The type and degree of salinized soils together shape the composition of phoD-harboring bacterial communities, thereby altering the effectiveness of soil phosphorus cycling.

Limitations in soil nutrient content, particularly phosphorus (P), are key factors constraining saline soil ecosystems. Soil phosphorus-cycling functional microorganisms contribute to the conversion of insoluble phosphorus and increase available phosphorus (AP) levels in phosphorus-deficient soils. However, there is limited knowledge on how soil phoD-harboring bacterial communities regulate AP availability across varying salinization types and degrees. This work evaluated the diversity, composition, assembly, and co-occurrence network properties of phoD-harboring bacteria, and explored their relationship with AP in salinized soils of Ningxia. First, TP, APi, and CaP levels were high in all salinized soils, whereas bioavailable fractions (AP, MBP, CaP, and CaP) were significantly low, limiting plant phosphorus uptake. Notably, the phoD gene, which is the most abundant functional gene involved in phosphorus cycling in saline soils, exhibits a pronounced salt-stress attenuation pattern along with the Shannon and Chao1 indices of the phoD-harboring bacterial community. Consistent with this pattern, the network complexity and stability of these bacteria were overall negatively affected by saline stress pressure when compared to non-saline soils. Furthermore, as evidenced by the distribution variations among bacteria such as Bradyrhizobium, Skermanella, Pseudomonas, Streptomyces, and Mesorhizobium, the type and degree of salinization jointly shape the composition of soil phoD-harboring bacterial communities. Importantly, the composition of these bacteria communities significantly regulates alkaline phosphatase ALP activity, thereby increasing soil AP levels. Consequently, the type and degree of salinized soil can indirectly regulate AP levels by influencing the composition of the phoD-harboring bacterial community. The research findings highlight that the composition of the phoD-harboring bacteria community is critical for the regulation of phosphorus efficiency in saline-affected soils, which holds significant theoretical and practical implications for the management of phosphorus in salinized soils and sustainable agricultural practices.