Seasonal variation in dormancy and light sensitivity in buried seeds of eight annual weed species

1997 ◽  
Vol 75 (11) ◽  
pp. 1998-2004 ◽  
Author(s):  
Per Milberg ◽  
Lars Andersson
Keyword(s):  
Seasonal Variation ◽  
Seasonal Changes ◽  
Light Exposure ◽  
Light Sensitivity ◽  
Light Treatment ◽  
Weed Species ◽  
Light Requirement ◽  
Papaver Rhoeas ◽  
Buried Seeds ◽  
Urtica Urens

We recorded germination in three different light environments (light, dark, and after a short light exposure) in eight annual weed species. Seeds were buried outdoors at the end of November 1994 and exhumed monthly from March 1995 to April 1996. All species exhibited substantial seasonal changes in dormancy level, and the patterns suggest that seeds of Papaver rhoeas germinate strictly in the autumn; Capsella bursa-pastoris, Descurainia sophia, Spergula arvensis, and Urtica urens mainly in the autumn; Chenopodium suecicum strictly in the spring; and Matricaria perforata mainly in the spring. Lapsana communis showed inconsistent dormancy changes over the year. All species had acquired a light requirement for germination after being in the soil, and in many cases the short light exposure (1050 μmol∙m−2) was enough to fulfil this requirement. The demonstrated seasonal changes in light sensitivity in several of the species will have to be taken into account in attempts to photocontrol weeds. By using the short-light treatment, we were able to detect seasonal dormancy changes that would not have been obvious by testing for germination in only light and darkness. Hence, light is not a simple dichotomous factor in its effect on germination. Key words: dormancy, germination, light, seed, Sweden, weed.

Phytochrome Controlled Changes in Dormancy and Germination of Buried Weed Seeds

Weed Science ◽  
1972 ◽  
Vol 20 (5) ◽  
pp. 417-422 ◽  
Author(s):  
R. B. Taylorson
Keyword(s):  
Seed Germination ◽  
Seasonal Change ◽  
Red Light ◽  
Light Sensitivity ◽  
Light Treatment ◽  
Weed Species ◽  
Barbarea Vulgaris ◽  
Dormancy Period ◽  
Weed Seeds ◽  
Before And After

Seeds of six weed species were buried in the field at depths of 2.5, 7.6, and 15.2 cm. Seed germination after various light and temperature treatments was determined before burial and after recoveries in darkness at 3-month intervals over 12 and 20-month periods. In one experiment the five species studied were ungerminable before burial. After 6 months burial, most species responded to light but became ungerminable again after this time. These results suggest cycles of dormancy where seeds pass from total dormancy at maturation to a phytochrome-controlled dormancy after burial and then return to total dormancy. During the phytochrome-controlled dormancy period, some species were highly light sensitive. In another experiment the response of yellow rocket(Barbarea vulgarisR. Br.) seeds to thirteen light and temperature treatments was determined before and after burial. Without light treatment, germination of the recovered seeds at various temperatures was low. Germination was usually high after brief exposures to red light, particularly in seeds recovered from 15.2 cm. Very large increases in germination were induced by light exposures of 3 × 10−9Einsteins cm−2incident in the 600 to 680-nm region (1 sec). The evidence suggests changes in total phytochrome (Ptot) are responsible for a seasonal change in light sensitivity and a previously undescribed type of dormancy.

scholarly journals Seasonal feeding plasticity can facilitate coexistence of dominant omnivores in Neotropical streams

2021 ◽  
Author(s):  
Mayara P. Neves ◽  
Pavel Kratina ◽  
Rosilene L. Delariva ◽  
J. Iwan Jones ◽  
Clarice B. Fialho
Keyword(s):  
Seasonal Variation ◽  
Fish Species ◽  
Resource Availability ◽  
Seasonal Changes ◽  
Dry Season ◽  
Diet Overlap ◽  
Isotopic Niche ◽  
Neotropical Streams ◽  
Feeding Plasticity ◽  
The Impact

AbstractCoexistence of ecomorphologically similar species in diverse Neotropical ecosystems has been a focus of long-term debate among ecologists and evolutionary biologists. Such coexistence can be promoted by trophic plasticity and seasonal changes in omnivorous feeding. We combined stomach content and stable isotope analyses to determine how seasonal variation in resource availability influences the consumption and assimilation of resources by two syntopic fish species, Psalidodon aff. gymnodontus and P. bifasciatus, in the Lower Iguaçu basin. We also tested the impact of seasonality on trophic niche breadth and diet overlap of these two dominant omnivores. Seasonal changes in resource availability strongly influenced the consumption and assimilation of resources by the two fish species. Both species exhibited high levels of omnivory, characterized by high diversity of allochthonous resources in the wet season. Terrestrial invertebrates were the main component of diet during this season. However, in the dry season, both species reduced their isotopic niches, indicating diet specialization. High diet overlap was observed in both seasons, but the isotopic niche overlap was smaller in the dry season. Substantial reduction in the isotopic niche of P. bifascistus and a shift toward aquatic invertebrates can facilitate coexistence during this season of resource shortage. Feeding plasticity allows omnivorous fish to adjust their trophic niches according to seasonality, promoting the exploitation of different resources during periods of greater resource diversity. This seasonal variation could be an important mechanism that contributes to the resource partitioning and coexistence of dominant omnivores in Neotropical streams.

Vitamin D (25-OH) concentrations in hospitalized patients, outpatients and dialysis patients depending on seasonal variation

2015 ◽  
Vol 51 (3) ◽  
pp. 209-212
Author(s):  
Magdalena Maria Ostrowska ◽  
Ewa Szulc-Mysińska ◽  
Dagna Bobilewicz ◽  
Marta Faryna
Keyword(s):  
Vitamin D ◽  
Seasonal Variation ◽  
Seasonal Changes ◽  
Hospitalized Patients ◽  
Optimum Concentration ◽  
Dialysis Patients ◽  
Total Vitamin ◽  
Different Seasons ◽  
Mean Concentration ◽  
Global Health Problem

Vitamin D deficiency, which is a global health problem, may result in numerous diseases, such as rickets in children and osteoporosis and osteomalacia in adults. The occurrence of the above-mentioned disorders is promoted by the wintertime and higher latitudes. The aim of the study was to compare the concentrations of vitamin D (25-OH) in hospitalized patients and outpatients in different seasons of the year (summer and winter), as well as in dialysis patients in December and May. The Roche test for the quantitativedetermination of total vitamin D (25-OH) was used in the study. The range from 30 to 80 ng/ml was accepted as the optimum concentration. In hospitalized patients and outpatients, both in summer and winter mean concentration of vitamin D (25-OH) reached the values below 30 ng/ml in over 80% of the patients. Only in the hospitalized patient group mean concentration of vitamin D (25-OH) in the summer was significantly higher than in the winter (p=0.0016). In the dialysis patients mean concentration of vitamin (25-OH) in May was significantly higher than in December (p=0.0085) and the percent of the results below 30 ng/ml amounted to 96.39% in December and 77.27% in May. In conclusion, the 25(OH)D concentrations in the whole population under study are lower than those recommended and undergo periodical seasonal changes in hospitalized patients.

Seasonal Changes in General Condition and Lipid Content of Cod from Inshore Waters

1967 ◽  
Vol 24 (3) ◽  
pp. 607-612 ◽  
Author(s):  
P. M. Jangaard ◽  
H. Brockerhoff ◽  
R. D. Burgher ◽  
R. J. Hoyle
Keyword(s):  
Seasonal Variation ◽  
Nova Scotia ◽  
Lipid Content ◽  
General Condition ◽  
Seasonal Variations ◽  
Seasonal Changes ◽  
Oil Content ◽  
Gadus Morhua ◽  
Male Fish ◽  
Inshore Waters

The seasonal variations in lipid content and general "condition" of cod, Gadus morhua L., from an inshore population have been determined.Four female and four male fish were chosen from 20 live cod brought in monthly from Terence Bay, Halifax County, Nova Scotia, the fish were pooled and the lipid content determined on the flesh, livers, and gonads. The flesh lipids varied from 0.57% to 0.74% and the oil content of the livers from 15% to 75%.The general "condition" of the fish as expressed by [Formula: see text], the liver condition by [Formula: see text], and the fat content of the liver all showed seasonal variation with maxima in the fall and minima in the spring. KF varied from 0.79 to 1.05 and KL from 1.0 to 4.5. No seasonal variation in the amount of flesh lipids could be detected.

Oestrous activity in three subtropical sheep breeds in Upper Egypt and response to long-day light treatment

1991 ◽  
Vol 116 (1) ◽  
pp. 139-143 ◽  
Author(s):  
A. M. Aboul-Naga ◽  
H. Mansour ◽  
M. B. Aboul-Ela ◽  
M. T. Mousa ◽  
Ferial Hassan ◽  
...  
Keyword(s):  
Breeding Season ◽  
Seasonal Changes ◽  
Nile Delta ◽  
Reproductive Activity ◽  
Light Treatment ◽  
Continuous Exposure ◽  
Upper Egypt ◽  
Sheep Breeds ◽  
Awassi Sheep ◽  
Long Day

SUMMARYOestrous activity in local Rahmani and Ossimi sheep and imported subtropical Awassi sheep at different times of the year in Upper Egypt and the effect of continuous exposure to long-day conditions from July till December on this activity was studied in 1986. The three breeds differed substantially in oestrous activity but differences did not seem to be directly related to latitude of origin. Rahmani ewes from the Nile Delta were mostly cyclic all year round; the percentage coming to oestrus each month never fell below 70%. Ossimi ewes originating from mid-Egypt had a very long breeding season; 74% had an anoestrous period of 68·8 days (v. 27% for Rahmani ewes). All Awassi ewes, except one, had an anoestrous period of 96·5 days on average.Awassi ewes also showed more response to continuous exposure to long days (14 h) than Ossimi ewes, seen in a shorter reaction interval and a greater decrease in the percentage of ewes coming into oestrus (27 and 90% in control and treated Awassi ewes, respectively). The results indicated that changes in daylength, although small in subtropical regions, may be a major factor controlling seasonal changes in reproductive activity in subtropical sheep breeds, the more seasonal breed being more responsive to changes in daylength. The possibility of selection within these breeds for continuous reproductive activity is also indicated.

Seasonal Changes in the Germination Responses of Buried Witchgrass (Panicum capillare) Seeds

Weed Science ◽  
1986 ◽  
Vol 34 (1) ◽  
pp. 22-24 ◽  
Author(s):  
Jerry M. Baskin ◽  
Carol C. Baskin
Keyword(s):  
Seasonal Changes ◽  
Late Summer ◽  
Late Spring ◽  
Seasonal Temperature ◽  
Temperature Changes ◽  
Late Autumn ◽  
Buried Seeds ◽  
Autumn And Winter

Buried seeds of witchgrass (Panicum capillare L., # PANCA) exposed to natural seasonal temperature changes in Lexington, KY, for 0 to 35 months exhibited annual dormancy/nondormancy cycles. Seeds were dormant at maturity in early October. During burial in late autumn and winter, fresh seeds and those that had been buried for 1 and 2 years became nondormant. Nondormant seeds germinated from 76 to 100% in light at daily thermoperiods of 15/6, 20/10, 25/15, 30/15, and 35/20 C, while in darkness they germinated from 1 to 24%. In late spring, seeds lost the ability to germinate in darkness, and by late summer 63 to 100% of them had lost the ability to germinate in light. As seeds became nondormant, they germinated (in light) at high (35/20, 30/15 C) and then at lower (25/15, 20/10, and 15/6 C) temperatures. As seeds reentered dormancy, they lost the ability to germinate (in light) at 15/6 C and at higher thermoperiods 2 to 3 months later.

scholarly journals Sustainable Illumination for Baroque Paintings with Historical Context Considerations

2020 ◽  
Vol 12 (20) ◽  
pp. 8705
Author(s):  
Pedro Luengo
Keyword(s):  
Eighteenth Century ◽  
Seasonal Changes ◽  
Light Exposure ◽  
Historical Context ◽  
Zero Energy ◽  
Museum Displays ◽  
Zero Energy Building ◽  
Sustainable Conservation ◽  
Scholarly Attention ◽  
Selection Of

The topic of museum illumination and conservation has been richly developed in recent years to take steps toward a zero-energy building concept. Most artworks preserved in museums’ expositions were designed for specifically defined light contexts, wherein daylight and seasonal changes were part of the artistic effect, an issue which has received little scholarly attention. From this premise, this paper aims to prove that defining the original illuminative context of artworks is required for a sustainable conservation, perception, and ultimate interpretation. To do this, a selection of seventeenth and eighteenth century churches and palaces from Europe, the Americas, and Asia will be presented using modern conservation frameworks for artworks. The results demonstrate that both aspects, chosen materials and light exposure, were connected, allowing the spaces to be effective without consuming too much electric lighting. This leads to a discussion about if museum displays should incorporate this context, if it is a more sustainable solution, and if it presents the artworks more accurately to visitors, even as other problems may arise.

Cyclic AMP has no effect on the generation, recovery, or background adaptation of light responses in functionally intact rod outer segments: With implications about the function of phosducin

2000 ◽  
Vol 17 (6) ◽  
pp. 887-892 ◽  
Author(s):  
HANA JINDROVA ◽  
PETER B. DETWILER
Keyword(s):  
Outer Segment ◽  
Light Exposure ◽  
Cell Voltage ◽  
Light Sensitivity ◽  
Rod Outer Segments ◽  
Light Responses ◽  
Outer Segments ◽  
Sequence Of Events ◽  
Background Adaptation ◽  
Dependent Processes

In retinal rods, light exposure decreases the total outer segment content of both cGMP and cAMP by about 50%. The functional role of the light-evoked change in cAMP is not known. It is postulated to trigger changes in the phosphorylation state of phosducin, a phosphoprotein that is phosphorylated in the dark by cAMP-dependent protein kinase (PKA) and dephosphorylated by basal phosphatase activity when PKA is inhibited by the light-evoked drop in cAMP. In biochemical studies, dephosphorylated phosducin binds to free βγ dimer of transducin (Tβγ) and prevents the regeneration of heterotrimeric transducin by blocking the re-association of the βγ and α subunits. Phosducin's interaction with Tβγ is blocked when it is phosphorylated on a single residue by PKA. To evaluate the effect of the light-evoked fall in cAMP, functionally intact isolated lizard rod outer segments were dialyzed in whole-cell voltage clamp with a standard internal solution and electrical light responses were recorded with and without adding cAMP to the dialysis solution. Since the total outer segment content of cAMP in darkness is ∼5 μM, internal dialysis with solution containing a much higher concentration (100 μM) of cAMP (or 8-bromo-cAMP) will overcome the effects of a light-evoked decrease in its concentration by keeping cAMP-dependent processes fully activated. Neither cyclic nucleotide had any influence on the generation, light sensitivity, recovery, or background adaptation of the flash response. These results also argue against the participation of phosducin in the sequence of events that are responsible for these aspects of rod function. This does not exclude the possibility of phosducin being involved in adaptation caused by higher light levels than used in the present study, that is, bleaching adaptation, or in light-dependent processes other than phototransduction.

Flowering and fruiting phenologies of seasonal and aseasonal neotropical forests: the role of annual changes in irradiance

2007 ◽  
Vol 23 (2) ◽  
pp. 231-251 ◽  
Author(s):  
Jess K. Zimmerman ◽  
S. Joseph Wright ◽  
O. Calderón ◽  
M. Aponte Pagan ◽  
S. Paton
Keyword(s):  
Soil Moisture ◽  
Seasonal Variation ◽  
Solar Irradiance ◽  
Seasonal Changes ◽  
Light Availability ◽  
Barro Colorado Island ◽  
Wet Season ◽  
Neotropical Forests ◽  
Seasonally Dry ◽  
Solar Declination

The seasonality of both rainfall and solar irradiance might influence the evolution of flowering and fruiting in tropical forests. In seasonally dry forests, to the degree that soil moisture limits plant productivity, community-wide peaks in reproduction are expected during the rainy season, with seedfall and germination timed to allow seedlings to become well established while soil moisture is available. Where soil moisture is never seasonally limiting, seasonal changes in light availability caused by periods of cloudiness or seasonally low zenithal sun angles should favour reproduction during seasons when irradiance levels are high. To evaluate these predictions, we documented the timing of flower and fruit fall for 10 and 15 y at El Verde, Puerto Rico, and Barro Colorado Island (BCI), Panama. At El Verde, rainfall is abundant year-round and solar declination largely determines seasonal variation in irradiance. At BCI, rainfall is abundant throughout the 8-mo wet season while drought develops and average solar irradiance increases by 40–50% over the 4-mo dry season. Seasonal variation in the number of species flowering and fruiting at both sites was generally consistent with the hypothesis that seasonal variation in irradiance limits the evolution of reproductive phenologies. Community-level metrics provided no evidence for a similar role for moisture availability at BCI. Seasonal variation in irradiance also strongly influenced seed development times at both sites. Thus, community-wide phenologies reveal a strong signature of seasonal changes in irradiance, even in those forests that exhibit some degree of seasonality in rainfall.

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