École nationale supérieure agronomique de Rennes

About: École nationale supérieure agronomique de Rennes is a based out in . It is known for research contribution in the topics: Population & Gene. The organization has 590 authors who have published 578 publications receiving 27954 citations. The organization is also known as: Ecole nationale superieure agronomique de Rennes & ENSAR.

The effects of organic inputs over time on soil aggregate stability – a literature analysis

Abstract: Since the beginning of the last century, many studies have reported evidence describing the effects of organic inputs on soil aggregate stability. In 1965, Monnier proposed a conceptual model that considers different patterns of temporal effects on aggregate stability depending on the nature of the organic inputs: easily decomposable products have an intense and transient effect on aggregate stability while more recalcitrant products have a lower but longer term effect. We confronted this conceptual model with a literature review of experimental data from laboratory and field experiments. This literature analysis validated the conceptual model proposed by Monnier and pointed out gaps in our current knowledge concerning the relationships between aggregate stability and organic inputs. Noticeably, the experimental dataset confirmed the biological and temporal effects of organic inputs on aggregate stability as proposed in the model. Monnier's model also related the evolution of aggregate stability to different microbial decomposing agents, but this relationship was not made clear in this literature analysis. No direct or universal relationship was found between the aggregative factors induced by organic input decomposition (binding molecules or decomposers of biomass) and temporal aggregate stability dynamics. This suggests the existence of even more complex relationships. The model can be improved by considering (i) the direct abiotic effect of some organic products immediately after the inputs, (ii) the initial biochemical characteristics of the organic products and (iii) the effects of organic products on the various mechanisms of aggregate breakdown. For now, no trend is evident in the effect of the rate of organic inputs or the effect of the soil characteristics (essentially carbon and clay contents) on aggregate stability

Nitrate transport and signalling

Abstract: Physiological measurements of nitrate (NO(3)(-)) uptake by roots have defined two systems of high and low affinity uptake. In Arabidopsis, genes encoding both of these two uptake systems have been identified. Most is known about the high affinity transport system (HATS) and its regulation and yet measurements of soil NO(3)(-) show that it is more often available in the low affinity range above 1 mM concentration. Several different regulatory mechanisms have been identified for AtNRT2.1, one of the membrane transporters encoding HATS; these include feedback regulation of expression, a second component protein requirement for membrane targeting and phosphorylation, possibly leading to degradation of the protein. These various changes in the protein may be important for a second function in sensing NO(3)(-) availability at the surface of the root. Another transporter protein, AtNRT1.1 also has a role in NO(3)(-) sensing that, like AtNRT2.1, is independent of their transport function. From the range of concentrations present in the soil it is proposed that the NO(3)(-)-inducible part of HATS functions chiefly as a sensor for root NO(3)(-) availability. Two other key NO(3)(-) transport steps for efficient nitrogen use by crops, efflux across membranes and vacuolar storage and remobilization, are discussed. Genes encoding vacuolar transporters have been isolated and these are important for manipulating storage pools in crops, but the efflux system is yet to be identified. Consideration is given to how well our molecular and physiological knowledge can be integrated as well to some key questions and opportunities for the future.

Genetic and epigenetic consequences of recent hybridization and polyploidy in Spartina (Poaceae)

Abstract: To study the consequences of hybridization and genome duplication on polyploid genome evolution and adaptation, we used independently formed hybrids (Spartina x townsendii and Spartina x neyrautii) that originated from natural crosses between Spartina alterniflora, an American introduced species, and the European native Spartina maritima. The hybrid from England, S. x townsendii, gave rise to the invasive allopolyploid, salt-marsh species, Spartina anglica. Recent studies indicated that allopolyploid speciation may be associated with rapid genetic and epigenetic changes. To assess this in Spartina, we performed AFLP (amplified fragment length polymorphism) and MSAP (methylation sensitive amplification polymorphism) on young hybrids and the allopolyploid. By comparing the subgenomes in the hybrids and the allopolyploid to the parental species, we inferred structural changes that arose repeatedly in the two independently formed hybrids. Surprisingly, 30% of the parental methylation patterns are altered in the hybrids and the allopolyploid. This high level of epigenetic regulation might explain the morphological plasticity of Spartina anglica and its larger ecological amplitude. Hybridization rather than genome doubling seems to have triggered most of the methylation changes observed in Spartina anglica.