CHARACTERIZATION OF NITROGEN FIXING BACTERIA INSOILSFROM ENTRE RIOSIN SYMBIOSIS WITHLOTUS Spp FORAGE SPECIES

VANINA GISELLE MAGUIRE; ANDRES ALBERTO RODRIGUEZ; BOUILLY PJ; EZQUIAGA JP; ANDRES GARRIZ; OSCAR ADOLFO RUIZ

Congreso; Congreso Conjunto SAIB-SAMIGE 2020; 2020

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 Vertisolorder, characterized by low edaphic phosphorus and nitrogen concentration anda 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 nitrogenmore efficiently than the commercial strainsusedforLotus spp forage species, we grew 100 Lotus spp.?trap plants?in pots containingVertisol soil samples collected inrice-pasture rotation systems, the maincropmanagement strategyused 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 32isolatedbacterial strains, 8 were exhaustivelytested in L. corniculatus plantsfor nitrogen fixation efficiency, along with the reference strain NZP2213, acommercial inoculant(NITRASOIL®) and control plantsirrigated withinorganic 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 thecommercial 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 contentsin 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 RIZ35show valuablepotentials for the formulation of inoculants for Lotusspp.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 N15isotopic 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.