# A Smart and Sustainable Future for Viticulture Is Rooted in Soil: How to Face Cu Toxicity
## 2 Current Challenges
### Soil Management Considering the Root-Microorganism Interactions (Rhizosphere Management)
In addition, soil management also comprises fertilization strategies, which also strongly affect rhizosphere dynamics. For instance, the source of N supply (NO3- or NH4+) affects the pH at the soil-root interface both in annual and perennial plant species [28]. Nitrate-based fertilizers induce an enhanced anion root uptake with proton consumption and a consequent alkalization of the rhizosphere. On the other hand, ammonium-based fertilizers trigger enhanced proton release by roots, resulting in significant rhizosphere acidification. Even though nitrate usually predominates over ammonium in agricultural soils due to the very rapid microbial nitrification processes, preferential ammonium uptake might still occur in acid soils, at low soil temperatures, or shortly after the application of ammonium fertilizers, organic fertilizers and/or nitrification inhibitors [28]. Soil management should thus comprise fertilization-induced root activities, since Cu availability in soil is strongly pH dependent and might undergo mobilization processes, exacerbating its toxicity. Moreover, an adequate nutritional balance for a crop seems to be decisive in mitigating the effects of Cu toxicity when the metal is already present in relevant quantities. Vineyards in calcareous soils represent a clear example. In fact, in this case, the edaphic conditions (essentially soil pH values) should theoretically restrain the availability of Cu to the plants. However, if the Fe availability for crops becomes limited as a consequence of the chemical-mineralogical nature of the soil, the activation of the plant's adaptive responses to this deficiency (including the acidification of the rhizosphere [98]) could transform the Cu problem from potential to real. The complexity of rhizosphere dynamics highlights that soil management, and particularly the management of nutrients, in agricultural agroecosystems such as vineyards needs a comprehensive overview and an appropriate knowledge of the soil-plant system and its dynamics. Indeed, such knowledge could be crucial in counteracting the negative effects of toxic concentrations of heavy metals like Cu and/or exploiting beneficial synergism between elements to benefit the agricultural production. Future studies should therefore focus on a holistic approach that also includes the third main actor involved in rhizosphere processes, i.e., microorganisms. Even though microorganisms are known to increase plant growth and stress resilience, little is known about the effect of Cu stress on their composition and functionality in the rhizosphere in real agroecosystems such as vineyards. To date, most studies have been lab-based and recreate artificial metal stress conditions; thus, they still provide an insufficient understanding of the microbiome functioning and the mechanisms of plant-microbiome-soil interactions. Large-scale experiments at the field level are thus essential in order to give a complete overview of the effect of Cu on the complex interplay between soil, plants and microorganisms involved in the biogeochemical cycles of nutrients at the agroecosystem level.