Reduced vegetation growth but limited microbial restructuring in soils exposed to road deicing salts

Winter application of road deicing salts creates recurrent pulses of anthropogenic salinity in temperate roadside soils upon snowmelt, yet the impact of such salinity pulses on soil microbial communities remains poorly understood relative to naturally saline and hypersaline ecosystems. Here, using a cross-sectional design, we compared fungal, bacterial and archaeal communities in Estonian control soils, Estonian deicing salt-affected roadside soils, Saudi naturally saline soils, and Saudi hypersaline soils. The Saudi soils were included as an ecological reference outgroup rather than as geographically or edaphically matched controls . Differences in soil electrical conductivity and sodium content defined the main environmental gradient, while soil pH and nutrient contents were of lower importance. Plant height was almost two-fold and biomass more than two-fold lower at deicing salt-affected sites than those at nearby control sites. However, the deicing salt-affected microbial communities retained substantial similarity to local control soils, particularly for bacteria and archaea, indicating moderate restructuring rather than complete replacement. Saudi hypersaline reference soils contained fewer detected taxa and showed greater community differentiation. Limited OTU-incidence-based patterns consistent with convergence were detected for archaea toward both Saudi reference groups and for bacteria toward the Saudi hypersaline group. Responses differed among microbial kingdoms. Fungal diversity declined with increasing soil electrical conductivity. Bacterial communities showed pronounced compositional turnover without uniform diversity loss. Archaeal communities showed comparatively limited restructuring among dominant taxa . Exploratory taxonomy-based functional predictions indicated broad retention of major saprotrophic and chemoheterotrophic profiles, while selected lower-abundance functional categories varied among soil contexts. Overall, deicing salt exposure was associated with substantially lower vegetation growth but only moderate, kingdom-specific microbial restructuring, demonstrating that vegetation and microbial communities can differ markedly in their responses to roadside salinization.