Effects of Bacillus velezensis strain GH1-13 seed-soaking inoculation on rice productivity and greenhouse gas (CH4 and N2O) emissions in a paddy soil during cultivation: A pot experiment

In this study, a pot experiment was carried out to evaluate the effect of seed-soaking inoculation of Bacillus velezensis (B. velezensis) GH1-13 on rice productivity and GHG (greenhouse gas) emissions during the cultivation season in four different treatments (presence or absence of inoculation with organic matter application which was added as rice straw at rates of 0 and 5 Mg ha-1, respectively). Inoculation of B. velezensis increased rice productivity, but no significant differences were observed among all the treatments. Global warming potential including CH4 and N2O emissions significantly increased with the inoculation (2.7 g CH4 pot-1 and 15.0 mg N2O pot-1) compared to the control (2.2 g CH4 pot-1 and 8.4 mg N2O pot-1) in non-OM (organic matter) soils. In OM-amended soils, CH4 and N2O emissions increased more than that in non-OM soils with the inoculation (31.4 g CH4 pot-1 and 12.8 mg N2O pot-1) compared to the control (19.3 g CH4 pot-1 and 12.3 mg N2O pot-1). Although there is no significant increase in CH4 emissions, the fluxes increased in both non-OM and OM-treated soils by the inoculation, which might be due to the stimulation of organic matter degradation by producing cellulase enzyme and other metabolites related to carbon cycling from B. velezensis, leading to increase global warming potential (789.2 CO2 eq. pot-1) in the OM treatment soils compared to the control (486.4 CO2 eq. pot-1) during cultivation. These results suggest that rice seed-soaking of the B. velezensis may influence CH4 and nitrogen cyclings in different OM conditions, which could be a pioneering option for potentially reducing GHG emissions in paddy soils. Conclusively, beneficial microorganisms, isolated from rice paddy soils which might play a role in CH4 oxidizers or N2O reducers, are needed to be screened for mitigating GHG emissions as well as stimulating rice yield for further studies.Effects of Bacillus sp. inoculation greenhouse gas emissions (CH4 and N2O).