Effects Of Root Pruning Agent With Copper Ions On Morphology,physiology,and Function Of Containerized Golden Dewdrop(duranta Erecta)seedlings

Copper is a necessary microelement for plant growth.Excessive copper would affect plant growth,metabolism,and even cause toxicity,which is the theory of chemical root pruning of container-grown seedlings.The screening and evaluation of appropriate concentrations of copper,and their impacts on the physiological functions of roots and above-ground growth have not been systematically and deeply studied although the technique has been applied.Contain-grown Duranta erecta seedlings were used to investigate the effects of different concentrations of copper hydroxide（Cu（OH）₂）（40,80,100,120,140,160 g/L）on the morphology,structure,and function of roots;the distribution,accumulation,and transfer of copper ions in the vegetative organs of the roots,stems,and leaves;the responses of aboveground growth,morphology,physiological function,nutrient uptake,and transport capacity to high concentrations of copper ions.In addition,hydroponic culture experiment on the roots of D.erecta with copper ion concentrations of 0,0.05,0.5,5,50,and 500 mg/L was carried out to further elucidate the functions of copper ions on the roots and plant growth of containerized seedlings.The results are as follows:（1）40 and 80 g/L Cu（OH）₂ did not significantly control the root entanglement of container-grown D.erecta seedlings.140 and 160 g/L Cu（OH）₂ best controlled root circling apparently,but the negatively affected the growth and physiological functions of roots and leaves.The flowering number decreased by 54.5%,the contents of phosphorus,calcium,and soluble sugars in leaves decreased by 19.7%,20.5%,and 38.8%,and the specific leaf weight decreased by 13.1%compared with the control.（2）100 and 120 g/L Cu（OH）₂ not only effectively controlled root entanglement,but also improved nutrient absorption and lateral root germination which resulted in even distribution of roots in the container.100 and 120 g/L Cu（OH）₂ increased plant height by 80.4%,carotenoids content by 44.6%,root biomass by 32.7%,root tissue density by 34.3%,root activity by 32.4%,magnesium content by 85.6%,and potassium content by 64.1%than the control.120 g/L was more suitable than 100 g/L based on all physiological parameters.（3）Root is the main organ to absorb and accumulate copper ions.The copper contents in the roots,stems,and leaves of D.erecta seedling increased with the Cu（OH）₂ concentration.On average,the copper transport coefficient of seedling grown under the Cu（OH）₂ treatments was 14.0%lower than that in the control,indicating that roots block the upward transport of copper.（4）On average,the lignin content of the roots under Cu（OH）₂ treatments was 25.2%higher than that in the control.The cell walls of the old roots were damaged by high concentrations of copper.Copper ions stimulated more new root germination.The root activity of the mixed roots of the new and old roots did not decrease.（5）The cross sections of root tips under the Cu（OH）₂ treatments were bigger than those in the controls,with the largest at 140 g/L Cu（OH）₂,followed by 120 g/L.There was no significant difference in the cross sections of roots tips between 40,80,and 100 g/L Cu（OH）₂ treatments and the controls.The cortex cells under 140 and 160 g/L Cu（OH）₂ deformed,especially the endodermis and pericycle cells were incomplete under 160 g/L Cu（OH）₂.The epidermis thickness and the damage degree of parenchyma cells increased with the increase of copper ion concentrations.The layer of exodermis was correlated with the effects of copper treatment.（6）Hydroponic culture experiment showed that 5,50,and 500 mg/L copper ions reduced the root activity by 16.1%,21.4%,and 21.6%and inhibited root growth.100 to 120 g/L were the most suitable Cu（OH）₂ concentrations for root pruning of D.erecta seedlings,not only controlling the root entanglement,but also improving lateral root growth and the absorption of nutrients and water.The roots distributed more evenly in the containers.Low concentrations of 40 and 80 g/L Cu（OH）₂ could not effectively control root entanglement and caused damages to some extent.140 and 160 g/L caused toxic effects on roots and aboveground growth although they apparently best controlled root circling.