Specialization of the entomopathogenic nematode Steinernema scapterisci with its mutualistic Xenorhabdus symbiont

The level of specialization of the entomopathogenic nematode Steinernema scapterisci with its native Xenorhabdus symbiont was investigated by testing (1) the influence of non-native bacterial strains on nematode fitness within an insect-host (Galleria mellonella) and (2) specificity of the association between the nematode infective juveniles and non-native bacteria. All non-native Xenorhabdus spp. or Photorhabdus spp. strains tested were mutualistically associated with other entomopathogenic nematodes in nature. We showed that most of the Xenorhabdus spp. strains tested led to an insignificant difference of the nematode's fitness compared to the one obtained with the native bacterium. Conversely, Photorhabdus spp. strains almost entirely abolished nematode reproduction. The phylogenetic analysis of bacterial strains tested, showed that there was a negative correlation between S. scapterisci's reproduction rate with a bacterial strain and the genetic distance of this bacterial strain from the native one. We also showed that the native bacterium was the only one which was transmitted by S. scapterisci's infective juveniles. All these results, suggested a specialization between S. scapterisci and its native Xenorhabdus. As the same phenomenon was already demonstrated in the association between S. carpocapsae and X. nematophila, specialization between partners would not be an exception in entomopathogenic nematode-bacteria interactions. Nevertheless, S. scapterisci showed a dramatically higher compatibility with non-native Xenorhabdus spp. strains than did S. carpocapsae, suggesting differences in the co-evolutionary processes between nematodes and bacteria in these two model systems.Table 1 List of the bacterial strains, native nematode species with their geographical origin, accession numbers of bacterial 16S rDNA partial sequences and number of combination experiments for each bacterium tested

Determination of canthaxanthin in the red coral (<Emphasis Type="Italic">Corallium rubrum</Emphasis>) from Marseille by HPLC combined with UV and MS detection

Corallium rubrum is the most famous and precious coral due to the intense characteristic red colour of its skeleton. We have determined the presence of carotenoids in natural samples of C. rubrum from Marseille, Riou, and investigated their chemical composition. Analysis was performed both on soft tissues and hard tissues including spicules and skeleton. Since hard tissues are made of a mineral fraction and an organic fraction obtained after demineralization, extraction was performed both with and without demineralization by EDTA. The extracts were analyzed by complementary methods of TLC, HPLC/DAD and HPLC/MS. The components were separated by RP-18 chromatography column using acetonitrile/methanol for HPLC/DAD and acetonitrile/water gradient for HPLC/MS analysis. Our results give the first evidence of the presence of canthaxanthin, 4,4′-diketo-β-carotene, as the major carotenoid in all samples. Spicules exhibited higher content in carotenoids than skeleton. Demineralization treatment improved the efficiency of carotenoid extraction by an average factor of 5 and showed that organic matrix contains canthaxanthin.     

Potential allelopathic effect of Pinus halepensis in the secondary succession: an experimental approach

Summary. Recent economic and social changes in north Mediterranean regions have led to an important rural depopulation. Consequently, meadows developed on abandoned agricultural lands (characterized by high species richness) undergo reforestation. These former fields are mainly colonized by Pinus halepensis Miller, which is known to synthetize a wide range of secondary metabolites, among these, some could influence plant succession through allelopathy. The allelopathic potential of P. halepensis, was tested against two target species (Lactuca sativa L. and Linum strictum L.) with aqueous extracts obtained from different organs (root and needle) taking into account the individual age (±10, ±30 and > 60 years old). Root and needle extracts affected differently germination and growth of the two target species, the responses varying with concentration of extracts, age and organs tested. The strongest inhibitory effect was observed on the germination and growth of L. strictum, exposed to needle extracts of young P. halepensis (±10 years old), and root extracts of older P. halepensis (> 30 years old). These extracts contained several phenolic acids (e.g. 4-hydroxybenzoic acid and p-coumaric acid), which are known as allelochemicals and their concentrations vary with age and organ tested. Hence, P. halepensis could influence secondary succession through the release of potential allelochemicals in the environment by leaf leachates or root exudates.     

加拿大北方森林过去、当前和未来的火灾频率:对于森林可持续经营的意义

在过去的几十年里,对基于对历史上自然干预动力的理解的森林经营方法的开发兴趣日益增加.这一方法的理由是,有利于景观组成和林分结构及自然生态系统的经营活动也应当保持生物多样性和基本的生态功能.在火灾居支配地位的景观,用森林经营替代火灾这一方法只在当前火频率和未来火频率比工业化以前的火频率低得多的情况下才有可能.通过将当前火频率、未来火频率与在加拿大北方森林中再现的森林火灾历史的比较,我们讨论了这一问题.对于多块研究地而言,当前火频率和2倍CO.及3倍CO2情形下模拟的未来火频率都低于过去火频率,这暗示着森林经营可以被用于重建受控于火灾的、工业化以前景观的林木年龄结构.但对目前的同龄林经营来说,还有一些重要的限制因子.     

Laboratory leaching studies of oryzalin and diuron through three undisturbed vineyard soil columns

The leaching of diuron and oryzalin through undisturbed soil columns was studied in the laboratory using three vineyard soils from Vosne-Romanée (Burgundy): a rendosol, a calcosol and a vegetated calcosol. After 845 mm of simulated rainfall in 15 days, soil leachates contained higher amounts of diuron (3.2%, 11.8% and 18.8% of applied diuron, respectively) than oryzalin (0.2%, 4.9%, 3.7%, respectively). A greater proportion of soil extractable residues was obtained for diuron (42.5%, 26.8% and 32.2%, respectively) than for oryzalin (14.7%, 12% and 15.5%, respectively). The greater mobility of diuron might be related to its higher water solubility (36.4 mgl(-1) compared with 2.6 mgl(-1) for oryzalin) and smaller adsorption coefficient (400 lkg(-1), compared with 700-1100 lkg(-1) for oryzalin). The mobility of the two herbicides was greater in the two calcosols than in the rendosol, not only due to different organic carbon contents but also different soil textures and structures.     

Spatial distribution of pollution in an urban stormwater infiltration basin

Infiltration basins are frequently used for stormwater drainage. Because stormwater is polluted in highly toxic compounds, assessment of pollution retention by infiltration basins is necessary. Indeed, if basins are not effective in trapping pollution, deep soil and groundwater may be contaminated. This study's objective is to investigate soil pollution in infiltration basins: spatial distribution of soil pollution, optimisation of the number of soil samples and a contamination indicator are presented. It is part of a global project on long-term impact of stormwater infiltration on groundwater. Soil sampling was done on a basin in suburban Lyon (France). Samples were collected at different depths and analysed for nutrients, heavy metals, hydrocarbons and grain size. Pollutant concentrations decrease rapidly with depth while pH, mineralisation and grain size increase. Sustainable metal concentrations are reached at a 30-cm depth, even after 14 years of operation; hydrocarbon pollution is deeper. Principal component analysis shows how pollutants affect each level. The topsoil is different from other levels. Three specifically located points are enough to estimate the mass of pollution trapped by the basin with a 26% error. The proposed contamination indicator is calculated using either average level concentrations or maximum level concentrations. In both cases, the topsoil layer appears polluted but evaluation of lower levels is dependent on the choice of input concentrations.