[Mechanisms of Salinity Affect Microbial Nutrient Metabolism in Coastal Saline Soils]

Microbial elemental utilization strategies play a crucial role in regulating soil organic carbon accumulation. However, the mechanisms of microbial metabolic limitations and elemental utilization efficiency in saline soils are unclear, limiting our understanding of how microorganisms in saline soils participate in organic carbon and nutrient cycling processes. Therefore, this study employed enzyme stoichiometry and ecological stoichiometric models to analyze the effect of microbial metabolic characteristics in agricultural and natural soils with salinity in the coastal region of eastern China. This study compared the microbial metabolic characteristics and elemental utilization efficiency in low-salinity and high-salinity soils. Based on this, we explored the contributing factors of microbial elemental utilization efficiency under different salinity conditions, integrating soil physical, chemical, and microbial properties. The results indicated that compared to those in low-salinity soils, microbial carbon and phosphorus limitations significantly increased in high-salinity soils, while microbial carbon and phosphorus utilization efficiencies decreased. In contrast, compared to those in natural soils, microbial carbon and phosphorus limitations significantly decreased in agricultural soils, leading to increased microbial carbon and phosphorus utilization efficiencies. Microbial carbon and phosphorus utilization efficiencies were influenced by available organic carbon and available phosphorus in agricultural soils, whereas microbial carbon and phosphorus limitations impacted them in natural soils, respectively. Under high-salinity conditions, soil chemical properties had the most significant effect on microbial carbon and phosphorus utilization efficiencies, while under low-salinity conditions, microbial properties and soil chemical properties were the primary influences on carbon and phosphorus utilization efficiencies, respectively. Structural equation modelling results indicated that microbial carbon limitation and phosphorus utilization efficiency were the two key factors regulating microbial carbon utilization efficiency. In summary, compared to in low-salinity soils, microbial metabolic limitations increased, and elemental utilization efficiencies decreased in high-salinity soils in the coastal region of eastern China. Therefore, revealing the patterns of microbial elemental utilization and their key influencing factors under different salinity conditions is of significant theoretical importance for guiding organic carbon accumulation and fertility enhancement in saline soils.