Resilience and variability in soil nematode communities under nickel contamination: the mitigating role of olive trees

This study explores the effect of nickel contamination on the nematode community and assesses whether the presence of olive plants mitigates its impact. Soil samples were collected from both olive-cultivated and bare plots across a gradient of nickel concentrations (40, 70, and 120 ppm) in a Mediterranean agroecosystem. The results indicate that, even at high nickel concentrations (120 ppm), the presence of olive plants promoted the nematode community, while lower concentrations (40 ppm) favored the proliferation of bacterivorous nematodes (i.e., Panagrolaimus). The genus Ditylenchus exhibited resilience and dominance regardless of plant presence, while Aphelenchus also showed high abundance. Furthermore, plant presence maintained significantly higher biodiversity at 120 ppm compared to the intermediate concentration (70 ppm) in plant-absent conditions. In bare soils at 120 ppm Ni, nematode populations were entirely absent, while olive-cultivated soils still supported diverse communities, indicating a strong plant-mediated buffering effect. Diversity profiles and functional indices (maturity, enrichment, and structure index) revealed that olive trees not only buffered the negative effects of nickel but also promoted a more functionally diverse and stable nematode community, shifting dominance from fungivores to bacterivores at lower Ni concentrations. Multivariate analyses further demonstrated that both deterministic (Ni toxicity) and stochastic (plant-driven microhabitat heterogeneity) processes shaped community assembly, with olive trees enhancing resilience under stress. These findings highlight the importance of integrating plant-mediated remediation strategies in managing heavy metal-polluted soils and support the use of soil nematode communities as sensitive bioindicators for soil health assessment under environmental stress.