Effects of different LED light sources on the growth of citrus seedlings

Abstract: 【Objective】Light significantly influences plant growth and development. LED light sources are frequently employed in plant lighting due to their energy-saving property and high efficiency. Consequently, in the present study LED light sources were employed to examine the impact of distinct LED light qualities and light combinations on the growth of citrus seedlings, with the objective of identifying the optimal parameters of efficient light formulations conducive to the growth of citrus seedlings. 【Methods】In this experiment, The total of 9 light qualities including white light (W), red light (R), blue light (B), and polychromatic light (WR1∶1, WB1∶1, RB4∶1, WRB2∶1∶1, WRB5∶4∶1 and WRB5∶ 4∶1+FR) were selected. The impact of varying light quality on the growth of seedlings was investigated. The changes in plant height, stem diameter, leaf area and biomass were quantified and analysed. The spectral proportions suitable for optimising seedling growth were identified according to the growth indexes. The experimental results indicated that a three- factor, three-level orthogonal experiment wouldbe the most appropriate methodology used to investigate the effects of different light combinations on the morphology, biomass, chlorophyll content, photosynthetic characteristics, and chlorophyll fluorescence characteristics of the seedlings. The orthogonal experimental factors and levels are specifically described as follows: photoperiod (12 h/12 h, 16 h/8 h and 18 h/6 h light/dark cycle), light quality (WR1∶ 1, WRB2∶1∶1 and WRB1∶4∶1) and light intensity (100, 150, 200 μmol·m-2 ·s -1 ). Finally, the synthesis was carried out by applying the affiliation function.【Results】The results demonstrated that different light quality treatments had a significant impact on the growth of Citrus reticulata‘Chachi’and Red limonia seedlings. Specifically, the RB4∶1 treatment significantly promoted the growth of plant height, leaf number, leaf area, fresh weight and dry weight of C. reticulata‘Chachi’seedlings. Conversely, the WR1∶1 treatment significantly promoted the growth of plant height, stem diameter, leaf area, fresh weight and dry weight of Red limonia seedlings. In comparison to monochromatic light, the combined light quality was more conducive to the growth of seedlings. Furthermore, increasing the proportion of red light in the composite light can significantly promote the vegetative growth of seedlings. The results of orthogonal experiments demonstrated that an extended period of light exposure could effectively promote the vegetative growth of C. reticulata‘Chachi’and Red limonia seedlings. The plant height, stem diameter, fresh weight, dry weight, chlorophyll content and actual photosynthetic efficiency photosystem Ⅱ (ΦPSⅡ) of C. reticulata‘Chachi’seedlings significantly increased under L6 combination (light period 16/8 h light/dark cycle, light quality white∶red∶blue 1∶4∶1, and light intensity 100 μmol·m-2 ·s -1 ). The Red limonia seedlings exhibited the highest plant height, stem diameter, leaf number, leaf area and fresh weight at L7 combination (photoperiod 18 h/6 h light/dark cycle, light quality white∶red 1∶1, and light intensity 200 μmol· m- 2 ·s - 1 ). The results demonstrated that the light combinations treatments had no promoting effect on the photosynthesis of C. reticulata‘Chachi’and Red limonia seedlings. The duration of illumination and the proportion of red light had a negative impact on the stomatal conductance (Gs), transpiration rate (Tr) and photosynthetic electron transfer rate (ETR) of seedling leaves, as well as the photosynthetic efficiency of the seedlings.【Conclusion】The study found that the growth of C. reticulata‘Chachi’and Red limonia seedlings could be effectively promoted through photoregulation. It is evident that different varieties have specific light quality, light intensity, and photoperiod supplemental light needs. The identification of these differences can provide a theoretical reference for the rapid breeding of seedlings. The RB4∶1 and L6 treatments can be used as a reference for the light supplement of C. reticulata‘Chachi’seedlings, the WR1∶1, and L7 treatments can be used as reference parameters for Red limonia seedlings to supplement light. By reasonably supplementing light, the growth of citrus seedlings can be accelerated and the nursery cycle can be shortened. This study can provide theoretical and practical references for rapid nursery.