Effects of Deficit Irrigation on Leaf Gas Exchange, Water Potential and Biomass of Two Ornamental Species: Photinia × fraseri ‘Red Robin’ and Viburnum opulus L.

The purpose of this study was to examine the effect of deficit irrigation on water relations in two ornamental species at nursery stage with different behavior and water requirement: Photinia × fraseri ‘Red Robin’ (evergreen) and Viburnum opulus L. (broadleaf). The experiment investigated the plant physiological response during the treatment. It was conducted in the nursery of Cespevi (Pistoia, Italy) where three plots of same age individuals grown under three water regimes during four months of acclimation. The control plot received enough water to replace the transpiration loss while two plots were respectively under severe water deficit (SWD=33% C) and moderate water deficit (MWD=66% C). Leaf gas exchange (carbon dioxide assimilation and transpiration) and predawn and minimum water potential were assessed during the study period, eventually the biomass. Carbon assimilation is not affected consistently by water deficit. Similar values between treatments are observed in the morning in both species and measurements at midday evidence markedly high carbon assimilation in C group of Photinia. Leaf transpiration is reduced in SWD although the differences between treatments are minor in both species. On the other hand, predawn and minimum leaf water potentials decreased in SWD. Concerning the biomass allocation, SWD groups in both species recorded lower biomass with major allocation in roots.