CHARACTERIZATION OF NITROGEN FIXING BACTERIA IN SOILS FROM ENTRE RIOS IN SYMBIOSIS WITH LOTUS Spp FORAGE SPECIES

MAGUIRE V.; RODRIGUEZ A.A.; BOUILY P.J.; EZQUIAGA J.P.; GARRIZ A.; RUIZ O.A.

MENDOZA

Congreso; SAIB-SAMIGE 2020; 2020

SAIB-SAMIGE

Entre Ríos is the second most important province for rice production in Argentina. The most suitable soils for rice cultivation are those belonging to the Vertisol order, characterized by low edaphic phosphorus and nitrogen concentration and a highly diverse microbial community (Maguire et al APSOIL2020 https://doi.org/10.1016/j.apsoil.2020.103535). In order to isolate, select and identify indigenous microorganisms able to fix nitrogen more efficiently than the commercial strains used for Lotus spp forage species, we grew 100 Lotus spp. ?trap plants? in pots containing Vertisol soil samples collected in rice-pasture rotation systems, the main crop management strategy used in Chajarí (Entre Rios, Argentina). Nitrogen fixing bacteria were isolated from harvested root nodules, and BOX-PCR analysis were performed in order to discard duplicate strains. From a total of 32 isolated bacterial strains, 8 were exhaustively tested in L. corniculatus plants for nitrogen fixation efficiency, along with the reference strain NZP2213, a commercial inoculant (NITRASOIL®) and control plants irrigated with inorganic N. Under our experimental conditions, the RIZ17 and RIZ35 strains showed a clear tendency to increase stem and root dry weight in inoculated plants. RIZ17, NZP2213, RIZ35, RIZ24 and the commercial strain were the treatments that showed the highest impact in leaf areas. Plants inoculated with RIZ17, despite showing the highest nodule number, present the lowest mean nodule weight. Infection with RIZ17, RIZ35 and RIZ20 did not lead to differences in total N contents in stems from those found in plants inoculated with the commercial, NZP2213 and control plants. At last, the variable stem dry weight was best explained by nodule weight (r=0.86) and total nodule area (r=0.73). We conclude that RIZ17 and RIZ35 show valuable potentials for the formulation of inoculants for Lotus spp. After sequencing and analyzing the ribosomal marker gene 16S rRNA, RIZ17 and RIZ35 were taxonomically classified as Mesorhizobium sp. and Variovorax paradoxus, respectively. Moreover, through the N15 isotopic abundance technique, the ability of L. corniculatus to fix nitrogen through its association with native rhizobia was evaluated, and the amount of N derived from the atmosphere (%Ndfa) was equal to 82.6%. After L. corniculatus ?B factor? determination, a potential 2,5 kg N/ha fixation was estimated in rice pasture rotation in Vertisol soils.