Physiological performance and biomass production of two ornamental shrub species under deficit irrigation

Drought acclimation is attained by avoidance mechanisms in the short term and by adaptation changes in the long term. In this study, we applied deficit irrigation at nursery stage to elicit species-specific physiological responses and biomass production in two ornamental shrub species, comparing two settings: open air (OA) and greenhouse (GH). Viburnum opulus L. and Photinia x fraseri ‘Red robin’ were compared under three irrigation levels: severe water deficit (SWD), moderate water deficit (MWD) and control (C). In both experiments, SWD induced lower values of water potentials in both species whereas MWD had similar effects to C. In OA, SWD reduced earlier stomatal conductance in V. opulus and photosynthesis rate in P. x fraseri and in GH V. opulus showed a reduction of gas exchange even in MWD. P. x fraseri showed greater stomatal control capacity. In contrast, treatments did not affect PSII efficiency even if P. x fraseri proved a greater capacity to differentiate the I–P phase of the fluorescence transient in SWD conditions. In both experiments, SWD and MWD affected leaf area by lowering the number of leaves in P. x fraseri and reducing leaf surface in V. opulus. Moreover, V. opulus showed early leaf senescence and premature fall. Deficit irrigation had effects also on leaf characteristics: smaller leaf area unit in V. opulus, reduced biomass and leaf mass per area and succulence in both species, increase of spongy tissue thickness. Eventually, we can state that P. x fraseri can withstand 30 % evapotranspiration, while maintaining functionality.