排序方式： 共有16条查询结果，搜索用时 15 毫秒
1.
M Liebman Z J Miller C L Williams P R Westerman P M Dixon A Heggenstaller A S Davis F D Menalled D N Sundberg 《Weed Research》2014,54(3):293-306
Weed seeds in and on the soil are the primary cause of weed infestations in arable fields. Previous studies have documented reductions in weed seedbanks due to cropping system diversification through extended rotation sequences, but the impacts of different rotation systems on additions to and losses from weed seedbanks remain poorly understood. We conducted an experiment in Iowa, USA, to determine the fates of Setaria faberi and Abutilon theophrasti seeds in 2‐, 3‐ and 4‐year crop rotation systems when seed additions to the soil seedbank were restricted to a single pulse at the initiation of the study. Over the course of the experiment, seedlings were removed as they emerged and prevented from producing new seeds. After 41 months, seed population densities dropped >85% for S. faberi and >65% for A. theophrasti, but differences between rotation systems in the magnitude of seedbank reductions were not detected. Most of the reductions in seedbank densities took place from autumn through early spring in the first 5 months following seed deposition, before seedling emergence occurred, suggesting that seed predation and/or seed decay was important. For S. faberi, total cumulative seedling emergence and total seed mortality did not differ between rotation systems. In contrast, for A. theophrasti, seedling emergence was 71% lower and seed mortality was 83% greater in the 3‐ and 4‐year rotation systems than in the 2‐year system. Results of this study indicate that for certain weed species, such as A. theophrasti, crop rotation systems can strongly affect life‐history processes associated with soil seedbanks. 相似文献
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Duppong LM Delate K Liebman M Horton R Romero F Kraus G Petrich J Chowdbury PK 《Crop science》2004,44(3):861-869
Because of expanding markets for high-value niche crops, opportunities have increased for the production of medicinal herbs in the USA. An experiment was conducted in 2001 and 2002 near Gilbert, IA, to study crop performance, weed suppression, and environmental conditions associated with the use of several organic mulches in the production of two herbs, catnip (Nepeta cataria L.) and St. John's wort (Hypericum perforatum L. 'Helos'). Treatments were arranged in a completely randomized design and included a positive (hand-weeded) control, a negative (nonweeded) control, oat straw, a flax straw mat, and a nonwoven wool mat. Catnip plant height was significantly greater in the oat straw than the other treatments at 4 wk through 6 wk in 2001; at 4 to 8 wk in 2002, catnip plant height and width was significantly lower in the negative control compared with the other treatments. Catnip yield was significantly higher in the flax straw mat than all other treatments in 2001. In 2002, St. John's wort yields were not statistically different in any treatments. All weed management treatments had significantly fewer weeds than the non-weeded rows in 2002. Total weed density comparisons in each crop from 2 yr showed fewer weeds present in the flax straw and wool mat treatments compared with positive control plots. There was no significant weed management treatment effect on the concentration of the target compounds, nepetalactone in catnip and pseudohypericin-hypericin in St. John's wort, although there was a trend toward higher concentrations in the flax straw treatment. 相似文献
3.
Greater adoption and refinement of low-external-input (LEI) farming systems have been proposed as ways to ameliorate economic, environmental and health problems associated with conventional farming systems. Organic soil amendments and crop diversification are basic components of LEI systems. Weed scientists can improve the use of these practices for weed management by improving knowledge of four relevant ecological mechanisms. First, multispecies crop rotations, intercrops and cover crops may reduce opportunities for weed growth and regeneration through resource competition and niche disruption. Secondly, weed species appear to be more susceptible to phytotoxic effects of crop residues and other organic soil amendments than crop species, possibly because of differences in seed mass. Thirdly, delayed patterns of N availability in LEI systems may favour large-seeded crops over small-seeded weeds. Finally, additions of organic materials can change the incidence and severity of soil-borne diseases affecting weeds and crops. Our research on LEI sweetcorn and potato production systems in central and northern Maine (USA) suggests that these mechanisms can reduce weed density and growth while maintaining crop yields. Low-external-input farming systems will advance most quickly through the application of interdisciplinary research focused on these and other ecological mechanisms. 相似文献
4.
Michelle D. Staudinger Katherine E. Mills Karen Stamieszkin Nicholas R. Record Christine A. Hudak Andrew Allyn Antony Diamond Kevin D. Friedland Walt Golet Meghan Elisabeth Henderson Christina M. Hernandez Thomas G. Huntington Rubao Ji Catherine L. Johnson David Samuel Johnson Adrian Jordaan John Kocik Yun Li Matthew Liebman Owen C. Nichols Daniel Pendleton R. Anne Richards Thomas Robben Andrew C. Thomas Harvey J. Walsh Keenan Yakola 《Fisheries Oceanography》2019,28(5):532-566
The timing of recurring biological and seasonal environmental events is changing on a global scale relative to temperature and other climate drivers. This study considers the Gulf of Maine ecosystem, a region of high social and ecological importance in the Northwest Atlantic Ocean and synthesizes current knowledge of (a) key seasonal processes, patterns, and events; (b) direct evidence for shifts in timing; (c) implications of phenological responses for linked ecological‐human systems; and (d) potential phenology‐focused adaptation strategies and actions. Twenty studies demonstrated shifts in timing of regional marine organisms and seasonal environmental events. The most common response was earlier timing, observed in spring onset, spring and winter hydrology, zooplankton abundance, occurrence of several larval fishes, and diadromous fish migrations. Later timing was documented for fall onset, reproduction and fledging in Atlantic puffins, spring and fall phytoplankton blooms, and occurrence of additional larval fishes. Changes in event duration generally increased and were detected in zooplankton peak abundance, early life history periods of macro‐invertebrates, and lobster fishery landings. Reduced duration was observed in winter–spring ice‐affected stream flows. Two studies projected phenological changes, both finding diapause duration would decrease in zooplankton under future climate scenarios. Phenological responses were species‐specific and varied depending on the environmental driver, spatial, and temporal scales evaluated. Overall, a wide range of baseline phenology and relevant modeling studies exist, yet surprisingly few document long‐term shifts. Results reveal a need for increased emphasis on phenological shifts in the Gulf of Maine and identify opportunities for future research and consideration of phenological changes in adaptation efforts. 相似文献
5.
The rupture mechanism of edge-supported liquid films appears to involve the viscous and drag energies as well as previously postulated kinetic and surface energies. Although details are obscure, the mechanism appears to involve a liquid-gathering process at the free edge, followed by fragmentation of this thickened edge into drops whose radii are approximately 50 times the film's original thickness. 相似文献
6.
Liebman JC Flynn JT Jenkins DR Hales EB Krzywoblocki MZ 《Science (New York, N.Y.)》1966,153(3737):688-692
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Diversified cropping systems can have high soil microbial biomass and thus strong potential to reduce the weed seedbank through seed decay. This study, conducted in Iowa, USA, evaluated the hypothesis that weed seed decay is higher in a diversified 4‐year maize–soyabean–oat/lucerne–lucerne cropping system than in a conventional 2‐year maize–soyabean rotation. Mesh bags filled with either Setaria faberi or Abutilon theophrasti seeds and soil were buried at two depths in the maize phase of the two cropping systems and sampled over a 3‐year period. Setaria faberi seed decay was consistently greater at 2 cm than at 20 cm burial depth and was higher in the more diverse rotation than in the conventional rotation in 1 year. Abutilon theophrasti seeds decayed very little in comparison with seeds of S. faberi. Separate laboratory and field experiments confirmed differences in germination and seed decay among the seed lots evaluated each year. Fusarium, Pythium, Alternaria, Cladosporium and Trichoderma were the most abundant genera colonising seeds of both species. A glasshouse experiment determined a relationship between Pythium ultimum and S. faberi seed decay. Possible differences in seed susceptibility to decay indicate the need to evaluate weed seedbank dynamics in different cropping systems when evaluating overall population dynamics and formulating weed management strategies. 相似文献
9.
P Neve J N Barney Y Buckley R D Cousens S Graham N R Jordan A Lawton‐Rauh M Liebman M B Mesgaran M Schut J Shaw J Storkey B Baraibar R S Baucom M Chalak D Z Childs S Christensen H Eizenberg C Fernández‐Quintanilla K French M Harsch S Heijting L Harrison D Loddo M Macel N Maczey A Merotto Jr D Mortensen J Necajeva D A Peltzer J Recasens M Renton M Riemens M Sønderskov M Williams 《Weed Research》2018,58(4):250-258
Weedy plants pose a major threat to food security, biodiversity, ecosystem services and consequently to human health and wellbeing. However, many currently used weed management approaches are increasingly unsustainable. To address this knowledge and practice gap, in June 2014, 35 weed and invasion ecologists, weed scientists, evolutionary biologists and social scientists convened a workshop to explore current and future perspectives and approaches in weed ecology and management. A horizon scanning exercise ranked a list of 124 pre‐submitted questions to identify a priority list of 30 questions. These questions are discussed under seven themed headings that represent areas for renewed and emerging focus for the disciplines of weed research and practice. The themed areas considered the need for transdisciplinarity, increased adoption of integrated weed management and agroecological approaches, better understanding of weed evolution, climate change, weed invasiveness and finally, disciplinary challenges for weed science. Almost all the challenges identified rested on the need for continued efforts to diversify and integrate agroecological, socio‐economic and technological approaches in weed management. These challenges are not newly conceived, though their continued prominence as research priorities highlights an ongoing intransigence that must be addressed through a more system‐oriented and transdisciplinary research agenda that seeks an embedded integration of public and private research approaches. This horizon scanning exercise thus set out the building blocks needed for future weed management research and practice; however, the challenge ahead is to identify effective ways in which sufficient research and implementation efforts can be directed towards these needs. 相似文献
10.
Lateral diffusion of visual pigment in photorecptor disk membranes 总被引：22，自引：0，他引：22
Visual pigment molecules are found to move transversely, but not longitudinally, in both rod and cone outer segments of mud puppy and frog. This is consistent with the idea that they are immersed in a two-dimensional fluid disk membrane. The diffusion coefficient for the motion is about 5 x 10(-9) square centimeters per second at 20 degrees C, corresponding to a root-mean-square molecular displacement of 0.3 micrometer in 1 second. 相似文献