18 19 Adding P on Lotus tenuis and Festuca arundinacea, pure or mixed, on growth, nitrogen (N) 20 and phosphorus (P) acquisition and associations with soil microorganisms was studied to 21 investigate the establishment of Lotus for competing with Festuca. Triple-superphosphate was 22 applied on a Typic Natraquoll where Lotus grows spontaneously. Biomass, N-P uptake, 23 arbuscular mycorrhizal colonization and rhizobia nodulation were measured. Lotus achieved 24 the highest biomass, N-P uptake in fertilized stands and Festuca the lowest in fertilized and 25

Background and aimsThe aim of this work was to evaluate the ability of P fertilization and phosphatesolubilizing bacteria (PSB) inoculation to promote the growth of L. tenuis in typical soils of the Salado River Basin (Argentina) with low P availability. Methods Aboveground biomass and P and N levels were evaluated in field-grown L. tenuis plants inoculated with Pantoea eucalypti M91, either without fertilization or in combination with phosphate rock and triple superphosphate (TSP). The impact of P fertilization and inoculation on the symbiotic interactions between L. tenuis and native rhizobia bacteria and arbuscular mycorrhizal fungi was also evaluated. Results Inoculation with M91 increased the L. tenuis biomass production and P concentration in shoots, at an early stage of plant growth. The combined treatment of inoculation with M91 and TSP significantly increased the P and N content in shoots compared to noninoculated plants, fertilized or not. P. eucalypti M91 was found to endophytically colonize roots and leaves of L. tenuis plants grown in vitro and also under field conditions. Conclusions The results suggesting that inoculation of L. tenuis with the PSB such as P. eucalypti M91 strain might allow more efficient use of N and P and a more sustainable option for grasslands producers from the Salado River Basin, in order to reduce costs and avoid increased levels of P insoluble in soils.

The Salado River Basin region is the most important livestock breeding area in Argentina, wherethe Lotus species has been traditionally cultivated as forages. Nearly 60% of their land surface is dominated by salt-affected soils with severe constraints for crop cultivation. In order to cope with that limitation, farmers have utilized species such as non-native L. tenuis (ex-Lotus glaber), which shows a very good adaptation. As a result, inter-seeding of L. tenuis has been proposed as a strategy of choice for improving forage production in marginal areas. The increase in soil quality by these means is achieved by an increment of the organic matter content, improvement of soil fertility as well as microbial biodiversity. Thus, the introduction of L. tenuis and/or other Lotus genotypes could have enormous benefits for similar constrained lands around the world. We are developing an integrated analysis of the changes that occur in soils under legume production. We will not only analyze the microbial diversity associated, but also soil physical and chemical characteristics and the impact of different legume-microbes association on mitigation of GHG emissions. In addition, we are identifying the main genetic determinants associated with interesting agronomic traits such as plant tolerance against biotic and abiotic stresses and the content of condensed tannins. Our future and present research will build a solid base for the improvement of agronomicallyimportant species and the development of better strategies for the management of constrained lands such as the lowlands in the Argentinean Pampas.

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