Effects of canopy light gap and early emergence on the growth and reproduction of Geranium maculatum

1987 ◽  
Vol 65 (2) ◽  
pp. 242-245 ◽  
Author(s):  
Theresa Schutte Dahlem ◽  
Ralph E. J. Boerner
Keyword(s):  
Genetic Recombination ◽  
Early Spring ◽  
Leaf Expansion ◽  
Carbon Gain ◽  
Canopy Closure ◽  
Gap Formation ◽  
Early Emergence ◽  
Short Period ◽  
Fruit Abortion ◽  
Light Gap

Biomass and reproduction of Geranium maculatum L. were measured in an artificial canopy light gap and under a closed canopy. The effects of emergence date were also compared. Increased light in the canopy gap resulted in increased biomass, rhizome mass, and percent of plants flowering in the second growing season after gap formation. The importance of proximate carbon in reducing fruit abortion was determined experimentally. The rate of fruit abortion increased and the number of days required for leaf expansion decreased when the plants were shaded by neutral screens. The reproductive effort of G. maculatum is thus primarily controlled by the previous year's carbon gain, while the proportion of flowers that matured to seeds was a function of proximate carbon gain. Shoots of G. maculatum emerged over a period of approximately 6 weeks in early spring, with canopy closure occurring midway through this interval. Early emergence of plants under the intact canopy permitted exploitation of the increased light levels in the period prior to canopy closure. This led to slightly increased aboveground growth and rhizome storage and a significant increase in the time spent in leaf expansion, though no differences in reproductive output existed between early and later emerging plants. Early emergence was less advantageous for gap plants. The role of gap-phase growth in G. maculatum is in increased genetic recombination and dispersal during this short period when the balance of sexual versus asexual reproduction is altered.

Seasonal pattern of leaf production and its effects on assimilation in giant summer-green herbs in deciduous forests in northern Japan

2006 ◽  
Vol 84 (1) ◽  
pp. 87-98 ◽  
Author(s):  
Tomokazu Tani ◽  
Gaku Kudo
Keyword(s):  
Dark Respiration ◽  
Seasonal Pattern ◽  
Light Availability ◽  
High Irradiance ◽  
Tree Canopy ◽  
Deciduous Forests ◽  
Carbon Gain ◽  
Canopy Closure ◽  
Leaf Production ◽  
Short Period

Understory vegetation of northern deciduous forests in far eastern Asia is characterized by giant summer-green herbs. We examined the patterns of height growth, leaf accumulation, photosynthetic characteristics, daily net assimilation, and dry matter allocation within aboveground parts of six giant summer-green herbs with reference to light conditions in deciduous forests. Plant height, leaf number, and total leaf area per plant increased with progressing tree-canopy closure in five species ( Cacalia hastata L. subsp. orientalis Kitam., Cirsium kamtschaticum Ledeb., Filipendula kamtschatica (Pall.) Maxim. f. kamtschatica, Senecio cannabifolius Less., and Urtica platyphylla Wedd.) that had continuous leaf production throughout the growing season, whereas one species ( Veratrum album L. subsp. oxysepalum Hulten) with early leaf production, completed leaf production mostly before the beginning of tree-canopy closure. Maximum photosynthetic and dark respiration rates decreased seasonally in all species. Species with continuous leaf emergence accumulated leaves acclimatized to shade conditions, which offset the decreasing photosynthesis of individual leaves with progressing tree-canopy closure, resulting in stable carbon gain even under decreasing light availability. In contrast, V. album assimilated vigorously during the short period of high irradiance before tree-canopy closure, and decreased its assimilation rate continuously thereafter.

Effects of grazing dates on forage and beef production of mixed prairie rangeland

1999 ◽  
Vol 79 (3) ◽  
pp. 335-341 ◽  
Author(s):  
M. P. Schellenberg ◽  
N.W. Holt ◽  
J. Waddington
Keyword(s):  
Carrying Capacity ◽  
Average Daily Gain ◽  
Bouteloua Gracilis ◽  
Early Spring ◽  
Forage Yield ◽  
Canadian Prairies ◽  
Crested Wheatgrass ◽  
Forage Digestibility ◽  
Short Period ◽  
Mixed Prairie

Conventional belief is that mixed prairie range is harmed by early spring use but not by moderate grazing after the grasses have flowered. Our hypothesis was that mixed prairie range may be grazed for a limited period in the growing season providing rest is allowed for the remainder of the year. This 6-yr test was established on a rolling site of range pasture, which contained, by area, 65% upland mixed prairie, 5% lowland bluegrass (Poa spp.) and 30% crested wheatgrass (Agropyron cristatum). The species mix is commonly found in southern Canadian prairies. The mixed prairie grasses were needle and thread (Stipa comata), northern wheatgrass (Elymus lanceolatus), western wheatgrass (Pascopyrum smithii) and blue grama (Bouteloua gracilis). Each pasture was 1.6 ha and was grazed with yearling beef cattle once a year beginning mid-May; the end of June; mid-August or late September. Forage yields in grazing-exclusion cages averaged 580, 2960, and 1370 kg ha−1 for the mixed prairie, lowland grasses, and crested wheatgrass, respectively. The date of grazing in the previous year did not affect current-year maximum forage yield. The main determinant of maximum forage yield was a combination of spring soil moisture plus April to June precipitation. Available forage for grazing, on average, doubled from mid-May until the end of June for the three forage types. There were year-by-grazing date interactions, which were related to distribution of precipitation. Mixed prairie was the preferred forage at the last two grazing dates. Forage digestibility, N and P content were highest during the May and June grazing period and declined thereafter. Average daily gain of the steers decreased from 0.9 kg d−1 in May and late June to 0.2 kg d−1 by late September. Annual carrying capacity (in standard animal units) was 40 d ha−1 in May and averaged 55 d ha−1 for the other dates, which were not different. Grazing mixed prairie did not have a negative effect on the yield of native grasses when used for only one short period per year. Delayed use from mid May to end of June increased available forage and carrying capacity. Key words: Mixed grass prairie, crested wheatgrass, grazing, weather effects

scholarly journals PrimPol-dependent single-stranded gap formation mediates homologous recombination at bulky DNA adducts

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Ann Liza Piberger ◽  
Akhil Bowry ◽  
Richard D. W. Kelly ◽  
Alexandra K. Walker ◽  
Daniel González-Acosta ◽  
...  
Keyword(s):  
Homologous Recombination ◽  
Dna Adducts ◽  
Mammalian Cells ◽  
Genetic Recombination ◽  
Gap Formation ◽  
Dna Damage Tolerance ◽  
Strand Breaks ◽  
Bulky Dna Adducts ◽  
Fork Stalling ◽  
Stalled Replication Forks

AbstractStalled replication forks can be restarted and repaired by RAD51-mediated homologous recombination (HR), but HR can also perform post-replicative repair after bypass of the obstacle. Bulky DNA adducts are important replication-blocking lesions, but it is unknown whether they activate HR at stalled forks or behind ongoing forks. Using mainly BPDE-DNA adducts as model lesions, we show that HR induced by bulky adducts in mammalian cells predominantly occurs at post-replicative gaps formed by the DNA/RNA primase PrimPol. RAD51 recruitment under these conditions does not result from fork stalling, but rather occurs at gaps formed by PrimPol re-priming and resection by MRE11 and EXO1. In contrast, RAD51 loading at double-strand breaks does not require PrimPol. At bulky adducts, PrimPol promotes sister chromatid exchange and genetic recombination. Our data support that HR at bulky adducts in mammalian cells involves post-replicative gap repair and define a role for PrimPol in HR-mediated DNA damage tolerance.

Cooler temperatures favour growth of wild leek (Allium tricoccum), a deciduous forest spring ephemeral

Botany ◽  
2012 ◽  
Vol 90 (11) ◽  
pp. 1125-1132 ◽  
Author(s):  
Antoine Bernatchez ◽  
Line Lapointe
Keyword(s):  
Temperature Regime ◽  
Deciduous Forest ◽  
Plant Biomass ◽  
Photochemical Efficiency ◽  
Early Spring ◽  
Photochemical Quenching ◽  
Spring Ephemerals ◽  
Spring Ephemeral ◽  
Short Period ◽  
Allium Tricoccum

Allium tricoccum Aiton is a common spring ephemeral of hardwood deciduous forests of northeastern North America. It takes advantage of the short period of high light conditions between snowmelt and canopy closure to complete its vegetative life cycle and accumulate carbohydrate reserves for the following year. Previous studies on other spring ephemerals have shown that growth of these species is enhanced when grown at low temperature, typical of very early spring. We thus quantified the effect of three growth temperature regimes, i.e., 18 °C day – 14 °C night, 12 °C day – 8 °C night, and 8 °C day – 6 °C night, which have previously been tested on Erythronium americanum, another spring ephemeral. Gas exchange, chlorophyll a fluorescence, and plant biomass were measured repeatedly throughout the growth season. Growth was greatest under the 12 °C day – 8 °C night temperature regime, consistent with enhanced net photosynthetic rates (Pn), photochemical quenching (qP), and photochemical efficiency of photosynthesis (ΦPSII) at this temperature regime throughout the season. Pn was similar at 18 °C day – 14 °C night and 8 °C day – 6 °C night, but leaves had a greater duration at 8 °C day – 6 °C night; however, bulb biomass was not greater at 8 °C day – 6 °C night than at 18 °C day – 14 °C night. This study corroborates the general sensitivity of spring ephemerals to warmer temperatures. It also highlights species differences that might be caused by their specific carbon metabolism at the bulb level.

scholarly journals Seasonal courses of photosynthetic parameters in sun- and shade-acclimated spruce shoots

Beskydy ◽  
2017 ◽  
Vol 10 (1-2) ◽  
pp. 49-56 ◽  
Author(s):  
Otmar Urban ◽  
Petr Holub ◽  
Karel Klem
Keyword(s):  
Photosynthetic Capacity ◽  
Dark Respiration ◽  
Carbon Assimilation ◽  
Growing Season ◽  
Early Spring ◽  
Total Carbon ◽  
Carbon Gain ◽  
Carbon Uptake ◽  
Photosynthetic Parameters ◽  
Sun And Shade

Exponential attenuation of light intensity passing through forest canopies leads to the formation of sun- and shade-acclimated leaves contributing to overall canopy carbon gain. Using a gas-exchange technique, seasonal changes in photosynthetic parameters were investigated in situ to test the hypothesis that the relative contributions of sun- and shade-acclimated Norway spruce shoots to total carbon gain vary during the growing season and that the contribution of sun-acclimated shoots to total carbon uptake may be reduced during the hot and dry summer season. In agreement with the tested hypothesis, we found reduced photosynthetic capacity as well as reduced light-use efficiency for carbon assimilation in sun-acclimated shoots during summer months while these remained almost unchanged in shade-acclimated shoots. Reduction of photosynthetic capacity was primarily associated with reduced stomatal conductance. On the other hand, seasonal courses of mitochondrial dark respiration, quantum efficiency of photosynthetic reactions, and compensation irradiance were primarily driven by changes in temperature. Accordingly, the photosynthetic characteristics of sun- and shade-acclimated shoots tended to converge in early spring and late autumn when temperature was low. Such seasonal dynamics result in an increased contribution of shade-acclimated shoots to total carbon uptake at the beginning and end of the growing season as well as during hot and dry summer periods.

Phenology of Salt Rabbitbrush (Chrysothamnus nauseosusssp.consimilis) and Greasewood (Sarcobatus vermiculatus)

Weed Science ◽  
1981 ◽  
Vol 29 (4) ◽  
pp. 448-454 ◽  
Author(s):  
Bruce A. Roundy ◽  
James A. Young ◽  
Raymond A. Evans
Keyword(s):  
Rapid Growth ◽  
Growth Period ◽  
Early Spring ◽  
Herbicide Application ◽  
Flower Buds ◽  
Sarcobatus Vermiculatus ◽  
Chrysothamnus Nauseosus ◽  
Simultaneous Control ◽  
Short Period ◽  
Phenoxy Herbicides

Salt rabbitbrush [Chrysothamnus nauseosus(Pallas) Britt., ssp.consimilis(Greene)] and greasewood [Sarcobatus vermiculatus(Hook.) Torr.] grow slowly in early spring until mid to late May. They then begin a period of rapid growth, at which time susceptibility to foliar herbicides is probably greatest. Greasewood ceases rapid growth in mid June to early July, but salt rabbitbrush continues to grow rapidly until early August. Greasewood that resprouts after herbicide application has a longer rapid-growth period than shrubs in an untreated stand. An average leader length of 4 cm indicates that rapid growth of salt rabbitbrush is underway, and first opening of the flower buds indicates that rapid growth is over. Appearance of greasewood staminate spikes indicates that rapid growth has begun, and the first appearance of dried spikes indicates that growth has ceased. Simultaneous control of these shrubs with a single application of phenoxy herbicides may only be possible during the relatively short period when both are growing rapidly. This period may only occur from late May to mid June in some stands and years, but may occur from mid May to early July in other cases.

scholarly journals PrimPol-dependent single-stranded gap formation mediates homologous recombination at bulky DNA adducts

2019 ◽  
Author(s):  
Ann Liza Piberger ◽  
Akhil Bowry ◽  
Richard D W Kelly ◽  
Alexandra K Walker ◽  
Daniel Gonzalez ◽  
...  
Keyword(s):  
Homologous Recombination ◽  
Dna Adducts ◽  
Mammalian Cells ◽  
Genetic Recombination ◽  
Sister Chromatid Exchanges ◽  
Environmental Carcinogens ◽  
Gap Formation ◽  
Bulky Dna Adducts ◽  
Fork Stalling ◽  
Dna Template

AbstractObstacles on the DNA template can lead to DNA replication fork stalling and genomic rearrangements. RAD51-mediated homologous recombination (HR) can promote restart and repair of stalled forks, but also post-replicative repair once the obstacle has been bypassed. Bulky DNA adducts are important replication-blocking lesions induced by environmental carcinogens, but it is not known whether they activate HR directly at stalled forks, or at gaps left behind ongoing forks. Here we show that in mammalian cells, bulky adducts predominantly induce HR at post-replicative gaps formed by the DNA/RNA primase PrimPol. Using BPDE and other bulky model lesions, we report that RAD51 is not recruited to stalled or collapsed forks, but instead to long gaps formed by PrimPol re-priming activity and resection by MRE11 and EXO1. In contrast, RAD51 loading at DSBs does not require PrimPol. At bulky adducts, PrimPol is required for the induction of sister chromatid exchanges and genetic recombination. Our data support that HR at bulky adducts in mammalian cells involves post-replicative gap repair and define a role for PrimPol in DNA damage tolerance by homologous recombination.

Elevated CO2 protects poplar (Populus trichocarpa × P. deltoides) from damage induced by O3: identification of mechanisms

2005 ◽  
Vol 32 (3) ◽  
pp. 221 ◽  
Author(s):  
Simon D. L. Gardner ◽  
Peter H. Freer-Smith ◽  
J. Tucker ◽  
Gail Taylor
Keyword(s):  
Cell Wall ◽  
Elevated Co2 ◽  
Populus Trichocarpa ◽  
Leaf Expansion ◽  
Air Pollutant ◽  
Co2 Concentrations ◽  
Wall Properties ◽  
Short Period ◽  
Ozone Episodes ◽  
Cell Wall Properties

CO2 concentrations in the Earth’s atmosphere will rise to between 550 and 700 μL L–1 by 2100 (IPCC 2001). In much of the world, ozone (O3) is the air pollutant most likely to be having adverse effects on the growth of plants. Here we describe the impacts of CO2 and O3 episodes (rising to 100 nL L–1), singly and in mixtures on the growth and physiology of an interamerican hybrid poplar (Populus trichocarpa L. (Torr. & Gray ex Hook.) × P. deltoids Bartr. ex Marsh). 700 μL L–1 CO2 increased all growth variables relative to values in 350 μL L–1. Mainstem dry weight showed a 38% increase in year 1 and a 32% increase in year 2. Ozone episodes reduced mainstem dry mass by 45% in 350 μL L–1 CO2 and by 34% in 700 μL L–1 CO2. A / Ci analysis showed limited effects on photosynthetic efficiency of 700 μL L–1 CO2 but in contrast, Vcmax was reduced by O3 episodes. CO2 tended to increase leaf expansion but O3 episodes reduced expansion rates generally although a short period of increased leaf expansion in response to O3 was also observed. O3 reduced leaf solute potentials (Ψs) and increased turgor (P) in young leaves. Cell wall properties (elasticity and plasticity) were both stimulated by ozone and this was associated with increased leaf expansion. A new mechanism is proposed which suggests that O3 may act directly on the cell wall, attacking polysaccharides in the wall that result in altered cell wall properties and leaf growth. O3 episodes increased leaf loss, elevated CO2 delayed abscission and O3 was less effective at accelerating leaf loss in elevated CO2. Overall CO2 increased growth, O3 caused decreases and the treatment combination gave intermediate effects. Thus O3 episodes are less likely to be detrimental to P. trichocarpa × P. deltoides in the CO2 concentrations of the future.

The Origin of the Moon and its Relationship to the Origin of the Solar System

1962 ◽  
Vol 14 ◽  
pp. 133-148 ◽  
Author(s):  
Harold C. Urey
Keyword(s):  
Solar System ◽  
The Moon ◽  
The Past ◽  
The Earth ◽  
Short Period ◽  
Origin Of The Moon

During the last 10 years, the writer has presented evidence indicating that the Moon was captured by the Earth and that the large collisions with its surface occurred within a surprisingly short period of time. These observations have been a continuous preoccupation during the past years and some explanation that seemed physically possible and reasonably probable has been sought.

the effects of resonance with Jupiter in the system of short-period comets

1974 ◽  
Vol 22 ◽  
pp. 193-203
Author(s):  
L̆ubor Kresák
Keyword(s):  
Structural Effects ◽  
Order Resonance ◽  
Mean Motion ◽  
Short Period ◽  
The Mean ◽  
Compound Effect ◽  
Low Order

AbstractStructural effects of the resonance with the mean motion of Jupiter on the system of short-period comets are discussed. The distribution of mean motions, determined from sets of consecutive perihelion passages of all known periodic comets, reveals a number of gaps associated with low-order resonance; most pronounced are those corresponding to the simplest commensurabilities of 5/2, 2/1, 5/3, 3/2, 1/1 and 1/2. The formation of the gaps is explained by a compound effect of five possible types of behaviour of the comets set into an approximate resonance, ranging from quick passages through the gap to temporary librations avoiding closer approaches to Jupiter. In addition to the comets of almost asteroidal appearance, librating with small amplitudes around the lower resonance ratios (Marsden, 1970b), there is an interesting group of faint diffuse comets librating in characteristic periods of about 200 years, with large amplitudes of about±8% in μ and almost±180° in σ, around the 2/1 resonance gap. This transient type of motion appears to be nearly as frequent as a circulating motion with period of revolution of less than one half that of Jupiter. The temporary members of this group are characteristic not only by their appearance but also by rather peculiar discovery conditions.

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