Role of dispersal date and changes in physiological responses in controlling timing of germination in achenes of Geum canadense

1985 ◽  
Vol 63 (9) ◽  
pp. 1654-1658 ◽  
Author(s):  
Jerry M. Baskin ◽  
Carol C. Baskin
Keyword(s):  
High Temperatures ◽  
Low Temperatures ◽  
Physiological Responses ◽  
Early Spring ◽  
Early Summer ◽  
Test Conditions ◽  
Temperature Requirement ◽  
Before And After ◽  
Germination Requirements

This study examines the importance of the date of dispersal, and of the changes in the physiological responses of achenes before and after dispersal, in regulating timing of germination in Geum canadense Jacq. The effect of dispersal date on germination was tested by collecting achenes from the parent plants from September through June and sowing them on soil in an unheated greenhouse. Changes in germination responses were monitored by testing achenes of each collection in light and darkness over a range of thermoperiods. Regardless of test conditions, achenes required light for germination. At maturity in September, 90% of the achenes germinated at the September thermoperiod (30:15 °C (maximum:minimum)), but none germinated in November at the November thermoperiod (15:6 °C). Achenes sown in September germinated that autumn and the following spring, but none of those sown in November germinated until spring. As achenes overwintered on plants in the field, germination percentages decreased at 20:10, 25:15, and 30:15 °C and increased at 15:6 and 5 °C. Thus, achenes sown in early spring germinated immediately, while those sown in early summer did not germinate until later. Germination requirements of the achenes also changed after dispersal. Stratification lowered the temperature requirement for germination, and thus achenes sown in autumn germinated in March at temperatures that had inhibited germination in the autumn. Achenes dispersed in May and June did not regain the ability to germinate at high temperatures during summer, and they lost the ability to germinate at low temperatures. Therefore, most of these latter achenes did not germinate until the following spring, after they had been stratified during the winter.

scholarly journals Changes in the role of Pacific decadal oscillation on sea ice extent variability across the mid-1990s

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Hyerim Kim ◽  
Sang-Wook Yeh ◽  
Soon-Il An ◽  
Se-Yong Song
Keyword(s):  
Sea Ice ◽  
Pacific Decadal Oscillation ◽  
Far East ◽  
Low Frequency ◽  
Early Summer ◽  
Sea Ice Extent ◽  
The Pacific ◽  
Before And After ◽  
Relationship Of

Abstract Characteristics of sea ice extent (SIE) have been rapidly changing in the Pacific Arctic sector (PAS) in recent years. The SIE variability in PAS during the late spring and early summer (i.e., April–May–June, AMJ) plays a key role in determining the SIE during the following fall when SIE is at a minimum. We find that the Pacific Decadal Oscillation (PDO), which is the most dominant variability of sea surface temperature (SST) on the low-frequency timescales, differently influences the SIE in PAS during AMJ before and after the mid-1990s. While a positive phase of PDO during the previous winter acts to increases SIE during AMJ before the mid-1990s, it acts to decrease SIE during AMJ after the mid-1990s. Further analysis indicates that atmospheric circulation associated with PDO differently influences the variability of SIE in the PAS during AMJ by modulating poleward moisture transport across the Alaska or the Far East Asia peninsula. This results in the change in the relationship of PDO and SIE in the PAS before and after the mid-1990s.

The Brain Damage Hypothesis of the Seasonality of Births in Schizophrenia and Major Affective Disorders: Evidence from Computerised Tomography

1992 ◽  
Vol 160 (3) ◽  
pp. 390-397 ◽  
Author(s):  
Emilio Sacchetti ◽  
Alessandro Calzeroni ◽  
Antonio Vita ◽  
Andrea Terzi ◽  
Franco Pollastro ◽  
...  
Keyword(s):  
Brain Damage ◽  
Affective Disorders ◽  
Early Spring ◽  
Early Summer ◽  
Cortical Atrophy ◽  
Primary Role ◽  
Seasonal Factors ◽  
History Of ◽  
The Brain

Although the excess of schizophrenic births in the winter and early spring has been replicated and some non-conclusive work supports the same seasonal birth trend in patients with major affective disorders, the aetiopathogenetic foundations of this phenomenon remain uncertain. The primary role of perinatal seasonal factors that predispose to the development of schizophrenia via induction of brain damage has been invoked, as has a tendency for patients to conceive during the spring and early summer. In order to test these two hypotheses, cerebral ventricular size and cortical atrophy in 206 schizophrenics and 107 patients with major affective disorders were assessed by CT and analysed in relation to month of birth. Compared with schizophrenics born during the remainder of the year, those born between December and April, particularly in cases lacking a family history of schizophrenia, showed increased chances for ventricular enlargement, but not for cortical atrophy. No association between season of birth and central or cortical atrophy was found for patients with major affective disorders. This suggests that the brain-damaging effect played by perinatal seasonal factors has both a disease and an anatomical specificity.

scholarly journals On the Iceberg Severity off Newfoundland and its Prediction

1962 ◽  
Vol 4 (32) ◽  
pp. 161-172
Author(s):  
Irving I. Schell
Keyword(s):  
High Temperatures ◽  
Low Temperatures ◽  
Pressure Difference ◽  
Early Spring ◽  
Relative Strength ◽  
General Area ◽  
Period 1880 ◽  
Westerly Winds ◽  
The Relationship

AbstractAn analysis of the iceberg count off Newfoundland for the period 1880–1925 shows that stronger than usual north-westerly winds off the Labrador and Newfoundland coasts and relatively low temperatures over Newfoundland during the months from December to March lead to greater than average berg counts off Newfoundland in the following months, mainly April to June. Conversely, lighter than usual north-westerly winds and relatively high temperatures lead to lower than average berg counts in the following months. The relative strength of winds can be measured by the pressure difference between Belle Isle and Ivigtut. The relationship investigated provides a basis for predicting the berg count each year at the end of March. A comparison of the computed values of the berg count with the actual values on scale 0 to 10 for the following period 1927–61 shows marked agreement.It is further indicated that a more detailed representation of the winds, temperatures and other elements during the winter and early spring in that general area would lead to a closer relationship with the berg count and a broader basis for its prediction.

New Thermal and Photochemical Routes to Dewar Furan and Other Isomers on the C4H4O Energy Surface: the Role of Isobenzofuran as a Trapping Agent

1991 ◽  
Vol 44 (9) ◽  
pp. 1275 ◽  
Author(s):  
RN Warrener ◽  
IG Pitt ◽  
RA Russell
Keyword(s):  
High Temperatures ◽  
Low Temperatures ◽  
Energy Surface ◽  
Thermal Study ◽  
Diels Alder ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis ◽  
Benzene Oxide ◽  
Trapping Agent

Photolysis of the specially synthesized substrate (39) leads to quantitative fragmentation into the phthalimide (56) and Dewar furan (4a). Dewar furan has only transient existence even at -65°, yet can be trapped effectively with isobenzofuran but not furan. Rapid isomerization to cycloprop-2-enecarbaldehyde (57) occurs at the photolysis temperatures and this product is also trapped by the isobenzofuran . In the absence of trapping agent, photolysis of (39) produces some furan but no 1H n.m.r . evidence can be obtained for (4a) or (57), even at low temperatures (-85°). Separate irradiation of (57) causes extensive polymerization, without yielding other recognizable products. Furan is concluded, therefore, to arise from photoisomerization of (4a) rather than photochemical or thermal isomerization of (57). Separate thermal study of (57) shows that isomerization to furan only occurs above 420°. Flash vacuum pyrolysis of the polycyclic epoxide (72) provides a new retro- Diels-Alder route to (57) which likely proceeds via (4a) as an intermediate. At high temperatures (57) is isomerized to furan. A new Dewar benzene oxide (41) and Dewar benzene (45) are reported en route to the photosubstrates (39) and (50) respectively. Photolysis of (50) provides a high-yielding source of cyclobutadiene , which in the absence of trapping agent yields the syn-dimer (59).

scholarly journals A theory of Spring Persistence Barrier on ENSO. Part I: The role of ENSO period

2020 ◽  
pp. 1-35
Author(s):  
Yishuai Jin ◽  
Zhengyu Liu
Keyword(s):  
Phase Shift ◽  
Langevin Equation ◽  
Null Hypothesis ◽  
Southern Oscillation ◽  
Phase Locking ◽  
Early Spring ◽  
Early Summer ◽  
Enso Predictability ◽  
Similar Phase

AbstractIn this paper, we investigate the role of El Niño-Southern Oscillation (ENSO) period in the spring persistence barrier (SPB) mainly using the neutral recharge oscillator (NRO) model both analytically and numerically. It is suggested that a shorter ENSO period strengthens the SPB. Moreover, in contrast to the strict phase locking of the SPB in the Langevin equation, the phase of a SPB is no longer locked exactly to a particular time of the calendar year in the NRO model. Instead, the phases of the SPB for different initial months shift earlier with the maximum persistence decline lag months. In particular, the phase of a SPB will be shifted from the early summer to early spring, corresponding to the initial months of the early half year and later half year. This feature demonstrates that for later half year, ENSO predictability decreases as the presence of ENSO period. For realistic parameters, the range of the phase change is modest, smaller than 2-3 months. Similar phase shift is also identified for the SPB in the damped ENSO regime, unstable ENSO regime and observation. Our theory provides a null hypothesis for the role of ENSO period in SPB.

Thermal Conductivity of Waste Forms and Geologic Media

1982 ◽  
Vol 15 ◽  
Author(s):  
R. O. Pohl ◽  
J. W. Vandersande
Keyword(s):  
Thermal Conductivity ◽  
Grain Boundaries ◽  
High Temperatures ◽  
Low Temperatures ◽  
Phonon Scattering ◽  
Lamellar Structures ◽  
Waste Forms ◽  
Thermal Conductivities ◽  
Geologic Media

ABSTRACTIn order to predict the range of thermal conductivities to be expected in waste forms and in geologic media, an understanding of the pertinent phonon scattering processes is required. It has been shown that grain boundaries in polycrystalline media are unimportant at low temperatures relative to lamellae which arise from twinning, exsolution, or foreign inclusions within the grains. The possible role of lamellar structures on the conductivity at high temperatures will be discussed.

Seasonal changes in leaf and stem loline alkaloids in meadow fescue

2011 ◽  
Vol 62 (3) ◽  
pp. 261 ◽  
Author(s):  
Brian Patchett ◽  
Ravi Gooneratne ◽  
Lester Fletcher ◽  
Bruce Chapman
Keyword(s):  
Seasonal Changes ◽  
Seasonal Pattern ◽  
Late Summer ◽  
Early Spring ◽  
Early Summer ◽  
Sharp Decline ◽  
Meadow Fescue ◽  
Accumulation Pattern ◽  
Loline Alkaloids

Leaf and stem loline alkaloid concentration in 10 European meadow fescue (Festuca pratensis Huds.) lines grown in a field in Canterbury, New Zealand, were determined in samples collected six times between early spring 2004 and late autumn 2005. Significant differences in loline alkaloid concentrations were noted between lines and between harvest times. Higher total loline alkaloid concentrations (up to 4990 µg g–1) were found in stems compared to leaf (up to 1770 µg g–1). However, the seasonal accumulation pattern of different loline alkaloid concentrations in leaf and stem varied. In most lines, stem loline concentration peaked sharply in late spring and declined during early summer and autumn. The seasonal pattern of leaf loline alkaloid concentration followed the stem concentration except for a sharp decline in early summer followed by an increase in late summer. In most instances, the concentration of N-formyl loline was the highest > N-acetyl loline > N-acetyl norloline > N-methyl loline. The possible role of stem and leaf loline alkaloids to deter pasture-feeding insects is briefly discussed.

Role of temperature in regulating the timing of germination in Portulaca oleracea

1988 ◽  
Vol 66 (3) ◽  
pp. 563-567 ◽  
Author(s):  
Jerry M. Baskin ◽  
Carol C. Baskin
Keyword(s):  
High Temperature ◽  
Minimum Temperature ◽  
Early Summer ◽  
Portulaca Oleracea ◽  
Late Spring ◽  
Daily Maximum ◽  
Temperature Requirement

The peak of germination of autumn-sown seeds of Portulaca oleracea was between 21 May and 21 June, when mean daily maximum and minimum temperatures were 30.7 and 17.4 °C, respectively. Fresh seeds collected in October germinated to 13 and 94% at 30:15 and 35:20 °C thermoperiods, respectively, in light, and to 0% in darkness. Seeds were buried in October 1975 and exhumed in December 1975 through September 1976. In light, exhumed seeds germinated to 69–100% at 30:15 and 35:20 °C,to 1–80% at 20:10 °C, and to 0–52% at 15:6 °C; in darkness they germinated to 5–55% at 30:15 and 35:20 °C and to0% at 20:10 and 15:6 °C. Germination at 20:10 °C did not exceed 50% until mid-April, and it did not exceed 50% at 15:6 °C until June. Fresh seeds were buried at 5, 15:6, 20:10, 25:15, 30:15, and 35:20 °C, and after 0, 1, 3, and 5 months, seeds from each temperature were tested in light and darkness at the five thermoperiods. The minimum temperature at which 50% or more of the seeds germinated in light decreased with an increase in afterripening temperature. The high temperature requirement for complete afterripening and for germination of partially afterripened seeds prevents germination of this summer annual in temperate regions until late spring and early summer.

scholarly journals On the Iceberg Severity off Newfoundland and its Prediction

1962 ◽  
Vol 4 (32) ◽  
pp. 161-172 ◽  
Author(s):  
Irving I. Schell
Keyword(s):  
High Temperatures ◽  
Low Temperatures ◽  
Pressure Difference ◽  
Early Spring ◽  
Relative Strength ◽  
General Area ◽  
Period 1880 ◽  
Westerly Winds ◽  
The Relationship

Abstract An analysis of the iceberg count off Newfoundland for the period 1880–1925 shows that stronger than usual north-westerly winds off the Labrador and Newfoundland coasts and relatively low temperatures over Newfoundland during the months from December to March lead to greater than average berg counts off Newfoundland in the following months, mainly April to June. Conversely, lighter than usual north-westerly winds and relatively high temperatures lead to lower than average berg counts in the following months. The relative strength of winds can be measured by the pressure difference between Belle Isle and Ivigtut. The relationship investigated provides a basis for predicting the berg count each year at the end of March. A comparison of the computed values of the berg count with the actual values on scale 0 to 10 for the following period 1927–61 shows marked agreement. It is further indicated that a more detailed representation of the winds, temperatures and other elements during the winter and early spring in that general area would lead to a closer relationship with the berg count and a broader basis for its prediction.

Cyclic Variations of Twin Births at Isle-aux-Coudres: A Case/Control Approach

1987 ◽  
Vol 36 (3) ◽  
pp. 381-388 ◽  
Author(s):  
P. Philippe
Keyword(s):  
Case Control ◽  
Early Spring ◽  
Early Summer ◽  
Control Approach ◽  
Time Period ◽  
Control Comparison ◽  
Monthly Distribution ◽  
Cyclic Variations ◽  
Age At Birth

AbstractTwins and singletons were matched for several confounding factors. The monthly distribution of twin births and that of singleton births were compared with a uniform allocation of births over the year. Opposite seasonal variations emerged that were confirmed by a case/control comparison. Twins occurred more often in winter and early spring while singletons proved to be relatively few; singleton peaked in the fall season when the risk of a twin birth was low. These trends held across maternal age at birth and the time period of birth. Results suggest that the conception of a twin pair is higest in spring and early summer and lowest in winter. The role of sunlight in the twinning liability is discussed along with the role of sexual intercourse. That twin-prone mothers are usually more fecund in spring and early summer is a distinct possibility.

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