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Repens L. (repen + l)
Kinds of Repens L. Selected AbstractsTracking larval insect movement within soil using high resolution X-ray microtomographyECOLOGICAL ENTOMOLOGY, Issue 1 2004Scott N. Johnson Abstract., 1. In contrast to above-ground insects, comparatively little is known about the behaviour of subterranean insects, due largely to the difficulty of studying them in situ. 2. The movement of newly hatched (neonate) clover root weevil (Sitona lepidus L. Coleoptera: Curculinidae) larvae was studied non-invasively using recently developed high resolution X-ray microtomography. 3. The movement and final position of S. lepidus larvae in the soil was reliably established using X-ray microtomography, when compared with larval positions that were determined by destructively sectioning the soil column. 4. Newly hatched S. lepidus larvae were seen to attack the root rhizobial nodules of their host plant, white clover (Trifolium repens L.). Sitona lepidus larvae travelled between 9 and 27 mm in 9 h at a mean speed of 1.8 mm h,1. 5. Sitona lepidus larvae did not move through the soil in a linear manner, but changed trajectory in both the lateral and vertical planes. [source] The influence of below-ground herbivory and defoliation of a legume on nitrogen transfer to neighbouring plantsFUNCTIONAL ECOLOGY, Issue 2 2007E. AYRES Summary 1Both foliar and root herbivory can alter the exudation of carbon from plant roots, which in turn can affect nitrogen availability in the soil. However, few studies have investigated the effects of herbivory on N fluxes from roots, which can directly increase N availability in the soil and uptake by neighbouring plants. Moreover, the combined effects of foliar and root herbivory on N fluxes remains unexplored. 2We subjected the legume white clover (Trifolium repens L.) to defoliation (through clipping) and root herbivory (by an obligate root-feeding nematode, Heterodera trifolii Goggart) to examine how these stresses individually, and simultaneously, affected the transfer of T. repens -derived N to neighbouring perennial ryegrass (Lolium perenne L.) plants using 15N stable-isotope techniques. We also examined the effects of defoliation and root herbivory on the size of the soil microbial community and the growth response of L. perenne. 3Neither defoliation nor root herbivory negatively affected T. repens biomass. On the contrary, defoliation increased root biomass (34%) and total shoot production by T. repens (100%). Furthermore, defoliation resulted in a fivefold increase in T. repens -derived 15N recovered in L. perenne roots, and increased the size of the soil microbial biomass (77%). In contrast, root herbivory by H. trifolii slightly reduced 15N transfer from T. repens to L. perenne when T. repens root 15N concentration was included as a covariate, and root herbivory did not affect microbial biomass. Growth of L. perenne was not affected by any of the treatments. 4Our findings demonstrate that defoliation of a common grassland legume can substantially increase the transfer of its N to neighbouring plants by directly affecting below-ground N fluxes. These finding require further examination under field conditions but, given the prevalence of N-limitation of plant productivity in terrestrial ecosystems, increased transfer of N from legumes to non-N-fixing species could alter competitive interactions, with implications for plant community structure. [source] Yield and stability of yield of single- and multi-clover grass-clover swards in two contrasting temperate environmentsGRASS & FORAGE SCIENCE, Issue 3 2009B. E. Frankow-Lindberg Abstract Diversity of clovers in grass-clover swards may contribute to greater herbage yields and stability of yield. This possible effect was evaluated in an experiment carried out over three harvest years at two contrasting sites, differing in precipitation and soil composition, using mixed swards containing either one, two or three clover species sown together with timothy (Phleum pratense L.) and meadow fescue (Festuca pratensis L.). The clover species were red clover (Trifolium pratense L.), white clover (Trifolium repens L.) and alsike clover (Trifolium hybridum L.) sown in various proportions in a total of ten treatments. All swards were fertilized with nitrogen with amounts that increased from year to year, and three harvests were taken in three consecutive years. There was a significant interaction between site and species mixture on total dry matter (DM) yields (range 27,32 tonnes ha,1) and DM yields of clovers (range 5,15 tonnes ha,1); red clover as a single species or in a mixture was superior at the dry site while multi-clover species mixtures were superior at the wet site. Alsike clover was the least productive species of clover. Stability of yield of clovers was generally higher by including white and red clover in the seed mixture but total DM yield was not. [source] Thresholds of economic damage by clover seed weevil (Apion fulvipes Geoff.) and lesser clover leaf weevil (Hypera nigrirostris Fab.) on white clover (Trifolium repens L.) seed cropsGRASS & FORAGE SCIENCE, Issue 4 2008L. M. Hansen Abstract Severe reductions in the seed yield of white clover can occur because of feeding by the white clover seed weevil Apion fulvipes and the lesser clover leaf weevil Hypera nigrirostris which together can reduce the seed yield by more than 0·50. From 2002 to 2006 five field experiments were carried out to investigate the relationship between the density of these two weevil species and seed yield of white clover. Damage caused by the weevils was calculated as the difference in the number of weevils and the difference in seed yield between the average of insecticide-treated and untreated plots. Loss of seed yield was expressed as a proportion of the seed yield in insecticide-treated plots, which allowed for a comparison between years as yields in insecticide-treated plots varied. A multiple regression approach was chosen in which proportional loss in seed yield was the response variable and the weevils A. fulvipes and H. nigrirostris were the independent variables. Data obtained from the experiments were used to construct the following threshold model of economic damage: [source] Performance of white clover varieties combined in blends and alone when grown with perennial ryegrass under sheep and cattle grazingGRASS & FORAGE SCIENCE, Issue 1 2003T. A. Williams Abstract Two experiments were carried out to evaluate the performance of blends of three white clover (Trifolium repens L.) varieties in comparison with the component varieties and three other varieties sown individually in a mixture with perennial ryegrass (Lolium perenne L.). The plots were grazed rotationally in Experiment 1 by cattle and sheep and in Experiment 2 by sheep alone. In both experiments, the blend was composed of three medium-leaved varieties (AberDai, AberVantage and AberHerald), but with different relative contributions of the three varieties in the two experiments. Dry matter (DM) yields of white clover and perennial ryegrass were assessed in replicate plots for two years (1999 and 2000) after the establishment year. In Experiment 1, there was no significant difference between the DM yields of white clover or perennial ryegrass in either year. The decline in DM yield of white clover between years that was observed for some varieties was not found for the blend. In Experiment 2, significant differences were found in DM yields of white clover in both years. In 1999, AberDai had the highest DM yield. In 2000, AberHerald and AberVantage had the highest DM yields, and AberDai showed a decline in DM yield that was mirrored by the mean for all the white clover varieties. In both experiments, the blend did not show significantly higher DM yield than one or more of its components; indeed, in Experiment 2, it was significantly lower yielding than AberDai in 1999. However, where one component of the blend declined in DM yield between years, this was compensated for by an increase in the yield of another component. These preliminary findings suggest that the yield stability of blends may give them a potential role in agricultural practice. [source] Relationships between the yield of perennial ryegrass and of small-leaved white clover under cutting or continuous grazing by sheepGRASS & FORAGE SCIENCE, Issue 3 2001T. A. Williams Seven varieties or advanced breeding lines of white clover (Trifolium repens L.), all of small leaf size, were grown separately in mixtures with perennial ryegrass (Lolium perenne L.) in an experiment encompassing three harvest years. Harvestable dry-matter (DM) yield measurements were taken of these mixtures and of perennial ryegrass monocultures under two management regimes: cutting and continuous sheep grazing. Considerable differences were observed in the harvestable DM yields of white clover, perennial ryegrass and total yields of the mixtures between plots containing different white clover varieties. White clover yields were generally higher under cutting, and perennial ryegrass yields were higher under grazing. The difference between perennial ryegrass yield in monoculture and in mixture was variable. In the second harvest year, a significant interaction effect was seen between management and white clover variety for white clover yield but not for perennial ryegrass yield. The relationship between clover yield and grass yield differed between the two management regimes. Under cutting, a negative correlation was observed, indicative of competitive effects. However, under grazing, no such correlation was seen. Possible mechanisms underlying these outcomes are discussed. [source] How does the vertical and horizontal structure of a perennial ryegrass and white clover sward influence grazing?GRASS & FORAGE SCIENCE, Issue 2 2001P. Carrčre Mixtures of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) sown in alternate rows or in a thoroughly mixed matrix were grazed by sheep, either continuously or during short grazing tests, and were used to investigate the influence of the vertical and horizontal components of the sward structure on defoliation by sheep. In an experiment under continuous grazing, the defoliation intensity was greater for white clover compared with perennial ryegrass leaves (0·80 and 0·58 respectively). In spring, perennial ryegrass leaves were more defoliated than white clover leaves, whereas the reverse was observed in summer. The ratio of the proportion of white clover to perennial ryegrass leaves grazed was negatively correlated with the difference between the surface height of the perennial ryegrass and white clover rows in spring. In both spring and summer, white clover leaves of the same extended leaf length had a higher proportion of them grazed than perennial ryegrass leaves. In another experiment, during short grazing tests with perennial ryegrass,white clover swards that were grazed at the same sward surface height and at the same white clover content as in the previous experiment, there were no significant differences in the proportion of white clover and perennial ryegrass leaves grazed between strips of the two species and thoroughly mixed structures. The proportion of white clover leaves grazed was higher than that of perennial ryegrass leaves. These results show that the differential defoliation by sheep of perennial ryegrass and white clover leaves varies according to their vertical distribution in the mixed canopy, but is little affected by their horizontal distribution. Even small differences in sward surface height between mixed perennial ryegrass and white clover can affect diet selection by sheep to a rather large extent. [source] Response of Weed Communities to Legume Living Mulches in Winter WheatJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 2 2007J. Hiltbrunner Abstract In order to obtain information about the impact of legume cover crops on the weed community in organic farming, winter wheat (Triticum aestivum L.) was directly drilled in rows 0.1875 and 0.3750 m apart in living mulches that consisted of Trifolium repens L. (TRFRE), T. subterraneum L. (TRFSU), Medicago truncatula Gaertner (MEDTR), and Lotus corniculatus L. (LOTCO). A control treatment without cover crops (NAT, the site-specific weed community) was also established. The vegetation between the wide rows was either mulched or left undisturbed. The effect of liquid farmyard manure (60 m3 ha,1) was also tested. TRFRE, TRFSU, and LOTCO effectively suppressed Poa annua L. and Matricaria recutita L. at site 1 and P. annua, Capsella bursa-pastoris (L.) Med., and Stellaria media (L.) Vill. at site 2 when compared with NAT. MEDTR, which died during the winter, provided little weed suppression. Mulching significantly suppressed dicotyledonous weed species, but favoured Poa trivialis L. No manure effect was observed. Winter hardy legume cover crops contribute to weed suppression in winter wheat. However, careful evaluation of cover crop × weed × management interactions is necessary to understand the risk for the establishment of problematic weeds. [source] Purification and characterisation of two ACC oxidases expressed differentially during leaf ontogeny in white cloverPHYSIOLOGIA PLANTARUM, Issue 1 2000Deming Gong Two isoforms of ACC oxidase (ACO) (EC 1.4.3), expressed differentially during leaf ontogeny in white clover (Trifolium repens L.), have been identified and purified to homogeneity. One isoform, designated MGI, was purified from mature green leaf tissue while the second isoform, designated SEII, was purified from senescent leaf tissue. The isolation and purification of these isoforms were achieved using a combination of hydrophobic interaction chromatography, anion exchange chromatography, chromatofocusing and gel filtration column chromatography. The Mr of both MGI and SEII was determined to be 37.5 kDa by gel filtration, and 37 kDa (MGI), 35 kDa (SEII) by SDS-PAGE, indicating that both isoforms are active as monomers. During purification, both isoforms were recognised by a polyclonal antibody directed against a recombinant polypeptide derived from a white clover ACO gene expressed in mature green leaf tissue, TR-ACO2. In addition to molecular mass, differences between the two isoforms were observed in terms of pH optima, isoelectric point (pI), Km for ACC, optimal requirements for the co-substrate ascorbate, and NaHCO3 and Fe2+ as co-factors. The identification of distinct ACC oxidases from the same tissue at different developmental stages shows that the now widely observed transcriptional regulation of the ACO gene family in higher plants is also expressed in terms of differential regulation of enzyme isoforms. [source] Phytochemical investigation and antioxidant activity of Duranta repensPHYTOTHERAPY RESEARCH, Issue 12 2005Abdelaaty A. Shahat Abstract The ethylacetate fraction of the methanol extract of Duranta repens L. (Verbenaceae) showed radicalscavenging activity in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. Three compounds were isolated from this fraction, i.e. the phenylethanoid glycoside acteoside, the iridoid lamiide and the saponin pseudo-ginsenoside-RT1. Acteoside showed an IC50 of 3.05 ± 0.09 µg/mL in the DPPH assay, while lamiide and pseudo-ginsenoside-RT1 were not active. Copyright © 2005 John Wiley & Sons, Ltd. [source] Evaluation of the effects of resistance to stem nematode (Ditylenchus dipsaci) in white clover (Trifolium repens L.) under sheep grazing and cuttingPLANT BREEDING, Issue 4 2007T. A. Williams Abstract Two field experiments were carried out to analyze the performance of white clover varieties differing in their resistance to stem nematode. Varieties were compared under grazing and cutting regimes in mixed swards with or without the addition of nematode and dry matter yields of white clover and perennial ryegrass recorded over a 3-year period. The resistant variety did not show a yield advantage in the absence of nematode but did so in the presence of nematode in the first year and for several of the sampling dates in the second year. White clover yields under grazing were significantly less than under cutting in both experiments. The hypothesis that the additional stress of grazing would increase the benefits of resistance relative to a cutting management was not supported. [source] Seeking a sound index of competitive intensity: Application to the study of biomass production under elevated CO2 along a nitrogen gradientAUSTRAL ECOLOGY, Issue 4 2002MARIE-LAURE MAYAS Abstract The aim of this paper is to evaluate (i) the relevance of currently proposed measures of competitive intensity to elevated CO2 studies by means of an example analysis, hypothesizing that competitive intensity is increased under elevated CO2; and (ii) an alternative method for predicting species performance in mixtures from monocultures. Relative competition intensity (RCI), relative physiological performance and normalized ecological performance were used to characterize the competitive ability of two grasses (Danthonia riclwrdsonii Cashmore, Phalaris aquatica L.) and two legumes (Lotus pedunculatus Cav, Trifoliuni repens L.) grown in monocultures and mixtures of the four species along a N gradient under conditions of ambient and elevated CO2. Relative competition intensity could not be used to predict competitive outcomes in mixtures under conditions of elevated CO2 because it failed to account for changes in the size of interspecific differences along the N gradient and between CO2 concentrations. Relative physiological performance and relative ecological performance were more useful for investigating biomass production in mixtures and to predict species performance in mixtures from their performance in monocultures. Both indices of relative performance showed an increase in competitive intensity under elevated CO2 conditions. They also showed a decrease in competitive intensity with increasing N supply over most of the range of N supply, but a reversal of that trend at high levels of N supply. The merits and utility of these relative performance indices for elevated CO2 are discussed. [source] | |||||||||||||