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Influence of root density on the critical soil water potential 总被引:1,自引:1,他引:0
Estimation of root water uptake in crops is important for making many other agricultural predictions. This estimation often
involves two assumptions: (1) that a critical soil water potential exists which is constant for a given combination of soil
and crop and which does not depend on root length density, and (2) that the local root water uptake at given soil water potential
is proportional to root length density.
Recent results of both mathematical modeling and computer tomography show that these assumptions may not be valid when the
soil water potential is averaged over a volume of soil containing roots. We tested these assumptions for plants with distinctly
different root systems. Root water uptake rates and the critical soil water potential values were determined in several adjacent
soil layers for horse bean (Vicia faba) and oat (Avena sativa) grown in lysimeters, and for field-grown cotton (Gossypium L.), maize (Zea mays) and alfalfa (Medicago sativa L.) crops. Root water uptake was calculated from the water balance of each layer in lysimeters. Water uptake rate was proportional
to root length density at high soil water potentials, for both horse bean and oat plants, but root water uptake did not depend
on root density for horse bean at potentials lower than −25 kPa. We observed a linear dependency of a critical soil water
potential on the logarithm of root length density for all plants studied. Soil texture modified the critical water potential
values, but not the linearity of the relationship. B E Clothier Section editor 相似文献
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Siu Keung Tse Shein Chung Chow Qingshu Lu Dennis Cosmatos 《Biometrical journal. Biometrische Zeitschrift》2009,51(1):159-170
The problem of testing treatment difference in the occurrence of a safety parameter in a randomized parallel‐group comparative clinical trial under the assumption that the number of occurrence follows a zero‐inflated Poisson (ZIP) distribution is considered. Likelihood ratio tests (LRT) for homogeneity of two ZIP populations are derived under the hypotheses that (i) there is no difference in inflation parameters, (ii) there is no difference in non‐zero means; and (iii) there is no difference in both inflation parameters and non‐zero means. Approximate formulas for sample size calculation are also obtained for achieving a desired power for detecting a clinically meaningful difference under the corresponding alternative hypotheses. An example concerning the assessment of the gastrointestinal (GI) safety in terms of the number of erosion counts of a newly developed compound for the treatment of osteoarthritis and rheumatoid arthritis is given for illustration purpose (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Shein I. V. Polyakova G. G. Zrazhevskaya G. K. Pashenova N. V. Vetrova V. P. 《Russian Journal of Plant Physiology》2001,48(2):216-221
Callus cultures of Siberian larch (Larix sibiricaLedeb.) and Siberian spruce (Picea obovataLedeb.) were used to demonstrate the elicitor activity of two ophiostomatoid fungal species, Ceratocystis laricicolaand Ceratocystis polonica, as the pioneer settlers on larch and spruce, respectively. The extract from C. laricicolamycelium stimulated the accumulation of lignin in larch cells by 37% and that of bound proanthocyanidins by 25%. In spruce callus cultures, C. laricicolaand C. polonicaincreased the bound PA content by 25 and 46%, respectively. In the callus cultures of larch and spruce, the addition of extract of C. laricicolaincreased the concentration of p-hydroxybenzoic acid 13-fold and nearly 4-fold, respectively. The metabolic characteristics of accumulation of phenolic compounds in conifer cells are discussed. 相似文献
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Cultures of cloned neuroblastoma cells (N1E) in stationary phase and cloned glioma cells (C21) in confluency showed substantial differences in phospholipid composition. As a percentage of lipid P, N1E contained more phosphatidylcholine, less ethanolamine phosphoglycerides and much less sphingomyelin than C21. When incubated with 32Pi both cell lines incorporated comparable amounts of radioactivity into total phospholipids. In NIE, phosphatidylcholine contained much more and phosphatidylinositol and phosphatidic acid somewhat less label as compared to C21. The presence in the incubation medium of either norepinephrine or carbamylcholine failed to elicit stimulation of 32P incorporation into any phospholipid class. 相似文献
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M. M. Shashurin I. A. Prokopiev A. A. Shein G. V. Filippova A. N. Zhuravskaya 《Russian Journal of Plant Physiology》2014,61(4):484-488
Experimental evidence is presented that continuous exposure of hoary plantain (Plantago media L.) seedlings to the electromagnetic field (EMF) of power-line frequency may disturb physiological, biochemical, and cytological characteristics of these plants. The increase in EMF strength in the range from 230 to 1800 V/m (350–2000 nT) was found to reduce the percentage of seed germination, the rate of cell division, and the rates of DNA and protein biosyntheses in tissues of 8-day-old seedlings. The action of EMF with the strength of 500–1000 V/m (800–1150 nT) stimulated root growth, elevated the content of malondialdehyde and low-molecular antioxidants, and enhanced the activity of superoxide dismutase. Direct correlation was revealed between lipid peroxidation rates and the activity of cellular antioxidant defense system. The wavelike changes in the content of photosynthetic pigments were observed in plantain seedlings exposed to EMF of various strengths. 相似文献
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Polyphosphoinositides in normal and neoplastic rodent astrocytes 总被引:3,自引:0,他引:3
Polyphosphoinositides were identified in dispersed cell cultures of normal newborn hamster astrocytes and of a chemically transformed adult rat astrocytoma (C6) and are therefore presumed to be constituents of immature astrocytes in brain. Small amounts were also detected in astrocytomas grown as subcutaneous tumors. These lipids were metabolically highly active, accounting for a substantial fraction of 32Pi incorporated into phospholipids. Astrocytes may thus contain a small pool of polyphosphoinositides metabolically distinct from that in myelin. 相似文献
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