Germination of Seeds of Perennial Pepperweed (Lepidium latifolium)

Perennial pepperweed (Lepidium latifoliumL. # LEPLA) is a serious weed of meadows and riparian habitats in the intermountain area of the western United States. Germination of seeds of this species was tested at 55 constant- and alternating-temperature regimes. No significant differences were found in mean germination at a range of temperatures varying from 0 to 40 C for seedlots collected at the same site in different years or at different locations in the same year. Optimum germination not significantly (P = 0.01) lower than the maximum observed occurred most frequently at 5/40 C (5 C for 16 h and 40 C for 8 h), and 10/40 and 15/40 C. Germination was enhanced by alternating regimes with low night temperatures (0, 2, or 5 C) and high day temperatures (35 and 40 C), in comparison with more moderate constant-temperature regimes.

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Dormancy break and germination requirements in acorns of two bottomland Quercus species (Sect. Lobatae) of the eastern United States with references to ecology and phylogeny

Seed Science Research ◽

10.1017/s0960258520000264 ◽

2020 ◽

Vol 30 (3) ◽

pp. 199-205

Author(s):

Tracy S. Hawkins

Keyword(s):

United States ◽

Cold Stratification ◽

Eastern United States ◽

Closely Related Species ◽

Temperature Regimes ◽

Quercus Species ◽

Physiological Dormancy ◽

Alternating Temperature ◽

Incubation Temperatures ◽

Germination Requirements

AbstractQuercus species are ecologically and economically important components of deciduous forests of the eastern United States. However, knowledge pertinent to a thorough understanding of acorn germination dynamics for these species is lacking. The objectives of this research were to determine dormancy break and germination requirements for acorns of two eastern United States bottomland species, Quercus nigra and Quercus phellos (Section Lobatae), and to present results within ecological and phylogenetic contexts. Three replicates of 50 acorns of each species received 0 (control), 6, 12 or 18 weeks of cold stratification, followed by incubation in alternating temperature regimes of 15/6, 20/10, 25/15 and 30/20°C. Eighteen weeks of cold stratification were not sufficient for dormancy break in Q. nigra acorns. Cumulative germination percentages at 4 weeks of incubation were ≥77%, but only in incubation temperatures of 25/15 and 30/20°C. Dormancy break in Q. phellos acorns was achieved with 18 weeks of cold stratification, and cumulative germination percentages were ≥87% at 4 weeks of incubation in all test temperature regimes. Gibberellic acid solutions were not an effective substitute for cold stratification in either species. Phylogenetically, Q. nigra and Q. phellos are closely related species and, ecologically, both grow in the same habitat. Acorns of both species possess deep physiological dormancy (PD), but dormancy break and germination requirements differ in acorns of these two Quercus species.

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Germination of leafy spurge (Euphorbia esula L.) seeds under alternating temperatures: the effects of amplitude, midpoint, and imbibition in gibberellic acid

Canadian Journal of Plant Science ◽

10.1139/cjps-2015-0269 ◽

2016 ◽

Vol 96 (3) ◽

pp. 321-328

Author(s):

Michael E. Foley

Keyword(s):

Gibberellic Acid ◽

Constant Temperature ◽

Temperature Regime ◽

Initial Temperature ◽

Leafy Spurge ◽

Euphorbia Esula ◽

Amplitude Difference ◽

Temperature Regimes ◽

Alternating Temperature

Germinability of dormant seeds or the capacity to germinate under particular conditions is sometimes enhanced by a diurnal alternating temperature regime relative to a constant temperature. Alternating temperature regimes vary in amplitude (difference between the minimum and maximum) and midpoint (average). The aim of this research was to test the effects of amplitude and midpoint regimes on germination of dormant leafy spurge seed from a Fargo, ND population in water and gibberellic acid (GA3). The optimal regimes for germination in both water and GA3 were 20:30 °C (16 h:8 h) and 20:35 °C (19 h:5 h), which provided amplitudes of 10 °C and 15 °C, respectively, with both conditions having a midpoint temperature of 23.3 °C. However, midpoint temperature of 22 °C to 27 °C were equally effective for germination under the 20:30 °C and 20:35 °C alternating temperature regimes. Additional alternating temperature regimes with amplitudes of 15 °C (15:30 °C and 10:25 °C), 20 °C (10:30 °C), and 25 °C (10:35 °C) generally displayed reduced germination in both water and GA3, which is likely attributable to the low initial alternating temperature (≤15 °C) component of the regime relative to the higher initial temperature of 20 °C for the optimum regimes of 20:30 °C and 20:35 °C. Under the alternating temperature regimes tested, seeds germinated in GA3 generally displayed higher germination (≥80%) compared with seeds in water (30%–50%).

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Perennial Pepperweed (Lepidium latifolium): Properties of Invaded Tidal Marshes

Invasive Plant Science and Management ◽

10.1614/ipsm-d-09-00015.1 ◽

2010 ◽

Vol 3 (2) ◽

pp. 130-138 ◽

Cited By ~ 14

Author(s):

Laura K. Reynolds ◽

Katharyn E. Boyer

Keyword(s):

United States ◽

San Francisco ◽

Soil Characteristics ◽

San Francisco Estuary ◽

Western United States ◽

Tidal Marshes ◽

Lepidium Latifolium ◽

Sarcocornia Pacifica ◽

Structural And Functional Properties ◽

Wetland Habitats

AbstractLepidium latifolium (perennial pepperweed) is recognized as a threat to wetland habitats throughout much of the western United States, but its role in tidal marshes has not been explored. Over three seasons in three regions of San Francisco Estuary (Suisun, San Pablo, and South San Francisco bays), we characterized locations in tidal marshes where monotypic stands of L. latifolium are replacing the native Sarcocornia pacifica (pickleweed). Soils within L. latifolium stands had significantly lower moisture, salinity, organic matter, and carbon : nitrogen (C : N) and higher pH than in adjacent S. pacifica stands at similar elevation and distance from channels. In addition, L. latifolium canopies were 2 to 3 times taller, thus increasing light reaching soils, and tended to support different insect/spider assemblages (sampled only at the Suisun site). Patterns were generally consistent across the three sites, although less pronounced for some measures at the South Bay site. Overall, these data suggest that L. latifolium invasion of tidal marshes is leading to modification of both structural and functional properties, several of which might further facilitate spread of the invader; however, additional study is needed to determine cause vs. effect for several soil characteristics.

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GERMINATION RESPONSE OF FORAGE LEGUMES TO CONSTANT AND ALTERNATING TEMPERATURES

Canadian Journal of Plant Science ◽

10.4141/cjps73-154 ◽

1973 ◽

Vol 53 (4) ◽

pp. 797-800 ◽

Cited By ~ 9

Author(s):

J. D. McELGUNN

Keyword(s):

Constant Temperature ◽

Germination Percentage ◽

The Other ◽

Field Conditions ◽

Birdsfoot Trefoil ◽

Sweet Clover ◽

Forage Legumes ◽

Melilotus Officinalis ◽

Temperature Regimes ◽

Alternating Temperature

Daily germination counts were made on alfalfa (Medicago media Pers.), sainfoin (Onobrychis viciaefolia Scop.), sweet clover (Melilotus officinalis L.), and birdsfoot trefoil (Lotus corniculatus L.) seeds germinated at constant and alternating temperatures for 21 days. Total germination was similar at all temperature regimes except the regime employing 2 C for 12 h followed by 13 C for 12 h (2C/12h/13C/12h). The emergence at 8 days after seeding was similar for constant and alternating temperature regimes (at 8 days) except for the 7C/24h vs. 2C/12h/13C/12h regime. Sweet clover germinated faster than alfalfa and birdsfoot trefoil; alfalfa and birdsfoot trefoil had similar rates of germination and sainfoin had the slowest rate of germination. The 2C/12h/13C/12h regime reduced total germination of all legumes, with sainfoin being less affected than the other legumes. Alfalfa, cult Rambler and Drylander, and sainfoin showed slight enhancement of germination percentage at some regimes as compared with the germination percentage at 21C/24h (check). It was concluded that cold alternating temperature, such as encountered during spring field conditions, reduced both rate and total germination of the legumes, whereas cold constant temperature reduced the rate of germination but did not affect final germination.

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Thermoperiodicity in Shoot Elongation of Purple Nutsedge

Journal of the American Society for Horticultural Science ◽

10.21273/jashs.124.2.140 ◽

1999 ◽

Vol 124 (2) ◽

pp. 140-144 ◽

Cited By ~ 4

Author(s):

Wen-Hao Sun ◽

Roy K. Nishimoto

Keyword(s):

Constant Temperature ◽

Shoot Elongation ◽

Cyperus Rotundus ◽

Daily Temperature ◽

Purple Nutsedge ◽

Temperature Cycles ◽

Temperature Regimes ◽

Optimal Duration ◽

Alternating Temperature

The effect of single and daily alternating temperature cycles on elongation of emerged buds of purple nutsedge (Cyperus rotundus L.) was characterized to determine whether shoot elongation responded to alternating temperature as a thermoperiodic function. Glasshouse-grown tubers with emerged buds of 2 to 5 mm in length were used in experiments. Shoot extension increased at 35 °C after 7 days, but no significant shoot extension occurred at all other constant temperatures of 20, 25, 30, 40, and 45 °C. However, 2- to 8-fold increases in shoot extension occurred at alternating temperatures of 25/15, 30/20, 35/25, 40/30, 41/35, 42/38, and 45/35 °C (12/12 hours) as compared to the respective mean constant temperatures. Daily temperature differences of 2 and 4 °C did not stimulate shoot elongation, while temperature differences of 8 and 12 °C caused an 8-fold shoot stimulation when compared to the 24 °C constant temperature. Shoot elongation increased with increasing numbers of alternating temperature cycles. The optimal duration of the lower and upper temperature phases differed depending on temperature regimes; at 40/30 °C, maximal elongation occurred with daily exposures of 40 °C for 1 to 3 hours and 30 °C for 23 to 21 hours respectively, while at 30/20 °C, maximal elongation occurred with daily exposures of 30 °C for 15 hours and 20 °C for 9 hours. These results suggest that elongation of purple nutsedge tuber buds responds to alternating temperature as a thermoperiodic function.

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Writing Time in Metaphors

10.3366/edinburgh/9781474423939.003.0004 ◽

2018 ◽

Author(s):

Jennifer J. Smith

Keyword(s):

United States ◽

The United States ◽

Western United States ◽

Entire System ◽

Language And Culture ◽

Space Race ◽

Do So

Coherence of place often exists alongside irregularities in time in cycles, and chapter three turns to cycles linked by temporal markers. Ray Bradbury’s The Martian Chronicles (1950) follows a linear chronology and describes the exploration, conquest, and repopulation of Mars by humans. Conversely, Louise Erdrich’s Love Medicine (1984) jumps back and forth across time to narrate the lives of interconnected families in the western United States. Bradbury’s cycle invokes a confluence of historical forces—time as value-laden, work as a calling, and travel as necessitating standardized time—and contextualizes them in relation to anxieties about the space race. Erdrich’s cycle invokes broader, oppositional conceptions of time—as recursive and arbitrary and as causal and meaningful—to depict time as implicated in an entire system of measurement that made possible the destruction and exploitation of the Chippewa people. Both volumes understand the United States to be preoccupied with imperialist impulses. Even as they critique such projects, they also point to the tenacity with which individuals encounter these systems, and they do so by creating “interstitial temporalities,” which allow them to navigate time at the crossroads of language and culture.

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