Abstract <p>Rice cultivation in saline-alkaline land affects soil properties, but the mechanistic links between rice cultivation duration, inorganic phosphorus (P_i) fractions, and microbial PLFA (phospholipid fatty acid) remain poorly understood.&#xa0;A chronosequence approach was used to study soils with 0–51 years of rice cultivation. Soil analyses included P_i fractions, PLFA, and phosphorus mass balance to evaluate long-term P dynamics.&#xa0;Rice cultivation increased total P and available P in saline soil. In the 0Y, 1Y, 5Y, and 10Y plots, the percentage of Ca-P fractions represented 64%, 71%, 57%, and 61% of the P_i in the soil. By contrast, 20Y, 29Y and 51Y plots exhibited high proportions of moderately labile P_i fraction (Al-P and Fe-P), accounting for 40–57% of P_i. Poorly crystalline and organic bounded iron oxides in 20Y, 29Y and 51Y plots concurrently higher than that in 0Y, 1Y, 5Y, and 10Y plots. Rice cultivation in saline-alkaline soil increased the microbial biomass P and PLFA and reached the highest level in 29Y and 51Y plots. The mantel test and partial least squares path modeling revealed that soil salinity and alkalinity, organic matter, and Fe/Al oxides played a vital role in the regulation of P_i fractions. P mass balance was higher in 1Y, 5Y, and 10Y plots than in 20Y, 29Y and 51Y plots.&#xa0;Long-term rice cultivation in saline soils improves phosphorus availability, promotes phosphorus uptake by rice, and reduces soil P mass balance. This study provides actionable insights for sustainable P management in saline-alkaline agroecosystems.</p> Graphical Abstract <p></p>