Soil–Forest Floor Interactions Shape Soil Fertility, Nutrient Dynamics, Photosynthetic Performance, and Growth of Castanea sativa Mill. Seedlings

The present study investigated the effects of different soil substrates (mixtures, based on a mica schist-derived soil), on the plant growth, soil chemical properties, nutritional status and photosynthetic parameters of chestnut (Castanea sativa) seedlings. The aim was to produce robust seedlings, suitable for plantations or reforestation of forest ecosystems, while also provide the necessary nutrient input during the early stages of development. A pot experiment was conducted comprising four treatments: (i) CONTROL, consisting of soil derived from mica schist weathering (MS), (ii) MS with inorganic fertilization (MS-FER), (iii) MS amended with forest floor, derived from evergreen broad-leaved trees (MS-EFF); and (iv) MS amended with forest floor, derived from chestnut trees (MS-CFF). Regarding seedlings’ growth, both types of forest floor exerted a positive effect similar to that observed after inorganic fertilization (MS-FER), while all treatments maintained a satisfactory and stable photosynthetic performance; however, an enhancement in leaf chlorophyll content (CCI) was specifically observed under inorganic fertilization. Except Olsen P and exchangeable Mg, which were significantly higher in the MS-FER treatment, all the other soil nutrients were higher either in the MS-EFF, or in the MS-CFF treatments. Overall, both types of forest floor proved effective as organic amendments, suggesting that they could serve as an alternative or complement to inorganic fertilization, potentially reducing fertilizer inputs in chestnut seedling production.