| The experiments developed in this doctoral thesis look at the effect of different deficit irrigation techniques on three ornamental species widely used in gardening (carnation, geranium and callistemon). 1 and 2-year-old seedlings were grown in pots, and experiments were conducted in controlled conditions (growth chamber) and in nursery conditions (greenhouse). The application of deficit irrigation strategies (moderate deficit irrigation and deficit irrigation outside the maximum flowering phase) in carnation did not affect flowering and reduced excessive plant growth, resulting in a more compact bearing and plants of greater gardening and ornamental value. Plants exposed to deficit irrigation responded by reducing stomatal conductance and leaf area. A decrease in the water content of leaves was accompanied by osmotic adjustment and changes in cell wall elasticity, which prevented loss of turgor and visual damage during water deficit periods. Geranium responded to water deficit by reducing photosynthesis and biomass accumulation, both of which were reversed when irrigation was restored, although the time necessary for full recovery depended on the parameter and on the stress level. Plant response was not only influenced by the quantity of water supplied to the plant, but also by the moment when the reduction was applied. The extent to which flowering was modified depended on the moment when stress was produced, the flowering phase being the most sensitive to water deficit. Deficit irrigation in callistemon produced a reduction of stomatal conductance values from the first weeks following the application of stress and a gradual increase in intrinsic water use efficiency (Pn/gs). Daily water consumption in this species, besides being closely related with climatic variables, depends on the active growth phase and the period of inflorescences formation. Experiments developed in this thesis revealed the response, effects and tolerance mechanisms of these species to water deficit and will enable growers to apply suitable irrigation strategies to reduce consumption and to maintain or even to improve ornamental plant quality. Plants of these species are able to withstand periods of moderate water stress, without losing their ornamental value, but the degree of the water stress imposed is critical for the response of each species. |
