Forests strongly depend on natural nutrient resources since fertilization is not a common forest management practice in most parts of the world. Soils and above- and belowground interactions play a crucial role in regulating the retention, distribution, and uptake of nutrients. The high relevance of nutrition for health and productivity of forests has been demonstrated by recent research data obtained by extensive forest monitoring around the world. For example, nutrient availability was the most decisive factor explaining net forest ecosystem productivity (NEP) for a global population of 92 forest sites (Fernández-Martínez et al., 2014). Also, changes in phosphorus (P) and nitrogen (N) nutrition have been emphasized in recent studies on European forests (Jonard et al., 2015; Etzold et al., 2020). These findings stress the necessity of addressing forest nutrition via holistic ecosystem approaches (Figure 1), as was recently outlined for P (Lang et al., 2016).