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71.
ML Reaves S Sinha JD Rabinowitz L Kruglyak RJ Redfield 《Science (New York, N.Y.)》2012,337(6093):470-473
A strain of Halomonas bacteria, GFAJ-1, has been claimed to be able to use arsenate as a nutrient when phosphate is limiting and to specifically incorporate arsenic into its DNA in place of phosphorus. However, we have found that arsenate does not contribute to growth of GFAJ-1 when phosphate is limiting and that DNA purified from cells grown with limiting phosphate and abundant arsenate does not exhibit the spontaneous hydrolysis expected of arsenate ester bonds. Furthermore, mass spectrometry showed that this DNA contains only trace amounts of free arsenate and no detectable covalently bound arsenate. 相似文献
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Louis Kan Koko Didier Snoeck Tacra Thierry Lekadou Assiri Alexis Assiri 《Agroforestry Systems》2013,87(5):1043-1052
A major challenge for cocoa producers in Côte d’Ivoire is to seek alternative shade trees or crop associations to adapt their planting devices and techniques to the shortage of forests. The recent tendency developed by farmers is to plant simplified orchards combining cacao and fruit trees. An on-farm trial was set up in a 5-year-old cocoa farm to compare a cacao monocrop planted at densities of 1,115 trees ha?1 with cacao intercropped with orange or avocado trees, both at 44 trees ha?1. Observations were done on incident light received by the cacao, vigour, growth and cocoa yields. On average, the cacaos received 100 % light in the monocrop, 89.6 % under orange trees and 80.6 % of incident light under avocado trees. They yielded 64.0 pods tree?1 year?1 in the monocrop (equivalent to 2.54 kg dry cocoa beans tree?1), 30.3 pods tree?1 when combined with orange trees and 28.3 pods tree?1 with avocado trees. The two combinations allowed cocoa yields equivalent to those observed in the region (0.58 kg dry cocoa beans tree?1). Vigour and yield were very highly correlated with the incident light received. Both the yield and the incident light are a logistic function of the planting distance from the shade tree. The inflexion point of the logistic functions corresponds to the minimum planting distance between the cacao and the intercropped fruit trees. On this basis, we suggest that the cacaos should not be planted closer than 6.50 ± 0.2 m to the orange or avocado trees. 相似文献
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Kouassi N’Guessan Louis Berenger Yao Koffi Marcellin Sangare Naminata Trokourey Albert Metongo Bernard Soro 《Journal of Soils and Sediments》2019,19(2):929-944
Journal of Soils and Sediments - Trace metals accumulate in the food web and can pose high risks to human health and aquatic biota. We investigated seasonal and spatial variations of Cu, Zn, Pb,... 相似文献
78.
Contribution of technic materials to the mobile fraction of metals in urban soils in Marrakech (Morocco) 总被引:5,自引:2,他引:3
Hicham El Khalil Christophe Schwartz Ouafae Elhamiani Jochen Kubiniok Jean Louis Morel Ali Boularbah 《Journal of Soils and Sediments》2008,8(1):17-22
Background, Aim and Scope In urban areas, soils are often dramatically altered by anthropogenic activity and these modifications distinguish these soils
(Anthrosols, Technosols) from those in natural systems. In urban environments, they receive considerable pollution from industry,
traffic and refuse. Since contaminated soil particles can be easily inhaled or ingested, there is a potential transfer of
toxic pollutants to humans. Risk assessment is essentially based on the determination of the total or mobile contents of pollutants
in soils using chemical extractions. This approach could be improved by taking into consideration the bioavailable fractions
of these toxic elements as measured by biotests. The coarse soil fraction usually neglected in analyses can nevertheless have
an effect on the concentration of metals in the soil solution. This coarse fraction is made up of the natural materials and
of technic materials constituting anthropogenic soils (plastic, paper, fabric, wood, bones, metallic elements and building
materials). These materials have variable capacities to release or adsorb trace elements. Samples representative of different
technic fraction components of Marrakech urban soils permit one to quantify their contribution to the enrichment of the soluble
metal concentrations. Works are carried out to achieve partial extractions of metals from the three fractions (less than 2
mm, coarse natural and coarse technic) of selected urban soils in order to determine their contribution to the metal contamination
of soils.
Materials and Methods Selected soils were collected from 9 sites according to a gradient of increasing anthropogenic influence from suburban to
urban zones. Soils were air-dried, homogenized, and sieved (2 mm). The coarse fraction was sorted to separate the different
technic materials and natural materials. Water extractions were run, on the natural, coarse fraction, on the complete technic
fraction of the 9 soils and on average samples made of technic materials sorted out of 58 topsoils sampled from different
sites in the city of Marrakech.
Results Results show that the percentage of the technic fraction increases while approaching the historic city center. It represented
about 14% in the most anthropogenically disturbed soils. Along this gradient, soils changed progressively from Anthrosols
to Technosols according to the WRB classification of urban and industrial soils. Analyses of metal contents showed that the
fine fraction (<2 mm) mainly contributed to the metallic contamination of the water soluble fraction. The natural coarse fraction
had the highest contribution to the copper release and was responsible for the release of all water-extractable copper in
some soils. Concerning the technic fraction, it has a significant contribution essentially in the most anthropogenically disturbed
soils as characterized by an elevated percentage of anthropogenic elements. The water extractable metal contents of average
samples of these anthropogenic elements shows that elevated metal concentrations were released by bones, wood, plastic and
fabric/paper.
Discussion This study concerns soils in urban areas, which are strongly impacted by human activities. Part of the soils can be classified
as Anthrosols, profoundly impacted through the addition of organic materials from household wastes, irrigation, or cultivation.
Other soils strongly impacted by human activities are Technosols dominated or strongly influenced by man-made materials. Technosols
appear mostly in urban and industrial areas and are more likely to be contaminated than Anthrosols. The composition and heterogeneity
of urban soils lead to modifications of the mobility and availability of pollutants depending on successive land-uses and
on the composition of technic materials. The fine fraction offers a high transferring surface capacity, leading to a high
mobilization of metals. The technic fraction contributes significantly to the metal release in the Technosols. This property
can be explained by a reversible adsorption of metals on the organic matter.
Conclusions Results confirm that anthropogenic activity causes a wide spatial diversity of soil quality in the urban and suburban area.
It introduces large amounts of technic materials in soils that could have an impact on the metal availability. It therefore
acts on the metal bioavailability in the urban Technosols.
Recommendations and Perspectives These results show that it is necessary, in addition to the characterization of the fine particles, to take into account the
contribution of the coarse fraction of the Technosols in the evaluation of risks of transfer of metals to the food chain. 相似文献
79.
Isabelle Le Viol Romain Julliard Louis de Redon Nathalie Machon 《Biological conservation》2008,141(6):1581-1590
Road verges should play a crucial role as a refuge for native flora and fauna in human dominated landscapes. However, the influence of construction choices, such as plantation of woody species, on the biodiversity supported by roadsides has received little attention, although the presence of hedgerows in roadsides is likely to enhance their role as a refuge, notably for woodland species. Using standardised methods, we assessed the impact of planted hedgerows on two taxonomic groups (plants and spiders) inhabiting highway verges within an intensive agricultural landscape. We examined community richness, taxonomic and functional composition in sites with and without planted hedgerows. At the site level, the response of plant and spider communities to the presence of planted hedgerows differed markedly: hedgerows were associated with significantly higher plant richness (higher α-diversity), but similar spider richness. Plant communities in sites without hedgerows appeared as a subset of communities in sites with hedgerows, whereas spider communities in non-planted sites were complementary to that of planted sites (increased β-diversity). The presence of planted hedgerows was also associated with increased taxonomic and functional trait diversity at the landscape level (γ-diversity), through an increased β-diversity in both plants and spiders. Our results thus suggest that a mosaic of planted hedgerows and grassland habitats is crucial for the maintenance of biodiversity at a landscape scale. By providing information for road practitioners and policy makers regarding their potential impact on biodiversity, these results have important direct implications for the management of road networks. 相似文献
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