Microbial composition in saline and alkaline soils regulates plant growth with P-solubilizing bacteria

Restoration of coastal wetland vegetation faces hurdles from salinity and alkalinity, especially due to high total soil phosphorus (P) with low bioavailability. P-solubilizing bacteria (PSB) can aid by converting organic and inorganic P forms into bioavailable phosphate. However, PSB's impact on nutrient availability and plant growth in coastal soils remains unclear due to salinity-alkalinity interactions. Potted Experiments used Suaeda salsa inoculated with salt-alkaline-tolerant PSB strains, Bacillus sp. DYS211 and Exiguobacterium sp. DYS212. Bacterial solution was applied to the soil twice during plant growth. Microbial diversity and composition in rhizosphere bacteria and fungi were studied, alongside soil properties and plant growth. PSB affected rhizosphere microbial composition but not diversity in non-stressed conditions. Under alkalinity, the microbial composition varied more than under salinity stress or mixed stress, suggesting the alkalinity's stronger influence. This is crucial for wetland ecosystem resilience. Microbial sensitivity to pH was reflected in diversity indices, notably a 20 % and 100 % increase in Shannon and Chao indices, respectively, under alkaline compared to salinity. Saline/alkaline stress was the primary driver of rhizosphere microbial diversity and composition, overshadowing PSB addition. Without salts, PSB inoculation decreased plant biomass by 4 % (DYS211) and 13 % (DYS212) due to limited P-solubilization. Under saline and alkaline stress, PSB inoculation decreased soil pH and increased available P, which shift in soil nutrient content then drove the microbial diversity and composition of the rhizosphere, thereby increasing resistance and consequently raised plant height and biomass. Soil total nitrogen (N), P, and potassium (K) ratios mainly shaped fungal communities, while pH and the ratios of ammonium, available P, and K primarily governed bacterial diversity and composition. It reveals specific ecological niches and strategies of fungi and bacteria. Regulating soil pH and nutrient ratios optimizes rhizosphere microbiome, ultimately promoting plant growth.