Browsing by Subject "Ornamental plant"

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Identifizierung und Quantifizierung von Trockenstressreaktionen an ausgewählten Zierpflanzenkulturen
(2013) Krato, Theresa; Wünsche, Jens Norbert
The present thesis gives attention to the development of a practicable screening process for the identification of drought-stress tolerant ornamental plants. Requirements are to be created in terms of reduced water use, market expansion to warmer regions and increased ability of transportation. The studies were included into a cooperative research project involving 4 plant breeding companies, research centre Jülich, research institute Geisenheim and the GFP. Scope of the thesis was the deployment and evaluation of an assessment scheme to quantify drought-stress reactions, the development of dehydration experiments under stationary climatic conditions and to search for physiological markers of drought-stress tolerance. The experiments were mainly conducted on Petunia Cultivars and Impatiens Neu Guinea Grp. Genotypes. Main results of the investigation are listed below: 1. The species specific assessment schemes are based on an accurate visual characterization of the wilting process. The wilting is rated using ranks from 1 ? 9. Assessed parameters were the phyllotaxy, surface texture and leaf color. The assessment schemes were proved to be acceptably objective and precise during the experiments and the genotypes were evaluated accordingly. 2. The plants were dried out under standardized conditions in climate chambers. The decrease of water as well as the occurrence of wilting was recorded. Climatic conditions (temperature, humidity and radiation) in dehydration experiments were set up to reach a rank of 9 in 5 to 9 days according to drought-stress tolerance and pretreatment of genotypes. For this reason, an adequate differentiation between genotypes was ensured even with a single assessment per day. However, the system weight (substrate and plant), which was used to characterize the stress intensity has to be corrected about the fresh weight of plants. The investigated genotypes of Impatiens behaved similarly regarding to their drought-stress tolerance in many replications and consequently allowed for a ranking. In contrast, the ranking order of investigated genotypes of Petunia was vague in experimental replications. However, an influence of water supply on the wilting behavior of plants was detected in this context. 3. In order to search for physiological markers of drought-stress tolerance, studies on water potential, gas exchange and thermal imaging were conducted in line with the dehydrogenation experiments. A tendency was shown, that drought-stress tolerant genotypes reacted later and less distinctive on drying of the substrate compared to susceptible plants. But a correlation between water potential of shoots and water supply in the substrate as well as a differentiation between genotypes was certainly week. This was mainly due to high variation of data. The transpiration rate of investigated plants reacted more on water supply though. The ranking, which was based on the parameter transpiration rate correlated well with the ranking of the wilting behavior from the dehydrogenation experiments. Consequently, the stomata management appears to be a promising indicator of drought-stress tolerance. Thermal imaging showed an increase of leaf temperature with decreasing moisture content of the substrate. Accordingly, the leaf temperature of Impatiens can serve as an indicator for the opening rate of stomata. 4. Currently, the dehydrogenation experiments can be considered as the easiest and most practicable approach to identify drought-stress tolerant genotypes of Impatiens and Petunia due to the results of the present thesis. Physiological measurements supported the ranking of genotypes, which was developed according to the dehydrogenation experiments. Especially, data on the opening rate of stomata illustrated differences between the tested genotypes. However, the dehydrogenation experiment does not provide information of the dependence of vegetative and generative performance of plants on water supply, which is very important for producers of ornamentals. 5. The ranking of drought-stress tolerance from climatic chambers corresponds only partly with results of experiments under field conditions. Therefore, a screening concept has to be developed in a subsequent project to investigate the complex context of climate-stress tolerance.
Zierpflanzen als Nahrungsquelle und Bewertung der Blütenmerkmale für die Attraktivität der Bestäuberinsekten im urbanen Raum
(2022) Marquardt, Melanie; Rosenkranz, Peter
Currently, an increasing extension of urban areas can be observed worldwide, which implies a concurrent loss in natural habitats. If the current biodiversity shall be preserved, efforts must be reinforced in order to provide alternative habitats for the flora and fauna in urban areas. Regarding the assessment of the ecological value of the habitat ‘city’, scientific studies came to varying conclusions. However, all of them emphasize the importance of green urban areas in promoting the urban biodiversity. It has been frequently pointed out that sufficient and suitable foraging resources are an important and basic requirement for the survival of flower-visiting insects. However, it has hardly been investigated whether ornamental plants are suitable foraging resources for insect pollinators. While this is still highly contentious, there is growing evidence that ornamental plants could contribute to the provision of pollen and nectar. But apparently, the attractivity of different ornamental plants varies widely and furthermore, not all pollinator groups can profit equally from the mostly exotic ornamental plants. At present, scientific data for all ornamental genera or even species are not available. So, the first aim of this study was the comparison of the attractivity of certain ornamental plants, in particular those with a high market value. In order to conduct such trials, already existing acquisition methods have been assessed and refined. A further and so far rarely considered focus of this thesis is the analysis of impact factors that might affect the composition and abundance of urban pollinators. In order to identify the pollinator friendliness of ornamental plants, field tests in urban areas and semi-field tests in flight tents were conducted during the years 2017 – 2019. In the first trail, raised flower beds with an identical set of ornamental plants were installed at 13 different locations in the city area of Stuttgart. During the summer months of the years 2017 and 2018, all flower beds were visited in weekly intervals. Over a time period of 20 minutes, the number of foraging insects – divided into different groups of insect pollinators – was recorded. In total, 10,565 nectar and/or pollen foraging insects were counted. First of all, this confirms that our selection of ornamental plants was used as a foraging resource by pollinating insects. The attractivity of the tested ornamental plants, however, varied to a considerable degree among the plant species and the number of counts ranged from 1.2 flower visits in 20 minutes on Bracteantha bracteata (strawflower) to 5.3 flower visits on Bidens (beggar-ticks). It is noteworthy, that the attractivity also varied within the cultivars of the same species, partly even to a greater extent than between species. Interestingly, not only the abundance but also the composition of pollinators varied among the different test plants. Furthermore, the applied statistical models indicate significant impacts of the study year and the location on the results. This highlights the need of a continuously testing of all ornamental plants in regard to insect friendliness, for which the described methods were found to be very appropriate (publication I). Pollinating insects often use characteristic floral traits of the plants for their decision to visit the respective flower. These floral traits are often genera-, species- or even cultivar-specific and have been well studied in the native plants. In contrast, very little is known about the role of floral traits in ornamental plants. This includes e. g. the petal colour, several floral morphomet-rics or the floral scent of different plants. The impact of these traits on attractivity for insects was analysed in semi-field experiments using Calibrachoa cultivars and Bombus terrestris as model pollinator. Similar to the first part of the thesis, the attractivity of the different cultivars varied significantly. While the floral scent explained the observed differences in attractivity only to a small extend, it could be shown unequivocally that the petal colour constitutes a significant factor in the attractivity on B. terrestris. For a better understanding on the impact of certain floral traits for pollinating insects, however, there is further research required (publication II).