Traits affecting early season nitrogen uptake in nine legume species

Legume crops are known to have low soil N uptake early in their life cycle, which can weaken their ability to compete with other species, such as weeds or other crops in intercropping systems. However, there is limited knowledge on the main traits involved in soil N uptake during early growth and for a range of species. The objective of this research was to identify the main traits explaining the variability among legume species in soil N uptake and to study the effect of the soil mineral N supply on the legume strategy for the use of available N sources during early growth. Nine legume species were grown in rhizotrons with or without N supply. Root expansion, shoot and root biomass, nodule establishment, N2 fixation and mineral soil N uptake were measured. A large interspecific variability was observed for all traits affecting soil N uptake. Root lateral expansion and early biomass in relation to seed mass were the major traits influencing soil N uptake regardless of the level of soil N availability. Fenugreek, lentil, alfalfa, and common vetch could be considered weak competitors for soil N due to their low plant biomass and low lateral root expansion. Conversely, peanut, pea, chickpea and soybean had a greater soil N uptake. Faba bean was separated from other species having a higher nodule biomass, a higher N2 fixation and a lower seed reserve depletion. Faba bean was able to simultaneously fix N2 and take up soil N. This work has identified traits of seed mass, shoot and root biomass, root lateral expansion, N2 fixation and seed reserve depletion that allowing classification of legume species regarding their soil N uptake ability during early growt

Les processus de complémentarité de niche et de facilitation déterminent le fonctionnement des associations végétales et leur efficacité pour l'acquisition des ressources abiotiques

Dans les peuplements monospécifiques constituant la majorité des écosystèmes cultivés, les plantes sont en compétition pour les ressources abiotiques car elles exploitent les mêmes niches écologiques. A contrario, dans les peuplements plurispécifiques, deux processus majeurs ont été mis en évidence pour expliquer les meilleures performances de ces systèmes, à savoir la complémentarité de niche et la facilitation. Les interactions entre espèces ont lieu à la fois au niveau aérien pour l’interception du rayonnement, et au niveau racinaire pour le prélèvement de l’eau et des nutriments. La partition spatiale d'une ressource du sol entre deux espèces associées se produit particulièrement lorsque ces dernières présentent des vitesses et des profondeurs d'enracinement différenciées. Il en va de même pour l’utilisation de la lumière lorsque les espèces associées présentent des architectures et/ou des dynamiques de croissance complémentaires. La complémentarité de niche sur un plan biogéochimique s’applique typiquement aux cas d'associations entre une légumineuse et une espèce non fixatrice d'azote ; elle est liée à la capacité de la légumineuse à fixer l’azote de l’air. Cette complémentarité est d’autant plus forte que les espèces sont cultivées en situation de faible disponibilité d’intrants azotés. Ainsi dans ces situations, les cultures associées ont montré de meilleures performances en termes de production de biomasse et de rendement, mais aussi de statut azoté et in fine de teneur en protéines de la céréale. La facilitation se produit lorsqu'une espèce peut mobiliser dans le sol un pool initialement non disponible par l'intermédiaire de processus rhizosphériques engendrés par l’autre espèce comme cela a été récemment mis en évidence dans le cas du phosphore.Crop stands are generally composed of monospecific communities in modern agro-ecosystems. Consequently, in such situations, plants compete for the same abiotic resources as they exploit the same ecological niches. Conversely, in multi-species communities, two major processes have been highlighted to explain their better performance compared to sole crops: niche complementarity and facilitation. In these systems, species interactions occur both at the aerial level for radiation interception and at root level for water and nutrient uptake from the soil. Thus, spatial partition of a soil resource operates particularly when intercropped species have different rooting depths and dynamics. Similarly, complementarity between species for light use occurs when species architecture and/or dynamics strongly differ. Biogeochemical niche complementarity is typically observed when intercropping a legume with a non-nitrogen fixing species. Indeed, while species are competing for the pool of soil mineral nitrogen, niche complementarity occurs due to the legume's ability to access the unlimited pool of atmospheric N2 through symbiotic nitrogen fixation. This process has been well documented for cereal-legume intercrops and its magnitude is higher in situations of low nitrogen inputs. Therefore, under such low nitrogen availability, intercrops have shown better performances than sole crops in terms of biomass production and yield but also of nitrogen status ultimately leading to higher protein concentration in cereal grains. Facilitation occurs when one specie is able to mobilize a pool in the soil that is initially non available through rhizosphere processes created by the other intercropped specie which have been recently demonstrated for phosphorus

Models, Developments, and Perspectives of Mutual Legume Intercropping

This paper presents the current state of our knowledge of mutual legume intercropping, with an emphasis on its utilization in continental and Mediterranean climates. Its novelty is primarily reflected in the carefully designed schemes for two main forms of mutual legume intercropping. The first one is establishing perennial forage legumes, such as red clover, alfalfa, and sainfoin, with annual legume, such as pea, where the latter acts as a bioherbicide and concurrently contributes to the total forage yield in the first cut of the former. Another form is intercropping annual legumes with each other respecting the same time of sowing, that is, in fall or in spring, similar growth habit, especially stem length, time of maturity for cutting or harvest, and that one component has good standing ability and supports the other one that is susceptible to lodging. Since the prominently pioneering character of this research, most of the presented results, both published and unpublished, shown here for the first time, deal with forage and grain yield and its economic reliability in the form of land equivalent ratio, since this would surely be of the primary interest to the farmers to get introduced with. The first and rather advanced efforts have also been made in the physiology, anatomy, and biotic stress of both forms of mutual intercropping schemes. We anticipate that, together with further research in the said fields along with underground aspects, will make mutual legume intercropping one of the most promising answers for protein-rich food and feed worldwide