Influence of container type and substrate composition on photosynthetic productivity and chlorophyll content in the leaves of container-grown apple plants

Container production of apple nursery trees is increasingly used in intensive horticulture because it improves transplant survival and allows flexible marketing; however, restricted root volume makes plant performance highly dependent on contai n er design and the physical and agrochemical properties of the growing medium. This study evaluated how container type and substrate composition affect photosynthetic performance of ‘Champion’ apple ( Malus domestica Borkh .) nursery trees grafted on two contrasting rootstocks (‘M.9’ and ‘MM.106’) in Kyiv region (Ukraine). A field container experiment was conducted in 2024–2025 at a commercial nursery site. Trees were grown in 12-L containers of two designs (air-pruning Air-Pot type and standard plastic container C12) filled with three substrates: peat; peat + conifer bark (1:1); and peat + conifer bark + sandy loam (2:1:1). Net photosynthetic productivity was determined in vivo as the 24-h increase in leaf dry matter per unit area, and chlor o phyll a and b contents were quantified spectrophotometrically ; total chlorophyll and the chlorophyll a/b ratio were calculated. Substrate composition was the dominant factor controlling net photosynthetic productivity across rootstocks and ages, with peat ensuring the highest rates and the peat + bark (1:1) mixture causing a significant decline, while container type and interactions were non-significant. Chlorophyll accumulation was rootstock-dependent: ‘MM.106’ showed consistently higher total chlor o phyll and greater pigment stability across treatments than ‘M.9’. Maximum pigment concentration was recorded in the peat + bark substrate in the C12 container, whereas the chlorophyll a/b ratio was significantly influenced by rootstock and container design, reflecting genotype-specific regulation of light-harvesting complexes. Overall, photosynthetic efficiency in container-grown apple nursery trees is primarily determined by substrate composition, and appropriate substrate optimization can co m pensate for differences in container design, supporting stable physiological performance and nursery tree quality.