Rice cultivation in saline-alkaline soil shifts the coupling of phosphorus functional genes and salt tolerance genes based on metagenomic analysis

Rice cultivation in saline-alkali soil can improve soil fertility and microbial activity. How this impacts the relative abundance of salt tolerance genes and phosphorus (P) cycling genes in soil, and their relationship, remains unclear. We studied the physicochemical and microbial properties of barren saline-alkali wasteland soil (WL) and saline-alkali wasteland cultivated with rice for 10, 21, or 30 years, in the Sognen Plain of northeastern China. Our results exhibited that rice cultivation in saline-alkaline soil reduced the saline-alkali properties of soil and mitigated osmotic stress to microorganisms. Rice planted in saline-alkaline soil reduced the abundance of microbial salt tolerance genes and the network interactions between salt tolerance and P cycling genes. Compared to 10-year and 21-year rice-planted saline-alkaline soils, rice planted 30 years ago had increased content of labile P, moderately labile P and organic P, resulting the decreases of the relative abundance of genes for organic P mineralization (phoD) and inorganic P solubilization (gcd) and the increase in the relative abundance of genes for low-affinity inorganic phosphate transporters (pit). Additionally, long-term rice cultivation decreased soil pH, leading to a decrease of abundance of inorganic P solubilization genes. The increase of soil P availability mitigated P limitation, resulting in the complexity of the P cycling gene network in 21-year and 30-year cultivated plots lower than in 10-year plot. These results suggest that reclamation of saline land for rice alleviates the effects of soil salinity on microbial activities, enhances soil P availability, and reduces the interaction of P cycling and salt tolerance genes, promoting the microbial P assimilation in soil.