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1.
《Field Crops Research》1999,62(1):35-52
A field study was conducted to investigate the effect of intermittent soil drying on resulting non-hydraulic and hydraulic root signals, leaf gas exchange, leaf growth, day of heading, leaf osmotic adjustment and yield of wheat grown in sand and loam soils in lysimeters. A 40-day-drought treatment was imposed when the flag leaf started to emerge and was terminated close to maturity. Soil water content and soil water potential of various soil layers were measured using the neutron moderation method and tensiometers, respectively. Soil drying in the top soil layers induced increase in both xylem and bulk-leaf abscisic acid (ABA) content and reduced the stomatal conductance and leaf growth even before a measurable change in leaf water potential could be detected in droughted plants when compared with fully watered plants. Further, heading and flowering occurred 4 days earlier in the droughted than in the well-watered plants before any loss in leaf water potential had occurred as compared with the fully watered plants. When more severe drought reduced the leaf water status, further accumulation of leaf ABA occurred and transpiration decreased in addition to gradual osmotic adjustment and senescence of older leaves. The osmotic adjustment sustained leaf turgor pressure during soil drying. At severe drought, the osmotic adjustment at full turgor in the flag leaves was 0.85 MPa. In sand, the kernel dry weight increased and as a result similar grain yield was obtained in both the treatments. In loam which had more water available than sand, no significant reduction in the final yield was induced by the drought. It is concluded that (1) non-hydraulic root signals caused early drought adaptation at mild water stress by reducing leaf growth and stomatal conductance and hastening of heading and flowering; (2) osmotic adjustment sustained turgor maintenance and hence the yield-forming processes during moderate and severe water stress. 相似文献
2.
梯度干旱胁迫对水稻叶片光合和水分状况的影响 总被引：3，自引：0，他引：3
采用温室营养液培养方式,通过添加0%、10%、20%、30%PEG6000模拟干旱胁迫,对水稻幼苗叶片的光合作用和水分状况进行比较分析。结果表明:1)在干旱胁迫下,水稻叶片的光合速率、气孔导度、叶肉导度、总导度和叶绿体内CO2浓度等都显著降低;2)在干旱胁迫条件下,限制光合作用的非气孔限制值并没有显著提高,而气孔限制值则大幅提高;与正常水分条件相比,扬稻6号和汕优63在30%PEG干旱胁迫下气孔限制值分别提高了42%和81%;3)光合速率与气孔导度、叶肉导度、总导度及叶绿体内CO2浓度呈正相关;4)在重度干旱胁迫下(20%和30%),叶片水势和含水量都显著下降,并且叶片水势与气孔导度、叶肉导度和总导度呈正相关。因此,气孔关闭导致的叶绿体内CO2浓度降低是限制光合作用的最主要因素,同时叶片水势的降低增加了叶片内CO2传输的阻力。 相似文献
3.
Daniel F Kripke Jeffrey A Elliott Shawn D Youngstedt Katharine M Rex 《Journal of circadian rhythms》2007,5(1):4-13
Background
The phase of a circadian rhythm reflects where the peak and the trough occur, for example, the peak and trough of performance within the 24 h. Light exposure can shift this phase. More extensive knowledge of the human circadian phase response to light is needed to guide light treatment for shiftworkers, air travelers, and people with circadian rhythm phase disorders. This study tested the hypotheses that older adults have absent or weaker phase-shift responses to light (3000 lux), and that women's responses might differ from those of men. 相似文献4.
Matthew?Rocco?Price Julie?Anita Marie?Kruse M?Eric?Galvez Annaka?M?Lorincz Mauricio?Avigdor Paul?D?Heideman
Background
Responsiveness to changing photoperiods from summer to winter seasons is an important but variable physiological trait in most temperate-zone mammals. Variation may be due to disorders of melatonin secretion or excretion, or to differences in physiological responses to similar patterns of melatonin secretion and excretion. One potential cause of nonphotoresponsiveness is a failure to secrete or metabolize melatonin in a pattern that reflects photoperiod length. 相似文献5.
Background
In spite of very low nutrient concentrations in its vicinity – both column and pore waters-, the Posidonia oceanica of the Revellata Bay displays high biomass and productivity. We measured the nutrient fluxes from the sediment into the water enclosed among the leaf shoots ("canopy water") to determine if it is possible source of nutrients for P. oceanica leaves. 相似文献6.
Background
Our aims were to examine the influence of different bright light schedules on mood, sleep, and circadian organization in older adults (n = 60, ages 60–79 years) with insomnia and/or depression, contrasting with responses of young, healthy controls (n = 30, ages 20–40 years). 相似文献7.
Background
Amphibians are sensitive indicators of environmental conditions and show measurable responses, such as changes in phenology, abundance and range limits to local changes in precipitation and temperature regimes. Amphibians offer unique opportunities to study the important ecological and evolutionary implications of responses in life history characteristics to climatic change. We analyzed a late-Holocene fossil record of the Tiger Salamander (Ambystoma tigrinum) for evidence of population-level changes in body size and paedomorphosis to climatic change over the last 3000 years. 相似文献8.
Daniel F Kripke Jeffrey A Elliott Shawn D Youngstedt Barbara L Parry Richard L Hauger Katharine M Rex 《Journal of circadian rhythms》2010,8(1):5
Background
Most mammals are seasonal breeders whose gonads grow to anticipate reproduction in the spring and summer. As day length increases, secretion increases for two gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH). This response is largely controlled by light. Light effects on gonadotropins are mediated through effects on the suprachiasmatic nucleus and responses of the circadian system. There is some evidence that seasonal breeding in humans is regulated by similar mechanisms, and that light stimulates LH secretion, but primate responses seem complex. 相似文献9.
Summary Leaf stomatal resistance varies considerably in response to changes in environmental conditions. Understanding cultivar differences
in the response of stomata to these conditions is important for effectively simulating water-use and growth.
In this study the stomatal resistance of three field grown potato (Solanum tuberosum L.) cultivars Atlantic. Monona and Norchip was observed in response to photosynthetic photon flux density, leaf to air vapour
pressure difference and root zone available soil water. Substantial variation in stomatal resistance was accounted for by
functions of the environmental variables for both Monona and Norchip. The explained variation for Atlantic was considerably
less. Light saturation occurred near 500 μmol m−2 s−1. Increasing stomatal resistance above 1000 μmol m−2s−1 was also observed but is likely an artifact of stomatal closure on days in which mid-day leaf water potentials dropped below
critical levels. Although the leaf presumably insufficient to obtain substantial effects. The soil water status was partially
linked to the average 1000 h to 1500 h stomatal resistance on clear, sunny days. Significant differences were observed among
the cultivars in the response of stomata to changes in the available soil water. 相似文献
10.
《Field Crops Research》2005,94(1):67-75
A study was conducted with the objective to determine the influence of (shallow water depth with wetting and drying) SWD on leaf photosynthesis of rice plants under field conditions. Experiments using SWD and traditional irrigations (TRI) were carried out at three transplanting densities, namely D1 (7.5 plants/m2), D2 (13.5 plants/m2) and D3 (19.5 plants/m2) with or without the addition of organic manure (0 and 15 t/ha). A significant increase in leaf net photosynthetic rate by SWD was observed with portable photosynthesis systems in two independent experiments. At both flowering and 20 DAF stages, photosynthetic rate was increased by 14.8% and 33.2% with D2 compared to control. SWD significantly increased specific leaf weight by 17.0% and 11.8% over the control at flowering and 20 DAF stages, respectively. LAI of D2 under SWD was significantly increased by 57.4% at 20 DAF. In addition, SWD with D2 significantly increased the leaf dry weight (DW) at both growing stages. At all the three densities, SWD increased the leaf N content and the increase was 18.9% at D2 density compared with the conventional control. In SWD irrigation, the leaf net photosynthetic rate was positively correlated with the leaf N content (R2 = 0.9413), and the stomatal conductance was also positively correlated with leaf N content (R2 = 0.7359). SWD enhanced sink size by increasing both panicle number and spikelet number per panicle. The increase in spikelet number per panicle was more pronounced in the 15 t ha−1 manure treatment than in the zero-manure treatment. Grain yield was also significantly increased by SWD, with an average increase of 10% across all treatments. SWD with D2 had the highest grain yield under the both cultivars with or without 15 t ha−1 manure treatment, which was 14.7% or 13.9% increase for Liangyoupeijiu and 11.3% or 11.2% for Zhongyou 6 over the control, respectively. 相似文献
11.
Background
The human body exhibits a variety of biological rhythms. There are patterns that correspond, among others, to the daily wake/sleep cycle, a yearly seasonal cycle and, in women, the menstrual cycle. Sine/cosine functions are often used to model biological patterns for continuous data, but this model is not appropriate for analysis of biological rhythms in failure time data. 相似文献12.
Background
The Brazilian Atlantic Forest is highly endangered and only about 7% of the original forest remains, most of which consists of fragments of secondary forest. Small mammals in the Atlantic Forest have differential responses to this process of fragmentation and conversion of forest into anthropogenic habitats, and have varying abilities to occupy the surrounding altered habitats. We investigated the influence of vegetation structure on the micro-scale distribution of five small mammal species in six secondary forest remnants in a landscape of fragmented Atlantic Forest. We tested whether the occurrence of small mammal species is influenced by vegetation structure, aiming to ascertain whether species with different degrees of vulnerability to forest fragmentation (not vulnerable: A. montensis, O. nigripes and G. microtarsus; vulnerable: M. incanus and D. sublineatus; classification of vulnerability was based on the results of previous studies) are associated with distinct vegetation characteristics. 相似文献13.
Background
Diversity patterns of different taxa typically covary in space, a phenomenon called cross-taxon congruence. This pattern has been explained by the effect of one taxon diversity on taxon diversity, shared biogeographic histories of different taxa, and/or common responses to environmental conditions. A meta-analysis of the association between environment and diversity patterns found that in 83 out of 85 studies, more than 60% of the spatial variability in species richness was related to variables representing energy, water or their interaction. The role of the environment determining taxa diversity patterns leads us to hypothesize that this would explain the observed cross-taxon congruence. However, recent analyses reported the persistence of cross-taxon congruence when environmental effect was statistically removed. Here we evaluate this hypothesis, analyzing the cross-taxon congruence between birds and mammals in the Brazilian Cerrado, and assess the environmental role on the spatial covariation in diversity patterns. 相似文献14.
Background
Many physiological processes of mammalian species exhibit daily rhythmicity. An intrinsic relationship exists between fat soluble vitamins (A, D, E and K) and several body functions. Few investigations on the rhythmic pattern of vitamins in domestic animals have been carried out. The present study evaluated the circadian rhythmicity of fat soluble vitamins in the horse. 相似文献15.
Keny Vanlalhriatpuia Vanlalnghaka Chhakchhuak Satralkar K Moses SB Iyyer MS Kasture AJ Shivagaje Barnabas J Rajneesh Dilip S Joshi 《Journal of circadian rhythms》2007,5(1):1-11
Background
We recently reported that the altitude of origin altered the photic and thermal sensitivity of the circadian pacemaker controlling eclosion and oviposition rhythms of high altitude Himalayan strains of Drosophila ananassae. The present study was aimed at investigating the effects of altitude of origin on the pacemaker controlling the adult locomotor activity rhythm of D. helvetica. 相似文献16.
Background
It is reported that the circadian rhythms of female mating activity differ among Drosophila species and are controlled by an endogenous circadian clock. Here, we found that the mating rhythm of D. ananassae differed from that of D. melanogaster. Moreover, to evaluate the effect of clock gene products on mating activities, we examined the mating activity of D. melanogaster timeless (tim 01) transgenic fly harboring heat-shock promotor driven-D. ananassae timeless (tim) gene (hs-AT tim 01). 相似文献17.
Background
Loss of pond habitat is catastrophic to aquatic larval amphibians, but even reduction in the amount of time a breeding site holds water (hydroperiod) can influence amphibian development and limit reproductive success. Using the landscape variation of a glacial valley in the Greater Yellowstone Ecosystem as the context for a natural experiment, we examined variation in growth pattern and life history of the salamander Ambystoma tigrinum melanostictum and determined how these developmental characteristics varied with hydroperiod over several summers. 相似文献18.
Leandro P Casiraghi Diego O Croci Francoise Poirier Gabriel A Rabinovich Diego A Golombek 《Journal of circadian rhythms》2010,8(1):4
Background
Recent evidence suggests a two-way interaction between the immune and circadian systems. Circadian control of immune factors, as well as the effect of immunological variables on circadian rhythms, might be key elements in both physiological and pathological responses to the environment. Among these relevant factors, galectin-1 is a member of a family of evolutionarily-conserved glycan-binding proteins with both extracellular and intracellular effects, playing important roles in immune cell processes and inflammatory responses. Many of these actions have been studied through the use of mice with a null mutation in the galectin-1 (Lgals1) gene. To further analyze the role of endogenous galectin-1 in vivo, we aimed to characterize the circadian behavior of galectin-1 null (Lgals1 -/-) mice. 相似文献19.
G. Levine 《Paddy and Water Environment》2007,5(4):279-284
The Lower Rio Grande Valley is a sub-tropical area with a productive irrigated agriculture, but with an over-committed single
water resource. It is experiencing a rapidly growing population that is placing increasing pressure on the water resource.
This, combined with expanding urban areas and land moving out of agriculture, has resulted in a vigorous water market, with
transfers from agriculture to municipal uses. For the US portion of the valley, transfers from agriculture to municipalities
are either short-term (usually 1 year) or permanent. Prices vary depending upon the location and timing, and result from negotiations
between the parties. Over time, and not without difficulty, the water market has been facilitated by appropriate enabling
legislation, water rights that have been validated judicially, and an efficient transfer mechanism that has a minimum of transaction
cost. Government involvement is primarily for protection of the public, and to facilitate the transfer process.
相似文献
| G. LevineEmail: |
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