Winter drying injury of Ligustrum lucidum associated with water and energy imbalance

Abstract

To prove the theory that meteorological factors, especially winter drying events, usually affect trees by inducing water and energy imbalance, systematic studies of winter drying damage to Ligustrum lucidum trees in Shandong, China in 2018 were performed by analyzing digital and thermal images of the trees and integrating the results with meteorological and geostatistical analysis and the results of osmotic stress tests in saturated sucrose solution. The results indicate that sap water can not only be transported upward with assistance from cohesion-tension force, but also can be turned back from the terminals of leaves and branches under the inverse pulling force. Under extreme conditions during winter drying events, the breakage of sap water column and reduction of the terminal tissues or organs occur. Similar “∧”-shaped leaf symptoms can also be induced by freezing, summer drought and osmotic stress. The results support the theory of transpiration surface reduction characterized by unity of freezing and drying. Therefore, severe damage to juvenile plants of Ligustrum lucidum under these conditions may be caused by the combined effects of low temperature, drought, strong irradiation and saline soil as well as by the sensitive status of the plants.