Selenium fertigation with nanobubbles influences soil selenium residual and plant performance by modulation of bacterial community

Although selenium (Se) is an essential microelement for humans and animals, it is a potentially toxic element due to its bioaccumulation potential. In this study, Se fertilizer was supplied in a greenhouse vegetable (cucumber) plantation using an innovative system consisting of nanobubbles (NB_Se) and compared to that under conventional conditions of fertigation (C_Se) with six doses. The results revealed that NB_Se significantly reduced soil Se accumulation (38%-144%) and increased cucumber Se content compared with the C_Se treatments at the same Se dose. NB_Se significantly lowered the soil bacterial diversity, with an initial increase and then decrease with the Se doses. Bacterial associations and potential keystone taxa also differed between the NB_Se and C_Se. The greater abundance of oxidizing bacteria (indicated by the function composition of bacterial community) and the improved soil redox environment created by NBs sustained more available Se for plants, leading to a reduction in soil Se residual and an increase in the plant Se content. Our results highlight the feasibility and efficiency of NB_Se and demonstrate the important implications of Se for the maintenance of soil health and sustainability.