Micro/nanobubble-oxygenated drip irrigation under excessive irrigation conditions improves tomato yield in mildly saline soils by regulating rhizosphere and root endophytic bacterial communities

Abstract

The purpose of this study was to explore the microecological mechanism by which micro/nanobubble-oxygenated drip irrigation promotes the growth of crops in saline soil under excessive quantities of irrigation water. This study focused on investigating the response of root bacterial communities to the cumulative effects of excessive irrigation water at different dissolved oxygen (DO) concentrations and analyzing the changes in the root–soil interdomain bacterial community network and their relationships with the soil microenvironment in the root zone and tomato yield. Compared with the noncultivated treatment in saline soil (CK), the high-DO concentration treatment (30 mg·L⁻¹, i.e., DO₃₀) led to a 94.51 % reduction in the soil electrical conductivity (EC) in the root zone, and the Shannon index of the rhizosphere soil bacterial communities increased by 3.94 %. DO₃₀ significantly increased the relative abundance of Bdellovibrionota, which are nitrate metabolism-related root endophytic bacteria, and Sphingomonas, which are root endophytic bacteria with a nitrogen fixation function. Additionally, the average root diameter and root volume of the tomato root system increased by 51.93 % and 151.36 %, respectively, compared with those under the low-oxygen (5 mg·L⁻¹, i.e., DO₅) treatment. These changes enhanced the influence of root–soil bacterial communities on tomato growth; therefore, the tomato yield increased by 87.20 % and 13.22 % compared with that under the DO₅ and moderate-DO concentration (15 mg·L⁻¹, i.e., DO₁₅) treatments, respectively. Compared with that under the CK treatment, the Shannon index of the rhizosphere soil bacterial community under the DO₁₅ treatment increased by 4.34 %, and the relative abundances of the beneficial root endophytic bacteria Nitrospirota, Myxococcota, Acidobacteriota, and Gemmatimonadota significantly increased. However, the effects on average root diameter, root volume, and soil EC reduction in the root zone were inferior to those under DO₃₀, limiting nutrient uptake by the roots. As a result, the yield was lower than that under DO₃₀ but 36.82 % higher than that under DO₅. Therefore, when micro/nanobubble-oxygenated drip irrigation under excessive irrigation conditions was used to promote tomato production in saline soils, DO₃₀ was preferentially recommended, followed by DO₁₅.