Impacts of Ambrosia psilostachya Invasion on Soil Properties and Microbial Communities in Caspian Coastal Ecosystems

Invasive alien plants can profoundly reshape soil properties and microbial communities, thereby disrupting key ecosystem processes. We investigated the impact of Ambrosia psilostachya invasion on soil physicochemical and biological characteristics in Guilan Province, Southwest Asia. Soil samples were collected from invaded and non-invaded sites across three contrasting locations: Anzali Free Zone (AFZ), Anzali Town (AT), and Anzali Beach (AB). We measured soil pH, electrical conductivity (EC), nutrient concentrations, organic matter, organic carbon, microbial biomass, and respiration.Across all sites, invasion by A. psilostachya consistently reduced soil pH while increasing EC. Nitrogen (N), phosphorus (P), and potassium (K) concentrations were generally enhanced, although P showed no significant change at AFZ and AB. Invaded soils also exhibited higher organic carbon, organic matter, and microbial biomass carbon. Microbial activity was markedly stimulated, as indicated by increased basal respiration (BR), substrate-induced respiration (SIR), and respiratory quotient (qCO₂).Overall, our findings demonstrate that A. psilostachya substantially modifies soil chemical and biological processes, creating conditions that may reinforce its establishment and competitive dominance. These insights highlight the role of soil–plant–microbe interactions in the success of invasive weeds and underscore the need for their consideration in management strategies.