Influence of peat-free substrates and fertilization on the morphology of European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) seedlings two years after field planting

Abstract The success of afforestation and reforestation depends to a large extent on the quality of nursery-grown seedlings, which is influenced by substrate composition and fertilization strategies. This study evaluates the effects of peat-free organic substrates and solid vs. liquid fertilization on the growth performance and root morphology of Fagus sylvatica L. and Quercus robur L. seedlings over two year’s growth in the forest. The experiment was conducted in a 2 × 2 × 4 experimental layout using a randomized complete block design with 3 repetitions of each treatment, comprising eight treatments that combined four substrate types (three novel organic substrates and one peat-based control) with two fertilizers (solid and liquid) for two tested species. The results confirmed that peat-free substrates, supported equal seedling development compared to traditional peat substrate. Solid fertilization enhanced height, shoot diameter, and root morphological traits, while liquid fertilization supports more uniform growth across all substrates. Pedunculate oak seedlings showed a dynamic shift in root development, transitioning from an initial dependence on total root length to greater reliance on root surface area and volume after two years of field growth, reflecting species-specific adaptation and the influence of substrate and fertilization treatments on root system maturation. The study further confirmed strong links between root traits and above-ground growth, highlighting the role of optimized nursery treatments in seedling adaptability.