PHYSIOLOGICAL QUALITY OF NURSERY PLANTS FOR URBAN DESIGN AND OVERCOMING TRANSPLANTING STRESS IN ROSA 'KNOCK OUT®'

Transplanted plants in urban area are often affected by drought stress. The physiological status of young plants plays a crucial role in overcoming this problem. When transplanting occurs in urban areas, stress is higher because of poor quality of soil and water, unfavorable environment and difficult management conditions. The aim of this research was to obtain high quality plants capable to overcome problems related to transplanting stress, through innovative management techniques concerning the introduction of different substances in typical substrates used by nursery plant growers. The research was conducted on Rosa ‘Knock Out®’, a typical and much appreciated ornamental woody shrub used in urban landscaping. Plants were cultivated in three growing media. The experiment was conducted in open air in a field located in central Italy, from summer 2011 to spring 2012. The tested substrates were i) the same mix used by plant growers in Pistoia area (peat 50% V:V, coconut fiber 20% V:V, pumice 30% V:V), as a control; ii) the same substrate added with 2 g/L of Luquasorb®, a superabsorbent polymer of potassium polyacrylate used for maintaining water reserve in pots; iii) a substrate in which 20% V:V peat fraction was substituted with urban compost. Chosen parameters for physiological response evaluation were: gas exchanges, Water Use Efficiency, chlorophyll a fluorescence and chlorophyll content in leaf tissues. Physiological aspects were then correlated to the aesthetic quality of plants evaluated by means of biometric parameters. In general, nursery plants grown on Luquasorb® substrate showed the best results in relation to biometrical and physiological parameters. The plants showed a vigorous growth and high water use efficiency. Also the Control substrate resulted in high quality standard plants. Compost substrate produced plants with a higher percentage of roots dry matter in comparison to the other substrates.