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排序方式: 共有215条查询结果,搜索用时 15 毫秒
101.
102.
Cornelia Flora Jan L. Flora Gary P. Green Frederick E. Schmidt 《Agriculture and Human Values》1991,8(3):19-24
During the 1980s many communities turned to grassroots activities to promote economic development, rather than relying on industrial recruitment strategies. We evaluate the characteristics of these projects, their benefits and costs, and obstacles they face in the development process. The data are drawn from a survey of more than one hundred communities in the United States. Self-development efforts do not appear to replace traditional rural economic development activities, but may complement them. Self-development activities produce a wide variety of jobs that are taken primarily by local residents. The cost and availability of credit are major obstacles for self-development projects. Although self-development strategies should not be considered the primary economic development strategy for most rural communities, they do enable communities to build a more viable local economy. 相似文献
103.
104.
An 3 Lysimetermonolithen unterschiedlichen Bodentyps (Braunerde ‐ L5, Pseudogley ‐ L7, Schwarzerde ‐ L10) sowie an deren Herkunftsflächen (H5, H7, H10) wurden verschiedene bodenbiologische Parameter untersucht. Die mikrobiologischen Aktivitäten wiesen in allen Proben einen ausgeprägten Tiefengradienten auf und waren sogar z. T. bis in Tiefen von 175 cm noch nachweisbar (Biomasse, Basalatmung, DMSO‐Reduktion, alkalische Phosphatase). Die metabolischen Quotienten für CO2 waren auf den Herkunftsflächen meist deutlich niedriger als in den Lysimetern. Ob dieser Befund ebenso wie die etwas niedrigeren Cmik/Corg‐Quotienten der Lysimeter auf einen verminderten C‐Umsatz in den Lysimetern hinweisen könnte, muß durch weitere Untersuchungen geklärt werden. Die Erfassung der Mesofauna ergab größere Individuendichten für Collembolen und Milben (Braunerde) bzw. nur für Milben (Schwarzerde) in den Lysimetern, allerdings war hier das Untersuchungsmaterial für verallgemeinernde Aussagen nicht ausreichend. 相似文献
105.
Roschni KALATHOOR Jens BOTTERWECK Andreas SCHFFER Burkhard SCHMIDT Jan SCHWARZBAUER 《土壤圈》2021,31(4):549-559
The proportion of organic matter and mineral composition are important factors determining the formation and type of non-extractable residues (NERs) of pesticides in soil. In this study, we investigated the enantioselectivity in degradation and NER formation of the chiral fungicide metalaxyl in soil particle size fractions (silt and clay). Microbial and extracellular enzyme activities during these processes were monitored in incubation of silt and clay samples isolated from sterilized and non-sterilized soil samples collected from a long-term agricultural field experimental site in Ultuna, Sweden. The temporal influence on the fate of the fungicide was noted by short-term (10-d) and long-term (92-d) incubations. Besides the acquisition of quantitative data with gas chromatography-mass spectrometry (GC/MS), stereoselective analyses were performed with chiral GC/MS. Quantitative results pointed to a higher metabolism rate of the pesticide through microbial activity than through extracellular enzyme activity. This was also confirmed by the enantioselective depletion of R-metalaxyl and the subsequent formation of R-metalaxyl acid in microbially active samples from non-sterilized soil. The silt fraction containing a high amount of organic matter exhibited a significant hydrolyzable proportion of metalaxyl NERs that was releasable under alkaline conditions. On the contrary, the clay fraction showed an enhanced affinity for covalently bound residues. Based on our results, we recommend differentiating between reversibly and irreversibly bound proportions of pesticides in persistence and environmental risk assessment because the reversible fraction contained potentially bioavailable amounts of residues that may be released under natural conditions. 相似文献
106.
Cornelia Kienle Miriam Langer-Jaesrich Daniela Baumberger Doris Hohmann Sergio Santiago Heinz-R. Köhler Daniel Zürrer Almut Gerhardt 《Journal of Soils and Sediments》2013,13(9):1611-1625
Purpose
In order to assess possible adverse effects originating from pulp deposits in a Swiss lake, a sediment quality triad approach was applied with chemical, ecotoxicological and ecological assessment methods.Materials and methods
To obtain an integrative picture of the potential ecotoxicological effects on organisms of different trophic levels, four test procedures were applied. The acute effects of pulp deposit pore water on a decomposer, the amphipod Gammarus fossarum, were monitored. Chronic toxicity of the pore water was evaluated on primary producers via a growth inhibition test with unicellular green algae (Pseudokirchneriella subcapitata) and on secondary consumers in a reproduction test with the water flea Ceriodaphnia dubia. To evaluate the effects of the pulp deposit on sediment inhabitants, a whole-life-cycle test with the non-biting midge Chironomus riparius was undertaken. Chemical assessment included dissolved organic carbon, extractable organic halogenic compounds, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) and heavy metals. The composition of the macrozoobenthos community was analysed in order to assess the ecological effects.Results and discussion
G. fossarum displayed increased locomotor activity at 12.5% but not at 25% sample concentration during a short-time exposure of 20 h. Chronic effects compromised the reproduction and growth of C. dubia (lowest observed effect concentration, 12.5% sample concentration) with zero population growth in 100% pulp deposit pore water. In 100% pulp deposit, C. riparius exhibited increased mortality at 10 and 17 days after oviposition. Pulp deposits of 50% and 100% concentration caused a significantly lower emergence compared with the reference treatments (lake sediment and quartz sand). Additionally, the locomotor activity of chironomids decreased significantly in 25–100% pulp deposit. No chronic effects of pulp deposit pore water on algae photosynthesis and growth could be detected. The bioassay results were in accordance with an elevated content of PAHs, PCBs and metals in the pulp deposit. Significantly more organisms known to be tolerant to organic pollution were present within the macrozoobenthos community.Conclusions
In general, for sediment inhabitants such as chironomids, the pulp deposit has to be classified toxic. In the present test setup, the toxicity of the pulp deposit was reflected better by the chronic test systems applied than by the acute ones. The applied testing framework could be a suitable tool to assess the risk of contaminated sites, and this information will help decide whether risk mitigation measures should be taken. In addition, with a similar approach, the success of any mitigation measures taken can be assessed. 相似文献107.
Contractor A Rogers C Maron C Henkemeyer M Swanson GT Heinemann SF 《Science (New York, N.Y.)》2002,296(5574):1864-1869
The site of induction of long-term potentiation (LTP) at mossy fiber-CA3 synapses in the hippocampus is unresolved, with data supporting both pre- and postsynaptic mechanisms. Here we report that mossy fiber LTP was reduced by perfusion of postsynaptic neurons with peptides and antibodies that interfere with binding of EphB receptor tyrosine kinases (EphRs) to the PDZ protein GRIP. Mossy fiber LTP was also reduced by extracellular application of soluble forms of B-ephrins, which are normally membrane-anchored presynaptic ligands for the EphB receptors. The application of soluble ligands for presynaptic ephrins increased basal excitatory transmission and occluded both tetanus and forskolin-induced synaptic potentiation. These findings suggest that PDZ interactions in the postsynaptic neuron and trans-synaptic interactions between postsynaptic EphB receptors and presynaptic B-ephrins are necessary for the induction of mossy fiber LTP. 相似文献
108.
Cornelia J. M. Almekinders 《Potato Research》1993,36(2):97-105
Summary A knowledge of the pattern of flowering and seed production is required for the development of large-scale field production
of True Potato Seed (TPS). At the highland experimental station of the International Potato Center in Peru, data on flowering
and seed production were collected from three cultivars planted at three densities.
Main stems in which flowering was delayed ceased shoot growth at an earlier stage and produced fewer inflorescences. Inflorescences
produced later had fewer flowers, a lower berry set and yielded less seed. Inflorescences flowering at the same time performed
similarly, irrespective of their position on the plant. Increasing plant density resulted in cessation of shoot growth at
an earlier stage and concentrated inflorescence and flower production at primary positions of early-flowering shoots. With
cvs Renacimiento and Yungay a higher plant density increased the percentage of flowers produced in the first three weeks of
the flowering period, but with cv. Atzimba the effect of plant density on the distribution of flower production was off-set
by a slower stem development. 相似文献
109.
110.
Drought effects on C,N, and P nutrition and the antioxidative system of beech seedlings depend on geographic origin
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Florian Netzer Carolin Thöm Nevenka Celepirovic Mladen Ivankovic Saleh Alfarraj Aikaterini Dounavi Judy Simon Cornelia Herschbach Heinz Rennenberg 《植物养料与土壤学杂志》2016,179(2):135-150
In future, prolonged summer drought and heat will constitute a major risk for the cultivation of shallow‐rooting beech in Central Europe and will negatively affect the productivity of beech forests. In a pot experiment under controlled conditions, the influence of long‐term (28 d) water deprivation on nitrogen (N), carbon (C), phosphate (Pi), and ascorbate (ASC) concentrations was examined in leaves and fine roots of beech seedlings (Fagus sylvatica L.) from six provenances originating from Central Europe (Germany: Neidenstein and Illertissen, intermediate habitats), the Balkan peninsula (Croatia: Zagreb and Gospic, wet habitats), and Southeast Europe (Bulgaria: Kotel, Greece: Paikos; dry habitats). The goal of the study was to identify beech provenances well adapted to water limitation during summer drought events. Our results suggest that N might be involved in the alleviation of water scarcity, whereas Pi might become a limiting factor for forest growth during drought periods. Drought stress resulted in significant changes of ASC pools in leaves and fine roots and the ASC redox state. Under well‐watered and under drought conditions, ASC in leaves was the most important factor causing differences between the provenances examined. Finally, a link between P nutrition and the capacity of antioxidative stress defense by ascorbate could be highlighted. Based on observations from this study, beech seedlings from three origins (Paikos, Zagreb, and Neidenstein) might constitute beech provenances well adapted to water shortage in summer. This conclusion is drawn from the high potential of these provenances to alleviate oxidative stress during water shortage. 相似文献