High-resolution DNA fingerprinting of parthenogenetic root-knot nematodes using AFLP analysis

Amplified fragment length polymorphism (AFLP) analysis has been used to characterize 15 root-knot nematode populations belonging to the three parthenogenetic species Meloidogyne arenaria , M. incognita and M. javanica. Sixteen primer combinations were used to generate AFLP patterns, with a total number of amplified fragments ranging from 872 to 1087, depending on the population tested. Two kinds of polymorphic DNA fragments could be distinguished: bands amplified in a single genotype, and bands polymorphic between genotypes (i.e. amplified in not all but at least two genotypes). Based on presence/absence of amplified bands and pairwise similarity values, all the populations tested were clustered according to their specific status. Significant intraspecific variation was revealed by AFLP, with DNA fragments polymorphic among populations within each of the three species tested. M. arenaria appeared as the most variable species, while M. javanica was the least polymorphic. Within each specific cluster, no general correlation could be found between genomic similarity and geographical origin of the populations. The results reported here showed the ability of the AFLP procedure to generate markers useful for genetic analysis in root-knot nematodes.     

Juncus bulbosus as a pioneer species in acidic lignite mining lakes: interactions, mechanism and survival strategies

Bulbous rush ( Juncus bulbosus ) initiates plant colonization in extremely acid lakes resulting from coal mining operations. Various analytical techniques (methylene blue/agar method, Ti³⁺-citrate solution) X-ray diffraction (XRD), scanning electron microscopy (SEM), and Energy-dispersive X-ray (EDX) were used to assess the mechanisms and strategies employed by J. bulbosus to overcome the extreme conditions. The plant releases oxygen into the rhizosphere in turn increasing the redox potential and inducing iron oxide plaque formation. XRD showed that the iron oxide of the plaque is mainly goethite that has been developed in the presence of CO₂; SEM showed that there is a micro-space between the roots and sand grains which is inhabited by microorganisms. Furthermore, SEM-EDX studies on internal iron distribution demonstrate that iron toxicity is delayed by the physiological and biochemical structure of the plant. It is suggested that J. bulbosus uses a variety of mechanisms and strategies (morphological, physiological and biochemical adaptation) which are mainly complementary and which interact with each other to help J. bulbosus to manage its growth and survival in an extreme environment.     

Soil environmental conditions rather than denitrifier abundance and diversity drive potential denitrification after changes in land uses

Land‐use practices aiming at increasing agro‐ecosystem sustainability, e.g. no‐till systems and use of temporary grasslands, have been developed in cropping areas, but their environmental benefits could be counterbalanced by increased N₂O emissions produced, in particular during denitrification. Modelling denitrification in this context is thus of major importance. However, to what extent can changes in denitrification be predicted by representing the denitrifying community as a black box, i.e. without an adequate representation of the biological characteristics (abundance and composition) of this community, remains unclear. We analysed the effect of changes in land uses on denitrifiers for two different agricultural systems: (i) crop/grassland conversion and (ii) cessation/application of tillage. We surveyed potential denitrification (PD), the abundance and genetic structure of denitrifiers (nitrite reducers), and soil environmental conditions. N₂O emissions were also measured during periods of several days on control plots. Time‐integrated N₂O emissions and PD were well correlated among all control plots. Changes in PD were partly due to changes in denitrifier abundance but were not related to changes in the structure of the denitrifier community. Using multiple regression analysis, we showed that changes in PD were more related to changes in soil environmental conditions than in denitrifier abundance. Soil organic carbon explained 81% of the variance observed for PD at the crop/temporary grassland site, whereas soil organic carbon, water‐filled pore space and nitrate explained 92% of PD variance at the till/no‐till site, without any residual effect of denitrifier abundance. Soil environmental conditions influenced PD by modifying the specific activity of denitrifiers, and to a lesser extent by promoting a build‐up of denitrifiers. Our results show that an accurate simulation of carbon, oxygen and nitrate availability to denitrifiers is more important than an accurate simulation of denitrifier abundance and community structure to adequately understand and predict changes in PD in response to land‐use changes.