Effects of salinisation on Cu-contaminated vineyard soils: Assessment of changes in microbial communities and resistance to salt, Cu, and antibiotics.

Climate change increases the risk of soil salinisation in Southern European vineyards. In this study, six of those soils were experimentally salinised, half of which were contaminated with Cu, a widely used fungicide. Changes in soil microbiota were assessed, including bacterial and fungal growth, respiration, carbon use efficiency calculation, and microbial community phospholipid fatty acids composition. The study also investigated whether salinisation induced a shift in the bacterial community toward increased tolerance to salt, Cu, and the antibiotics tetracycline and vancomycin. Results showed that experimental salinisation decreased bacterial growth and respiration, increased fungal growth, and limited fungal, bacterial, and microbial biomass. These effects were strongest in soils with high initial Cu content. In such soils, tolerance to salt stress was more pronounced, and salt-induced tolerance to vancomycin was observed. In contrast, tolerances to Cu and tetracycline antibiotic were not significantly increased by either Cu or salt. Subsequently, the soils underwent leaching, and analyses were repeated. Most changes in microbial parameters and tolerances were reversed, with soil texture being a particularly influential factor. However, leaching caused Cu tolerance in soils that had been salinised and had high Cu content to be greater than in soils that had not been salinised, regardless of whether they had high or low Cu content. After leaching, vancomycin tolerance also became positively correlated with soil Cu content in soils with low Cu levels. This preliminary study explored salinisation effects on soils, revealing possible bacterial resistance linked to past conditions and microbial shifts. Further research is needed to broaden the dataset and explore the underlying mechanisms and microbial species involved.