Biogeochemical cycles of nutrients in tropical Eucalyptus plantations: Main features shown by intensive monitoring in Congo and Brazil     

Jean-Paul Laclau  Jacques Ranger  José Leonardo de Moraes Gonçalves  Valérie Maquère  Alex V. Krusche  Armel Thongo M’Bou  Yann Nouvellon  Laurent Saint-André  Jean-Pierre Bouillet  Marisa de Cassia Piccolo  Philippe Deleporte 《Forest Ecology and Management》2010,259(9):1771-1785

The sustainability of fast-growing tropical Eucalyptus plantations is of concern in a context of rising fertilizer costs, since large amounts of nutrients are removed with biomass every 6–7 years from highly weathered soils. A better understanding of the dynamics of tree requirements is required to match fertilization regimes to the availability of each nutrient in the soil. The nutrition of Eucalyptus plantations has been intensively investigated and many studies have focused on specific fluxes in the biogeochemical cycles of nutrients. However, studies dealing with complete cycles are scarce for the Tropics. The objective of this paper was to compare these cycles for Eucalyptus plantations in Congo and Brazil, with contrasting climates, soil properties, and management practices.The main features were similar in the two situations. Most nutrient fluxes were driven by crown establishment the two first years after planting and total biomass production thereafter. These forests were characterized by huge nutrient requirements: 155, 10, 52, 55 and 23 kg ha^?1 of N, P, K, Ca and Mg the first year after planting at the Brazilian study site, respectively. High growth rates the first months after planting were essential to take advantage of the large amounts of nutrients released into the soil solutions by organic matter mineralization after harvesting. This study highlighted the predominant role of biological and biochemical cycles over the geochemical cycle of nutrients in tropical Eucalyptus plantations and indicated the prime importance of carefully managing organic matter in these soils. Limited nutrient losses through deep drainage after clear-cutting in the sandy soils of the two study sites showed the remarkable efficiency of Eucalyptus trees in keeping limited nutrient pools within the ecosystem, even after major disturbances. Nutrient input–output budgets suggested that Eucalyptus plantations take advantage of soil fertility inherited from previous land uses and that long-term sustainability will require an increase in the inputs of certain nutrients.  相似文献   

Non-target effects of chlorantraniliprole and thiamethoxam on Chrysoperla carnea when employed as sunflower seed treatments     

Pablo C. Gontijo  Valéria F. Moscardini  J. P. Michaud  Geraldo A. Carvalho 《Journal of pest science》2014,87(4):711-719

The use of systemic insecticides as seed treatments has raised concern about the possible impacts of these products on natural enemies. This study assessed the effects of sunflower seed treatments with chlorantraniliprole and thiamethoxam on Chrysoperla carnea by exposing larvae and adults to sunflower stem segments grown from treated seeds and the nectar secreted by their extrafloral nectaries. Confinement of larvae with stem segments for their entire developmental period had no effect on their survival or any life history parameter, except that the sex ratio of resulting adults was lower in the thiamethoxam treatment than in chlorantraniliprole. However, when adult pairs of C. carnea were exposed to treated stem segments during their maturation period, their subsequent survival and fecundity was significantly reduced by both materials, with thiamethoxam reducing median survival (LT₅₀) and fecundity to a greater degree than chlorantraniliprole. Insufficient offspring were obtained from adults exposed to thiamethoxam to permit assessment of their fitness, but the offspring in the chlorantraniliprole-exposed adults had reduced larval survival relative to controls. The greater impact of seed treatments on adult lacewings may be partly attributable to their greater consumption of extra-floral nectar. Our results indicate that seed treatment with systemic insecticides can cause negative effects on beneficial insects, potentially disrupting their population dynamics, and should not be assumed compatible with biological control and IPM simply because this mode of application limits direct exposure.  相似文献   

Relative timing of deglacial climate events in Antarctica and Greenland     

Morgan V  Delmotte M  van Ommen T  Jouzel J  Chappellaz J  Woon S  Masson-Delmotte V  Raynaud D 《Science (New York, N.Y.)》2002,297(5588):1862-1864

The last deglaciation was marked by large, hemispheric, millennial-scale climate variations: the B?lling-Aller?d and Younger Dryas periods in the north, and the Antarctic Cold Reversal in the south. A chronology from the high-accumulation Law Dome East Antarctic ice core constrains the relative timing of these two events and provides strong evidence that the cooling at the start of the Antarctic Cold Reversal did not follow the abrupt warming during the northern B?lling transition around 14,500 years ago. This result suggests that southern changes are not a direct response to abrupt changes in North Atlantic thermohaline circulation, as is assumed in the conventional picture of a hemispheric temperature seesaw.  相似文献   

Retinoic acid controls the bilateral symmetry of somite formation in the mouse embryo     

Vermot J  Gallego Llamas J  Fraulob V  Niederreither K  Chambon P  Dollé P 《Science (New York, N.Y.)》2005,308(5721):563-566

A striking characteristic of vertebrate embryos is their bilaterally symmetric body plan, which is particularly obvious at the level of the somites and their derivatives such as the vertebral column. Segmentation of the presomitic mesoderm must therefore be tightly coordinated along the left and right embryonic sides. We show that mutant mice defective for retinoic acid synthesis exhibit delayed somite formation on the right side. Asymmetric somite formation correlates with a left-right desynchronization of the segmentation clock oscillations. These data implicate retinoic acid as an endogenous signal that maintains the bilateral synchrony of mesoderm segmentation, and therefore controls bilateral symmetry, in vertebrate embryos.  相似文献   

Changes in the biological properties of an ordinary chernozem exposed to gamma radiation     

T. V. Denisova  K. Sh. Kazeev  S. I. Kolesnikov  V. F. Val’kov 《Eurasian Soil Science》2007,40(9):978-985

The dynamics of changes in the number of microorganisms and biochemical properties of an ordinary chernozem were studied in model experiments 3, 30, and 90 days after the soil was subjected to gamma radiation at doses of 0.12–2.0 Mrad. The microscopic fungi are the most radiosensitive soil microorganisms. In 90 days of incubation after the gamma radiation, the number of microorganisms remained lower than that in the control variant by 31–96% in accordance with the dose. The enzyme activity of the ordinary chernozem, as compared to that of the microorganisms, was more resistant to the gamma radiation. The integral index of the soil biological state (ISBSI) decreased by 20–63% upon the radiation depending on the dose applied. After 90 days, the ISBSI value was close to the control variant (doses of 0.1–0.5 Mrad), whereas, in the variants with high doses of radiation (1.0 and 2.0 Mrad), its values were 46 and 59% lower, respectively, than in the control. The rate of restoring of the biological properties was related to the dose of radiation: the less the dose, the quicker the rate of restoration of the biological properties of the ordinary chernozem. However, at the high levels of gamma radiation, some biological properties were not restored even after 90 days.  相似文献   

Detection of innocent systolic murmurs by auscultation and their relation to hematologic and echocardiographic findings in clinically normal Whippets     

Bavegems VC  Duchateau L  Polis IE  Van Ham LM  De Rick AF  Sys SU 《Journal of the American Veterinary Medical Association》2011,238(4):468-471

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In vivo and in vitro propagation and transmission of Toggenburg orbivirus     

Planzer J  Kaufmann C  Worwa G  Gavier-Widén D  Hofmann MA  Chaignat V  Thür B 《Research in veterinary science》2011,91(3):e163-e168

The Toggenburg orbivirus (TOV), a recently discovered virus related to bluetongue virus (BTV), has been identified in goats in Switzerland, Italy and Germany. Isolation of TOV in vitro has not yet been achieved and the transmission mechanisms are still unknown. In the experimental infection of pregnant goats described here, TOV could not be detected in secretion/excretion samples or fetal blood. Material from the goat experiment was used as inoculum for propagating the virus in vitro. To enhance the infectivity of TOV several modified protocols, e.g. pretreatment of the virus with trypsin, polyethylene glycol-mediated infection and lipofection were applied. Isolation of TOV, attempts to infect Culicoides nubeculosus by feeding TOV-positive blood and intracerebral inoculation of newborn mice were unsuccessful. The results of these studies suggest that TOV requires specific but different factors than other BTVs for infection and replication outside of its natural caprine host.  相似文献   

Seasonal Dynamics of Forage Shrub Nutrients     

Kelly L. Memmott  Val Jo Anderson  Rachel Fugal 《Herpetological Monographs》2011,33(6):12-16

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Alteration of virulence factors and rearrangement of pAsa5 plasmid caused by the growth of Aeromonas salmonicida in stressful conditions     

Daher RK  Filion G  Tan SG  Dallaire-Dufresne S  Paquet VE  Charette SJ 《Veterinary microbiology》2011,152(3-4):353-360

Aeromonas salmonicida, a fish pathogen, is the causative agent of furunculosis. It was already shown that growing this bacterium in stressful conditions such as temperature above 22°C might lead to virulence attenuation. Unfortunately, many veterinary microbiology services and reference centers still routinely cultivate A. salmonicida at 25°C. Here we tested the presence of virulence factors by growth on specific medium as well as the integrity of the pAsa5 plasmid, which bears an important virulence factor, the type III secretion system (TTSS), by PCR analysis in twenty strains, most of which were grown at 25°C in their laboratory of origin. The analysis revealed that strains, which encountered the more stressful growth conditions displayed the most frequent absence of A-layer protein and secreted proteolytic activity. Moreover, many strains had lost parts of the pAsa5 plasmid in which the TTSS region was almost always affected. To confirm the effect of stressful growth conditions on the plasmid, three strains with an intact pAsa5 were cultured at 25°C for two weeks. A low but significant fraction of the tested colonies displayed pAsa5 rearrangements. The rearrangement always affected the TTSS region and led to a loss of virulence in the Dictyostelium discoideum co-culture assay. These results demonstrate that the instability of pAsa5 did not lead to its complete loss as previously proposed but to a more complex rearrangement phenomenon and emphasizes the necessity to grow A. salmonicida in appropriate conditions to preserve the complete virulence of the bacterium.  相似文献   

Impact of lignin structure and cell wall reticulation on maize cell wall degradability   总被引：1，自引：0，他引：1  

Zhang Y  Culhaoglu T  Pollet B  Melin C  Denoue D  Barrière Y  Baumberger S  Méchin V 《Journal of agricultural and food chemistry》2011,59(18):10129-10135

In this study, eight maize recombinant inbred lines were selected to assess both the impact of lignin structure and the impact of cell wall reticulation by p-hydroxycinnamic acids on cell wall degradability independently of the main "lignin content" factor. These recombinant lines and their parents were analyzed for in vitro degradability, cell wall residue content, esterified and etherified p-hydroxycinnamic acid content, and lignin content and structure. Lignin structure and esterified p-coumaric acid content showed significantly high correlation with in vitro degradability (r=-0.82 and r=-0.72, respectively). A multiple regression analysis showed that more than 80% of cell wall degradability variations within these 10 lines (eight recombinant inbred lines and their two parents) were explained by a regression model including two main explanatory factors: lignin content and estimated proportion of syringyl lignin units esterified by p-coumaric acid. This study revealed new biochemical parameters of interest to improve cell wall degradability and promote lignocellulose valorization.  相似文献