Morpho-anatomical and physiological traits of two Bougainvillea genotypes trained to two shapes under deficit irrigation

Key message: The analysis of the growth behaviour, wood anatomical, and eco-physiological traits of two Bougainvillea genotypes, trained to two shapes and subjected to different irrigation regimes, fully supports the idea that structural properties interact with cultural practices (i.e., training) in determining the adaptive capability of plants, hence their productivity and survival.Abstract: Bougainvillea species are cultivated for landscaping in the arid Mediterranean region. In Bougainvillea spp., secondary xylem and phloem are formed by successive cambia leading to a peculiar stem anatomy which could favour water storage and plant adaptation under drought conditions. To achieve sustainable production of Bougainvillea ornamental shrubs, it is crucial to understand how different genotypes respond to deficit irrigation and how cultural practices, such as canopy training, may interact with morpho-anatomical traits in modifying the plants’ ability to withstand water deficit. A greenhouse experiment was conducted to determine the effects of deficit irrigation on plant growth, ecophysiology, and branch anatomy in two Bougainvillea genotypes [B. × buttiana ‘Rosenka’, B. ‘Lindleyana’ (=B. ‘Aurantiaca’)] trained to globe and pyramid shapes. Irrigation treatments were based on daily evapotranspiration (ET): control (C, 100 % ET) or deficit irrigation (DI, 25 % ET). The two genotypes exhibited morphological adaptations to cope with water deficit, including reductions in dry weight, leaf number, and lamina size. In both genotypes, the DI-induced increase in stomatal resistance was accompanied by a decrease in stomata size. Water deficit triggered adjustments in wood anatomical functional traits, also depending on canopy shape and genotype, favouring either water conduction efficiency or safety against embolism. The occurrence of a safer hydraulic system in the pyramid-trained plants suggests a better control of water transport, thus supporting better growth performance under DI conditions compared to globe-trained plants. Such differences, induced by different canopy-shape trainings, should be considered in the management of DI.