Effects of seedling containers on the growth, flowering, and physiology of purple-leaf Lagerstroemia indica seedling

Abstract [Objective] This study aims to examine the effects of container type and specification on the growth, blooming, and physiology of purple-leaf Lagerstroemia indica seedlings. The goal is to examine the optimal seedling container for the cultivation of purple-leaf L. indica seedlings and to provide basis for effective seedling breeding in containers. [Methods] Taking the excellent new variety ‘Ebony Embers’ of purple-leaf L. indica as research materials. Three type containers, black plastic nutrient cups (C1), white nonwoven beauty planting bags (C2), and black root-control containers (C3), with three specifications (diameter×height, cm) of 16×16 (D1), 21×21 (D2), and 25×25 (D3), were selected to set nine treatments. Seedlings under different treatments were measured for growth, flowering, and physiological indexes. [Results] (1) Different nursery containers had significant effects on the growth, flowering, and physiology of purple-leaf L. indica seedlings. The growth, root system, biomass, flowering period, flower diameter, inflorescence, soluble protein content, soluble sugar content, relative chlorophyll content, net photosynthesis rate, stomatal conductance, transpiration rate, and other indexes in the same container type were increased with the increase in the specification of the containers. (2) Diameter growth, total root length, total root surface area, total root volume, number of root tips, aboveground dry mass, belowground dry mass, total dry mass, and flowering time were greatest in the C3D3 treatment, which was higher than the smallest C1D1 treatment by 817.12%, 108.12%, 94.60%, 75.66%, 144.14%, 135.67%, 228.45%, 164.65% and 34.48%, respectively. Seedling height growth, crown growth, leaf area, and inflorescence length and width were the highest in the C1D3 treatment, which was higher than the lowest C1D1 treatment by 116.05%, 81.39%, 114.95%, 70.44%, and 65.79%, respectively. Relative chlorophyll content and water use efficiency were the greatest in the C3D3 treatment, while soluble protein and soluble sugar content, net photosynthetic rate, and stomatal conductance were the highest in the C1D3 treatment. The intercellular CO2 concentration and water use efficiency did not differ significantly among the treatments. (3) The comprehensive analysis score for each index was as follows: C3D3>C1D3>C2D3 >C3D2>C2D2>C1D2>C2D1>C3D1>C1D1. [Conclusion] The black root-control container performs well in terms of diameter growth, root growth index, biomass, flowering time and diameter, relative chlorophyll content, and net photosynthetic rate. The most suitable container for 2-year-old seedlings of purple- leaf L. indica is the black root-control container with a diameter of 25 cm and a height of 25 cm.