Copper pruning improves root morphology and structure as well as growth of container-grown Ligustrum lucidum seedings.

It is unclear how high concentrations of copper affect the structure and function of roots in the process of controlling root entanglement in containers although copper pruning technology has been widely applied. One-year-old glossy privet (Ligustrum lucidum) seedlings were treated with latex carrier (T1), 100 g L^{− 1} Cu(OH)₂ in combination with latex (T2), and a control (T0) without latex and Cu(OH)₂. The roots were classified into seven classes according to diameter and six root orders by branching order. There were 6 root orders under the T2, one more than that under the T1 and T0. The length sum of the first to fourth root orders under the T2 was 52.4% and 132.0% higher than that under the T1 and T0. The T1 treatment significantly increased the length of the finest roots less than 0.50 mm in diameter, especially the roots less than 0.25 mm in diameter. No root circling was observed under the T2 treatment where the length of the tap root decreased and root volume increased. The T2 treatment significantly improved the plant height (+ 62.2% and + 24.1%), maximum net photosynthetic rate (+ 70.5% and + 63.8%), leaf area (+ 4.10% and + 37.6%), and total leaf number (+ 143.0% and + 66.9%) compared to the T0 and the T1. Latex treatment enhanced the growth of the lateral roots by increasing humidity and temperature in the containers but could not control root circling, whose improvement mechanism was different from that of copper. [ABSTRACT FROM AUTHOR]