The impact of competitive stress on photosynthetic indices in apple tree leaves

Abstract

The aim of this study was to analyze the impact of planting distance on photosynthetic behavior of apple tree. Apple 'Auksis' was grafted on super-dwarfing P22 rootstock and planted at different distances (0.25, 0.5, 0.75, and 1 m in rows, between rows 3 m). Photosynthetic indices were measured at two heights: 0.8 m above ground inside the canopy and 1.5 m above ground outside the canopy. An average canopy leaf area and dry mass were evaluated in May, June and September. Increased density between apple trees from 0.5 to 1 m led to increased photochemical reflectance index and deceased leaf area. The lower light penetration in denser canopies within small planting distances also resulted in significant decrease of photosynthetic rate. Apple leaves accumulated significantly more dry mass at the beginning of apple maturity and during harvest time compared to spring, thus, no significant differences were found between summer and autumn. A significantly higher index of photochemical reflectance was also observed in the spring and a decreasing tendency was observed from spring to autumn. The optimal photosynthetic response was determined for apple trees planted at 0.75 m distance. The biggest yields per tree were obtained at the widest spacing between trees, whereas the biggest yield per hectare was achieved with the smallest spacing. This work was carried out within the framework of the long-term research program 'Horticulture: agro-biological basics and technologies' implemented by the Lithuanian Research Centre for Agriculture and Forestry.