Effects of Oxygen and Temperature on the Activity and. Survival of Nothanguina phyllobia

The effects of oxygen and temperature on the activity and survival of infective forth-stage juveniles of Nothanguina phyllobia Thorne were examined in aqueous suspension. Rate of movement was not affected by a wide range of O₂ concentration (0.8-8.6 ppm). Activity decreased below 0.8 ppm 0 2, and at 0.15 ppm O₂ nematodes became motionless. Activity increased as a linear function of temperature up to a thermal optimum of 24 C; beyond 24 C activity decreased. Survival was greatly prolonged at low temperature. At 23 C, 50% mortality occurred within 7 d, whereas at 4 C, 70% survived after 98 d.     

The discovery of Myriophyllum exalbescens Fernald (Haloragaceae) in Europe and the typification of M.spicatum L. And M.verticillatum L.

Myriophyllum exalbescens Fernald, hitherto regarded as a North American endemic, has been fund to occur widely as a native plant in northern Europe, where it has occasionally been distinguished as a subspecies or variety of M.spicatum L.under the epithet squamosum Linnacus original concept of M.spicalum appears to have included M.exalbescens (and also M. Alterniflorum DC.) but selection of Burser VII(1)79 at UPS as lectotvpe ensures the continued use of the epithet spicatum for the native Eurasian weed species to which it is customarily applied. .M.verlicillalum L., the name of a morphologically similar species, is also lectotypified in a way that preserves its current usage. Distinguishing features of M.exalbescens and M.spicatum are provided along with details of the synonymy and presently known distribution in Europe of M.exalbescens .     

Assessment of endangered synanthropic plants of Hungary with special attention to arable weeds

Abstract

In the present study, species were selected from the new Red List of the vascular flora of Hungary which can be regarded as a weed. For each species, current conservation status and the most important traits were assessed. Altogether 149 weed species were found to be at risk according to the International Union for Conservation of Nature (IUCN) categories: 11 species are extinct, 11 are critically endangered, 27 are endangered, 26 are vulnerable, 62 are near threatened and 12 are data deficient. These species belong to 37 plant families, from which the most important are Caryophyllaceae, Brassicaceae, Asteraceae, Scrophulariaceae, Chenopodiaceae, Poaceae and Fabaceae. The most significant chorological elements are Mediterranean (28%) and Eurasian (27%); endemic (Pannonian) taxa constitute only 5.4%. Over 90% of these species are of native or archaeophyte origin, according to their residence time. Considering the main habitat types, 46% of the species are originated from dry habitats, 23% from arable lands, 17.5% from wet habitats and 13.5% from ruderal habitats. In the life form spectra, a pronounced dominance of therophytes (81%) is represented. The factor that currently offers the greatest conflict to the conservation of endangered weed species in Hungary are side effects of strong eradication campaigns against the invasive Ambrosia artemisiifolia.     

Plant invasions in the rivers of the Iberian Peninsula,south-western Europe: A review

Aquatic and riparian ecosystems are known to be highly vulnerable to invasive alien species (IAS), especially when subjected to human-induced disturbances. In the last three decades, we have witnessed a growing increase in plant invasions in Portugal and Spain (Iberian Peninsula, south-western Europe), with very detrimental economic, social and ecological effects. Some of these species, such as the giant reed (Arundo donax L.) and the water hyacinth (Eichhornia crassipes (Mart.) Solms-Laub.), number among the world's worst weeds. We present an appraisal of this invasive alien river flora and the most problematic aquatic weeds. We review various aspects of invasion ecology, including spatial and temporal patterns of invasion, species invasiveness, species traits of invasive weeds, and relationships between human disturbance in rivers and surrounding areas and invasibility, and contextualize them in overall state-of-the-art terms. We also acknowledge the use of IAS as bioindicators of the ecological quality of rivers, wetlands and riparian zones. Remote-sensing tools and Geographic Information Systems for detecting and monitoring IAS in Iberian rivers are presented.     

Environmental gradients shift the direction of the relationship between native and alien plant species richness

Aim

To assess how environmental, biotic and anthropogenic factors shape native–alien plant species richness relationships across a heterogeneous landscape.

Location

Banks Peninsula, New Zealand.

Methods

We integrated a comprehensive floristic survey of over 1200 systematically located 6 × 6 m plots, with corresponding climate, environmental and anthropogenic data. General linear models examined variation in native and alien plant species richness across the entire landscape, between native‐ and alien‐dominated plots, and within separate elevational bands.

Results

Across all plots, there was a significant negative correlation between native and alien species richness, but this relationship differed within subsets of the data: the correlation was positive in alien‐dominated plots but negative in native‐dominated plots. Within separate elevational bands, native and alien species richness were positively correlated at lower elevations, but negatively correlated at higher elevations. Alien species richness tended to be high across the elevation gradient but peaked in warmer, mid‐ to low‐elevation sites, while native species richness increased linearly with elevation. The negative relationship between native and alien species richness in native‐dominated communities reflected a land‐use gradient with low native and high alien richness in more heavily modified native‐dominated vegetation. In contrast, native and alien richness were positively correlated in very heavily modified alien‐dominated plots, most likely due to covariation along a gradient of management intensity.

Main conclusions

Both positive and negative native–alien richness relationships can occur across the same landscape, depending on the plant community and the underlying human and environmental gradients examined. Human habitat modification, which is often confounded with environmental variation, can result in high alien and low native species richness in areas still dominated by native species. In the most heavily human modified areas, dominated by alien species, both native and alien species may be responding to similar underlying gradients.

     

Allelopathic effect of actinobacterial isolates against selected weeds

The taxonomic characteristics of weeds such as morphology of shoot, leaves, flowers, stem, fruits and seeds were recorded as Gynandropsis pentaphylla, DC, Amarantus spinosus Linn, Cyperus rotundus, Amarantus viridis Linn, Cassia occidentalis, Linn and Echinochilora orygicola. Totally 20 actinobacteria isolates were screened for herbicidal activity against the weed. Among the 20 isolates, only four actinobacterial isolates KA1-3, KA1-4, KA1-7 and KA23A showed significant herbicidal activity against C. rotundus. The herbicidal effect of actinobacterial culture filtrates on germination and seedling growth of C. rotundus was tested. The shoot and root growth of C. rotundus was severely affected when compared to control. The potent actinobacterial isolates KA1-4 and KA1-7 were characterised based on their morphological and molecular phylogenetic property and were identified as Streptomyces sp. The present study concludes that actinobacterial isolates will be used as bioherbicide against C. rotundus. Further studies are required to confirm the activity of actinobacterial isolates against C. rotundus under field conditions.     

New strigolactone mimics: Structure–activity relationship and mode of action as germinating stimulants for parasitic weeds

Strigolactones (SLs) are new plant hormones with varies important bio-functions. This Letter deals with germination of seeds of parasitic weeds. Natural SLs have a too complex structure for synthesis. Therefore, there is an active search for SL analogues and mimics with a simpler structure with retention of activity. SL analogues all contain the D-ring connected with an enone moiety through an enol ether unit. A new mechanism for the hydrolysis SL analogues involving bidentate bound water and an α,β-hydrolase with a Ser-His-Asp catalytic triad has been proposed. Newly discovered SL mimics only have the D-ring with an appropriate leaving group at C-5. A mode of action for SL mimics was proposed for which now supporting evidence is provided. As predicted an extra methyl group at C-4 of the D-ring blocks the germination of seeds of parasitic weeds.     

Organic farming affects the potential of a granivorous carabid beetle to control arable weeds at local and landscape scales

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A risk‐based inventory of invasive plant species of Queensland,Australia: Regional,ecological and floristic insights

Invasive alien plant species threaten agriculture and biodiversity globally and require ongoing management to minimise impacts. However, the large number of invasive species means that a risk‐based approach to prioritisation is needed, taking into account the spatial scale of management decisions and myriad of available information. Here, we developed a risk‐based inventory of invasive plants in Queensland, Australia, using both current species distribution/abundance and the severity of their impacts. Our assessment followed a comprehensive data collection process including a scoping of local government pest management plans, herbarium records, the published literature and structured elicitation of expert knowledge during a series of regional stakeholder workshops. From ~300 plant species that were identified as established and/or emerging invaders in the State, only one‐third were considered by practitioners to pose significant risks across regions to be considered management priorities. We aggregated regional species lists into a statewide priority list and analysed the data set (107 species) for historical, geographical, floristic and ecological patterns. Regions on the mainland eastern seaboard of the State share similar invasive plant communities, suggesting that these regions may form a single management unit, unlike the western/inland and the extreme far north (Torres Strait Islands) regions, which share fewer invasive plant species. Positive correlations were detected between invasiveness and time since introduction for some but not all plant life forms. Stakeholders identified research and management priorities for the invasive plant list, including biological control options, public awareness/education, effective herbicide use, ecology/taxonomy and risk analysis. In the course of the exercise, a statewide invasive plant priority list of high‐, medium‐ and low‐impact scores for policy, research and management was compiled. Finally, our approach to invasive plant species prioritisation highlighted that planning and policy documents are not necessarily reflected at the grass‐root level in terms of species identity and management priorities.     

Modelling seedling growth rates of 18 temperate arable weed species as a function of the environment and plant traits

BACKGROUND AND AIMS: The early growth rate of seedlings in the exponential phase is an important eco- physiological trait in crop/weed competition models based on assessments of relative weed green area. An understanding of the role of various plant traits in determining early growth rate may also be useful for identifying contrasting weed strategies for establishment before canopy closure. METHODS: The response of seedling relative growth rate (RGR) to the environment was measured in outdoor sand beds in the autumn and the spring for 18 temperate annual weed species and two crops. Seedling growth was modelled using thermal time and effective day-degrees (combining the effect of temperature and radiation). The contribution of various plant traits in determining variability in RGR was investigated using regression analysis. KEY RESULTS: The effective day-degree model was more effective for describing early weed growth than thermal time. Variability in RGR measured in the autumn was largely determined by differences between the species in net assimilation rate (NAR), whereas in the spring leaf area ratio (LAR) played a larger part. There were differences between the broadleaf and grass species in the relative contribution of NAR and LAR to RGR in both seasons. RGR in the spring was negatively correlated with initial seedling size. CONCLUSIONS: The parameters derived in this study can be used to calibrate empirical models of crop yield loss based on relative weed green area to different growing seasons and assessment dates. The grass weeds, which tended to have large seeds, had a higher investment in roots in the seedling stage, potentially making them more competitive later in the season when resources become limiting.