Inoculation of soybean seeds by rhizobia with nanometal carboxylates reduces the negative effect of drought on N₂ and CO₂ assimilation

The effect of individual nanometals (Co, Fe, Cu, Ge) carboxylates (NMC) as components of the suspension for seeds inoculation with rhizobia on the nitrogen fixation rate and the parameters of CO2 and H2O gas exchange in soybean plants grown under different water conditions was investigated. The scheme of trials included the following variants: 1 - seeds + strain B1-20; 2 - seeds + (strain B1-20 + nano-cobalt carboxylate); 3 - seeds + (strain В1-20 + nano-ferrum carboxylate); 4 - seeds + (strain B1-20 + nano-cuprum carboxylate); 5 - seeds + (strain B1-20 + nano-germanium carboxylate). The results showed that during the flowering period, drought (30% field capacity) significantly reduced the rates of nitrogen fixation (Nfx), CO2 net assimilation (An), and transpiration (Tr) in soybean plants. Inoculation of seeds by rhizobia with NMC before sowing reduced the negative effect of drought on these physiological processes. Close correlations were found between the rates of Nfx and An and the stomatal conductance for CO2 and An rates. It was concluded that pre-sowing treatment of seeds by rhizobia with NMC mitigates the negative effect of drought on the main components of soybean-rhizobia symbiosis productivity formation - nitrogen fixation and CO2 assimilation, and also contributes to their recovery after the removal of the stressor. The most effective for this was the use of Ge and Fe nanoparticle carboxylates.