Enrichment and granulation of Anammox biomass started up with methanogenic granular sludge

A sequencing batch reactor (SBR) seeded with methanogenic granular sludge was started up to enrich Anammox (Anaerobic Ammonium Oxidation) bacteria and to investigate the feasibility of granulation of Anammox biomass. Research results showed that hydraulic retention time (HRT) was an important factor to enrich Anammox bacteria. When the HRT was controlled at 30 days during the initial cultivation, the SBR reactor presented Anammox activity at t = 58 days. Simultaneously, the methanogenic granular sludge changed gradually from dust black to brown colour and its diameter became smaller. At t = 90 days, the Anammox activity was further improved. NH₄⁺-N and NO₂⁻N were removed simultaneously with higher speed and the maximum removal rates reached 14.6 g NH₄⁺-N /(m³ _reactor·day) and 6.67 g NO₂⁻-N /(m³ _reactor·day), respectively. Between t = 110 days and t = 161 days, the nitrogen load was increased to a HRT of 5 days (70 mg/l NH₄⁺ and 70 mg/l NO₂), the removal rates of ammonium and nitrite were 60.6% and 62.5% respectively. The sludge changed to red and formed Anammox granulation with high nitrogen removal activity.     

Dynamics of nitrogen remobilization in defoliated Phleum pratense and Festuca pratensis under short and long photoperiods

The impact of photoperiod on the rate and magnitude of N remobilization relative to uptake of inorganic N during the recovery of shoot growth after a severe defoliation was compared over 18 days in two temperate grass species, timothy (Phleum pratense L. cv. Bodin) and meadow fescue (Festuca pratensis Huds. cv. Salten). Plants were grown in flowing solution culture with N supplied as 20 mM NH₄NO₃ and pre-treated by extending the 11 h photosynthetically significant light period either by 1 h (short-day or SD plants) or 7 h (long-day or LD plants) of very low light intensity, during the 10 days prior to defoliation. Following a single severe defoliation, ¹⁵N-labelled NH₄⁺ or NH₄⁺+ NO₃^? was supplied over a 20-day recovery period under the same SD and LD conditions. Changes in the relative contributions of remobilized N and newly acquired mineral N to shoot regrowth were assessed by sequential harvests. Both absolute and relative rates of N remobilization from root and stubble fractions were higher in LD than SD plants of both species, with the enhancement more acute but of shorter duration in timothy than fescue. Remobilized N was the predominant source of N for shoot regrowth in all treatments between days 0 and 8 after cutting; on average more so for fescue than timothy, because the presence of NO₃^? reduced the proportional contribution of remobilized N to the regrowth of timothy but not of fescue. Net uptake of mineral N began to recover between days 4 and 6 after cutting, with NO₃^? uptake restarting 1 or 2 days earlier than NH₄⁺ uptake, even when NH₄⁺ was the only form of N supply. LD timothy plants supplied solely with NH₄⁺ were slowest to resume uptake of mineral N. Supplying NO₃^? in addition to NH₄⁺ after defoliation promoted shoot regrowth rate but not remobilization of N. Rates of regrowth (shoot dry weight production per plant) were not correlated with rates of N remobilization from stubble either over the short-term (days 0–8) or longer term (days 0–18), interpreted as evidence against a causal dependence of regrowth rate on N remobilization under these conditions. The results are discussed in relation to hypotheses for source/sink-driven rates of N remobilization and their interactions with mineral N uptake following defoliation.     

Utilization of Ammonium as a Nitrogen Source : Effects of Ambient Acidity on Growth and Nitrogen Accumulation by Soybean

Dry matter accumulation of plants utilizing NH₄⁺ as the sole nitrogen source generally is less than that of plants receiving NO₃⁻ unless acidity of the root-zone is controlled at a pH of about 6.0. To test the hypothesis that the reduction in growth is a consequence of nitrogen stress within the plant in response to effects of increased acidity during uptake of NH₄⁺ by roots, nonnodulated soybean plants (Glycine max [L.] Merr. cv Ransom) were grown for 24 days in flowing nutrient culture containing 1.0 millimolar NH₄⁺ as the nitrogen source. Acidities of the culture solutions were controlled at pH 6.1, 5.1, and 4.1 ± 0.1 by automatic additions of 0.01 n H₂SO₄ or Ca(OH)₂. Plants were sampled at intervals of 3 to 4 days for determination of dry matter and nitrogen accumulation. Rates of NH₄⁺ uptake per gram root dry weight were calculated from these data. Net CO₂ exchange rates per unit leaf area were measured on attached leaves by infrared gas analysis. When acidity of the culture solution was increased from pH 6.1 to 5.1, dry matter and nitrogen accumulation were reduced by about 40% within 14 days. Net CO₂ exchange rates per unit leaf area, however, were not affected, and the decreased growth was associated with a reduction in rates of appearance and expansion of new leaves. The uptake rates of NH₄⁺ per gram root were about 25% lower throughout the 24 days at pH 5.1 than at 6.1. A further increase in solution acidity from pH 5.1 to 4.1 resulted in cessation of net dry matter production and appearance of new leaves within 10 days. Net CO₂ exchange rates per unit leaf area declined rapidly until all viable leaves had abscised by 18 days. Uptake rates of NH₄⁺, which were initially about 50% lower at pH 4.1 than at 6.1, continued to decline with time of exposure until net uptake ceased at 10 days. Since these responses also are characteristic of the sequence of responses that occur during onset and progression of a nitrogen stress, they corroborate our hypothesis.     

Resistance of the European catfish (Silurus glanis) to channel catfish virus

European catfish (Silurus glanis) fingerlings (2 to 4 g each) were tested for susceptibility to channel catfish virus (CCV). They had supported CCV replication at 2 days after intraperitoneal injection with 0.1 ml of saline containing 10⁵ TCID₅₀. Homogenized visceral organs (liver, kidney and spleen) contained 10⁴ TCID₅₀/0.1 ml at 2 days post inoculation (PI) but at 4 days the titer decreased to 10¹ TCID₅₀. Bathing European catfish in CCV yielded only one positive sample with à titer of 10^0.83 TCID₅₀ per 0.1 ml of tissue. No clinical signs of CCV developed and no virus related deaths occurred.     

Pathogenicity of the entomogenous fungi Metarhizium anisopliae and Beauveria bassiana against crucifer pests and the honey bee

The susceptibility of the cabbage stem flea beetle (Psylliodes chrysocephala; Coleoptera: Chrysomelidae) to different isolates of the entomogenous, hyphomycete fungi Beauveria bassiana and Metarhizium anisopliae, all from heterologous hosts, was investigated. The most pathogenic isolates were of M. anisopliae (V208, V233, V234, V242, V245, and V248). Studies were conducted to determine the virulence of V208 and V245, and their specificity for three other crucifer pests, Phaedon cochleariae, Myzus persicae and Lipaphis erysimi and a beneficial insect, Apis mellifera. Flea beetle mortality rates increased with dose; the estimated LC₅₀ ^S of V208 and V245 at 14 days post‐inoculation were c. 10⁶ conidia ml^‐1. The respective estimated LT₅₀ values of V208 and V245 for P. chrysocephala at 1 × 10⁷ conidia ml^‐1 were 10.0 and 9.3 days, and at 1 × 10¹⁰ conidia ml LT₅₀s were 3.8 and 4.2 days. Both V208 and V245 were pathogenic for P. cochleariaeM. persicae and L. erysimi. Myzus persicae and L. erysimi died within 4 days of inoculation. Bees were less susceptible to infection at low doses, but at 1 × 10¹⁰ conidia ml^‐1almost all bees had died by day 5 when the estimated LT₅₀s for V208 and V245 were 4.4 and 8.5 days respectively.     

Response of oxidative stress defense systems in rice (Oryza sativa) leaves with supplemental UV-B radiation

The impact of elevated ultraviolet-B radiation (UV-B, 280–320 nm) on membrane systems and lipid peroxidation, and possible involvement of active oxygen radicals was investigated in leaves of two UV-B susceptible rice cultivars (Oryza sativa L. cvs IR74 and Dular). Rice seedlings were grown in a greenhouse for 10 days and then treated with biologically effective UV-B (UV-B_BE) radiation for 28 days. Oxidative stress effects were evaluated by measuring superoxide anion (O₂) generation rate, hydrogen peroxide (H₂O₂) content, malondialdehyde (MDA) concentration and relative electrolyte conductivity (EC) for IR74 and Dular at 0 (control), 6 or 13 kJ m^?2 day^?1 UV-B_BE. Significant increases in these parameters were found in rice plants grown at 13 vs 0 kJ m^?2 day^?1 UV-B_BE after 28 days; indicating that disruption of membrane systems may be an eventual reason for UV-B-induced injury in rice plants. There was a positive correlation between O₂^? generation and increases in EC or MDA in leaves. Activities of enzymatic and nonenzymatic free radical scavengers were measured for IR74 after 7, 14, 21 and 28 days of exposure to 13 or 0 UV-B_BE to evaluate dynamics of these responses over time. Activities of catalase and superoxide dismutase (but not ascorbate peroxidase) and concentrations of ascorbic acid and glutathione were enhanced by 13 vs 0 UV-B_BE after 14 days of UV-B exposure. Further exposure to 28 days of UV-B was associated with a decline in enzyme activities and ascorbic acid, but not glutathione. It is suggested that UV-B-induced injury may be associated with disturbance of active oxygen metabolism through the destruction and alteration of both enzymatic and nonenzymatic defense systems in rice.     

Simultaneous removal of phosphorus and nitrogen in sequencing batch reactor

In this research, investigations were made on material transfer mechanisms and optimum operation mode for sequencing batch reactor system removing phosphorus and nitrogen simultaneously. Phosphorus release characteristics were expressed in the Monod equation, in which the reaction rate was replaced with specific phosphorus release (SPR) rate. The rate of SPR was increased during the first 80 days, but increased sharply to reach 0.003 hr^-1 afterwards. Phosphorus removal efficiencies were about 60% in the first 80 days, 75% after 80 days, and above 95% after 120 days. After 120 days, phosphorus concentration in effluent was below 0.5 mgl^-1 when 8 mgl^-1 was in the influent and the released phosphorus after 3-hour-anaerobic period was 60 mgl^-1. In the proposed optimum operation strategy (2-hour anaerobic react, 3-hour aerobic react, 4-hour anoxic react, and 3-hour settle and draw), phosphorus reappeared if the oxidized nitrogen was completely denitrified. In order to prevent this undesirable phosphorus release, anoxic period should be reduced to the extent of which the minimal concentration of the oxidized nitrogen existed. Phosphorus removal efficiency was stable under shock load as 5 times high as normal phosphorus concentration.Abbreviations dP/dt Phosphorus release rate (mgl^-1 hr^-1) - K Phosphorus release yield constant (mg P mg TOC^-1) - dS/dt Substrate utilization rate (mgl^-1 hr^-1) - X Mixed liquor suspended solid (MLSS, mgl^-1) - S Soluble TOC (mgl^-1) - k-q_max (Y_max)^-1 Maximum substrate utilization rate - Y Yield coefficient (mg mg^-1) - K_s Saturation constant (mgl^-1) - P_max kK-Maximum phosphorus release rate (hr^-1) - P_rel Total released phosphorus (mgl^-1) - P_o Phosphorus in influent (mgl^-1) - P_e phosphorus in effluent (mgl^-1) - t Anaerobic period (hr)     

Chloride conductance of denervated gastrocnemius fibers from normal goats

Membrane potentials, cable parameters, and component resting ionic conductances of gastrocnemius fibers from normal goats were measured in vitro at six to 32 days following denervation by section of the tibial nerve. Denervated fibers were depolarized an average of 11.6 ± 1.5 mV (six preparations) from the control mean of 62.1 ± 1.0 mV (124 fibers) over the period studied. Fibrillation, tetrodotoxin-resistant action potentials, and anodebreak excitation were present in the denervated preparations after 13 days. The control cable parameters from 124 fibers (13 preparations) were membrane resistance, 1052 ± 70 ω·cm² and membrane capacitance, 6.2 μF/cm². In denervated fibers membrane resistance increased two to three times in the 13 to 32 day period; membrane capacitance increased about 50% in normal solution at eight to nine, 27–28, and 32 days. Myoplasmic resistivity was assumed to be 112 Ωcm. Measurements were made at 38°C. Component resting conductances were determined from the cable parameters in normal and chloride-free solution. Mean chloride conductance G_Cl and mean potassium conductance G_K of control fibers were 776 ± 49 μmhos/cm² and 175 ± 15 μmhos/cm² (92 fibers), respectively. Following denervation G_Cl increased slightly at six to nine days then fell to low values at 16 to 32 days that were close to or indistinguishable from zero. G_K increased significantly to 372 ± 40 μmhos/cm² and 499 ± 90 μmhos/cm² at 16 to 20 and 32 days, respectively. It was concluded from these findings that G_Cl and G_K of mammalian skeletal muscle are controlled by factors from the nerve and/or muscle action potentials. Goat muscle is different from frog muscle in which G_Cl does not change and G_K decreases during denervation.     

Nitrification inhibitors

Summary The effects of furano compounds, furfural (furfuraldehyde) and furfuryl alcohol (5, 10, 20 and 30% of N applied) on nitrification of ammonium sulfate and urea N were studied in a sandy clay loam in laboratory. Both furfural and furfuryl alcohol significantly retarded the nitrification rates of both the fertilizers by inhibiting the conversion of NH₄ ⁺ to NO₂ ^- without affecting the oxidation of NO₂ ^- to NO₃ ^--N. 10, 20 and 30% concentrations of the compounds were effective up to 75 days with ammonium sulfate but more or less up to 45 days with urea. re]19760322     

Studies of alveolar cell morphometry and mass clearance in the rat lung following inhalation of an enriched uranium dioxide aerosol

Summary Seventy-three rats were exposed to an aerosol of enriched uranium dioxide (UO₂), giving initial lung burdens of 26 to 447 µg at 6 days post-inhalation (PI). At 7 days PI 35 of these rats were further exposed to thermalised neutrons at a fluence of 1 x 10¹² neutrons CM^–2. There was no significant difference between the two groups in the clearance rate of the UO₂ particles from the lung, up to 590 days PI. The particles cleared relatively slowly over this period with a retention halftime in the lung of 160 to 176 days.Transmission electron microscope (TEM) studies of tissue from the alveolar region at 8 days PI showed that inhalation of UO₂ particles significantly increased the sizes of macrophage and type II cells, and the number of macrophage and type I cells. There was also a significant increase in the size of lysosomal granules within the macrophages after exposure to the UO₂ particles. The exposure to UO₂, neutrons and²³⁵U fission fragments had no significant effect on any of the cells above that observed in the animals exposed to UO₂ alone.Additional rats were exposed to the same neutron fluence without prior UO₂ inhalation. The alveolar cells of neutron-only exposed rats were, in size and number, typically no different from those in the completely unexposed control rats.     

Functional and molecular consequences of ionizing irradiation on large conductance Ca2+-activated K+ channels in rat aortic smooth muscle cells

AimsThe goal of this study was to evaluate the influence of γ-irradiation on Ca²⁺-activated K⁺ channel (BK_Ca) function and expression in rat thoracic aorta.Main methodsAortic cells or tissues were studied by the measurement of force versus [Ca²⁺]_i, patch-clamp technique, and RT-PCR.Key findingsStimulation of smooth muscle cells with depolarizing voltage steps showed expression of outward K⁺ currents. Paxilline, an inhibitor of BK_Ca channels, decreased outward K⁺ current density. Outward currents in smooth muscle cells obtained from irradiated animals 9 and 30 days following radiation exposure demonstrated a significant decrease in K⁺ current density. Paxilline decreased K⁺ current in cells obtained 9 days, but was without effect 30 days after irradiation suggesting the absence of BK_Ca channels. Aortic tissue from irradiated animals showed progressively enhanced contractile responses to phenylephrine in the post-irradiation period of 9 and 30 days. The concomitant Ca²⁺ transients were significantly smaller, as compared to tissues from control animals, 9 days following irradiation but were increased above control levels 30 days following irradiation. Irradiation produced a decrease in BK_Ca α- and β₁-subunit mRNA levels in aortic smooth muscle cells suggesting that the vasorelaxant effect of these channels may be diminished.SignificanceThese results suggest that the enhanced contractility of vascular tissue from animals exposed to radiation may result from an increase in myofilament Ca²⁺ sensitivity in the early post-irradiation period and a decrease in BK_Ca channel expression in the late post-irradiation period.     

Efficacy of entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae against Thaumetopoea pityocampa Shiff. (Lepidoptera: Thaumatopoeidae)

Abstract

In this study, Metarhizium anisopliae TR 106 and Beauveria bassiana TR 217 was tested against fourth instar larvae of Thaumetopoea pityocampa. The LT₅₀ and LT₉₀ of 1?×?10⁶ concentration of M. anisopliae against T. pityocampa were 3.60 and 4.11 for direct application, while these were 2.87 and 3.60?days, respectively in leaves application. The LT₅₀ and LT₉₀ of the 1?×?10⁸ concentration of the same isolate were 2.50 and 2.95?days for direct application, and 2.98 and 3.74?days for leaves application. The LT₅₀ of insect and leaves application for 1?×?10⁶ of B. bassiana were 3.75 and 3.49?days, respectively. The LT₉₀ of same concentration for insect application was 4.48?days, while LT₉₀ for leaves application was 4.63?days. Similarly, LT₅₀ of insect and leaves application for 1?×?10⁸ of B. bassiana were 3.03 and 3.31?days, while LT₉₀ were 3.68 and 4.29?days, respectively. Approximate 100% mycosis was observed in all treatments.     

Influence of inorganic nitrogen sources on K+/Na+ homeostasis and salt tolerance in sorghum plants

This work aimed to study the regulation of K⁺/Na⁺ homeostasis and the physiological responses of salt-treated sorghum plants [Sorghum bicolor (L.) Moench] grown with different inorganic nitrogen (N) sources. Four days after sowing (DAS), the plants were transferred to complete nutrient solutions containing 0.75 mM K⁺ and 5 mM N, supplied as either NO₃ ^? or NH₄ ⁺. Twelve DAS, the plants were subjected to salt stress with 75 mM NaCl, which was applied in two doses of 37.5 mM. The plants were harvested on the third and seventh days after the exposure to NaCl. Under the salt stress conditions, the reduction of K⁺ concentrations in the shoot and roots was higher in the culture with NO₃ ^? than with NH₄ ⁺. However, the more conspicuous effect of N was on the Na⁺ accumulation, which was severely limited in the presence of NH₄ ⁺. This ionic regulation had a positive influence on the K⁺/Na⁺ ratio and the selective absorption and transport of K⁺ in the plants grown with NH₄ ⁺. Under control and salt stress conditions, higher accumulation of free amino acids and soluble proteins was promoted in NH₄ ⁺ grown roots than NO₃ ^? grown roots at both harvesting time, whereas higher accumulation of soluble sugars was observed only at 7 days of salt stress exposure. Unlike the NH₄ ⁺ grown plants, the gas exchanges of the NO₃ ^? grown plants were reduced after 7 days of salt stress. These results suggest that external NH₄ ⁺ may limit Na⁺ accumulation in sorghum, which could contribute to improving its physiological and metabolic responses to salt stress.     

Phenotypic variation in the agronomic and morphological traits of <Emphasis Type="Italic">Pisum sativum</Emphasis> L. Germplasm obtained from different parts of the world

A total of 286 genotypes were collected from 39 countries of the world and were evaluated to determine the phenotypic diversity for 17 quantitative traits. Higher degree of coefficient of variation were recorded for grain yield⁻⁵ (52.46%), biomass⁻⁵ (45.73%), fresh pod width-10 (47.24%), dry pod weight⁻¹⁰ (40.33%), plant height⁻¹ (35.25%), harvest index (32.70%) and number of branches⁻⁵. Cluster-II clearly reflected that late genotypes were having lightest pods weight, shortest pod width, and pod length; low grain yield, biomass and harvest index. Width, and pod length; low grain yield, biomass and harvest index. While genotypes in Cluster-III were in contrast to Cluster-II having heaviest pods weight, longest pods width and length, highest grain yield, biomass and harvest index. Higher PC₋₁ values have been determined for days to flower initiation which consequently were contributing weighed positive to days to pods picking, days to flower completion, days to dry pod appearance, days to plant harvesting while negatively contributed to yield producing traits, indicating that late flowering pea germplasm emphasizes more on the vegetative growth and was low yielding. However, higher PC₋₂ values have been obtained for number of branches⁻⁵, grain yield and biomass while lower values for days to flowering, days to pods picking, days to flower completion, days to dry pod appearance and days to plant harvesting confirming the fact that early genotypes were high yielding.     

Influence of Lime and Organic Matter on the Mobility of Cadmium in Cadmium-Contaminated Soil in Relation to Nutrition of Spinach

Cadmium and cadmium compounds are water soluble, mobile in most soils, bio-available, and tend to bio-accumulate. A pot culture experiment was conducted on contaminated soil to study the influence of lime and organic matter on the mobility of cadmium in spinach and its rhizosphere soil. Application of lime (50% and 100% lime requirement) and organic matter (0.5 and 1% by weight of soil) to soil decreased the availability of Cd to the soil and plant throughout the crop growth. The highest diethylene triamine penta-acetic acid (DTPA) extractable Cd was 10.84 mg kg^?1 in the treatment OM₀ L₀ (No application of organic matter and lime) at 20 days after sowing of spinach. Likewise, the highest Cd concentration in spinach roots and shoots were 19.80 and 17.0 mg kg^?1 in the treatment OM₀ L₀ at 20 days after sowing. The Cd concentration in spinach roots and shoots were decreased by 63.23 and 71.88%, respectively, in the treatment OM₁ L₁₀₀ (application of FYM at 1.0% by weight of soil and lime at 100% lime requirement) after 60 days of growth. The lowest concentrations of Cd in the soil and plant after the harvest of the crop were 2.88 and 4.27 mg kg^?1, respectively, in the treatment OM₁ L₁₀₀ and resulted in 65.75 and 71.55% decrease over control (OM₀ L₀). The highest total chlorophyll content of leaves was 2.19 mg kg^?1 of fresh weight in the treatment OM₁ L₁₀₀ at 40 days of crop growth.     

Heterotrophic n(2) fixation and distribution of newly fixed nitrogen in a rice-flooded soil system

Rice (Oryza sativa L.) plants growing in pots of flooded soil were exposed to a ¹⁵N₂-enriched atmosphere for 3 to 13 days in a gas-tight chamber. The floodwater and soil surface were shaded with a black cloth to reduce the activity of phototrophic N₂-fixing micro-organisms. The highest ¹⁵N enrichments were consistently observed in the roots, although the total quantity of ¹⁵N incorporated into the soil was much greater. The rate of ¹⁵N incorporation into roots was much higher at the heading than at the tillering stage of growth. Definite enrichments were also found in the basal node and in the lower outer leaf sheath fractions after 3 days of exposure at the heading stage. Thirteen days was the shortest time period in which definite ¹⁵N enrichment was observed in the leaves and panicle. When plants were exposed to ¹⁵N₂ for 13 days just before heading and then allowed to mature in a normal atmosphere, 11.3% of the total ¹⁵N in the system was found in the panicles, 2.3% in the roots, and 80.7% in the subsurface soil. These results provide direct evidence of heterotrophic N₂ fixation associated with rice roots and the flooded soil and demonstrate that part of the newly fixed N is available to the plant.     

Estimation of leaf number and leaf area of hydroponic pak-choi plants (<Emphasis Type="Italic">Brassica campestns</Emphasis> ssp,<Emphasis Type="Italic">chinensis</Emphasis>) using growing degree-days

Temperature is a principal environmental factor that directly affects the growth and timing of appearance for crop leaves. To estimate the leaf number and leaf area of ‘Seoul’ pak-choi plants (Brassica campestns ssp.chinensis), we applied the concept of growing degree-days GDD=(T_avg-T_base) × days, where T_avg, T_base and days were the daily average air temperature, base temperature, and days after transplanting, respectively. Leaves that were beginning to unfold with a leaf area ≥1 cm₂ were counted every 2 to 3 d. Linear relationships were found between leaf number and days after transplanting as well as between leaf number and GDD. The rate of appearance and the number of leaves per GDD were 0.542 leaves d^-1 and 0.051 leaves oC^-1 d^-1, respectively. In contrast, the relationship was non-linear between leaf number and leaf area, with the latter being calculated as [(128.9+11.6×GDD-0.03×GDD²)/1+(0.051×GDD+3.5) /13.7)^-3.9] (cm₂oC¹ d^-1). Using model validation, we found that the estimated leaf number and leaf area showed strong agreement with measured values. our results demonstrate the usefulness of modeling to estimate total leaf area and growth from hydroponically grown pak-choi plants.     

Nitrogen Dynamics in Stream Wood Samples Incubated with [14C]Lignocellulose and Potassium [15N]Nitrate

Surface wood samples obtained from a Douglas fir log (Pseudotsuga menziesii) in a Pacific Northwest stream were incubated in vitro with [¹⁴C]lignocellulose in a defined mineral salts medium supplemented with 10 mg of N liter⁻¹ of ¹⁵N-labeled NO₃⁻ (50 atom% ¹⁵N). Evolution of ¹⁴CO₂, distribution and isotopic dilution of ¹⁵N, filtrate N concentrations, and the rates of denitrification, N₂ fixation, and respiration were measured at 6, 12, and 18 days of incubation. The organic N content of the lignocellulose-wood sample mixture had increased from 132 μg of N to a maximum of 231 μg of N per treatment after 6 days of incubation. Rates of [¹⁴C]lignocellulose decomposition were greatest during the first 6 days and then began to decline over the remaining 12 days. Total CO₂ evolution was also highest at day 6 and declined steadily over the remaining duration of the incubation. Filtrate NH₄⁺-N increased from background levels to a final value of 57 μg of N per treatment. Filtrate NO₃⁻ N completely disappeared by day 6, and organic N showed a slight decline between days 12 and 18. The majority of the ¹⁵N that could be recovered appeared in the particulate organic fraction by day 6 (41 μg of N), and the filtrate NH₄⁺ N fraction contained 11 μg of ¹⁵N by day 18. The ¹⁵N enrichment values of the filtrate NH₄⁺ and the inorganic N associated with the particulate fraction had increased to approximately 20 atom% ¹⁵N by 18 days of incubation, whereas the particulate organic fraction reached its highest enrichment by day 6. Measurements of N₂ fixation and denitrification indicated an insignificant gain or loss of N from the experimental system by these processes. The data show that woody debris in stream ecosystems might function as a rapid and efficient sink for exogenous N, resulting in stimulation of wood decomposition and subsequent activation of other N cycling processes.     

Aflatoxin B1, zearalenone and deoxynivalenol production on irradiated corn kernels: Influence of inoculum size

The influence of inoculum size on aflatoxin B₁ (AFB₁), zearalenone (ZEN) and deoxynivalenol (DON) production was examined on irradiated corn kernels. Spore concentrations were determined in serial dilutions and adjusted to 10,10²,10³,10⁵ and 10⁶ spores/ml. Aflatoxin B₁ production was dependent on the inoculum size. The high levels of aflatoxin B₁ produced byA. parasiticus (21 and 30 mg/kg) were obtained with 10² and 10³ spores/ml after 35 and 20 days incubation. There was no spore concentration influence on zearalenone and deoxynivalenol production after 10, 20 and 35 days incubation. At 28°C and 0.97 water activity (aw), the mean levels of zearalenone production were 382, 267 and 520 μg/kg and the mean levels on deoxynivalenol production were 697,465 and 782 μg/kg.