Modelling pasture production and soil temperature,water and carbon fluxes in Mediterranean grassland systems with the Pasture Simulation model

Grasslands play important roles in agricultural production and provide a range of ecosystem services. Modelling can be a valuable adjunct to experimental research in order to improve the knowledge and assess the impact of management practices in grassland systems. In this study, the PaSim model was assessed for its ability to simulate plant biomass production, soil temperature, water content, and total and heterotrophic soil respiration in Mediterranean grasslands. The study site was the extensively managed sheep grazing system at the Berchidda‐Monti Observatory (Sardinia, Italy), from which two data sets were derived for model calibration and validation respectively. A new model parameterization was derived for Mediterranean conditions from a set of eco‐physiological parameters. With the exception of heterotrophic respiration (Rh), for which modelling efficiency (EF) values were negative, the model outputs were in agreement with observations (e.g., EF ranging from ~0.2 for total soil respiration to ~0.7 for soil temperature). These results support the effectiveness of PaSim to simulate C cycle components in Mediterranean grasslands. The study also highlights the need of further model development to provide better representation of the seasonal dynamics of Mediterranean annual species‐rich grasslands and associated peculiar Rh features, for which the modelling is only implicitly being undertaken by the current PaSim release.     

Interaction of ethylene,oxygen and carbon dioxide in the control of fruit ripening

Ethylene production during the climacteric in many fruits, in vegetative tissue treated with IAA, and in flowers which have been emasculated, pollinated or treated with IAA applied to their stigma, increases rapidly and then returns to a low rate. In root sections exposed to IAA this timing apparently is due to the fact that the rate of ethylene production reflects the internal IAA content; the latter increases initially after auxin is applied but rapidly decreases again due to induction or activation of the enzyme systems conjugating and destroying IAA. A similar mechanism may be involved in the induction of ethylene production in fruits.In vivo ethylene is derived from methionine, possibly after the amino acid is activated to form S-adenosyl methionine, by decarboxylation of C₁, transfer of C₂ possibly as a folic acid derivative, formation of ethylene from C₃–C₄, and transfer of the S-methyl to a suitable receptor molecule.Analogue studies indicate that ethylene attaches (K_A=6×10^–10M) to a metal containing receptor by one end through a non-covalent bond. This attachment is competitively inhibited by CO₂ (K_I=4.9×10^–4M) thus explaining the ability of this gas to antagonize most biological responses to ethylene, including fruit ripening. CO₂ does not inhibit ethylene production, but may influence fruit ripening and induce certain physiological disorders by binding to metal containing enzymes such as catalase. Ethylene production is inhibited at low O₂ concentrations; the receptor has an O₂ affinity closely similar to that of cytochrome oxidase. In addition O₂ is required for ethylene action, and the kinetics best describing the situation are those in which O₂ binds to the receptor (K_S=4×10^–5M) or indirectly oxidizes it before ethylene can attach. This effect of low pO₂ is not dependent upon a respiratory inhibition for it occurs at O₂ concentrations which are not low enough to inhibit respiration and cannot be duplicated by respiratory poisons. Thus low concentrations of O₂ retard fruit ripening both by inhibiting ethylene production and action.The rate of gas exchange and hence the internal concentration of ethylene within a fruit depends upon the diffusion coefficient of ethylene in air. As this is a function of atmospheric pressure, storing fruits at a subatmospheric pressure reduces their ethylene content. In addition this condition automatically decreases the O₂ partial pressure thus greatly extending the storage life of preclimacteric fruits.

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Zusammenfassung In vegetativen Geweben, die mit IAA (-Indolessigsäure) behandelt wurden, in sterilisierten oder befruchteten Blüten, oder in solchen, bei denen die Narbe mit IAA behandelt wurde sowie in vielen Früchten während des Klimakteriums, steigt die Äthylenbildung zunächst rasch an und sinkt dann auf eine niedrige Produktionsrate ab. In Wurzelschnitten, die mit IAA behandelt wurden, spiegelt der zeitliche Verlauf der Äthylenbildung die Zusammenhänge zwischen innerer IAA-Konzentration und Äthylen-Produktionsrate wider. Nach Auxin-Applikation steigt der IAA-Gehalt zunächst an, sinkt dann jedoch wiederum rasch ab. Dieses Verhalten lässt sich mit der Induktion und Aktivierung des Enzymsystems erklären, das die IAA bindet und abbaut. Ein ähnlicher Mechanismus mag bei der Induktion der Äthylenbildung eine Rolle spielen.In vivo wird das Äthylen aus dem Methionin gebildet. Dabei erfolgt wahrscheinlich zunächst eine Überführung in das S-Adenosyl-Methionin, wonach das C₁ decarboxyliert wird. Anschliessend wird das C₂ — vermutlich als Folsäurederivat — abgespalten und das Äthylen aus dem C₃ und C₄, nach Übertragung der Methylmercapto-Gruppe auf ein geeignetes Rezeptor-Molekül, gebildet.Analoge Untersuchungen zeigen, dass sich das Äthylen mit einem Ende an einen metallhaltigen Rezeptor in Form einer nicht kovalenten Bindung anlagert (K_A=6×10^–10M). Diese Bindung wird durch das CO₂ kompetitiv gehemmt (K_I=4,9×10^–4M). Hierdurch ist die Fähigkeit des CO₂ erklärt, in sehr vielen biologischen Prozessen, einschliesslich der Fruchtreife, zum Äthylen antagonistisch zu wirken. Das CO₂ verhindert nicht die Äthylenbildung, aber es kann die Fruchtreife beeinflussen und bestimmte physiologische Störungen durch Bindung metallhaltiger Enzyme — beispielsweise der Katalase — hervorrufen. Bei niedrigen O₂-Konzentrationen ist die Äthylenbildung gehemmt. Der Rezeptor hat eine weitgehend ähnliche O₂-Affinität wie die Cytochrom-Oxidase. Darüberhinaus ist O₂ für die Wirksamkeit des Äthylen erforderlich. Die reaktionskinetischen Vorstellungen, die die Situation am besten beschreiben, sind folgende: O₂ verbindet sich mit dem Rezeptor (K_S=4×10^–5M) oder oxidiert ihn indirekt, bevor das Äthylen ihn erreichen kann. Der Effekt, den ein geringer O₂-Partialdruck hervorruft, besteht nicht in einer Atemhemmung, denn er spielt sich auf einem O₂-Konzentrationsniveau ab, das für Atemhemmungen nicht niedrig genug ist. Ausserdem kann der Effekt durch Atemgifte nicht verdoppelt (vergrössert) werden. Eine geringe O₂-Konzentration kann daher die Fruchtreife auf zwei Weisen verzögern: Senkung der Bildungsrate und Verringerung der Wirksamkeit des Äthylens.Der Umfang des Gas-Austausches und somit die Äthylen-Konzentration innerhalb einer Frucht hängen vom Diffusions-Koeffizienten von Äthylen in Luft ab. Da dieser eine Funktion des atmosphärischen Druckes ist, senkt Aufbewahrung von Früchten bei Unterdruck ihren Äthylen-Gehalt. Diese Bedingung vermindert darüberhinaus den O₂-Partialdruck, wodurch die Lagerfähigkeit von Früchten im Vorklimakterium stark erweitert wird.

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Resume La production d'éthylène pendant la phase climactérique de nombreux fruits, dans les tissus végétatifs traités à l'acide indole acétique (AIA), et dans les fleurs qui ont été émasculées, pollinisées ou traitées à l'AIA au niveau du pistil, augmente rapidement, puis s'abaisse jusqu'à une vitesse faible. Dans des sections de racines traitées à l'AIA, ce processus est apparemment dû au fait que la vitesse de production de l'éthylène reflète le contenu interne en AIA. Ce contenu augmente initialement après que l'auxine est appliquée, mais décroît rapidement à nouveau à cause de l'induction ou l'activation du système enzymatique de synthèse et de dégradation de l'AIA. Un mécanisme similaire peut être impliqué dans la production de l'éthylène dans les fruits.In vivo l'éthylène provient de la méthionine, probablement après l'activation de l'acide aminé pour former la S-adénosyl-méthionine, par décarboxylation du C1, transfer possible de C₂ comme dérivé de l'acide folique, formation d'éthylène à partir du C₃–C₄, et transfer du S-méthyl à une molécule réceptrice adéquate.Des études analogues indiquent que l'éthylène se lie (K_A=6×10^–10M) à une extrémité d'un récepteur contenant un métal, par un lien non convalent. Cette liaison est compétitivement inhibée par CO₂ (K_I=4,9×10^–4M) ce qui explique la propriété de ce gaz en tant qu'antagoniste dans la plupart des réponses biologiques de l'éthylène, y compris dans la maturation des fruits. Le CO₂ n'inhibe pas la production même d'éthylène, mais peut influencer la maturation du fruit et induire certaines perturbations physiologiques en se liant à des enzymes contenant un métal comme la catalase. La production d'éthylène est inhibée par de faibles concentrations en oxygène; le récepteur a une affinité pour l'oxygène très proche de celle de la cytochrome oxydase. En outre, l'oxygène est nécessaire à l'action de l'éthylène, et les cinétiques décrivant le mieux la situation sont celles dans lesquelles l'oxygène se lie au récepteur (K_S=4×10^–5M) ou oxyde celui-ci indirectement, avant que l'éthylène ne puisse s'y lier. Cet effet des pressions basses en oxygène ne dépend pas de l'inhibition respiratoire puisqu'il se produit à des concentrations d'oxygène qui ne sont pas assez faibles pour inhiber la respiration, et puisqu'il ne peut pas être remplacé par les effets des poisons respiratoires. Donc de faibles concentrations en oxygène retardent la maturation du fruit, à la fois en inhibant la production et l'action de l'éthylène.La vitesse des échanges gazeux, et par conséquent la concentration interne d'éthylène à l'intérieur d'un fruit, dépend du coefficient de diffusion de l'éthylène dans l'air. Comme celui-ci est une fonction de la pression atmosphérique, la conservation des fruits à des pressions inférieures à celles de l'atmosphère réduit contenu en éthylène. De plus, cette condition fait automatiquement diminuer la pression partielle en oxygène, et augmente ainsi considérablement la durée de vie en conservation des fruits préclimactériques.

     

Impact of biodiversity-climate futures on primary production and metabolism in a model benthic estuarine system

Background

A territory as a prerequisite for breeding limits the maximum number of breeders in a given area, and thus lowers the proportion of breeders if population size increases. However, some territorially breeding animals can have dramatic density fluctuations and little is known about the change from density-dependent processes to density-independence of breeding during a population increase or an outbreak. We suggest that territoriality, breeding suppression and its break-down can be understood with an incomplete-control model, developed for social breeders and social suppression.

Results

We studied density dependence in an arvicoline species, the bank vole, known as a territorial breeder with cyclic and non-cyclic density fluctuations and periodically high densities in different parts of its range. Our long-term data base from 38 experimental populations in large enclosures in boreal grassland confirms that breeding rates are density-regulated at moderate densities, probably by social suppression of subordinate potential breeders. We conducted an experiment, were we doubled and tripled this moderate density under otherwise the same conditions and measured space use, mortality, reproduction and faecal stress hormone levels (FGM) of adult females. We found that mortality did not differ among the densities, but the regulation of the breeding rate broke down: at double and triple densities all females were breeding, while at the low density the breeding rate was regulated as observed before. Spatial overlap among females increased with density, while a minimum territory size was maintained. Mean stress hormone levels were higher in double and triple densities than at moderate density.

Conclusions

At low and moderate densities, breeding suppression by the dominant breeders, But above a density-threshold (similar to a competition point), the dominance of breeders could not be sustained (incomplete control). In our experiment, this point was reached after territories could not shrink any further, while the number of intruders continued to increase with increasing density. Probably suppression becomes too costly for the dominants, and increasing number of other breeders reduces the effectiveness of threats. In wild populations, crossing this threshold would allow for a rapid density increase or population outbreaks, enabling territorial species to escape density-dependency.     

Intermittent drainage in paddy soil: ecosystem carbon budget and global warming potential

Intermittent drainage of rice fields alters soil redox potential and contributes to the reduction of CH₄ emission and thus may reduce net global warming potential (GWP) during rice cultivation. Incorporation of green biomass helps maintaining soil organic matter, but may increase CH₄ emission. We investigated net ecosystem carbon budget (NECB) and net GWP under two water management regimes—continuous flooding and intermittent drainage—having four biomass incorporation levels (0, 3, 6 and 12 Mg ha^?1). Water management and biomass incorporation level demonstrated significant (P < 0.05) interaction effect on the NECB and GWP. Intermittent drainage decreased the NECB by ca. 6–46 % than continuous flooding under same rates of cover crop biomass (CCB) incorporation. Moreover, intermittent drainage reduced seasonal CH₄–C fluxes by ca. 54–58 % and net GWP by 35–58 % compared to continuous flooding. There was also no significant reduction in rice yield because of intermittent drainage under similar CCB. This implies that incorporation of 3 Mg ha^?1 CCB and intermittent drainage could be a good option for reducing net GWP and higher grain yield.     

Impact of biodiversity-climate futures on primary production and metabolism in a model benthic estuarine system

Background  

Understanding the effects of anthropogenically-driven changes in global temperature, atmospheric carbon dioxide and biodiversity on the functionality of marine ecosystems is crucial for predicting and managing the associated impacts. Coastal ecosystems are important sources of carbon (primary production) to shelf waters and play a vital role in global nutrient cycling. These systems are especially vulnerable to the effects of human activities and will be the first areas impacted by rising sea levels. Within these coastal ecosystems, microalgal assemblages (microphytobenthos: MPB) are vital for autochthonous carbon fixation. The level of in situ production by MPB mediates the net carbon cycling of transitional ecosystems between net heterotrophic or autotrophic metabolism. In this study, we examine the interactive effects of elevated atmospheric CO₂ concentrations (370, 600, and 1000 ppmv), temperature (6°C, 12°C, and 18°C) and invertebrate biodiversity on MPB biomass in experimental systems. We assembled communities of three common grazing invertebrates (Hydrobia ulvae, Corophium volutator and Hediste diversicolor) in monoculture and in all possible multispecies combinations. This experimental design specifically addresses interactions between the selected climate change variables and any ecological consequences caused by changes in species composition or richness.     

Behavior of carbon dioxide in soils affected by tillage systems

Agricultural management plays an important role in the storage of carbon in soils. The behavior of soil CO₂ in an Andisol in two different tillage systems (no tillage and tillage) was studied. Soil-column incubation experiments were performed for a period of 150 days to conduct this study. Soil CO₂ flux, under no-tillage and tillage treatments, was observed to be 0.557 and 0.616 gCO₂-C m^?2 d^?1, respectively. The cumulative CO₂ flux under tillage treatment was observed to be higher than that under no-tillage treatment, but no distinct difference in the soil carbon stock was observed between both treatments. The soil CO₂ concentration under no-tillage treatment was clearly much higher than that under tillage treatment, except at a depth of 2.5 cm. Tillage decreased soil dry bulk density and enhanced soil air-filled porosity. Soil gas diffusivity, which depends on air-filled porosity, was increased by tillage at a depth of 0–15 cm, which contributed to their lower soil CO₂ concentration. CO₂ flux through the soil profile, calculated from the CO₂ concentration, decreased with depth. Compared to the deep soils, the surface soil (0–5 cm) showed greater variation in CO₂ flux. The CO₂ production at depths of 0–10 cm accounted for 62.2 and 51.7 % of the whole CO₂ production of the 0–30-cm soil profile for no-tillage and tillage treatments. CO₂ production was higher for soil under no tillage at depths of 0–10 cm, but contrary results were observed for soil at depths of 10–30 cm.     

Blackspot of Russet Burbank potatoes and the carbon dioxide content of soil and tubers

These studies were designed to elucidate the influence of CO₂ on blackspot susceptibility of Russet Burbank potatoes. The influence of tuber CO₂ environment on blackspot was tested. Tubers from 1–4 and 6–8 inches deep in the soil were scored for blackspot and moisture samples were taken from their vicinity. Blackspot was worse in shallow tubers and in tubers from drier soil. Plowing under corn stover, covering the soil with plastic, and excessive irrigation failed to cause blackspot susceptible tubers. Diffusing CO₂ into the soil atmosphere under plastic sheets slightly increased the intensity of spot discoloration but the discoloration was atypical blackspot. Effects on blackspot by changing tuber gases was tested. Tubers whose gases had been evacuated and replaced by O₂, N₂, and CO₂ had lower blackspot scores than untreated tubers. Increasing the time tubers were soaked in water after gaseous evacuation reduced blackspot. Hydration consistently decreased tuber blackspot. In chemical studies, tubers were tested for blackspot and analyzed for CO₂ content. The relationship between tissue CO₂ and blackspot appeared to be inverse. Tuber CO₂ content was not influenced by time of day. Tuber blackspot scores immediately, 1, 3, and 7 hours after digging were the same, but tissue CO₂ content increased linearly with time after harvest.     

Methane emission from irrigated rice ecosystem: relationship with carbon fixation,partitioning and soil carbon storage

Rice is a major agricultural crop and accounts for 40 % of the total food grain production of India. A field experiment was conducted for two successive seasons (December–June, 2012–13 and December–June, 2013–14) to assess the efficiency of rice varieties for methane (CH₄) emission in relation to atmospheric carbon fixation, partitioning of carbon, and storage in the soil. Six high yielding rice varieties, Bahadur, Cauvery, Dinanath, Joymoti, Kanaklata, and Swarnabh were grown under irrigated condition. Results of the present investigation depicted differences in photosynthetic rate among the varieties accompanied by differential ability for plant biomass partitioning between the shoots and the roots. Stomatal frequency of flag leaf at panicle initiation stage was found to have strong influence on photosynthesis. Low CH₄-emitting rice varieties, Bahadur and Dinanath, were found to have lower size of the xylem vessels than the high CH₄-emitting rice varieties, Joymoti and Kanaklata, and found to influence the CH₄ flux. Soil organic carbon storage of 0.505 Mg C ha^?1 y^?1 in the plough layer of soil (0–15 cm) confirmed that irrigated rice ecosystem is an effective sink of carbon. These findings suggest that selection of suitable rice varieties with higher photosynthetic efficiency and lower emission of CH₄ can be a suitable biological mitigation of this greenhouse gas. Although an inverse relationship of CH₄ with carbon dioxide (CO₂) efflux was observed, irrigated rice ecosystem has a good potential to store substantial amount of carbon in the soil.     

Dyeing of meta-aramid fibers with disperse dyes in supercritical carbon dioxide

Dyeing characteristics of meta-aramid fibers were investigated in supercritical carbon dioxide by employing three disperse dyes and a carrier. The effects of dyeing temperature, pressure, time, dye concentration, CO₂ flow, and carrier concentration on dyeing properties were investigated. The results showed that meta-aramid fiber could be dyed in supercritical carbon dioxide. Its color depth was improved with increasing dyeing temperature, pressure, time, dye concentration, CO₂ flow, and carrier concentration. Moreover, the color depth could be significantly improved by adding the carrier. The dyeing procedure of supercritical carbon dioxide fluid did not influence the chemical structure and antistatic properties of the meta-aramid fiber. The maximum decomposition temperature and breaking strength of the dyed meta-aramid fiber are slightly increased. The dyed meta-aramid fiber in supercritical carbon dioxide had good fastness, which was rated at 4–5.     

A simple apparatus for measuring oxygen uptake and carbon dioxide output

Summary The respiration apparatus described is essentially a large-scale Warburg apparatus, with numerous details in the design which are considered essential for reliable results. The oxygen uptake is not derived from a manometric reading however, but from replacement of the oxygen by a measured amount of water. By this means frequent calibration of the apparatus for differing quantities of material is avoided. The use of the apparatus for measuring respiration in both air and gas mixtures is described.

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Zusammenfassung Der hier beschriebene Respirations-Apparat ist im wesentlichen ein volumin?ser Warburg-Apparat mit zahlreichen Einzelheiten in der Konstruktion, die für das Erreichen von verl?sslichen Resultaten wesentlich sind. Die Sauerstoffaulnahme erhalten wir nicht durch die Ablesung am Manometer, sondern durch die Verdr?ngung des Sauerstoffs durch eine gemessene Wassermenge. Hierdurch ist das h?ufige Kalibrieren des Apparates für verschiedene Mengen des Materials vermieden. Die Verwendung des Apparates zur Messung der Atmung sowohl in Luft-als in Gasmischungen ist beschrieben.

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Résumé L'appareil respiratoire décrit ici est en somme la reproduction en grand de l'appareil de Warburg, avec de nombreux détails de construction jugés indispensables pour obtenir des résultats súrs. Cependant, la consommation d'oxygène n'est pas connue par une lecture manométrique mais par le remplacement de l'oxygène par une quantité d'eau mesurée. De cette facon, les fréquents jaugeages de l'appareil pour différentes quantités de substance sont évités. L'emploi de l'appareil est décrit pour les mesures de la respiration, aussi bien dans l'air que dans de mélanges gaseux.

     

Modeling the effects of light, carbon dioxide, and temperature on the growth of potato

This study examined the effects of light, temperature and carbon dioxide on the growth of potato (Solanum tuberosum L.) in a controlled environment in order to ascertain the best growing conditions for potato in life support systems in space. 'Norland' and 'Russet Burbank' were grown in 6-L pots of peat-vermiculite for 56 d in growth chambers at the University of Wisconsin Biotron. Environmental factor levels included continuous light (24-h photoperiod) at 250, 400, and 550 micromoles m-2 s-1 PPF; constant temperature at 16, 20, and 24 degrees C; and CO2 at approximately 400, 1000, and 1600 microliters L-1. Separate effects analysis and ridge analysis provided a means to examine the effects of individual environmental factors and to determine combinations of factors that are expected to give the best increases in yields over the central design point. The response surface of Norland indicated that tuber yields were highest with moderately low temperature (18.7 degrees C), low CO2 (400 microliters L-1) and high light (550 micromoles m-2 s-1 PPF). These conditions also favored shorter stem growth. Russet Burbank tuber yields were highest at moderately low temperature (17.5 degrees C), high CO2 (1600 microliters L-1) and medium analyses will be used to project the most efficient conditions for growth of potatoes in closed ecological life support systems (CELSS) in space colonies.     

Nitrogen nutrition and temporal effects of enhanced carbon dioxide on soybean growth

Plants grown on porous media at elevated CO2 levels generally have low concentrations of tissue N and often appear to require increased levels of external N to maximize growth response. This study determines if soybean [Glycine max (L.) Merr. Ransom'] grown hydroponically at elevated CO2 requires increases in external NO3- concentrations beyond levels that are optimal at ambient CO2 to maintain tissue N concentrations and maximize the growth response. This study also investigates temporal influences of elevated CO2 on growth responses by soybean. Plants were grown vegetatively for 34 d in hydroponic culture at atmospheric CO2 concentrations of 400, 650, and 900 microliters L-1 and during the final 18 d at NO3- concentrations of 0.5, 1.0, 5.0 and 10.0 mM in the culture solution. At 650 and 900 microliters L-1 CO2, plants had maximum increases of 31 and 45% in dry weight during the experimental period. Plant growth at 900 microliters L-1 CO2 was stimulated earlier than at 650 microliters L-1. During the final 18 d of the experiment, the relative growth rates (RGR) of plants grown at elevated CO2 declined. Elevated CO2 caused increases in total N and total NO3(-)-N content and leaf area but not leaf number. Enhancing CO2 levels also caused a decrease in root:shoot ratios. Stomatal resistance increased by 2.1- and 2.8-fold for plants at the 650 and 900 microliters L-1 CO2, respectively. Nitrate level in the culture solutions had no effect on growth or on C:N ratios of tissues, nor did increases in CO2 levels cause a decrease in N concentration of plant tissues. Hence, increases in NO3- concentration of the hydroponic solution were not necessary to maintain the N status of the plants or to maximize the growth response to elevated CO2.     

Effects of carbon dioxide on the physiological disorders observed in onion bulbs during CA storage

Onions (Allium cepa L.) stored for 162–3 or 224–6 days in CA containing 10% CO₂ and 3 to 5% O₂ at 1°C showed physiological disorders. The same disorder appeared in all onion bulbs stored in sealed polythene bags containing over 10% CO₂. Microscopic study of the epidermis and parenchyma of fleshy scales have demonstrated a process of destruction in walls of the onion cells. Free cellulose micelles were found inside such preparations due to hydrolitic enzyme activity. Alterations of the ultra-structure of the mitochondria were also observed. A high free amino acid content was found in onion bulbs with this physiological disorder. Total animo acid content was higher in the internal than in the external scales of onion bulbs.

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Zusammenfassung Zwiebeln Allium cepa L. zeigten während einer 162–3 oder 224–6 tägigen Lagerung in CA mit einem 10% igem CO₂-Gehalt und 3 bis 5% O₂ bei einer Temperatur von 1°C physiologische Schäden. Die gleichen Schäden traten in allen Zwiebeln auf, die in geschlossenen Polyäthylen beuteln mit einem CO₂-Gehalt von über 10% gelagert worden waren.Die regulären mikroskopischen Untersuchungen der Epidermis und des Parenchyms der Schalen zeigten eine Zerstörung der Wandzellen der Zwiebeln.Die freien Zelulosemicellen traten ins Innere der Präparate als Folge der Aktivität der hydrolytischen Enzyme. Es wurden auch Änderungen der Mitochondrien beobachtet.Den höchsten Gehalt an freien Aminosäuren hatten Zwiebeln mit physiologischen Schäden.Der Gesamtgehalt an Aminosäuren war in den inneren Zwiebelschalen höher als in den äusseren.

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Résumé L'oignon (Allium cepa L.) conservé pendant 162–3 jours et 224–6 jours dans une atmosphère controlée contenant 10% de CO₂ et de 3 à 5% O₂ à la température 1°C a montré des lésions physiologiques. Les mêmes lésions parurent chez tous les oignons conservé dans des sacs fermés en polyethylène qui contenaient plus de 10% de CO₂. Des observations régulières, faites au microscope de l'épiderme de l'écaille interne d'oignon ont demontré la décomposition des parois des cellules de l'oignon. Des micelles libres de cellulose apparurent à l'intérieur des cellules à la suite de l'activité des enzymes hydrolytiques. On a observé de même des changements de l'ultrastructure des mitochondries.On a pu constater un taux plus élevé des aminoacides dans les oignons avec lésions physiologiques. Le contenu total des aminoacides était plus grand dans les écailles extérieures de l'oignon que dans les écailles intérieures.

     

Crystallization and molecular relaxation of poly(ethylene terephthalate) annealed in supercritical carbon dioxide

Poly(ethylene terephthalate) was annealed at different temperature and pressure of supercritical carbon dioxide (CO₂) using samples quenched from the melt. Crystallization and molecular relaxation behavior due to CO₂-annealing of samples were investigated using differential scanning calorimetric and dynamic mechanical measurements. The glass transition and crystallization temperatures significantly decreased with increasing temperature and pressure of CO₂. The dynamic mechanical measurement of samples annealed at 150 °C in supercritical CO₂ showed three relaxation peaks, corresponding to existence of different amorphous regimes such as rigid, intermediate, and mobile domains. As a result, the mobile chains were likely to facilitate crystallization in supercritical state. It also led to the decreased modulus of CO₂-annealed samples with increasing pressure.     

Night temperature,rubber production,and carbon exchange in guayule

Guayule (Parthenium argentatum Gray), a native of the Chihuahuan desert, produces the majority of its rubber during the winter months. Increased rubber production is thought to be induced by cold night temperatures, but the factors involved in rubber induction are not completely understood. The purpose of this study was to answer three questions about rubber production in the winter: (1) how do immature plants (<180 days) respond to cold night temperatures?; (2) how is rubber production in mature plants (≈1 year) related to night temperature?; and (3) what is the relationship between carbon exchange and rubber production under cold night temperatures? Plants were grown in differentially heated enclosures over three consecutive winters. The warm-night plants were exposed to simulated summer night temperatures and the cold-night plants to ambient winter night temperatures. Plant responses to different night temperatures were monitored by measuring growth, carbon exchange, fresh and dry weight, and resin and rubber production. Immature plants exposed to cold nights had higher rubber concentration than the warm-night plants only in the first year, which had the lowest night temperatures. For the mature plants, dry weight was not significantly different between treatments, but rubber concentration and yield were significantly greater in the cold-night than the warm-night plants. Plants in both treatments had similar carbon exchange rates. Therefore, the similarity in dry weight between treatments was most likely due to increased growth in the warm-night plants and increased rubber deposition in the cold-night plants. Rubber concentration was significantly related to night temperature in both mature and immature plants and appears to be stimulated most by temperatures below 10 °C.     

Direct lipase-catalyzed lipophilization of chlorogenic acid from coffee pulp in supercritical carbon dioxide

The direct esterification of chlorogenic acid (5-CGA) by immobilized Candida antarctica lipase B (Novozym 435) in supercritical CO₂/t-butanol has been studied. The Taguchi approach was applied to evaluate the effects of temperature (35–55 °C), pressure (150–250 bar), t-butanol (2–10%, v/v), and the enzyme amount (10–30 mg/ml), on the ester concentration and overall conversion. Optimum reaction conditions were established at: 150 bar, 55 °C, 10% t-butanol (v/v), 20 mg/ml of lipase. Addition of 20 mg/ml of molecular sieves (3 Å) was also necessary to minimize the inhibiting effect of the increasing water concentration. Maximum conversions reached 77, 82 and 85% in 25 h using geraniol, pentanol and heptanol as aliphatic chain donors, respectively. HPLC analysis demonstrated the selective esterification of 5-CGA from a coffee pulp aqueous-methanolic extract, which reached a conversion to heptyl ester of 65% at the optimal condition. The supercritical CO₂ selectivity towards the esterified product was the working principle of this study, by which minimized interphase transport limitations and enhanced mass-transfer phenomena substantially improved the reaction kinetics.     

Studies on the toxicity of acetone, acrolein and carbon dioxide on stored-product insects and wheat seed

In laboratory experiments toxicity of acetone, acrolein and carbon dioxide were investigated against 4 species of stored-product insects. In all experiments, acrolein was the most toxic compound to the tested insects. In empty-space trials, estimated LD50 values of acrolein for adults of Tribolium castaneum (Herbst) (Tenebrionidae), Rhizopertha dominica (F.) (Bostrychidae), Sitophilus oryzae L. (Curculionidae) and Oryzaephilus surinamensis L. (Silvanidae) were 7.26, 6.09, 6.37 and 5.65 microl L(-1), respectively. Penetration tests revealed that acetone and acrolein vapors could penetrate into the wheat mass and kill concealed insects in interkernel spaces. Comparison of LD50 values of acrolein between empty-space tests and penetration experiments indicated that the increase in penetration toxicity was 4.96, 4.54, 3.64 and 3.43-fold for T. castaneum, R. dominica, S. oryzae and O. surinamensis, respectively. The effect of carbon dioxide on the toxicity of acrolein and acetone was synergistic. In the hidden infestation trials, the acrolein vapors destroyed the developmental stages of S. oryzae concealed inside the wheat kernels and resulted in a complete control with concentration of 80 microl L(-1) for 24 h and subsequently observed during 8 weeks after the exposure. Wheat germination and plumule length was reduced following exposure to all doses of acrolein. Acetone and carbon dioxide were harmless to wheat seed viability. The mixture of carbon dioxide with acrolein can be considered as a potential fumigant for replacing methyl bromide or phosphine under ambient storage conditions specifically in empty-space fumigations.     

Net production of herbage from a continuously stocked Lolium perenne-dominated sward in late autumn

Preliminary studies were carried out on the effect of stocking rate during late autumn on a continuously stocked Lolium perenne -dominated sward at an upland site in central Scotland. Measurements were made of L. perenne tiller population density on 29 September and 2 November and of L. perenne net production, mean sward height and total herbage mass in early and late October and early and late November. Stocking rates were 12 ewes per ha during October and 8 and 16 ewes per ha during November. Sward height and herbage mass declined with time and more rapidly at the higher stocking rate. L. perenne growth per tiller and per unit area was influenced by time but not by stocking rate and was closely related to the 5·5°C soil temperature at 10 cm depth. Tiller senescence was greatly reduced at the higher stocking rate and/or the consequentially lower sward height and herbage mass. Tiller net production was therefore sustained at a positive level on the higher stocked sward throughout November while on the lower stocked sward it fell below zero early in November.     

A quick method of obtaining samples for the estimation of carbon dioxide,oxygen and volatiles in the potato tuber

A 5 min evacuation technique utilizing the purging effect of steam, and the vacuum produced by its condensation, was used to collect and compare O₂, CO₂, ethanol and ethylene from potato tubers surface treated with substances inhibiting normal respiratory exchange.     

Emissions of ammonia,nitrous oxide and carbon dioxide from urban gardens in Niamey,Niger

Urban and peri-urban agriculture (UPA) contributes significantly to meet increasing food demands of the rapidly growing urban population in West Africa. The intensive vegetable cultivation in UPA gardens with its high nutrient inputs is often reported to operate at large surpluses of nutrients and presumably high turnover rates of organic matter (OM) and nitrogen (N) losses via emanation and leaching. Many of these claims are lacking solid data which would allow suggesting mitigation strategies. Therefore, this study aimed at quantifying gaseous emissions of ammonia (NH₃), nitrous oxide (N₂O), and carbon dioxide (CO₂) in three representative urban gardens of Niamey, Niger using a closed chamber gas monitoring system. Mean annual N emissions (NH₃-N and N₂O-N) in two gardens using river water for irrigation reached 53 and 48 kg N ha^?1 yr^?1, respectively, while 25 and 20 Mg C ha^?1 yr^?1 was lost as CO₂-C. In the garden irrigated with sewage water from the city's main wadi, N₂O was the main contributor to N losses (68%) which together with NH₃ reached 92 kg N ha^?1 yr^?1, while CO₂-C emissions amounted to 26 Mg ha^?1 yr^?1. Our data indicate that 28% of the total gaseous C emissions and 30–40% of the N emissions occur during the hot dry season from March to May and another 20–25% and 10–20% during the early rainy season from June to July. Especially during these periods more effective nutrient management strategies in UPA vegetable gardens should be applied to increase the nutrient use efficiency in UPA vegetable gardens.