EFFECTS OF IRRIGATION TREATMENTS ON PHYSIOLOGICAL PARAMETERS IN PHOTINIA × FRASERI 'RED ROBIN' AND IN VIBURNUM 'LUCIDUM' GROWN UNDER DROUGHT CONDITIONS

The aim of this research was to evaluate the effects of different irrigation treatments on plant development and photosynthesis performances of two broadleaf hedge shrubs species, Photinia × fraseri ‘Red Robin’ and Viburnum odoratissimum, also known as Viburnum ‘Lucidum’, in order to assess their adaptability to drought stress conditions and to optimise their use in urban hedges. The plants were grown in pots filled with peat and pumice (1:1) inside a greenhouse placed in central Italy during summer-autumn season. Treatments consisted in four different irrigation regimes differentiated by water restitution when substrate moisture reached value of 73%, 66% or 80% of container capacity plus a treatment where the moisture was maintained constantly at 73%. The irrigation was managed automatically by FDR sensors. Net photosynthesis, transpiration, stomatal conductance, water use efficiency, chlorophyll a fluorescence and biometric parameters were periodically monitored during the experiment. A parallel experiment was conducted by growing these two species in open field with different irrigation frequencies with the goal to evaluate their behavior under natural conditions, similar to those typical in urban landscape. Photinia ‘Red Robin’ showed a higher adaptability to water stress, especially when water supply was reduced in terms of irrigation frequency. On the contrary, Viburnum ‘Lucidum’ showed a lower adaptability; in fact, less stressed treatments showed more developed plants with respect to the other ones.