Invasion essentials: does secondary chemistry plasticity contribute to the invasiveness of Thymus vulgaris L.?

Increasing our understanding of spatial patterns of plant secondary chemistry variation may help us understand the mechanisms that underlie plant invasions involving species which exhibit chemical phenotypic variation. We analysed qualitative and quantitative variation in the essential oil terpenes produced by Thymus vulgaris L. (thyme) plants inside and at the edge of thyme-invaded plant communities on north- and south-facing slopes at ten sites across Central Otago, New Zealand. We tested the hypotheses that (1) there are foliar terpene composition quantitative and qualitative differences between the inside and edge of thyme-invaded communities and that these differences vary between north- and south-facing slopes and (2) that environmental variables affect the quantity and quality of thyme essential oil composition. Terpene concentrations were determined using ethanol extraction and GC FID/MS. Environmental data were collected from inside, at the edge and outside of thyme stands. We used multivariate statistical analysis to test differences in foliar terpene composition and linear modelling to investigate the effects of environmental variables on terpene composition. We found no evidence of a link between aspect- and invasion edge-related patterns of variation of thyme’s essential oil chemistry. Site-related differences for aspect and position in thyme stands indicated that thyme’s terpene production may be modulated by environmental factors such as soil moisture, clay, carbon, silt, sand, colloid, N and NH₄ ⁺. The role of thyme’s novel chemistry in the processes that underlie the spatial patterns of thyme’s successful invasion is modulated by environmental factors.     

Arsenic stability and mobilization in soil at an amenity grassland overlying chemical waste (St. Helens, UK)

A 6.6 ha grassland, established on a former chemical waste site adjacent to a residential area, contains arsenic (As) in surface soil at concentrations 200 times higher than UK Soil Guideline Values. The site is not recognized as statutory contaminated land, partly on the assumption that mobility of the metalloid presents a negligible threat to human health, groundwater and ecological receptors. Evidence for this is evaluated, based on studies of the effect of organic (green waste compost) and inorganic (iron oxides, lime and phosphate) amendments on As fractionation, mobility, plant uptake and earthworm communities. Arsenic mobility in soil was low but significantly related to dissolved organic matter and phosphate, with immobilization associated with iron oxides. Plant uptake was low and there was little apparent impact on earthworms. The existing vegetation cover reduces re-entrainment of dust-blown particulates and pathways of As exposure via this route. Minimizing risks to receptors requires avoidance of soil exposure, and no compost or phosphate application.     

Lead and potential health risks from subsistence food crops in urban Kenya

Lead, zinc and cadmium were analysed in a range of subsistence crops cultivated in and around Nairobi city centre. Lead was found to be the only contaminant of concern, being widely dispersed with elevated levels found in crops and soils from both suburban and city centre areas. Extremely high concentrations were recorded in the edible portions of a variety of crops, and high soil Pb levels were recorded within 30m of busy roads. Based on these data, it is estimated that subsistence on a diet of crops cultivated in and around Nairobi could increase Pb intake by 10–100 times the FAO/WHO maximum tolerable levels, potentially contributing substantially to existing health problems.     

Cadmium phytoextraction using short-rotation coppice Salix: the evidence trail

A substantial body of evidence has now accumulated that raises expectations that clean-up of Cd-contaminated land can be achieved through cultivation and harvest of selected clones of short-rotation coppice willow within a realistic crop lifecycle. Cd uptake rates into Salix are high compared to other trace elements and to other plant species. Effective phytoextraction would require (i) careful targeting of hotspots, (ii) repeated harvest prior to leaf fall and (iii) final removal of the root bole.     

SURFACE WATER QUALITY IMPACTS OF TILLAGE PRACTICES UNDER LIQUID SWINE MANIJRE APPLICATION1

ABSTRACT: Field studies were conducted to investigate the effects of tillage practices on the saturated hydraulic conductivity, and quantity and quality of surface runoff water resulting from the application of the liquid swine manure as a fertilizer. As part of the study, infiltration experiments were conducted on silt-loam soil with no-tillage (NT) and disk tillage (DT) practices. Liquid swine manure was applied on test plots, and the rainfall was applied by the portable rainfall simulator. The infiltration data was analyzed for the saturated hydraulic conductivity (K8) and runoff volume determinations. The surface runoff water was analyzed for total N, total P, ammonia, and nitrate concentration determinations. The study indicated that the tillage had significant effects on K_s, and quantity and quality of runoff water. The K_s values of the NT plots were found to vary from 0.693 to 1.734 mm/min, with a mean of 1.494 mm/min, while they varied from 1.056 to 2.543 mm/min, with a mean of 2231 mm/mm in the DT plots. The total N, total P, ammonium nitrogen and nitrate nitrogen concentrations were lower in runoff generated from DT plots, compared to that from the NT plots. The chemical concentration levels were significantly different in runoff waters collected one-day after manure application than in those collected 40-days after the manure application. Study suggested that the DT practice must be preferred over the NT practice if liquid swine manure is used as the fertilizer. The study is further continued to assess the long-term impacts of swine manure application and tillage on the quantity and quality of surface runoff water.     

TARGETING REMEDIAL MEASURES TO CONTROL NONPOINT SOURCE POLLUTION1

ABSTRACT_: The watershed model GAMES is used for the evaluation of a targeting approach to control fluvial sedimentation arising from soil erosion in agricultural areas. The data considered for the analysis consists of output from the application of the model to existing and hypothetical soil and crop management systems in two small watersheds of southern Ontario, one in the rolling uplands and the other in a very flat lowland area. The model output includes estimates of spring sediment yield from field-size cells to the stream outlet for existing agricultural management conditions, and estimates of sediment yield resulting from the successive implementation of two levels of soil erosion controls under four remedial measures strategies. The results reveal that, for the rolling upland watershed exhibiting a wide range of soil erosion and sediment yield rates, targeted control programs can be expected to provide an extremely effective approach to sediment control. For flat lowland watersheds, exhibiting relatively uniform soil erosion and sediment yield rates, the strategy of targeting controls may be somewhat more effective than a random approach to control, but not as efficient as in the case of watersheds in more rolling terrain. It is evident from the study that a screening model such as GAMES provides a very useful tool for the planning and evaluation of erosion and sediment control programs.     

Prolonged mating in the milkweed leaf beetle Labidomera clivicollis clivicollis (Coleoptera: Chrysomelidae): a test of the “sperm-loading” hypothesis

Summary Female milkweed leaf beetles (Labidomera clivicollis clivicollis) frequently mate with more than one male, and pairs form mating associations which last for up to 42 h in the field. I tested the hypothesis that males remaining with females for long periods of time benefit by numerically overwhelming the sperm of their competitors. Male L.c.clivicollis copulated intermittently with females throughout an 11 hour period in the laboratory. When virgin females were allowed a single copulation, 94.3% of the sperm they received were located in the spermatheca immediately afterward. Males were not sperm-depleted, for they had large numbers of sperm available after one copulation (mean=230,000±43,200); the maximal number of sperm a male transferred to a female in 24 h was 30,500. There was a positive linear relationship between the number of sperm transferred and time up to 24 h after mounting (r ²=0.178, P<0.003). These data suggest that males transfer increasing numbers of sperm throughout a 24-h-period. Mating duration was the most important determinant of paternity when females were placed with one male for 24 h and another male for 6 hours. Females whose first matings were longer showed first male sperm predominance (as determined by starch-gel electrophoresis), while females whose second matings were longer showed last male sperm predominance. In view of these data, it is puzzling that males do not inseminate with large numbers of sperm immediately after mounting the female. It is possible that female refractory behaviors make insemination difficult and favor prolonged mating by male milkweed leaf beetles.     

Micronutrient deficiencies in maternity and child health: a review of environmental and social context and implications for Malawi

It is well documented that micronutrient malnutrition is of increasing concern in the developing world, resulting in poor health and high rates of mortality and morbidity. During pregnancy, deficiency of iron and zinc can produce cognitive and growth impairment of the foetus, which may continue into infancy. Iron and zinc are essential micronutrients for both plant growth and human nutrition. Despite significant work in the areas of soil fertility, crop biofortification and dietary interventions, the problems of micronutrient deficiencies persist in Africa. There is a need to examine why communities have not embraced intervention strategies which may offer health benefits. Bottom-up, interdisciplinary approaches are required to effectively study the relationships between local communities and their environment, and to assess the impact their behaviour has on the cycling of micronutrients within the soil–plant–human system. From a detailed consideration of diverse influencing factors, a methodological model is suggested for studying the barriers to improving micronutrient uptake within rural communities. It combines environmental understanding with health and social factors, emphasising the need for and potential benefits of understanding and coherence in true interdisciplinary working.     

SELECTION OF APPROPRIATE EVAPORATION ESTIMATION TECHNIQUE FOR CONTINUOUS MODELING1

ABSTRACT: The importance of evaporation in hydrologic modeling has been investigated by analysis of water budget at various scales and application of a water management model at plot scale. The data at all scales indicate that evaporation constitutes a major hydrological output. Accurate determination of watershed evapotranspiration depends upon appropriate accounting for the various components of evapotranspiration and their areal and temporal variability. An application of a water management model has revealed that the ranking of the sensitivity of input parameters depends upon the method of determination of evapotranspiration.     

Natural History Traits Associated with Detecting Mortality Within Residential Bird Communities: Can Citizen Science Provide Insights?

Cat predation of birds in residential landscapes is ephemeral, unpredictable, and spatially dispersed, and thus requires many person-hours to observe. We sought to identify whether specific behaviors, traits, or feeding ecologies of birds contribute to their probability of cat-caused mortality around residences across temperate North America. In addressing this question, we evaluated citizen science data with respect to peer-reviewed species accounts (Birds of North America, BNA). Using information on cat predation from the BNA, we found that species that glean their prey from the ground or breed in nest boxes were three times more likely to be depredated by cats, while birds that hawk were over two times less likely to become cat prey than would be predicted by random chance. Data from citizen science sources also showed that birds using nest boxes had increased susceptibility to cat predation, as did those that use feeders and that glean from foliage. We caution that observations of predation by citizen science volunteers may be biased towards detection at feeders. Future research should focus on developing volunteer survey techniques for improving estimates of bird mortality rates and sources.