Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Heterocysts reduce triphenyl tetrazolium chloride (TTC) faster than vegetative cells apparently because the absence of the O2-evolving photosystem II and the high electron transport activity in these cells. Although the rate of TTC reduction in vegetative cells is increased by the continuous removal of O2 evolved in photosynthesis, it has not been possible to obtain rates of TTC reduction comparable with those in heterocysts probably because of the continued competition for electrons between TTC and O2. The use of nitro-blue tetrazolium chloride (NBT) as a redox indicator has revealed the presence in filaments under aerobic conditions of a gradient of electron transport activity with strongest reducing power in the heterocysts, proheterocysts and vegetative cells next to heterocysts, and with gradually diminishing activity midway between two heterocysts. This pattern is indistinct in filaments grown under micro-aerophilic conditions. The strong electron transport activity in vegetative cells adjacent to heterocysts appears to promote reducing conditions in the heterocysts. Both, red-formazan formation in the heterocysts and blue-formazan deposition in vegetative cells greatly inhibit nitrogenase activity, and this was adversely affected also by the detachment of heterocysts from vegetative cells. The findings are consistent with the idea that the association of heterocysts with vegetative cells in essential for nitrogen fixation to occur in heterocystous blue-green algae.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1432-0789
    Keywords: Key words Tree legumes ; Dinitrogen fixation ; Rhizobiology ; Timber species
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Rhizobiology of four tree legumes, Abarema bigemina (endemic), Adenanthera bicolor (endemic), Humboldtia laurifolia (indigenous) and Pericopsis mooniana (indigenous), was studied by: (1) observations of their in situ root nodulation, (2) characterization and authentication of rhizobia isolated from them, and (3) an examination of the infectivity and effectivity of the rhizobial isolates using the respective hosts and the broad-spectrum host, siratro (Macroptillium atropurpureum). Investigations were also conducted to evaluate the effect of rhizobial inoculation on growth and N fixation of the valuable timber species, P. mooniana, during its early stages of growth. All the hosts revealed in situ nodulation, except A. bicolor which had nodule-like swellings on its roots. While four rhizobial isolates were obtained from A. bigemina, four from H. laurifolia and 18 from P. mooniana, no authentic rhizobia were isolated from A. bicolor. The nodule-like structures did not show acetylene reduction activity, and the plants failed to nodulate upon inoculation with rhizosphere soil. A. bicolor was therefore tentatively assigned as a non-nodulating species. This report includes the first description of root nodules in the endemic species A. bigemina and the indigenous species H. laurifolia and the isolation and characterization of rhizobia from them. Significant differences were observed among the isolates with regard to their infectivity and effectivity. One isolate from P. mooniana was outstanding in its infectivity and effectivity on the original host, as well as on siratro. Inoculation of P. mooniana with this isolate together with a reference strain significantly improved nodulation and N fixation and gave a 50% increase in plant dry matter under a low level of N fertilizer, during a 12-month growth period. It is suggested that the nursery culture of P. mooniana could be improved by inoculation under low N-input conditions. The ability of these rhizobia to persist in the soil for a 12-month period was observed by the use of strains marked with antibiotics.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1432-0789
    Keywords: Key words Azorhizobium caulinodans ; Rice ; Inoculum survival ; Inoculum carriers ; Sesbania rostrata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Azorhizobium caulinodans strongly colonized the rhizosphere of rice plants after incorporation of Sesbania rostrata in a field trial throughout the growing season and during the fallow period until 19 weeks after incorporation of S. rostrata. A. caulinodans became well established in the rhizosphere (7.17 log cfu g–1 dry rice root) and colonized subsequent S. rostrata test plants. Three traditional and three improved high-yielding rice varieties were inoculated with A. caulinodans under gnotobiotic conditions. In none of the combinations did acetylene reduction activity significantly increase. Ethylene production on colonized rice roots only started after the growth medium had been supplemented with an extra C source (0.1 to 0.25% Na-lactate). This indicates that the bacterial nitrogenase activity is limited by energy supply. Four possible inoculant-carriers (peat, coir dust, bagasse, rice straw) were compared for long-term survival of the bacterial strain. Independent of the storage temperature (26  °C or 4  °C), the survival of A. caulinodans in peat and coir dust was very high during a 12-month period (〉8 log cfu g–1 dry carrier), whereas the bagasse and rice straw carriers showed a serious decline from 3 months onwards.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1432-0789
    Keywords: Biological N2 fixation ; Sesbania speciosa ; Sesbania rostrata ; Green manure ; N transfer ; Wetland rice ; 15N isotopic techniques
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary We used 15N technology to investigate N2 fixation by Sesbania speciosa and Sesbania rostrata and its transfer to a lowland rice crop after incorporation of the Sesbania spp. into soil as green manure. During the first 50 days after establishment in November–December 1989, S. speciosa and S. rostrata produced 1126 and 923 kg dry matter ha-1 respectively. They gathered 31 and 23 kg N ha-1 respectively, of which 62%±5% and 55%±3% respectively, came from N2 fixation. Both these species produced a greater biomass during September–October 1989, with S. rostrata producing more than S. speciosa. These results reflected differential responses by the plants to different day lengths at different times of the year. Furthermore, the dry matter yield and %N of 15N-labelled S. speciosa were smaller than those of the unlabelled plants, possibly due to inhibition of N2 fixation in root nodules by the chemical N fertilizers added during labelling. These differences were not so pronounced in the stem-nodulated S. rostrata. The increased grain yield of rice fertilized with N in the form of chemical fertilizer or green manure was a result of an increased number of panicles per hill. The rice crop manured with S. speciosa produced a lower grain yield, with a lower grain weight than that manured with S. rostrata. This was due to a low uptake of soil N by rice manured with S. speciosa. Recovery of N from the green manure in rice straw with S. speciosa was significantly higher than from rice manured with S. rostrata, because of the higher applied N uptake by rice manured with the former.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 1432-0789
    Keywords: Key words Leaves ; Low moisture ; Decomposition ; Nitrogen release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract During the dry season in the tropics, agriculture which is solely dependent upon rainfall as its source of water is frequently affected by soil moisture stress, resulting in crop failures. Farmers therefore depend mainly on other sources of limited water supply during this period, such as ground water. Soil moisture conservation measures, especially surface mulching with loppings and, occasionally, leaf litter and crop residues, are practised. Our objective was to study the decomposition and nitrogen (N) release from these plant materials under continuously wet, low moisture regimes, i.e. comparable to those which prevail in the mulches used in the agriculture. A greenhouse experiment was conducted with fresh, chopped leaves of six leguminous trees, wild sunflower and rice, which were spread as a mulch on a layer of soil. They were maintained at eight moisture levels (a total of between zero and 43l water m–2 applied over 8 weeks) by spraying water. Different optimal moisture requirements for the rapid decomposition of these species were observed. These were presumably determined by different physical and chemical properties of the leaves. The amount of water received to the mulches and their soluble polyphenolic and carbon (C) concentrations played an important role in determining the decomposition and the mode of N release under non-limiting conditions of leaf N. Specifically, the C concentration governed N release, while the effect of polyphenolics was important when their concentration was low, as a result of leaching under relatively high moisture regimes. Leaves with a high polyphenolic and C content, which were subjected to high leaching losses of these fractions, underwent a change in their N dynamics from net immobilization to mineralization. This study indicates that leaves with a fast rate of decomposition should be mixed with other species, leaves which decompose more slowly in order to increase the conservation of soil moisture and also improve the synchronization between N release from the mulch and its demand by crops.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 1432-0789
    Keywords: Key words Leaves ; Decomposition ; Nitrogen release ; Soil properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Identifying the determinants of the N dynamics of plant prunings or litter is important for the efficient management of agroecosystems in order to improve their productivity. The plant materials in these ecosystems are managed as soil surface mulches or are incorporated into the soil. Numerous studies have been conducted to investigate which plant chemical parameter best governs N release. In these studies, different plant materials have been incorporated into a soil with a set of known characteristics. The objective of the present study was to examine the effects of different soil properties on N release from plant leaves, when they were incorporated into soils under non-leaching conditions. A laboratory incubation experiment (for 8 weeks) was carried out with dried and ground leaves of six leguminous plants and wild sunflower, which were mixed with three soils (alfisol; ultisol, udult; ultisol, humult). Leaf cellulose was the major chemical parameter that determined leaf N release in the alfisol and ultisol, udult. In the ultisol, humult, the C/N ratio and hemicellulose concentration were better related to N release. Cellulose was not a good indicator of N release in the ultisol, humult, possibly due to a low soil pH which did not favour the activity of the cellulose-degrading enzymes of microbes active in decomposition. Soil pH determined the specific C source that was used to generate energy for microbial action and N mineralization/immobilization. It also had an effect on the nitrification of the mineralized N. The levels of labile soil C fractions governed the mode or nature of N release (i.e. mineralization or immobilization). The levels of labile leaf C fractions incorporated into the soils governed the extent of N release. The soil N concentration in the decomposable organic matter pool, as compared to the leaf N concentration, determined whether leaf N limited its own release. It is recommended from this study that, in grouping different leaf materials as sources of N, the properties of soils into which they are incorporated should also be considered, in addition to leaf quality in terms of its chemical composition. In future studies, the relationships identified under laboratory conditions in this experiment should be verified under field conditions.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 7
    ISSN: 1573-0972
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Description / Table of Contents: Résumé On examine sur le terrain l'effet de cinq doses d'application d'urée (de 0 à 40 kg d'azote par ha) et de trois doses d'application de K+ (de 0 à 65 kg/ha) sur la fève ailée. Les activités spécifiques de nitrogénase sont inhibées par des doses croissantes d'urée jusqu'à 75 jours après le semis (j.a.s.) mais ceci n'est pas aussi apparent 90 j.a.s. Les activités de nitrogénase augmentent proportionnellement aux doses de fertilisation par le K+, surtout pendant les premiers temps de la croissance (de 30 à 60 j.a.s.) et se maintiennent même en cas d'ajout de fertilisant azoté. Les activités de nitrogénase sont mieux correlées avec les poids secs des nodules qu'avec les nombres de nodules. Tant les nombres de nodules que les poids secs de nodules diminuent de manière significative par ajout d'azote. K+ a un effet significatif tant sur les nombres de nodules que sur les poids secs de nodules. Des plants agés de 45 jours démontrent des nombres élevés de nodules mais les poids secs les plus élevés de nodules sont enregistrés chez des plants agés de 75 jours. La fertilisation par K+ stimule la croissance précoce des racines (de 30 à 45 j.a.s.) mais les biomasses radiculaires totales à la fin de l'expérimentation sont semblables quelque soit le traitement potassique. Les poids de pousses augmentent avec les doses d'azote mais pas avec les doses de K+.
    Notes: Summary Five rates of urea application (0 to 40 kg N/ha) and three rates of K+ (0 to 65 kg/ha) on the nitrogen-fixing activity of two varieties (‘SLS-40’ and ‘SLS-44’) of winged bean were examined in the field. Specific activity of nitrogenase was inhibited with increasing amounts of urea up to 75 days after sowing (d.a.s.), but this was not so apparent at 90 d.a.s. Nitrogenase activity increased in proportion to K+ fertilization especially during the early stages of growth (30 to 60 d.a.s.) and continued even with added N fertilizer. Nitrogenase activities correlated better with nodule dry weight than with nodule number. Nodule number and nodule dry weight were significantly decreased by added N. K+ had a significant effect on nodule number and nodule dry weight. Forty-five day-old plants gave high nodule number but the highest nodule dry weight was recorded on 75 day-old plants. K+ fertilizer stimulated early root growth (30 to 45 d.a.s.) but the overall root biomass at the end of the experiment was similar under all K+ treatments. The shoot weight increased with N but not with K+.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 8
    ISSN: 1573-0972
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Description / Table of Contents: Résumé Azolla contre moustiques: quelques expériences avec Culex quinquefasciatus. Les effets des lits superficiels d'Azollapinnata var.imbricata sur la ponte et la survie des moustiques à l'état immature ont été étudiés au laboratoire en utilisant comme modèle expérimentalCulex quinquefasciatus. Les lits superficiels continus d'azolla inhibent complètement la ponte et déterminent une mortalité de 42 à 85% à l'état immature. Les résultats montrent que les lits d'azolla n'ont pas d'effet sur la respiration des larves de cette espèce de moustiques, mais provoquent une forte mortalité lors de l'éclosion des adultes, la plupart des jeunes adultes étant incapables de pénétrer la barrière physique du lit d'azolla.
    Abstract: Resumen Azolla vs mosquitos: experimentos con Culex quiquefasciatus El efecto de capas superficiales deAzolla pinnata var.imbricata en la ovoposición de mosquitos y la supervivencia de inmaduros se ha estudiado en laboratorio utilizandoCulex quinquefasciatus como modelo experimental. Capas completas de azolla inhibieron totalmente la ovoposición y causaron entre 42–85% de mortalidad Centre los inmaduros. Los resultados obtenidos muestran que las capas de azolla, no afectan la respiración de las larvas pero causan una elevada mortalidad en el momento de la emergencia de los adultos, ya que la mayoría de jovenes adultos son incapaces de astravesar la barrera física de las capas de azolla.
    Notes: Summary The effects of surface layers ofAzolla pinnata var.imbricata on mosquito oviposition and immature survival were investigated in the laboratory usingCulex quinquefasciatus as the experimental model. Complete surface mats of azolla totally inhibited oviposition and caused 42–85% mortality of immature mosquitoes. The results show that the azolla mats did not affect larval respiration in this species, but caused heavy mortality at adult emergence, most of the young adults being unable to penetrate through the physical barrier of the azolla layers.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...