Seasonal dynamics and functional diversity of soil nematode communities under treated wastewater irrigation in abandoned agricultural soils

The use of treated wastewater (TWW) for agricultural irrigation is becoming more popular as a sustainable alternative to freshwater due to increasing water scarcity. While considerable research exists on the effects of TWW on soil microorganisms, its impact on soil nematodes, key indicators of soil health remains unexplored. This study assessed the effects of two years of TWW irrigation on soil nematode communities in abandoned fields cultivated with Lavender, Anise, Olive and Pomegranate trees. Seasonal soil samples were analyzed for nematode abundance, community composition and ecological indices. TWW irrigation modified soil nematode community structure, favoring the dominance of bacterivores (Acrobeloides) while suppressing plant-parasitic nematodes (Pratylenchus, Bitylenchus). Nematode-based indices showed no significant differences between TWW- and freshwater-irrigated soils, indicating stable and resilient communities. Seasonal precipitation levels strongly influenced nematode abundances, highlighting environmental resilience. Plant species did not create ecological niches, probably due to the strong influence of precipitation and soil properties; nevertheless, plant establishment increased nematode diversity over time, with omnivores and predators emerging alongside bacterivores and fungivores, reflecting recovery dynamics. Even though TWW irrigation is considered a type of disturbance, it facilitated soil nematode diversity and maintained ecological stability. Properly treated wastewater serves as a sustainable irrigation method that enhances soil health and biodiversity, rendering it a viable alternative for agricultural systems in degraded and water-scarce areas under changing climatic conditions.