• Energy Research

Legume growing has many benefits. Indeed legumes provide plant proteins for animal feed and human food. Legumes fix atmospheric N2 and, in turn, provide cheap and green N fertilisers. Additionally, legumes are used as diversification crops in rotations based on oilseed rape and cereals. Despite those benefits, legume crops in Europe represent less than 4 % of arable lands, and European legume seeds are underused for animal and human nutrition. Nonetheless, European authorities are now fostering the development of legume crops for sustainable agriculture. Here, we analyse forage and grain legume-producing systems since 1950 in order to identify the actual constraints of legume development. We show that legumes can contribute to the agroecological transition for sustainable agriculture, food and energy and for sustainable agri-food systems. Then, we point out that high added-value niche markets are required for supporting legume production. The major research needs identified are (1) analysing the constraints of the current systems and identifying ways of moving towards systems that include more legumes, (2) identifying new and diversified uses for legumes in a sustainable food chain, (3) assessing and improving the ecosystem services provided by legumes at cropping system and territory scales and (4) promoting agroecology through and for legume crop management.

SummaryThree soil DNA extraction procedures (homemade protocols and commercial kit) varying in their practicability were applied to contrasting soils to evaluate their efficiency in recovering: (i) soil DNA and (ii) bacterial diversity estimated by 16S rDNA pyrosequencing. Significant differences in DNA yield were systematically observed between tested procedures. For certain soils, 10 times more DNA was recovered with one protocol than with the others. About 15 000 sequences of 16S rDNA were obtained for each sample which were clustered to draw rarefaction curves. These curves, as well as the PCA ordination of community composition based on OTU clustering, did not reveal any significant difference between procedures. Nevertheless, significant differences between procedures were highlighted by the taxonomic identification of sequences obtained at the phylum to genus levels. Depending on the soil, differences in the number of genera detected ranged from 1% to 26% between the most and least efficient procedures, mainly due to a poorer capacity to recover populations belonging to Actinobacteria, Firmicutes or Crenarchaeota. This study enabled us to rank the relative efficiencies of protocols for their recovery of soil molecular microbial biomass and bacterial diversity and to help choosing an appropriate soil DNA extraction procedure adapted to novel sequencing technologies.

SummaryAssessing soil microbial community structure by the use of molecular techniques requires a satisfactory sampling strategy that takes into account the high microbial diversity and the heterogeneous distribution of microorganisms in the soil matrix. The influence of the sample size of three different soil types (sand, silt and clay soils) on the DNA yield and analysis of bacterial and fungal community structure were investigated. Six sample sizes from 0.125 g to 4 g were evaluated. The genetic community structure was assessed by automated ribosomal intergenic spacer analysis (A‐RISA fingerprint). Variations between bacterial (B‐ARISA) and fungal (F‐ARISA) community structure were quantified by using principal component analysis (PCA). DNA yields were positively correlated with the sample size for the sandy and silty soils, suggesting an influence of the sample size on DNA recovery, whereas no correlation was observed in the clay soil. B‐ARISA was shown to be consistent between the different sample sizes for each soil type indicating that the sampling procedure has no influence on the assessment of bacterial community structure. On the contrary for F‐ARISA profiles, strong variations were observed between replicates of the smaller samples (<1 g). Principal component analysis analysis revealed that sampling aliquots of soil ≥1 g are required to obtain robust and reproducible fingerprinting analysis of the genetic structure of fungal communities. However, the smallest samples could be adequate for the detection of minor populations masked by dominant ones in larger samples. The sampling strategy should therefore be different according to the objectives: rather large soil samples (≥1 g) for a global description of the genetic community structure, or a large number of small soil samples for a more complete inventory of microbial diversity.

L'intensification agricole amorcée depuis les années 1950 a globalement conduit au déclin des cultures légumineuses, qui représentent aujourd'hui moins de 3 % des grandes culture françaises et européennes. Pourtant, les légumineuses présentent plusieurs atouts : (i) en tant que source de protéines végétales pour l'alimentation humaine ou animale et (ii) en tant que plantes fixatrices de l'azote de l'air, économes en intrants azotés, et (iii) en tant que cultures de diversification dans les systèmes de culture. Une analyse des systèmes de production des légumineuses à graines et fourragères en France montre que les différents facteurs freinant l'insertion de ces cultures relèvent d'un processus de " verrouillage " du régime socio-technique agricole dominant. Pourtant les légumineuses pourraient jouer un rôle majeur dans la transition agroécologique vers des systèmes agricoles, alimentaires et énergétiques plus durables. Une approche économique mobilisant l'approche multi-niveaux de la théorie des transitions a permis d'identifier des voies de déverrouillage de la production de légumineuses. A la lumière de cette analyse, quatre grands groupes de questions de recherche ont été identifiés, concernant (i) l'analyse des verrouillages et l'identification des leviers de transition vers des systèmes intégrant plus de légumineuses (ii) l'identification de débouchés nouveaux et diversifiés pour les légumineuses dans une chaine alimentaire durable, (iii) l'évaluation et l'amélioration des services écosystémiques rendus par les légumineuses à l'échelle des systèmes de culture et des territoires, et (iv) l'optimisation de la conduite des cultures de légumineuses dans une démarche globale d'intensification écologique. Intensification of agriculture since 1950 has globally led to the decline of grain legume crops, which currently represent less than 3 % of arable crops in France and Europe. Nevertheless, legumes haveseveral major assets (i) as plant proteins for animal feed and human food and (ii) as plants fixing atmospheric N2 and thereby saving nitrogen inputs in cropping systems, and (iii) as diversification crops.The analysis of forage and grain legume producing systems in France showed that the dominant system results in a lock-in of the different factors limiting legume insertion into the current systems. But legumes could have a major role to play in the agroecological transition towards more sustainable agricultural, food and energy systems. The multi-level perspective in the theory of transitions helped usto identify ways of unlocking legume production. Four groups of research questions were thus identified: (i) analysing the lock-ins in the current systems and identifying ways of moving towards systems thatinclude more legumes (ii) identifying new and more diversified outlets for legumes in a sustainable food chain, (iii) assessing and improving the ecosystem services provided by legumes at cropping systemand territory scales and (iv) optimising legume crop management in a global agroecological approach.