Effect of root pruning on competitive ability in Chinese jujube tree

Abstract

Introduction . The Chinese jujube tree always presents some unfavorable performances because its vegetative growth is very vigorous. Our study was conducted to apply root pruning to test whether it can effectively inhibit the vigorous vegetative growth by regulating the competitive ability of the root system for water and nutrients. Materials and methods . For our experiment, roots were cut at three different distances from the trunk (light, moderate and severe root pruning) on both inter-row sides of jujube trees to the depth of 20 cm. Roots of control jujube trees were not pruned. Then we determined for three years the competitive indicators of Chinese jujube trees including the length, number and thickness of primary branches; photosynthetic characteristics and nutrient concentrations of leaves; hormone contents in the jujube head, flower number and fruiting percentage, yield, and fruit quality. Results and discussion . In the early stage after root treatment, root pruning decreased lots of indicators such as concentrations of nitrogen, phosphorus, and potassium in leaves, photosynthesis, transpiration, stomatal conductance, and intercellular CO2 concentration of leaves, relative to the same indicators as the control group. With the gradual emergence of new roots, these indexes appeared to have adverse patterns with respect to those in the early stage after root pruning. Compared with the control, root pruning significantly decreased the length and number of primary branches and flower number, but thickened primary branches, enhanced fruiting percentage and increased the amount of ethylene release of the jujube head in the whole experiment. Fruit quality was improved with root pruning, as indicated by increases in vitamin C and total sugar and a decrease in titrable acidity. No effects of root pruning were noticed on yield. From our results, we conclude that the removal of the root system at a distance of three times the trunk diameter (severe pruning) from the trunk is the most effective in regulating the competitive ability of the Chinese jujube tree.