Response of the tomato rhizosphere bacterial community to water–oxygen coupling under micronanobubble oxygenated drip irrigation in mildly saline soil

Abstract

The deterioration of the soil water–air environment due to salinization can reduce soil bacterial activity and cause crop yield reduction. Micronanobubble oxygenated drip irrigation can significantly improve the nonsaline soil water–air environment and enhance bacterial activity, but its effect on salinized soil bacteria is unknown. In this study, we used a tomato cultivation experiment in mildly saline soil to evaluate the responses of the rhizosphere bacterial community to the soil microenvironment created by micronanobubble oxygenated drip irrigation. The results indicated that the soil environmental factors (including soil electrical conductivity, i.e., EC) (r = 0.46) and root length (r = −0.86) had important regulatory effects on bacterial community function, which had significant direct effects on tomato yield (r = 0.46). The moderate dissolved oxygen concentration treatment significantly reduced the EC by 63.22%–73.32% compared with CK (noncultivated soil treatment) and generally increased the root length; however, only the combination of a moderate dissolved oxygen concentration and excess irrigation (A₁₅W_1.2) significantly increased tomato yields by 190.90% compared with A₀W_0.8 (the combination of a low dissolved oxygen concentration and insufficient irrigation) because the irrigation water volume was the limiting condition affecting the benefits of the root length increase. The high dissolved oxygen concentration treatment significantly reduced the EC by 60.36%–92.31% and increased the bacterial community diversity by 4.08%–6.16% compared with CK; these aforementioned changes favored the increase in tomato yield. However, similar to the result of the moderate dissolved oxygen treatments, the tomato yields were significantly higher and among the highest of all treatments only when a high dissolved oxygen concentration was combined with sufficient irrigation or excess irrigation (A₃₀W₁ or A₃₀W_1.2) due to the limiting effect of the irrigation water volume. Therefore, accounting for the changes in EC, soil bacterial community, and tomato yields, A₁₅W_1.2, A₃₀W₁, and A₃₀W_1.2 are recommended for tomato production in mildly saline soils.