Effects of Rhizobium and Caballeronia sordidicola inoculation on growth and foliar nitrogen content of intercropped field pea and poplar

Sustainable agriculture emphasizes the necessity of enhanced nitrogen management in agroforestry. Using nitrogen-fixing legumes and plant growth-promoting bacteria (PGPB) is vital for increasing plant nitrogen accessibility and reducing chemical fertilizer reliance. Endophytic diazotrophic bacteria, which reside within plant tissues, may serve as an underexplored source of nitrogen input. This study investigates the co-inoculation of Rhizobium leguminosarum biovar viciae and Caballeronia sordidicola LS-S2r in field peas (Pisum sativum) and poplar (Populus spp.) to enhance foliar nitrogen content and growth under nutrient-poor conditions. These bacterial strains were isolated from the root zones of field peas and poplar and assessed for their effects on foliar nitrogen and plant biomass. Co-inoculation with both bacterial strains did not significantly improve field peas growth compared to the Rhizobium treatment (T2), with no notable increases in shoot or root biomass. Poplar exhibited minimal growth improvements with co-inoculation, suggesting host-specific effects. However, poplar root biomass was enhanced by inoculating Caballeronia sordidicola LS-S2r alone, suggesting other beneficial growth-promoting mechanisms. Notably, Caballeronia sordidicola LS-S2r did not form endophytic associations in either species but enhanced nutrient availability in their rhizospheric colonization. Co-inoculated field peas and poplar enhanced foliar nitrogen contents by 3.9% and 1.18%, compared to uninoculated controls. These results suggest that microbial inoculants could enhance nitrogen dynamics and plant growth promoting benefits in agroforestry systems and promoting sustainable agricultural practices.