Alejandra Navarro

Changes in leaf water relations, gas exchange, growth and flowering quality in potted geranium plants irrigated with different water regimes.

Geranium plants are an important part of urban green areas but suffer from drought, especially when grown in containers with a limited volume of medium. In this experiment, we examined the response of potted geraniums to different irrigation levels. Geranium (Pelargoniumxhortorum L.) seedlings were grown in a growth chamber and exposed to three irrigation treatments, whereby the plants were irrigated to container capacity (control), 60% of the control (moderate deficit irrigation, MDI), or 40% of the control (severe deficit irrigation, SDI). Deficit irrigation was maintained for 2 months, and then all the plants were exposed to a recovery period of 112 month. Exposure to drought induced a decrease in shoot dry weight and leaf area and an increase in the root/shoot ratio. Height and plant width were significantly inhibited by the SDI, while flower color parameters were not affected by deficit treatment. The number of wilting and yellow leaves increased, coinciding with the increase in the number of inflorescences and open flowers. Deficit irrigation led to a leaf water potential of about -0.8MPa at midday, which could have caused an important decrease in stomatal conductance, affecting the photosynthetic rate (Pn). Chlorophyll fluorescence (Fvm) values of 0.80 in all treatments throughout the experiment demonstrate the lack of drought-induced damage to PSII photochemistry. Pressure-volume analysis revealed low osmotic adjustment values of 0.2MPa in the SDI treatment, accompanied by increases in the bulk tissue elastic modulus (epsilon, wall rigidity) and resulting in turgor loss at lower leaf water potential values (-1.38MPa compared with -1.0MPa for the control). Leaf water potential values throughout the experiment below those for Psitlp were not found at any sampling time. By the end of the recovery period, the leaf water potential, stomatal conductance and net photosynthesis had recovered. We infer from these results that moderate deficit irrigation in geranium reduced the consumption of water, while maintaining the good overall quality of plants. However, when SDI was applied, a reduction in the number of flowers per plant was observed.

Changes in tissue-water relations, photosynthetic activity, and growth of Myrtus communis plants in response to different conditions of water availability

Summary The influence of different levels of water deficit on physiological and morphological alterations in Myrtus communis plants was investigated to evaluate their adaptability to such conditions. M. communis plants, growing under greenhouse conditions, were subjected to three irrigation treatments between February and August 2007: a control, and two water deficit treatments. Plants submitted to severe water deficit showed reduced shoot and root dry weights, leaf numbers, leaf areas, and plant heights, while moderate water deficit reduced only plant height. Leaf colour was not affected by either water deficit treatment. Root hydraulic resistance increased in proportion to the level of drought, and lower values of leaf water potential (Ψl) were observed at pre-dawn in both deficit treatments. The absence of osmotic adjustment could explain the reduction of leaf turgor potential at midday. Photosynthesis decreased in both water deficit treatments and was related to stomatal factors, since no significant changes in chlorophyll fluorescence, chlorophyll content, or ion leakage were observed. The highest Ψl values were found in the early morning, and the lowest at midday, in all treatments. The latter coincided with the minimum values of stomatal conductance. Significant differences in Ψl values during the day were noted between treatments, but were always highest in the control. Cell wall rigidity, measured as an increased bulk modulus of elasticity, increased under severe water stress, resulting in a loss of turgor at lower Ψl values.