Effect of alternating drip irrigation on soil gas emissions, microbial community composition, and root–soil interactions

Abstract The lack of knowledge on the effects of alternating drip irrigation (ADI) on soil gas emissions limits the understanding of the trade-off between irrigation and soil gas emissions. To determine the effects of ADI on soil gas emissions, this study investigated soil gas emissions, microbial community composition and root–soil interactions in a tomato crop under ADI with different lower limits (50%, 60% and 70% field capacity (FC)), with mulched drip irrigation (MDI) used as a control. ADI with different lower limits differentially affected root growth and microbial community composition. These differences regulated root–soil interactions and affected soil gas emissions. Compared with ADI at 60% FC, ADI at 50% and 70% FC increased root fork numbers by 14.7% and 26.5%, respectively, and compared with MDI and ADI at 60% FC, these treatments also increased the abundance-based coverage estimators of bacterial communities. Furthermore, the total cumulative CO2 emissions from ADI at 50% and 70% FC were 42.1% and 46.8% greater than that of MDI, respectively, and the total cumulative N2O emissions from both treatments were 70.0% and 35.0% greater than those under MDI, respectively. Compared with MDI, ADI at 60% FC increased the total cumulative CO2 flux by 27.7%, although the latter decreased the root fork numbers and abundance-based coverage estimators of bacterial communities. Importantly, the tomato yield and water-use efficiency under ADI at 60% FC were intermediate for the various treatments, and the yield-scaled soil gas emissions were significantly lower than those under ADI at 50% and 70% FC. Therefore, ADI at 60% FC is a suitable irrigation method for optimizing tomato crop water-use efficiency and reducing gas emissions. Taken together, these results provide a new perspective for reducing soil gas emissions based on regulating the soil microbial community and root–soil interaction mechanisms through soil water management.