Research progress in effects of artificial light supplementation on the growth and development of fruit trees

Abstract: Fruit trees, as important economic crops, are significantly influenced by a variety of environmental factors, with light playing a particularly crucial role. Light not only serves as the primary energy source for photosynthesis, but also has a significant impact on the growth and development of fruit trees. The growth and development of fruit trees are influenced by various factors, including light quality, intensity, photoperiod and distribution. These light- related factors regulate multiple processes such as morphogenesis, flowering and fruiting. As an artificial light source, the supplemental lighting for plants can provide additional light to them, which plays a crucial role in regulating the growth and development of fruit trees, increasing yield and enhancing fruit quality. The advancement in science and technology has facilitated the gradual integration of artificial lighting technologies with horticulture, with applications extending to vegetables, flowers, fruit trees and other crops. The most commonly used forms of supplemental lighting include fluorescent lamps, high-pressure sodium lamps and LED lamps.Fluorescent lamps and high-pressure sodium lamps are characterized by high energy consumption and operating costs. Additionally, they contain various harmful substances, such as mercury and sodium, making waste disposal a significant environmental hazard. In contrast, LED lamps offer a broad spectral range, specific wavelengths, high efficiency, minimal heat dissipation, long lifespan, adjustable light quality and intensity, and low energy consumption, and also are free from mercury, sodium and other hazardous substances. Moreover, waste generated from LED lamps can be recycled without environmental contamination. These attributes have led to the increasing adoption of LED lamps as the preferred choice for plant lighting. Red and blue lights are key components of photosynthetically active radiation in natural light. Red light is primarily absorbed by chlorophyll, increasing chlorophyll content in leaves and promoting photosynthesis. Additionally, red light promotes the elongation and growth of roots and stems of fruit trees, which is beneficial for shaping tree morphology. Blue light is absorbed not only by chlorophyll but also by carotenoids. It influences plant growth, morphology and physiological metabolism, promotes stomatal opening, and enhances stomatal conductance, transpiration rate and photosynthetic efficiency in fruit trees. Different tree species have varying light requirements, and different red-to- blue light ratios have distinct effects on the same species. Based on the variety, growth stage and desired indicators of fruit trees, high-quality production can be achieved by adjusting the red and blue light ratio. Insufficient light can significantly inhibit the photosynthesis of fruit trees, leading to a reduction in photosynthetic products, which in turn affects the normal growth and development of fruit trees. This is characterized by weak-vigour trees, yellowing leaves, poor flower bud differentiation, severe flower and fruit drop, small fruit size and poor quality. On the other hand, excessive light also negatively impacts fruit trees. Overexposure can cause sunburn on leaves and even fruits, damage chloroplast structures, reduce photosynthesis and impair nutrient absorption in the affected areas, ultimately hindering the normal growth of fruit trees. In addition, uneven light quality distribution can cause the phenomenon of light spots on plants. Uneven light distribution in the canopy of fruit trees results in insufficient light reaching certain areas, leading to uneven growth and affecting the overall growth potential and yield distribution on the tree canopy. This paper summarizes the development process in plant supplemental lighting and reviews the effects of light quality, intensity, duration and distribution on the growth and development of fruit trees. Additionally, future research directions for artificial lighting in fruit cultivation are proposed, aiming to provide a reference for further studies on artificial light supplementation for fruit trees.