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Università degli studi di Catania (2010)

Risposta di specie ornamentali allo stress idrico

Toscano, Stefania

Titre : Risposta di specie ornamentali allo stress idrico

Auteur : Toscano, Stefania

Université de soutenance : Università degli studi di Catania

Grade : Dottorato di Ricerca 2010

In the areas characterized by Mediterranean climate, long periods of water deficit during the spring-summer season together with high temperatures, could determine severe water stress in many ornamental species utilized for urban landscape. Moreover, it is not always possible or convenient to satisfy plant water requirements, both in the nursery and in the following growth stages. Therefore, the growth and survival of these species is linked to their capacity to increase the water use efficiency. Nevertheless the importance of these issues, little investigation has been done on water stress of ornamental shrubs, and especially in the ones utilized for landscape. However the new trends on â sustainable landscapingâ have paid the attention on the individuation of biological and technical tools for a better valorization of water resources. In this frame, the general aim of the PhD thesis was to study, on several ornamental species, the effect of water stress determined by solutions with different osmotic potential during germination and by different restitution of water loss with evapotranspiration during growth cycle. The experimental trials concerned : A) The effects on water stress on germination and seedling growth in sunflower (Helianthus annuus L.). B) Morpho-physiological response of ornamental shrubs in different water stress conditions. C) Morpho-physiological mechanisms of water stress recovery in ornamental shrubs. The specific aim for each trial was : A) Study on six sunflower cultivars the effects of different water stress conditions on germination rate and seedling growth rate ; B) Analyze the behavior of several ornamental shrubs subjected in the first period of growth cycle to water stress to individuate the tolerance on water deficit in the substrate. Moreover the main mechanisms morpho-biometrical and physiological have been investigated. C) Evaluate on five ornamental shrubs largely used in the landscape, the recovery capacity to water stress after periodical cycles of suspension/recovery of irrigation. In the trial on the evaluation of water stress imposed with different osmotic potentials on sunflower germination, different results were obtained : a) the osmotic potential threshold (below this value germination does not start) ; b) different behavior of the studied cultivars in relation to water stress and germination ; c) the possibility to enhance the germination trough the adoption of solutions with low osmotic potentials. The different results in relation to the cultivars in the two steps (seed and seedling growth stages) need further investigation considering the noticeable interest to effectuate a quick and easy screening for evaluation of genotypes to water stress. The response of ornamental shrub seedlings to water stress has considered the plant changes to different water content in the substrate for the whole cultivation period and to frequent cycles of suspension/recovery of irrigation. Results showed that species seemed to be available in environments characterized by scarce water resources, and exhibited a different capacity to increase water efficiency. The tolerance to water stress is linked to morpho-biometrical and physiological changes, which have involved the photosynthesis and stomatal conductivity. In low water availability less tolerant species showed a reduction in leaf area, while the tolerant ones have increased the root systems. Among the physiological mechanisms, the modification of stomatal conductivity appears to be the main strategy to avoid water loss. However, as showed by the many physiological processes investigated, species showed a certain capability (different among the species) to recover their functional efficiency at the end of unfavorable period.


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