## 3 Results and Discussion
### Changes in Soil Cu
#### 3.3.3 Changes of Cu Potential Leaching  
There have been evidences of Cu migrating through soil profiles in vineyards, which pose an important risk for groundwater quality. This risk is especially high for acid soils and soils affected by intensive erosion [70]. The main hypothesis of our study was that climate change, due to increase of degradation of organic matter in the topsoil at higher temperatures, increases Cu leachability from vineyard soils into lower soil profiles or groundwater.  
During the 6-month soil incubation, organic matter degradation occurred and the greatest decrease was seen in the samples exposed to high temperature. However, since the results of Cu fractionation led to the fact that in our selected samples most Cu was bound to a fraction that is difficult to extract (residual fraction, or Step 4) and not to organic matter  
Figure 3: Bioavailability (**a,b**) and leaching (**c,d**) of Cu in soils before and after 6 months’ incubation under no stress (19 \({}^{\circ}\)C and 40% WHC), moisture (19 \({}^{\circ}\)C and 10% WHC), temperature (29 \({}^{\circ}\)C and 40% WHC), and combined stresses (29 \({}^{\circ}\)C and 10% WHC). Different letters denote significant differences between treatments within each soil type and management, according to [PERSON]’s multiple comparison test (\(p<0.05\)).  
(Step 3), the results of the potential leaching of Cu from the soil are even more important and relevant.  
From the results of TCLP extraction (Figure 3c,d and Table S3), we can see that the highest leaching can be expected from the acidic soils, both conventional (3.29 mg kg\({}^{-1}\)) and organic (2.87 mg kg\({}^{-1}\)). On the other hand, leaching from calcareous soils was quite low, 0.37 and 1.15 mg kg\({}^{-1}\) for conventional and organic management, respectively. The pH was measured in soils and in the TCLP extraction solutions, because of its role in the Cu solubilization. We could see that pH increased in treatments with temperature stress at optimal moisture, and the largest increase was observed in calcareous soils (Figure 1). A similar increase in pH was also observed in the extraction solutions with both 0.01 M CaCl\({}_{2}\) and TCLP (Table S3).  
Cu leaching decreased after 6 months of incubation in almost all soil samples as a result of the increase in pH. The only exception was acid conventional soil, where the average pH in the TCLP solution remained similar in all treatments, and Cu leaching increased in all treatments, with the largest increase in treatment simulating temperature stress (29 \({}^{\circ}\)C and 40% of WHC) from 3.29 mg kg\({}^{-1}\) before treatment to 5.04 mg kg\({}^{-1}\) after 6 months. To find out if there are some specific factors affecting Cu leaching from the soil based on soil chemical properties, we calculated the Pearson coefficient (Figure S3).  
Unless TCLP-Cu was strongly correlated with CaCl\({}_{2}\)-Cu, Cu Step 1, and Step 2, it is possible to note a significant negative correlation with either soil pH and TN, that is, a decrement of pH and TN is responsible for an increase of potentially leaching Cu. Surprisingly, neither TOC nor DOC showed a significant strong correlation.