Enhancing salt-stress tolerance in tomato (Solanum lycopersicum): The crucial role of bio-compost and rhizospheric Luteimonas spp

The rhizosphere microbiome, as the ‘second genome’ of plants, greatly extends the ability of plants to cope with various biotic and abiotic stresses. Organic amendments have also been demonstrated to elevate the tolerance of plants to salt-stress. However, the interlinking between rhizosphere microbiome, plant tolerance to salt-stress, and organic amendments remains unclear. Herein, two halotolerant microbial consortia (H1 and H2) expedited the composting process without affecting the quality of the resulting composts. Interestingly, both bio-composts (C-H1 and C-H2), especially C-H1, greatly improved the growth and photosynthetic ability of tomato under salt-stress by 25.63 % to 56.0 %. The levels of superoxide dismutase, peroxidase and catalase activities, and the content of malondialdehyde in tomato by C-H1 were 67.6 %, 76.9 %, 137.4 %, and 276.3 % higher, respectively, than those by the control compost (C). The 16S rRNA profiling analysis revealed that compost fertilization shifted the microbial community in the tomato rhizosphere, leading to a consistent enrichment of Luteimonas and a transient enrichment of Conexibacter, Solirubrobacter, Lactobacillus, and Ureibacillus, especially C-H1. In vitro analysis further confirmed that a Luteimonas bacterium which was over-represent in the rhizosphere of bio-compost-fertilized tomatoes promoted the growth of root by 29.9 % and 15.8 % at 0.4 % and 0.8 % NaCl, respectively. In conclusion, bio-compost could improve salt tolerance of tomato by stimulating the expression of salt-tolerance-related enzymes and recruiting beneficial Luteimonas spp.