The effects of seed endophytic bacterial consortia isolated from Lactuca serriola on improving soil available phosphorus under phosphorus deficiency

Abstract

Plants have maintained evolutionary relationships with plant-beneficial bacterial endophytes. Some of them live inside the seed, called seed endophytes, are transmitted vertically to the next generation, and are beneficial to the early growth of seedlings. One of the beneficial effects of seed endophytes is alleviating nutrient acquisition, and phosphate-solubilizing bacteria (PSB) are well known for enhancing P uptake by increasing soil P availability. Previous studies revealed the improvement of the P-solubilizing properties of PSB by inoculating it with other microbes. However, the study focused on the variation of P-solubilizing potentials in bacterial consortia is rare. In this study, we selected 7 bacterial strains isolated from the seed of Lactuca serriola. To assess the P-solubilizing properties of bacterial strains, we confirmed the effect of bacterial infection on L. serriola under P-deficiency stress. To further confirm the variations in P-solubilizing properties of bacterial consortia, we constructed dual-species bacterial mixtures and compared their effects on L. serriola with single inoculations. Among the 7 isolates, 6 strains improved the soil available P under P-deficiency stress compared to the uninfected control. Compared to the single isolate inoculation and the uninfected control, bacterial mixture inoculations composed of Kosakonia cowanii SD1 and Pantoea dispersa SD25 (D1+25), Xanthomonas spp. SD2 and Stenotrophomonas maltophilia SD8 (D2+8), and SD2 and Paenibacillus hunanensis SD13 (D2+13) enhanced the availability of P. These resulted from the synergistic effects among bacterial isolates in solubilizing insoluble P in soils. Synergistic effects of D1+25 on P-solubilizing were also confirmed in the NBRIP medium containing tricalcium phosphate. However, synergisms were not observed for D2+8 and D2+13 in the medium, which means those consortia are involved in different mechanisms of solubilizing insoluble soil P. Consequently, we showed synergistic effects of seed endophytic consortia on P-solubilizing properties under P-deficiency, which were connected to different mechanisms of P solubilization