Innovative Peat-Free Organic Substrates and Fertilizers Influence Growth Dynamics and Root Morphology of Fagus sylvatica L. and Quercus robur L. Seedlings One Year After Planting

This study evaluated the effects of six innovative peat-free substrate formulations, combined with either a conventional solid fertilizer or a novel liquid fertilizer developed by the research team, on the early growth and root morphology of Fagus sylvatica L. and Quercus robur L. seedlings. Treatments were analyzed through two-way ANOVA and species-specific linear regression models. Following one year of field growth, survival rates remained high across all treatments. While R22 (a peat-free substrate with liquid fertilizer) exhibited the highest mean values for seedling height and diameter, only height showed statistically significant variation among treatments (p < 0.05), with no significant differences observed for diameter increment. It was further, revealed that seedlings treated with peat-free substrates and liquid fertilizers exhibited adequate survival, with several combinations especially R22 showing comparable performance to traditional peat-based media with solid fertilizer. Root morphological traits, particularly fine root length (≤0.50 mm) were strong predictors of above-ground growth in F. sylvatica, but less so in Q. robur, which relied more on total root length. The results highlight species-specific root–shoot coordination strategies, with beech exhibiting above-ground growth pattern and oak a gravitropic one. The findings concluded that R22 substrates confirmed exceptional performance with enhanced root growth comparable to peat after one year of forest planting, indicating strong potential for future development without the environmental concerns associated with peat use.