Improvement of nodulation and biological nitrogen fixation in soybean through seed treatment with non-thermal plasma

Abstract

Among the most demanded nutrients by soybean crop (Glycine max (L.) Merr.), nitrogen ranks first. Biological nitrogen fixation (BNF), which occurs through the establishment of symbiotic associations between plants and bacteria, is one of the most important sources of nitrogen in soybean. In recent decades, great scientific efforts have been invested in studying strategies for harnessing the potential of BNF. Non-thermal plasmas (NTP) are partially ionized gases, usually generated by low-current electrical discharges that can be sprayed onto biological tissues. They are a novel and promising technology that might be employed for seed treatment before sowing as they allow enhancing seed health while promoting germination and vigor in a fast, cost-effective and eco-friendly way. In a previous research, we showed enhanced seed quality following soybean seed treatment with NPT. The NPT positive effects lasted the entire plant cycle, determining improvements in growth and yield. In this regard, the main objective of the present study was to characterize and demonstrate the effects of seed treatment with NTP on plant nodular development and on the BNF, as mechanisms that might explain the enhanced yields. Comparing plasma treatment with the control (non-treated), our results showed important differences regarding root growth, which correlated positively with increments of about 1.7 folds in GmEXP1 gene expression in roots. On the other hand, we found improvements of 25% in the number of nodules, and improvements of 70% and 55% in nodular biomass, fresh and dry (respectively). BNF was evaluated through the determination of nitrogenase activity and leghemoglobine content in nodules, which were enhanced by 60 and 100% (respectively) through seed treatment with NTP. These parameters correlated positively with plants biometry and total and partitioned (nodular, radical and aerial) nitrogen content. We propose the NTP technology for seed treatment before sowing for improving crop yield while protecting the environment.