Effects of B. licheniformis SA03 on the photosynthesis of Chrysanthemum plants under saline–alkaline stress. After 10 days of bacterial inoculation, the non-inoculated (NI) and inoculated (I) were subjected to saline–alkaline treatment for 2 and 4 weeks, respectively. The treated plants were used to measure (A) total chlorophyll content; (B) Fv/Fm; (C) ΦPSII; and (D) Pn. In addition, transmission electron micrographs of chloroplast ultrastructure in mesophyll cells of plants. Chloroplast ultrastructure of the non-inoculated (E) and inoculated plants (G) before the stress treatment, and (F,H) indicated locally amplified view in (E,G), respectively. Chloroplast ultrastructure of the non-inoculated (I) and inoculated plants (K) after the stress treatment, and (J,L) indicated locally amplified view in (I,K), respectively. Scale bar = 1 μm. BS, before the stress treatment; AS, after the stress treatment. Data are expressed as the mean values of three replicates (±SE) with 10 plants each. Different letters indicate significant differences using two-way ANOVA followed by the Duncan’s multiple range test at P < 0.05.