Salt-alkali is the main threat to global crop production. The functioning of phosphorus (P) in alleviating damage to crops from saline-alkaline stress may be dependent on the variety of crop but there is little published research on the topic. This pot experiment was conducted to study if P has any effect on rice (Oryza sativa L.) yield, dry matter and P accumulation and translocation in salt-alkaline soils. Plant dry weight and P content at heading and harvest stages of two contrasting saline-alkaline tolerant (Dongdao-4) and sensitive (Tongyu-315) rice varieties were examined under two saline-alkaline (light versus severe) soils and five P supplements (P0, P50, P100, P150 and P200 kg ha⁻¹). The results were: in light saline-alkaline soil, the optimal P levels were found for P150 for Dongdao-4 and for P100 for Tongyu-315 with the greatest grain dry weight and P content. Two rice varieties obtained relatively higher dry weight and P accumulation and translocation in P0. In severe saline-alkaline soil, however, dry weight and P accumulation and translocation, 1000-grain weight, seed-setting rate and grain yield significantly decreased, but effectively increased with P application for Dongdao-4. Tongyu-315 showed lower sensitivity to P nutrition. Thus, a more tolerant variety could have a stronger capacity to absorb and translocate P for grain filling, especially in severe salt-alkaline soils. This should be helpful for consideration in rice breeding and deciding a reasonable P application in saline-alkaline soil.

Soil microbial communities are vital for saline-alkaline ecosystem functioning; however, their succession during land degradation and their influence on phosphorus (P) transformation remain unclear. To address this gap, this study investigated the dynamics of soil microbial communities and P fractions along a degradation gradient from native grassland to Suaeda salsa vegetation and ultimately to bare land in the Songnen Plain, China. The results revealed that progressive saline-alkaline degradation significantly altered soil properties, increased the proportion of stable P fractions, and reduced microbial alpha diversity. Network analysis revealed that bacterial communities shifted from competition to cooperation along the salinity–alkalinity degradation gradient, indicating a cooperative strategy to cope with environmental stress. Fungal networks exhibit progressively reduced complexity and stability with increasing degradation. Partial least squares path modeling confirmed that soil pH and electrical conductivity directly and indirectly regulated P fractions by reshaping microbial communities, with bacteria exhibiting a stronger total effect than fungi. In conclusion, saline-alkaline degradation drives microbial community succession, which mediates the transformation of soil P into more stable forms and exacerbates P limitation. This study provides a scientific basis for targeted restoration and sustainable management of saline-alkaline ecosystems.