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  • 1
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Lolium multiflorum (Italian ryegrass), an annual weed invading wheat and barley cropping systems, has evolved resistance to diclofop-methyl (DM) herbicide. Earlier studies on the mode of action of DM in susceptible L. multiflorum and L. rigidum populations have shown that herbicide promotes oxidative stress leading to senescence, a process reversible through the action of auxins. The disruption of cell membrane potential (Em) appears to be correlated with DM phytotoxicity in susceptible populations, suggesting that the continuous H+ extrusion from plasmalemma to extracellular space is inhibited. L. multiflorum usually establishes a symbiotic relationship with fungal endophytes of the Neotyphodium genus. This fungus confers to host plants higher survival at sublethal dosages of DM, probably due to the production of auxinic compounds. Our goal was to characterize DM-resistant and DM-susceptible L. multiflorum populations infected (E+) and non-infected (E−) with endophytes, by studying the capacity of H+ bumping of plasmalemma of intact roots under DM selection. We correlated the effects of DM on H+ disruption with plant survival. DM inhibited acidification markedly more in susceptible than in resistant populations. Continued extrusion of H+ by DM-resistant cell membranes was positively related to plant survival and growth. There was no detectable difference in the capacity of bumping H+ between DM-susceptible E+ and E− seedlings, even though survival was higher in E+ plants. The basis for the differential response in H+ extrusion between resistant and susceptible populations of L. multiflorum is discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Melbourne, Australia : Blackwell Publishing Asia
    Plant species biology 15 (2000), S. 0 
    ISSN: 1442-1984
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Weed invasion in cropland can be estimated by measuring specific constancy (Number of fields of occurence/Number of fields surveyed). Since the beginning of this century, many floristic surveys have been carried out in fields with similar soil types in the Pampas of Argentina. Thus, weed species with high constancy in maize or wheat crops over more than 60 years could be identified. Convergence among species of any trait having a selective advantage in the cropping environment would be expected. However, no evidence of such convergence was found in seed bank persistence or in dormancy and germination characteristics of summer or winter annuals selected as model species: Amaranthus retroflexus, Datura ferox, Echinochloa crus-galli, Tagetes minuta, Avena fatua, Galinsoga parviflora. On the other hand, changes in dormancy and germination traits were recorded in seeds of E. crus-galli and A. fatua in different agricultural systems, suggesting an adaptive value for invasion of human disturbed habitats. We used a simulation approach to investigate the importance of ecophysiologic seed phenotypes for the invasion of plants into specific human disturbed habitats. Results of the simulations showed that rainfall pattern and soil type interactions changed relative fitness of the tested phenotypes.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Pty
    Austral ecology 30 (2005), S. 0 
    ISSN: 1442-9993
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract  Lolium multiflorum is a successful invader of postagricultural succession in the Inland Pampa grasslands in Argentina, becoming a dominant species in the plant community. Individual plants of this annual species are naturally highly infected with fungal endophytes (Neotyphodium sp.) from early successional stages. We assessed the effect of Neotyphodium infection on the biology of L. multiflorum. We evaluated growth attributes between endophyte infected (E+) and uninfected (E–) plants under non-competitive conditions during the normal growing season. E+ plants produced significantly more vegetative tillers and allocated more biomass to roots and seeds. Although seed germination rates were greater in endophyte free plants, the rate of emergence and the final proportion of emerged seedlings were similar between the biotypes. The greater production of vegetative tillers, and the greater resource allocation to roots and seeds are likely to confer an ecological advantage to E+ plants, thus enabling their dominance over the E– individuals in natural grasslands.
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 409 (2001), S. 78-81 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Symbiotic microorganisms that live intimately associated with terrestrial plants affect both the quantity and quality of resources, and thus the energy supply to consumer populations at higher levels in the food chain. Empirical evidence on resource limitation of food webs points to primary ...
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  • 5
    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Zea mays L.) vegetative and reproductive characteristics were measured. Multivariate statistical analyses were applied to the data to determine potential indicators of soil quality. Soil and crop variables explained more than 70% of the variance in soil quality among agricultural histories. The edaphic indicators that showed the greatest change from pristine conditions were organic C, total N, P, Mg, K, B, Ca, and Zn contents and cation exchange capacity. Using crop variables, leaf length, maximum fraction of intercepted photosynthetically active radiation, grain yield, kernel number, prolificacy, and total dry matter at physiological maturity, served to establish a soil quality gradient. Variation of maize growth was associated with edaphic indicators of soil quality and revealed the importance of soil aggregate stability in determining changes in soil quality for crop production.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-2137
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Glycine max (L.) Merr.] fields in the Rolling Pampa, Argentina, to identify floristic and functional (life cycles, origin, and morphotypes) structure in fields with different management practices and to explore the association between weed species, cultural history, and crop yield. We surveyed 18 and 42 different fields in 1994 and 1995, respectively, in soybean cropped with conventional and no-tillage practices. In 1994, we recorded presence of weed species and in 1995 we recorded weed presence and abundance, and management information (type of tillage, number of agricultural cycles, grain yield, planting date, and weed control). We used multivariate analysis to examine relationships among variables. We distinguished four communities and eight floristic groups, related to crop yield and tillage system. The presence of Floristic Groups II [Oxalis chrysantha (Kunth) Prog., Sonchus oleraceus L., and Veronica persica Poir.], VII [Carduus acanthoides L., Stellaria media (L.) Vill., Physalis viscosa L., Taraxacum officinale Weber, and coronopus didymus (L.) Sm.], and IV [Bidens subalternans DC., Cirsium vulgare (Savi) Ten., and Cyperus sp.L.] may be an indicator of high potential crop yield (low soil degradation), and their absence may be an indicator of low potential crop yield (increasing soil degradation). Functional structure (life cycles, origin, and morphotypes) was similar between communities, indicating that agroecosystems preserve function, despite management practices. The main variables explaining weed distribution in the surveyed region were tillage system, crop yield, planting date, and the number of agricultural cycles.
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  • 7
    Publication Date: 2014-03-26
    Print ISSN: 0716-078X
    Electronic ISSN: 0717-6317
    Topics: Biology , Geosciences
    Published by BioMed Central
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  • 8
    Publication Date: 2006-03-01
    Description: In the Pacific Northwest, a mixture of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and red alder (Alnus rubra Bong.) often results when red alder regenerates naturally in planted conifer stands. The relationships among stand structure, tree mortality, tree size, and understory development in the two species mixtures were explored at two sites for the first 16 years after planting. Treatments included a range of species proportions, and red alder was either planted simultaneously with Douglas-fir or planting was delayed for 5 years. Red alder was also removed from some simultaneously planted proportions. Both replacement effects (total stand density held constant) and additive effects (stand density doubled) of the interaction were considered. Red alder grew relatively better at Cascade Head Experimental Forest in the Coast Range, while Douglas-fir grew better at H.J. Andrews Experimental Forest in the less temperate Cascade Mountains. Possible production benefits from mixed plantings were examined using two methods of calculation. Potential production benefits from certain planted proportions of the two species occurred at H.J. Andrews Experimental Forest. No planting time or species proportion resulted in yield improvements over monoculture stands at Cascade Head Experimental Forest. Understory species also varied because of differences in site and stand characteristics that resulted from the differences in planting times and species proportions.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 9
    Publication Date: 2000-11-01
    Print ISSN: 0002-1962
    Electronic ISSN: 1435-0645
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley
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  • 10
    Publication Date: 2001-05-01
    Print ISSN: 0002-1962
    Electronic ISSN: 1435-0645
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley
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