temperature on photosynthesis and nutrient uptake by Ulva prolifera: implications for the explosion in green tides

The green-tide macroalga, Ulva prolifera, was tested in the laboratory to determine its nutrient uptake and photosynthesis under different conditions. In the nutrient concentration experiments U. prolifera showed a saturated uptake for nitrate but an escalating uptake in the tested range for phosphorus. Both N/P and NO₃ ^?/NH₄ ⁺ ratios influenced nutrient uptake significantly (p?<?0.05) while the PSII quantum yield [Y(II)] (p?>?0.05) remained unaffected. The maximum N uptake rate (33.9?±?0.8 μmol g^?1 DW h^?1) and P uptake rate (11.1?±?4.7) was detected at N/P ratios of 7.5 and 2.2, respectively. U. prolifera preferred NH₄ ⁺-N to NO₃ ^?-N when the NO₃ ^?-N/NH₄ ⁺-N ratio was less than 2.2 (p?<?0.05). But between ratios of 2.2 and 12.9, the uptake of NO₃ ^?-N surpassed that of NH₄ ⁺-N. In the temperature experiments, the highest N uptake rate and [Y(II)] were observed at 20 °C, while the lowest rates were detected at 5 °C. P uptake rates were correlated with increasing temperature.     

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.     

Effect of different doses of organic fertilizer (cow dung) on pond productivity and fish biomass in stillwater ponds

The effects of five (5 000, 10 000, 15 000, 20 000, 24 000 kg ha^?1 year^?1) different doses of organic fertilizer (cow dung) were studied on pond productivity in terms of plankton production and fish biomass in freshwater fish ponds. The grow out period was 60 days. Physico-chemical factors of pond waters were also monitored. With an increase in the fertilizer dose, biochemical oxygen demand (BOD) (1.7 ± 0.1 – 10.35 ± 0.05 mg L^?1), O-PO₄ (0.04 ± 0.0 – 0.77 ± 0.02 mg L^?1) and NH₄-N (0.03 ± 0.02 – 0.32 ± 0.02 mg L^?1) increased significantly (P < 0.05). Alkalinity (79.0 ± 1.6 – 164.0 ± 3.8 mg L^?1) also increased with the increase in fertilizer dose, declining after 60 and 75 days (48.8 ± 1.13 – 67.9 ± 2.1 mg L^?1). NO₃-N was maximum (1.66 ± 0.2 mg L^?1) in the ponds which received cow dung at 15 000 kg ha^?1 year^?1, and declined (0.94 ± 0.5 mg L^?1) at higher doses. Dissolved oxygen (DO) remained significantly high (4.7 mg L^?1) up to the third (15 000 kg ha^?1 year^?1) treatment. Highest plankton population (phytoplankton 17 350.0 ± 1 250.0 no L^?1), zooplankton (373.0 ± 22.0 no L^?1), species diversity (phytoplankton 3.0, zooplankton 2.3), fish biomass (4.45 kg) and specific growth rate (SGR) (2.36 % body weight (BW) d^?1) were also observed in ponds which were treated with fertilizer at 15 000 kg ha^?1 year^?1. However, at higher doses, a decline in these parameters (phytoplankton, 0.0 – 8 810.0 ± 690.0 no L^?1; zooplankton, 0.0 – 205.0 ± 25.0 no L^?1; fish biomass, 2.3 kg; SGR, 1.25 % body weight (BW) d^?1) was observed. Furthermore, with a decrease in the water temperature from 24 °C (on day 60) to 21 °C (on day 75), a decline in nutrient release, plankton population L^?1 and species diversity was observed. Sediment analysis indicated that with an increase in the fertilizer dosage, a significant and progressive increase in the accumulation of organic carbon (0.787 ± 0.006 – 0.935 ± 0.01), total nitrogen (0.877 ± 0.071 – 1.231 ± 0.03), NH₄-N (54.4 ± 0.57 – 68.95 ± 0.81), NO₃-N (78.5 ± 1.21 – 98.5 ± 0.35), total P (140.0 ± 0.50 – 151.0 ± 1.27) and soluble P (7.15 ± 0.18 – 10.1 ± 0.56) took place; similarly, electrical conductivity (EC) values of sediment also increased progressively (from 200.0 ± 7.1–300.0 ± 10.63 μ mhos cm^?1).     

Heterotrophic nitrification and aerobic denitrification by a novel Halomonas campisalis

A novel halophilic strain that could carry out heterotrophic nitrification and aerobic denitrification was isolated and named as Halomonas campisalis ha3. It removed inorganic nitrogen compounds (e.g. NO₃ ^?, NO₂ ^? and NH₄ ⁺) simultaneously, and grew well in the medium containing up to 20 % (w/v) NaCl. PCR revealed four genes in the genome of ha3 related to aerobic denitrification: napA, nirS, norB and nosZ. The optimal conditions for aerobic denitrification were pH 9.0, at 37 °C, with 4 % (w/v) NaCl and sodium succinate as carbon source. The nitrogen removal rate was 87.5 mg NO₃ ^?–N l^?1 h^?1. Therefore, this strain is a potential aerobic denitrifier for the treatment of saline wastewater.     

The effect of root temperature on the uptake of nitrogen and the relative size of the root system in Lolium perenne. I. Solutions containing both NH+4 and NO3−

Abstract Lolium perenne L. cv. S23 was grown in flowing culture solution, pH 5, in which the concentrations of NH₄⁺, NO₃^? and K⁺ were frequently monitored and adjusted to set values. In a pre-experimental period, plants were acclimatized to a regime in which roots were treated at 5°C with shoots at 25°C. The root temperature was then changed to one of the following, 3, 7, 9, 11, 13, 17 or 25°C, while air temperature remained at 25°C. When root temperature was increased from 5X, the relative growth rate of roots increased immediately while that of shoots changed much less for a period of approximately 9 d (phase 1). Thus, the root: shoot ratio increased, but eventually approached a new, temperature-dependent, steady value (phase 2). The fresh: freeze-dried weight ratio (i.e. water content) in shoots (and roots) increased during the first phase of morphological adjustment (phase 1). In both growth phases and at all temperatures, plants absorbed more NH₄⁺ than NO₄⁺, the tendency being extreme at temperatures below 9° where more than 85% of the N absorbed was NH₄⁺. Plants at different root temperatures, growing at markedly different rates, had very similar concentrations of total N in their tissues (cells) on a fresh weight basis, despite the fact that they derived their N with differing preference for NH₄⁺. Specific absorption rates for NH₄⁺, NO_x^?, K⁺ and H₂PO₄^? showed very marked dependence on root temperature in phase 1, but ceased to show this dependence once a steady state root: shoot ratio had been established in phase 2. The results indicate the importance of relative root size in determining ion fluxes at the root surface. At higher temperatures where the root system was relatively large, ‘demand’ per unit root was low, whereas at low temperatures roots were small relative to shoots and ‘demand’ was high enough to offset the inhibitory effects of low temperature on transport processes.     

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 different nitrogen forms on photosynthetic rate and the chlorophyll fluorescence induction kinetics of flue-cured tobacco

Net photosynthetic rate (P _N) of tobacco plants grown with NH₄-N as the only N source was the lowest all the times, while P _N grown only with NO₃-N was the greatest until 22^nd day, and P _N grown with both NO₃-N and NH₄-N (1 : 1) was the greatest. Maximal photochemical efficiency of photosystem 2 (PS2), F_v/F_m, and actual quantum yield of PS2 under actinic irradiation (Φ_PS2) in plants grown with only NH₄-N were greatest at early stage and then decreased and were smaller than those of other treatments. Photochemical quenching coefficient (q_P) and non-photochemical quenching coefficient (q_NP) in the NH₄-N plants were the greatest at all times. Hence excessive NH₄-N can decrease not only photochemical efficiency but also the efficiency of utilization of photon energy absorbed by pigments for photosynthesis. Therefore, excessive NH₄-N is a hindrance to photosynthesis of flue-cured tobacco. On the other hand, tobacco cultured with an appropriate mixture of NO₃-N with NH₄-N can sufficiently utilize photon energy and increase the efficiency of energy transformation.     

The influence of nitrogen concentration and ammonium/nitrate ratio on N-uptake,mineral composition and yield of citrus

In short-term water culture experiments with different ¹⁵N labeled ammonium or nitrate concentrations, citrus seedlings absorbed NH₄ ⁺ at a higher rate than NO₃ ^–. Maximum NO₃ ^– uptake by the whole plant occurred at 120 mg L^–1 NO₃ ^–-N, whereas NH₄ ⁺ absorption was saturated at 240 mg L^–1 NH₄ ⁺-N. ¹⁵NH₄ ⁺ accumulated in roots and to a lesser degree in both leaves and stems. However, ¹⁵NO₃ ^– was mostly partitioned between leaves and roots.Adding increasing amounts of unlabeled NH₄ ⁺ (15–60 mg L^–1 N) to nutrient solutions containing 120 mg L^–1 N as ¹⁵N labeled nitrate reduced ¹⁵NO₃ ^– uptake. Maximum inhibition of ¹⁵NO₃ ^– uptake was about 55% at 2.14 mM NH₄ ⁺ (30 mg L^–1 NH₄ ⁺-N) and it did not increase any further at higher NH₄ ⁺ proportions.In a long-term experiment, the effects of concentration and source of added N (NO₃ ^– or NH₄ ⁺) on nutrient concentrations in leaves from plants grown in sand were evaluated. Leaf concentration of N, P, Mg, Fe and Cu were increased by NH₄ ⁺ versus NO₃ ^– nutrition, whereas the reverse was true for Ca, K, Zn and Mn.The effects of different NO₃ ^–-N:NH₄ ⁺-N ratios (100:0, 75:25, 50:50, 25:75 and 0:100) at 120 mg L^–1 total N on leaf nutrient concentrations, fruit yield and fruit characteristics were investigated in another long-term experiment with plants grown in sand cultures. Nitrogen concentrations in leaves were highest when plants were provided with either NO₃ ^– or NH₄ ⁺ as a sole source of N. Lowest N concentration in leaves was found with a 75:25 NO₃ ^–-N/NH₄ ⁺-N ratio. With increasing proportions of NH₄ ⁺ in the N supply, leaf nutrients such as P, Mg, Fe and Cu increased, whereas Ca, K, Mn and Zn decreased. Yield in number of fruits per tree was increased significantly by supplying all N as NH₄ ⁺, although fruit weight was reduced. The number of fruits per tree was lowest with the 75:25 NO₃ ^–-N:NH₄ ⁺-N ratio, but in this treatment fruits reached their highest weight. Rind thickness, juice acidity, and colour index of fruits decreased with increasing NH₄ ⁺ in the N supply, whereas the % pulp and maturity index increased. Percent of juice in fruits and total soluble solids were only slightly affected by NO₃ ^–:NH₄ ⁺ ratio.     

The nitrogen balance of Raphanus sativus x raphanistrum plants. II. Growth, nitrogen redistribution and photosynthesis under NO3− deprivation

Abstract. Wild radish plants deprived of, and continuously supplied with solution NO^?₃ for 7 d following 3 weeks growth at high NO^?₃ supply were compared in terms of changes in dry weight, leaf area, photosynthesis and the partitioning of carbon and nitrogen (NH₂-N and NO^?₃-N) among individual organs. Initial levels of NO^?₃-N accounted for 25% of total plant N. Following termination of NO^?₃ supply, whole plant dry weight growth was not significantly reduced for 3 d, during which time plant NH₂-N concentration declined by about 25% relative to NO^?₃-supplied plants, and endogenous NO^?₃-N content was reduced to nearly zero. Older leaves lost NO^?₃ and NH₂-N, and roots and young leaves gained NH₂-N in response to N stress. Relative growth rate declined due both to decreased net assimilation rate and a decrease in leaf area ratio. A rapid increase in specific leaf weight was indicative of a greater sensitivity to N stress of leaf expansion compared to carbon gain. In response to N stress, photosynthesis per unit leaf area was more severely inhibited in older leaves, whereas weight-based rates were equally inhibited among all leaf ages. Net photosynthesis was strongly correlated with leaf NH₂-N concentration, and the relationship was not significantly different for leaves of NO₃^?-supplied compared to NO^?₃-deprived plants. Simulations of the time course of NO^?₃ depletion for plants of various NH₂-N and NO^?₃ compositions and relative growth rates indicated that environmental conditions may influence the importance of NO^?₃ accumulation as a buffer against fluctuations in the N supply to demand ratio.     

Contrasting nitrogen uptake by diatom and Phaeocystis-dominated phytoplankton assemblages in the North Sea

This paper documents ambient concentrations of nutrients in the Belgian coastal waters of the North Sea during the spring of 1996 and 1997. The paper elaborates the differences of uptake rates of oxidised nitrogen (NO₃⁻) and reduced nitrogen (NH₄ and urea) by Phaeocystis and diatoms. The nitrogen concentrations were dominated by NO₃⁻ with a maximum concentration of 30 μM (January 1997) and 40 μM (March 1996). In 1996, Phaeocystis dominated the spring biomass with a maximum of 521 μg C l⁻¹, while maximum diatom biomass was 174 μg C l⁻¹. In 1997, the maximum Phaeocystis spring biomass was 1600 μg C l⁻¹ and diatom maximum biomass was below 100 μg C l⁻¹. A maximum bacteria biomass of about 55 μg C l⁻¹ was observed in mid-May 1996. The maximum nitrogen uptake rates were recorded during spring and were dominated by NO₃⁻ (0.005 h⁻¹ in 1996 and 0.032 h⁻¹ in 1997). Maximum specific NH₄ uptake rates were between 0.005 h⁻¹ in May 1996 and 0.006 h⁻¹ in April 1997. The NO₃⁻ uptake rates displayed exponential decrease versus increasing ambient reduced nitrogen concentrations (ammonium and urea), whereas the reduced nitrogen uptake increased but never compensated the decreased nitrate uptake. The NH₄ uptake kinetics of diatoms displayed lower v_max compared to Phaeocystis. Consequently, Phaeocystis showed ability to increase their NH₄ uptake capacity when more NH₄ became available while diatoms failed to do so, after ammonium had exceeded their saturation concentration (>1 μM). Although reduced nitrogen has a negative effect on the uptake of NO₃⁻, Phaeocystis have more advantage than diatoms on the uptake of ammonium. This might be contributing to the biomass domination shown by Phaeocystis over extended periods in spring.     

马尾松组培苗对氮素形态的生长响应

马尾松属高氮需求树种,然而在苗木培育中马尾松对氮素,尤其是不同形态氮素的需求尚不明确。该文以马尾松组培苗为试验材料,采用基质培养方法,针对硝态氮、铵态氮两种氮素形态均分别设置了2、4、8、16 mmol·L~(-1)4个处理,以不添加氮素为对照,对苗木的高径生长、根构型参数(总根长、总表面积、总体积、平均直径和根尖数)以及生物量的变化进行了分析。结果表明:(1)在2～8 mmol·L~(-1)硝态氮处理下,除根冠比外,苗高、地径、根构型参数、生物量均不低于对照,其中以2 mmol·L~(-1)水平下苗木生长效果最好,苗高、地径、根构型参数、生物量均高于对照;在16 mmol·L~(-1)硝态氮处理下,苗高、总根长与根尖数低于对照。(2)在2～16 mmol·L~(-1)供试范围内,铵态氮处理下的苗木根冠比小于对照,但其苗高、地径、根构型参数、生物量均不低于对照,整体上以4 mmol·L~(-1)处理下的苗木生长表现最佳。(3)在任一供氮水平,除根冠比和2mmol·L~(-1)处理下的根总表面积与根尖数在两种氮素形态间无明显差异外,铵态氮处理下的苗木生长情况显著优于硝态氮处理,这说明马尾松组培苗偏好于吸收和利用铵态氮。综上结果表明,外施硝态氮、铵态氮均能促进马尾松组培苗生长,但需控制在适宜浓度范围内,其中以2 mmol·L~(-1)硝态氮和4 mmol·L~(-1)铵态氮处理效果较佳。高浓度硝态氮会抑制苗木高度及根系发育,且在相同施肥水平下,对苗木生长的促进效果大多弱于铵态氮。因此,今后为达到培育优质壮苗和提高肥效、减少肥害的目的,可考虑使用铵态氮肥。     

The effect of nutrients and environmental conditions on biomass and oil production in Botryococcus braunii Race B strains

The green alga Botryococcus braunii is widely recognized as a source of non-fossil oil. However, limitations in Botryococcus biomass production hamper its commercial exploitation. This study examines the effects of nutrients (nitrogen and iron) and environmental conditions (temperature, light intensity and photoperiod) on biomass and oil production in two B. braunii Race B strains, Kossou-4 and Overjuyo-3. The highest biomass and oil production were obtained at a nitrogen concentration of 750 mg l^?1, iron concentration of 6 mg l^?1, at 25°C and at 135 µmol photons m^?2 s^?1 with a photoperiod of 16 h light:8 h darkness. Culturing the strains in Blue-green (BG11) medium containing optimized nutrients under optimal conditions resulted in an up to ~10.6-fold increase in biomass. In Kossou-4 and Overjuyo-3 strains, biomass increased from 1.647 g 10 l^?1 and 3.137 g 10 l^?1 respectively in normal BG11 medium to 17.390 g 10 l^?1 and 21.721 g 10 l^?1 in optimized BG11 media and growth conditions. This was accompanied by ~8–10.5-fold increase in oil production compared with that in normal BG11 medium. Oil (0.324 g 10 l^?1 and 0.211 g 10 l^?1) was produced in normal BG11 medium in Kossou-4 and Overjuyo-3 strains respectively, compared with 2.642 g 10 l^?1 (Kossou-4) and 2.206 g 10 l^?1 (Overjuyo-3) in modified BG11 media under optimized conditions. Therefore, optimization of nutrients and environmental conditions can increase biomass and oil production in the two strains of B. braunii.     

Biomass and terpenoids produced by mutant strains of <Emphasis Type="Italic">Arthrospira</Emphasis> under low temperature and light conditions

The filamentous Cyanobacterium Arthrospira is commercially produced and is a functional, high-value, health food. We identified 5 low temperature and low light intensity tolerant strains of Arthrospira sp. (GMPA1, GMPA7, GMPB1, GMPC1, and GMPC3) using ethyl methanesulfonate mutagenesis and low temperature screening. The 5 Arthrospira strains grew rapidly below 14?°C, 43.75 μmol photons m^?2 s^?1 and performed breed conservation at 2.5?°C, 8.75 μmol photons m^?2 s^?1. We used morphological identification and molecular genetic analysis to identify GMPA1, GMPA7, GMPB1 and GMPC1 as Arthrospira platensis, while GMPC3 was identified as Arthrospira maxima. Growth at different culture temperatures was determined at regular intervals using dry biomass. At 16?°C and 43.75 μmol photons m^?2 s^?1, the maximum dry biomass production and the mean dry biomass productivity of GMPA1, GMPB1, and GMPC1 were 2057?±?80 mg l^?1, 68.7?±?2.5 mg l^?1 day^?1, 1839?±?44 mg l^?1, 60.6?±?1.8 mg l^?1 day^?1, and 2113?±?64 mg l^?1, 77.7?±?2.5 mg l^?1 day^?1 respectively. GMPB1 was chosen for additional low temperature tolerance studies and growth temperature preference. In winter, GMPB1 grew well at mean temperatures <10?°C, achieving 3258 mg dry biomass from a starting 68 mg. In summer, GMPB1 grew rapidly at mean temperatures more than 28?°C, achieving 1140 mg l^?1 dry biomass from a starting 240 mg. Phytonutrient analysis of GMPB1 showed high levels of C-phycocyanin and carotenoids. Arthrospira metabolism relates to terpenoids, and the methyl-d-erythritol 4-phosphate pathway is the only terpenoid biosynthetic pathway in Cyanobacteria. The 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) gene from GMPB1 was cloned and phylogenetic analysis showed that GMPB1 is closest to the Cyanobacterium Oscillatoria nigro-viridis PCC711. Low temperature tolerant Arthrospira strains could broaden the areas suitable for cultivation, extend the seasonal cultivation time, and lower production costs.