Effects of Azotobacter and Carbon Dioxide Concentrations on the Growth and Yield of Rice Plants Grown in Two Paddy Soils

Abstract

Rice is an important staple crop influenced by rising CO2 and related climate change, but it is not well-known how N-fixing Azotobacter affects rice growth and yield under different CO2 concentrations. This study aimed to determine the effects of Azotobacter strains on the growth and yield of rice plants grown in two paddy soils under varying CO2 conditions. Rice plants inoculated with three Azotobacter strains were grown in a conventional rice soil (Dali) and an organic rice soil (Houlong) under 500 or 1000 ppm CO2. These three Azotobacter strains significantly increased the harvest index of rice plants grown in Dali soil under 1000 ppm CO2, but they did not significantly increase the harvest index for rice plants grown in Houlong soil under elevated CO2. Interestingly, only A. beijerinckii CHB 461 significantly promoted the thousand-grain weight of rice plants grown in both Dali and Houlong soils under elevated CO2. Dali soil had a high level of soil organic matter, exchangeable Ca and Mg, and available Cu and Zn, probably resulting in a better response of the rice plants to Azotobacter inoculation under elevated CO2. In conclusion, in the application of Azotobacter to promote rice growth and yield under future rising CO2 conditions, the soil properties and characteristics of Azotobacter strains may need to be considered.