Changes in cell volume of bacteria and heterotrophic nanoflagellates in a hypereutrophic pond

Changes in cell volume of planktonic bacteria and heterotrophic nanoflagellates (HNF) were examined in a hypereutrophic pond from April to October, 1997. There were marked changes in the abundance of bacteria, HNF and ciliates and in protistan bacterivory during this period. The cell volume of free-living bacteria (0.121 ± 0.031 m³, mean ± SD) was large relative to that reported in the literature. The cell volumes of HNF was 71.1 ± 24.8 m³. Both cell volumes did not follow a seasonal trend. The dominant size class of bacteria was seasonally variable, whereas density of filamentous bacteria was relatively high between August and September. Biomass of filamentous bacteria accounted for up to 33.6% of total bacterial biomass. A correlation analysis for cell volume of bacteria and HNF, density of filamentous bacteria and some microbial variates was performed. The positive correlations detected (p<0.05) were between density of bacteria and cell volume of HNF, and between density of filamentous bacteria and cell volume of HNF.     

<Emphasis Type="Italic">Azospirillum</Emphasis> spp. from native forage grasses in Brazilian Pantanal floodplain: biodiversity and plant growth promotion potential

A sustainable alternative to improve yield and the nutritive value of forage is the use of plant growth-promoting bacteria (PGPB) that release nutrients, synthesize plant hormones and protect against phytopathogens (among other mechanisms). Azospirillum genus is considered an important PGPB, due to the beneficial effects observed when inoculated in several plants. The aim of this study was to evaluate the diversity of new Azospirillum isolates and select bacteria according to the plant growth promotion ability in three forage species from the Brazilian Pantanal floodplain: Axonopus purpusii, Hymenachne amplexicaulis and Mesosetum chaseae. The identification of bacterial isolates was performed using specific primers for Azospirillum in PCR reactions and partial sequencing of the 16S rRNA and nifH genes. The isolates were evaluated in vitro considering biological nitrogen fixation (BNF) and indole-3-acetic acid (IAA) production. Based on the results of BNF and IAA, selected isolates and two reference strains were tested by inoculation. At 31 days after planting the plant height, shoot dry matter, shoot protein content and root volume were evaluated. All isolates were able to fix nitrogen and produce IAA, with values ranging from 25.86 to 51.26 mg N mL^?1 and 107–1038 µmol L^?1, respectively. The inoculation of H. amplexicaulis and A. purpusii increased root volume and shoot dry matter. There were positive effects of Azospirillum inoculation on Mesosetum chaseae regarding plant height, shoot dry matter and root volume. Isolates MAY1, MAY3 and MAY12 were considered promising for subsequent inoculation studies in field conditions.     

Seasonal variation in cell volume of epilimnetic bacteria

The relationship between bacterial cell volume and temperature was examined for field data collected over a 4-year period and through controlled chemostat incubations of aPseudomonas sp. Volumes of planktonic bacteria were found to decrease as water temperature increased. Changes in temperature accounted for 38% of the variation in average cell volume (P<0.001). Average planktobacterial cell volume fell 42% from 0.217m³ in mid-winter to 0.127m³ in mid-summer. Similar results were found for the size distribution of epibacterial cells. Controlled chemostat incubations of aPseudomonas sp. indicated that cell volume was significantly affected by temperature, growth rate, and the interaction of temperature and growth rate. The data suggest that a change in cell volume as a result of a change in temperature is an intrinsic property of planktonic bacteria.     

Antioxidants from carbon dioxide fixing Chlorella sorokiniana

Chlorella sorokiniana H-84, which has toleranceto high temperatures and high concentrations ofCO₂, has been isolated from a hot spring inJapan. Large-scale culturing of C. sorokinianawas carried out in air containing 10% CO₂.Analysis of the biomass shows that protein, carbohydrate and lipids comprised 68.5, 11.9 and10.0% of dry matter, respectively. The totalcarotenoids comprised 0.69% dry matter. The luteinand -carotene contents were 4300 and 600 gg^-1 dry weight, respectively. The-tocopherol content was 112 g g^-1 dry weight. These carotenoids and -tocopherolare known to possess radical scavenging activity.Two fractions with radical scavenging activity wereisolated from the aqueous extract of C.sorokiniana H-84. The extract showed several singlepeaks by reversed phase HPLC analysis and two of themhad molecular weights of 710 and 1286, respectively.     

Dry matter production and photosynthetic capacity in Gossypium hirsutum L. under conditions of slightly suboptimum leaf temperatures and high levels of irradiance

Summary Gossypium hirsutum L. var. Delta Pine 61 was cultivated in controlled-environment chambers at 1000–1100 mol photosynthetically active photons m^-2 s^-1 (medium photon flux density) and at 1800–2000 mol photons m^-2 s^-1 (high photon flux density), respectively. Air temperatures ranged from 20° to 34°C during 12-h light periods, whereas during dark periods temperature was 25° C in all experiments. As the leaf temperature decreased from about 33° to 27° C, marked reductions in dry matter production, leaf chlorophyll content and photosynthetic capacity occurred in plants growing under high light conditions, to values far below those in plants growing at 27° C and medium photon flux densities. The results show that slightly suboptimum temperatures, well above the so-called chilling range (0–12° C), greatly reduce dry matter production in cotton when combined with high photon flux densities equivalent to full sunlight.Abbreviations DW dry weight - F _v variable fluorescence yield - F _M maximum fluorescence yield - PFD photon flux density (400–700 nm)     

Fermentation ofCandida utilis for uricase production

Summary Conditions for the production of microbial uricase byCandida utilis were studied. For the selected strain, hypoxanthine proved to be the most effective inducer of uricase formation. The highest values of biomass as well as uricase activity in the mechanically agitated fermentor were obtained under the following conditions: 50 h, rotation impeller speed 7 s^–1, air flow rate 1.25×10^–5 m³s^–1, concentration of inducer 0.1%.List of symbols b width of baffle, m - c length of baffle, m - D diameter of cylindrical fermentor, m - d diameter of impeller, m - d ₁ diameter of impeller disc, m - Fr _m impeller Froud number - g gravitional acceleration, ms^–2 - H height of batch surface above bottom, m - H ₂ height of impeller disc above bottom, m - h height of impeller blade, m - Kp _g flow rate number - L length of impeller blade, m - N rotational speed of impeller, s^–1 - Re _m impeller Reynolds number - T time, h - V volume of batch, m³ - V _g air (gas) flow rate, m³s^–1 - x mass fraction of the dry matter of cells - x ₀ initial value of the mass fraction of the dry matter of cells - _r volume fraction of the dry matter of cells - <eta<₁ viscosity of pure liquid, Pa s - viscosity of batch (suspension of microbial suspension), Pa s - density of batch, kg m^–3     

Soil microbial population dynamics following bioaugmentation with a 3-chlorobenzoate-degrading bacterial culture

Changes in microbial populations were evaluated following inoculation of contaminated soil with a 3-chlorobenzoate degrader. Madera sandy loam was amended with 0, 500, or 1000 g 3-chlorobenzoate g^-1 dry soil. Selected microcosms were inoculated with the degrader Comamonas testosteroni BR60. Culturable bacterial degraderswere enumerated on minimal salts media containing 3-chlorobenzoate. Culturableheterotrophic bacteria were enumerated on R2A. Isolated degraders were grouped by enterobacterial repetitive intergenic consensus sequence-polymerase chain reaction fingerprints and identified based on 16S ribosomal-DNA sequences. Bioaugmentation increased the rate of degradation at both levels of 3-chlorobenzoate. In both the 500 and 1000 g 3-chlorobenzoate g^-1 dry soil inoculated microcosms, degradersincreased from the initial inoculum and decreased following degradation of 3-CB.Inoculation delayed the development of indigenous 3-chlorobenzoate degrading populations. It is unclear if inoculation altered the composition of indigenous degrader populations. In the uninoculated soil, degraders increased from undetectable levels to 6.6 × 10⁷ colony-forming-units g^-1 dry soil in the 500 g 3-chlorobenzoate g^-1 dry soil microcosms, but none were detected in the 1000 g 3-chlorobenzoate g^-1 dry soil microcosms. Degraders isolated from uninoculated soil were identified as one of two distinct Burkholderia species.In the uninoculated soil, numbers of culturable heterotrophic bacteria initially decreased following addition of 1000 g 3-chlorobenzoate g^-1 dry soil. Inoculation with C. testosteroni reduced this negative impact on culturable bacterial numbers. The results indicate that bioaugmentation may not only increase the rate of 3-chlorobenzoate degradation but also reduce the deleterious effects of 3-chlorbenzoate on indigenous soil microbial populations.     

Free amino compounds and cell volume regulation in erythrocytes from different marine fish species under hypoosmotic conditions: the role of a taurine channel

Erythrocytes from the marine fish species ballan wrasse (Labrus berggylta Ascanius), bullhead (Myoxocephalus scorpius L.), cod (Gadus morhua L.), dab (Limanda limanda L.), eelpout (Zoarces viviparus L.), flounder (Platichthys flesus L.), lumpfish (Cyclopterus lumpus L.), plaice (Pleuronectes platessa L.), sole (Solea solea L.) and turbot (Scophthalmus maxima L.) possess the capacity for regulatory volume decrease. This property was demonstrated in vitro by reduction of the osmolality of the incubation medium from 330 to 255 mosmol·kg^-1. During the 4-h incubation period only the lumpfish cells completely regained the original volume. Twenty-seven free amino compounds were present in detectable amounts in the erythrocytes. At normal osmolality the taurine content was between 14.0 mol·g dry weight^-1 (lumpfish) and 147.4 mol·g dry weight^-1 (sole). Except in the bullhead, taurine was the quantitatively dominating amino compound in the erythrocytes from all species, and accounted for betwee 23% (lumpfish) and 88% (sole) of the total content of free amino compounds. In each species the regulatory volume decrease was associated with a reduction in the cellular content of taurine. Taurine contributed to between 6% (lumpfish) and 36% (flounder) of the cell shrinkage. There was a significant negative correlation, however, between the cellular concentration of taurine at normal osmolality and the capacity of the cells for regulatory volume decrease. Gamma-aminobutyric acid and/or glycine also contributed to the process of volume regulation, but to a lesser extent than taurine. The volume regulatory efflux of taurine and -aminobutyric acid were mediated by taurine channels. It is suggested that these channels also mediated the reduction in the cellular contents of glycine.Abbreviations cmp counts per minute - dw dry weight - GABA -amino-n-butyric acid - MW molecular weight - SD standard deviation - ww wet weight     

Biofiltering efficiency in removal of dissolved nutrients by three species of estuarine macroalgae cultivated with sea bass (Dicentrarchus labrax) waste waters 1. Phosphate

The potential of three estuarine macroalgae (Ulvarotundata, Enteromorpa intestinalis andGracilaria gracilis) as biofilters for phosphate ineffluents of a sea bass (Dicentrarchus labrax) cultivationtank was studied. These seaweeds thrive in Cádiz Bay and were alsoselected because of their economic potential, so that environmental andeconomicadvantages may be achieved by future integrated aquaculture practices in thelocal fish farms. The study was designed to investigate the functioning of Pnutrition of the selected species. Maximum velocity of phosphate uptake (2.86mol PO₄ g^–1 dry wth^–1) was found in U. rotundata.This species also showed the highest affinity for this nutrient. At low flowrates (< 2 volumes d^–1), the three species efficientlyfiltered the phosphate dissolved in the waste water, with a minimum efficiencyof 60.7% in U. rotundata. Net phosphate uptake rate wassignificantly affected by the water flow, being greatest at the highest rateassayed (2 volumes d^–1). The marked decrease in tissue P shownby the three species during a flow-through experiment suggested that growth wasP limited. However, due to the increase in biomass, total P biomass increasedinthe cultures. A significant correlation was found between growth rates and thenet P biomass gained in the cultures. A three-stage design under low water flow(0.5 volumes d^–1) showed that the highest growth rates (up to0.14 d^–1) and integrated phosphate uptake rates(up to 5.8 mol PO₄ ^3– g^–1dry wt d^–1) were found in E.intestinalis in the first stage, with decreasing rates in thefollowing ones. As a result, phosphate become limiting and low increments oreven losses of total P biomass in these stages were found suggesting thatphosphate was excreted from the algae. The results show the potential abilityofthe three species to reduce substantially, at low water flow, the phosphateconcentration in waste waters from a D. labrax cultivationtank, and thus the quality of effluents from intensive aquaculture practices.     

Establishment of hairy root cultures of Psoralea species

Eight Psoralea species (Leguminosae) were inoculated with Agrobacterium rhizogenes, strains 8196 and 9402. Hairy roots were only induced by strain 9402. Attention was focussed on Psoralea lachnostachys. Transformed roots grew very rapidly in Gamborg B5 liquid medium with a doubling time of the culture of 38 hours. Whatever the culture conditions, the two furanocoumarins usually found in roots of Psoralea plants, psoralen and angelicin, were not detected in cultured transformed and non transformed roots even when some chitosan was added to the medium. However, 669 g.g^–1 dry matter of psoralen and 215 g.g^–1 dry matter of angelicin were found in roots from soil grown plants. A possible translocation of these compounds from the aerial parts to the roots is suggested.Abbreviations B5 medium Gamborg's medium (Flow laboratories's formulation) - NAA Naphthaleneacetic acid     

A new method to estimate individual dry weights of rotifers

Body and egg volumes of 12 rotifer species of Lake Constance were calculated from more than 18 000 individually measured animals using geometric approximations. Body (V _A) and egg (V _E) volumes of various rotifer species have an allometric relationship described by: V _E = 1272 · V _A ^0.3379, while the relation V _E/V _A for each species was constant ranging from 0.016 to 0.87. Dry weight of adult rotifers was assumed to be the sum of the egg dry weight plus a corrected weight increment from egg to adult. It was estimated with the formula W _A = W _E · (1 + a · F _A/F _E) where (a) was varied between 0 and 0.1. Egg dry weight content was assumed to be 35 % of fresh weight. The estimates of dry weight to wet weight ratios ranged from 0.57 % (Asplanchna priodonta) to 29.4 % (Kellicottia longispina). Dry weight estimates obtained with this method are comparable to those obtained with direct measurements of dry weight or carbon content.This investigation was supported by the Deutsche Forschungsgemeinschaft within the Special Collaboration Program (SFB) Cycling of Matter in Lake Constance.     

Dry to wet weight biomass conversion constant for Tetrahymena elliotti (Ciliophora,Protozoa)

Summary The wet and dry weights of both axenic and monoxenic cultures of the ciliate Tetrahymena were determined directly. These estimates are dependent upon the method of volume determination. Assuming a prolate spheroidal shape for the ciliate, we calculate a mean wet weight of 0.4157±0.0713 pg m^-3 and a mean dry weight of 0.2793±0.0652 pg m^-3. Using electronic cell sizing, our estimates are 0.7869±0.1659 pg m^-3 and 0.5239±0.1101 pg m^-3, respectively. Independent of the method of volume determination, we estimate a mean biomass conversion ratio (dry weight/wet weight) of 0.59±0.08.     

Interspecific and intraspecific differences in shoot and leaf lifespan of four Carex species which differ in maximum dry matter production

The effect of N supply on shoot and leaf lifespan was investigated in established stands of four herbaceous Carex species which differed in maximum dry matter production. These species were, in rank order of increasing maximum dry matter production (per unit ground area): Carex diandraC. rostrata. The observed patterns of shoot and leaf turnover were compared with data on leaf characteristics and nitrogen use efficiency indices of these species. There was no consistent difference in shoot production (number of shoots produced per unit ground area) between species with low production and those with high production: Carex diandra (low production) and C. lasiocarpa (high production) had high shoot production, while shoot production in c. rostrata (low production) and C. acutiformis (high production) was much lower. The rank order of the mean lifespan of shoots was: C. diandra. Thus, the lifespan of shoots increased with increasing maximum dry matter production of these Carex species. In all species, increased N supply led to a significant reduction in shoot lifespan. The reduction of shoot lifespans in response to enhanced N supply will result in increased nutrient turnover rates in these species. There was no consistent difference in the number of leaves produced per shoot between low-production and high-production species. C. diandra and C. lasiocarpa had relatively low leaf production, while C. rostrata and C. acutiformis had relatively high leaf production per shoot. Thus, this pattern is opposite to the pattern in shoot production. The rank order of the mean lifespan of leaves was: C. diandra. This implies that the high-production species had longer mean leaf lifespans than the low-production species. Mean leaf lifespan was not significantly affected by enhanced N supply, except in C. diandra, where leaf lifespan decreased in response to enhanced N supply. Shoot lifespans did not show any significant relation with the specific leaf area (SLA, leaf area per unit leaf mass) or the leaf area ratio (LAR, leaf area per unit plant mass) of the species under study. There was, however, a negative relation (r ²=0.71) with the nitrogen concentration in the leaves. Shoot lifespans were positively related (r ²=0.79) with whole-plant nitrogen use efficiency (NUE, dry matter production per unit N-loss) and with the mean residence time of nitrogen (MRT, the average time-span during which a unit of nitrogen is present in the plant) (r ²=0.78), but not with the nitrogen productivity (A, annual dry matter production per unit N in the plant). Leaf lifespan was positively related with the mean residence time of nitrogen in the plants (r ²–0.70). For all the other parameters, there were no significant relations with leaf lifespan. From these results we conclude that: (1) at the stand level, shoot and leaf lifespans are positively related with maximum dry matter production; and (2) shoot and leaf lifespan are important determinants of whole-plant nitrogen economy.     

The electrical response ofAvena coleoptile cortex to auxins

Solute mobilities of 28 compounds in isolated cuticular membranes (CM) from Capsicum annuum L. fruit, Citrus aurantium L. and Pyrus communis L. leaves were studied using unilateral desorption from the outer surface. First-order rate constants of desorption (k^*), which are directly proportional to the diffusion coefficient in the waxy outer limiting skins of cuticles were measured. When log k^* was plotted vs. molar volumes of test compounds linear graphs were obtained. The y-intercepts of these graphs (k^*) represent the mobility of a hypothetical molecule having zero molar volume and the slopes of the graphs () represent the size selectivity of the barrier and are related to the free volume available for diffusion. Thus, solute mobilities in cuticles are composed of two independent terms which are subtractive. If k^* and are known, k^* can be estimated for any solute from its molar volume (V_x) using the equation log k^*=log k^* –V_x. These parameters were used to analyse the effects of plant species, extraction of cuticular waxes and molecular structure of solutes on solute mobilities in plant cuticles. For aliphatic solutes, k^* was a factor of 10 smaller than for cyclic compounds, while was 0.011 and 0.012, respectively. The k^*-values for CM of the three species were very similar, but was higher for bitter-orange CM (0.012) than for those of pepper fruits and pear leaves (0.009). This has the consequence that differences in solute mobilities (k^*) among cuticles from different plan species increase with increasing molar volumes of solutes. Our data and our analysis provide evidence that constituents of cuticular waxes are mobile, at least in the solid amorphous wax fraction, but mobility decreases rapidly with increasing molar volume. For instance, if amounts to 0.01, mobilities of wax monomers decrease by a factor of 10 for every increase in molar volume of 100 cm³ · mol^–1. Thus, hexadecanoic acid is quite mobile in the amorphous wax fraction of Citrus (k^*=1.5×10^–6·s^–1), but for dotriacontane having twice the molar volume, k^* was only 2.5×10^–9·s^–1, which is almost three orders of magnitude smaller. Wax esters have even higher molar volumes and their mobilities will be even smaller (about 4×10^–12·s^–1 for a C₄₈-ester). Since low chain mobilities are a prerequisite for low mobilities and permeabilities, the selective advantage of high-molecular-weight wax monomers in plant cuticular waxes becomes obvious. Extracting cuticular waxes from pear leaf CM increased solute mobilities by a factor of 182, but it had no effect on size selectivity. We interpret this result as evidence to the effect that cuticular waxes reduce mobility by increasing tortuosity of the diffusion path, rather than by decreasing the mean free path of diffusional jumps and jump frequencies of diffusants.Abbreviations CM cuticular membrane(s) - 2,4-D 2,4-dichloro-phenoxyacetic acid - LAB lactic acid buffer - MX polymer matrix membranes - UDOS unilateral desorption from the outer surface     

Benthic bacterial biomass supported by streamwater dissolved organic matter

Bacterial biomass in surface sediments of a headwater stream was measured as a function of dissolved organic carbon (DOC) flux and temperature. Bacterial biomass was estimated using epifluorescence microscopic counts (EMC) and ATP determinations during exposure to streamwater containing 1,788g DOC/liter and after transfer to groundwater containing 693g DOC/liter. Numbers of bacteria and ATP concentrations averaged 1.36×10⁹ cells and 1,064 ng per gram dry sediment, respectively, under initial DOC exposure. After transfer to low DOC water, biomass estimates dropped by 53 and 55% from EMC and ATP, respectively. The decline to a new steady state occurred within 4 days from ATP assays and within 11 days from EMC measures. A 4°C difference during these exposures had little effect on generation times. The experiment indicated that 27.59 mg/hour of natural DOC supported a steady state bacterial biomass of approximately 10g C/g dry weight of sediment (from EMC determinations). Steady state bacterial biomass estimates on sediments that were previously muffled to remove organic matter were approximately 20-fold lower. The ratio of GTPATP indicated differences in physiological condition or community composition between natural and muffled sediments.     

Growth and macromolecular composition of Anacystis nidulans at different temperatures in Mg2+- and K+-limited chemostats

Alterations in dry weight, macromolecular composition and cell volume with temperature, were examined for Mg²⁺- and K⁺-limited Anacystis nidulans. The experiments were performed in chemostats with constant dilution rate. Increasing the temperature from 30–40°C resulted in a 2.1 times increase in yield (g dry weight/g ion) for the Mg²⁺-limited culture, while it increased 1.3 times in the K⁺-limited culture. This difference in yield increase with temperature was caused by a large accumulation of carbohydrate in the Mg²⁺-limited cells. The relation between RNA and protein was found to be independent of temperature in both cultures. This indicated that A. nidulans contained extra inactive RNA under the growth conditions used. These results are discussed to indicate that A. nidulans regulates the rate of protein synthesis by activating/inactivating RNA in protein synthesis. The filament size and cellular DNA content both increased 1.6 times in the Mg²⁺-limited cells when decreasing the temperature from 40 to 30°C. The chlorophyll content of A. nidulans was found to be independent of temperature in both cultures.     

Woody-tissue respiration for Simarouba amara and Minquartia guianensis,two tropical wet forest trees with different growth habits

We measured CO₂ efflux from stems of two tropical wet forest trees, both found in the canopy, but with very different growth habits. The species were Simarouba amara, a fast-growing species associated with gaps in old-growth forest and abundant in secondary forest, and Minquartia guianensis, a slow-growing species tolerant of low-light conditions in old-growth forest. Per unit of bole surface, CO₂ efflux averaged 1.24 mol m^–2 s^–1 for Simarouba and 0.83 mol m^–2s^–1 for Minquartia. CO₂ efflux was highly correlated with annual wood production (r ²=0.65), but only weakly correlated with stem diameter (r ²=0.22). We also partitioned the CO₂ efflux into the functional components of construction and maintenance respiration. Construction respiration was estimated from annual stem dry matter production and maintenance respiration by subtracting construction respiration from the instantaneous CO₂ flux. Estimated maintenance respiration was linearly related to sapwood volume (39.6 mol m^–3s^–1 at 24.6° C, r ²=0.58), with no difference in the rate for the two species. Maintenance respiration per unit of sapwood volume for these tropical wet forest trees was roughly twice that of temperate conifers. A model combining construction and maintenance respiration estimated CO₂ very well for these species (r ²=0.85). For our sample, maintenance respiration was 54% of the total CO₂ efflux for Simarouba and 82% for Minquartia. For our sample, sapwood volume averaged 23% of stem volume when weighted by tree size, or 40% with no size weighting. Using these fractions, and a published estimate of aboveground dry-matter production, we estimate the annual cost of woody tissue respiration for primary forest at La Selva to be 220 or 350 g C m^–2 year^–1, depending on the assumed sapwood volume. These costs are estimated to be less than 13% of the gross production for the forest.     

Water permeability and its activation energy of fertilized and unfertilized mouse ova

Summary A photomicroscopic method has been use to determine the kinetics of water loss at various constant temperatures from fertilized and unfertilized mouse ova. Ova were transferred into hypertonic saline solutions, photographed, and their volumes calculated from their cross-sectional areas as a function of time after transfer. Curves describing the observed water loss have been compared to those calculated using a programmed version of the classical water permeability equation. The hydraulic conductivity,L _p , was determined by changing its value in the calculation until the majority of the observed cell volumes fell on or very close to the calculated curve of volume vs. time. In this way, fertilized and unfertilized ova were found to have respective hydraulic conductivities of 0.43 and 0.44 m³/m²-min-atm at 20°C and respective activation energies for water permeability of 13.0 and 14.5 kcal/mol.     

A rationale for the appropriate amount of inoculum in ready biodegradability tests

Several screening methods at the so-called ready biodegradability level are suitable to test poorly soluble substances. Typical for these tests is that mineralization is evaluated from monitoring oxygen uptake or carbon dioxide production. Unfortunately, they suffer from a rather low precision in the calculated percentage of mineralization caused by subtracting a too high inoculum control measurement from the response in the test system. Criteria for blank oxygen consumption, due to the metabolic activity of the inoculum, are proposed from which maximum amounts of activated sludge or secondary effluent per litre test medium can be derived to be used as an appropriate inoculum. Both for current and future standardized tests the precision of the method can be kept within acceptable margins. Inoculum material was sampled from 40 communal biological waste water treatment plants. From endogenous respiration rates it was derived that the concentration of secondary effluent in the Closed Bottle Test can be increased up to 50 mL/L but that in respirometry tests inoculated with activated sludge the appropriate concentration is 10 mg/L dry matter or below, depending of the design of the test system.List of abbreviations BOD biological oxygen demand - CBT Closed Bottle Test - C _as inoculum concentration in mg dry solids of activated sludge per litre test medium - C _ef inoculum concentration in ml secondary effluent per litre test medium - C _ss dry weight content of activated sludge (g/L) - CFU colony forming units - DO_7d dissolved oxygen concentration (mg/L) after 7 days - ISO International Organization for Standardization - NEN Dutch Organization for Standardization - O _c oxygen capacity in mg oxygen per litre vessel volume - OECD Organisation for Economic Co-operation and Development - Ox _as oxygen consumption after one week in mg oxygen per mg dry weight activated sludge - Ox _ef oxygen consumption after one week in mg oxygen per mL secondary effluent - Ox _ef [n] oxygen consumption after one week in mg oxygen per n mL secondary effluent - Ox _flask oxygen uptake in mg per litre flask volume - RBT Ready Biodegradability Test - SLR sludge loading rate in kg O₂/kg dry weight·d - ThOD theoretical oxygen demand - TPCBT Two Phase Closed Bottle Test - V _a volumes of air and water per litre vessel - V _w volume, respectively - _a concentration of oxygen in air at 20° C and 101.5 kPa - _s saturation oxygen concentration in te aqueous phase     

The role of soil Phosphorus in differentiation of edaphic ecotypes in Aegilops peregrina

Summary The role of soil Phosphorus (P) availability on the ecotypic differentiation of plants was investigated. Populations of Aegilops peregrina (Hack.) were collected from four habitats which differed in their soil P. The four soils were: Meron (a P-deficient montmorillonitic xerochrept on dolomite), Malkiya (a P-fertile kaolinitic xerochrept on hard limestone), Har-Hurshan and Bet-Guvrin (lithic xerorthents on soft limestone with appreciable amounts of P, mainly as carbonate-apatite).Plants of the four populations were grown in pots with Meron soil which were previously equilibrated with four different amounts of soluble phosphate to give 1.2, 3.1, 10.7 and 18.9 gP g^-1 soil of sodium-bicarbonate extractable P. Plants originated from Malkiya population produced higher dry matter yields than the other three populations. Dry matter yields of the various populations were analyzed by means of a Mitcherlich's response function, versus sodium-bicarbonate extractable (available) soil P. The analysis revealed that Malkiya population plants had a significant advantage over Meron population plants in the response parameter c: this express the response rate of the plants to phosphate by means of dry matter production. With regard to the parameter Po, which represents the ability of plants to utilize barely-available fractions of soil P, the opposite was true. Har-Hurshan and Bet-Guvrin populations were intermediate in these two parameters. A version of the Mitcherlich response function is proposed, which expresses plant yield as a function of both soil available P and plant age.Meron plants contained the highest percentage of P in plant material, but compared to the other populations, they were the most inefficient in producing dry matter from the already absorbed P. Plants from the calcareous soils, Har-Hurshan and Bet-Guvrin, did not show any apparent trend.In soils which contain moderate amounts of lime, P may become a major limiting growth factor. Plant populations became adapted to low availability of P by (1) improving their ability to utilize barely-available soil P fractions and (2), by decreasing their productivity.