Micro/nanobubble-aerated drip irrigation affects saline soil microenvironments and tomato growth by altering bacterial communities

Abstract

The purpose of this study was to elucidate how micro/nanobubble-aerated drip irrigation affects the rhizosphere soil and root endophytic bacterial communities of crops grown in saline soil and to explore the microecological mechanism through which this irrigation promotes crop growth under these conditions. This study investigated the responses of root system architecture, the root zone soil microenvironment, and the rhizosphere soil and root endophytic bacterial communities to micro/nanobubble-aerated drip irrigation at different dissolved oxygen (DO) concentrations (5, 15, and 30 mg·L−1, denoted DO5, DO15, and DO30, respectively). Additionally, this study analyzed the changes in the root-soil interdomain bacterial community network as well as their relationships with root system architecture, the root zone soil microenvironment, and tomato yield. The results showed that the soil available nitrogen concentration and available phosphorus concentration in DO30 were 1.54 and 1.78 times greater than those in the noncultivated soil used as a control (CK); the mean diameter of the root system was 72.35% and 27.85% greater than that under DO5 and DO15, respectively; the root volume was 129.64% and 203.14% greater than that under DO5 and DO15, respectively; and the Shannon index and the number of characteristic species (genus level) of rhizosphere soil bacterial communities increased significantly. The root microenvironment created by DO30 was conducive to enhancing the metabolism of bacterial communities in the root-soil continuum and promoting tomato growth. The tomato yield was 56.11% and 14.09% greater than that under DO5 and DO15, respectively. Compared to the CK treatment, the DO15 treatment had 3.86 and 4.66 times greater soil available nitrogen and phosphorus concentrations, respectively, and significantly greater root length and number of forks on the tomato root system, ACE index of the root endophytic bacterial community, and relative abundance of the root endophytic bacterium Paenibacillus. These changes also promoted tomato growth, with the yield of tomato plants under DO15 being 36.82% greater than that under DO5. In general, in mildly saline soil under full irrigation, micro/nanobubble-aerated drip irrigation with different DO concentrations significantly affected the soil microenvironment in the tomato root zone and the root system architecture, resulting in differences in the composition and metabolic functions of the rhizosphere soil and root endophytic bacterial communities, which regulated tomato yield. This study provides a reference for promoting crop production in saline soil by regulating crop rhizosphere soil and root endophytic bacterial communities.