Browsing by Subject "Photosynthesis"
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Publication Photosynthesis, quantum requirements, and energy demand for crop production in controlled environments(2020) Schmierer, Marc; Asch, FolkardIn this work, energy costs for LED (light emitting diodes) lighting of a virtual plant stand exhibiting C3photosynthesis have been calculated via a model considering the quantum demand to build-up dry matter and energy efficiency of state-of-the art LEDs. Optimistic and pessimistic scenarios have been calculated by taking into account uncertainties regarding the H+/ATP stoichiometry of photosynthesis and different management strategies for indoor plant production. Energy costs were between 265 and 606 kWh for a production cycle ranging over 100 days and resulting in 2500 g dry matter per square meter for the optimistic and the pessimistic scenario respectively. The conversion efficiencies from electrical energy to energy bound in phytomass at the end of the production cycle were 2.07 % and 4.72 % (pessimistic and optimistic scenario, respectively). This was lower than the theoretical maximum values calculated for C3 plants that are given as 9.5 % in the literature. However, when the losses that occur during the conversion from electrical energy to light energy were excluded and only the efficiency of the conversion from incident light energy to phyto-energy was calculated, values increased to 4.0 and 9.1 %. The differences between the optimistic and the pessimistic scenario was caused by decreased photorespiration via carbon dioxide fertilization, which increased the conversion efficiencies by 38 %, followed by different assumptions about the H+ requirement for ATP production (34 %) and an increased rate of active absorption of light energy (24 %). Considering cumulative as well as feedback effects of all of the mentioned parameters, the conversion efficiency in the optimistic scenario was 2.3 times higher than in the pessimistic scenario. A system for measuring gas-exchange of whole plants or plant stands was developed in order to be able to investigate and improve the above mentioned management strategies in the future. CO2 sensors and temperature and humidity sensors were used to detect water loss and CO2. Readily available off-the-shelf electronic and mechanical materials were used in order to build a low-cost system that can be used in high throughput experiments. The results indicate that around 90 % of the transpirational water was detected by the system. We conclude that parts of the transpirational water condensed on the surfaces thus not leaving the chamber. When checking the accuracy of the H2O and CO2 sensors using an industry quality infrared gas analyser (IRGA), we found significant deviations from the values given by the IRGA and used this data for calibration of the CO2 sensors. The responses of the CO2-sensors were also linearly coupled to the H2O concentrations (about -0.1 % ppm CO2 / ppm H2O). A regression analysis was performed and the coefficients were used to correct the sensor readings. Since LEDs exhibit a higher energy-to-light ratio when operated at lower light levels, we tested a very small growing gibberellin (GA) deficient super dwarf rice genotype in a climate chamber experiment under different illumination levels and different levels of nitrogen supply to assess its suitability for crop production in artificial environments. A 25 % reduction in illumination lead to a 75 % reduction in yield, mainly due to a 60 % reduction in formed tillers and 20 % reduction in kernel weight, and an 80 % reduction in illumination caused total yield loss. Whereas leaf area under reduced illumination was significantly lower, only marginal changes in the dimensions of single leaves were observed. Photosynthesis at growing light conditions was not different between control plants and plants under 75 % illumination. This was explained by a higher photochemical efficiency under lower light conditions and a reduced mesophyll resistance. Therefore, we conclude that this genotype is an interesting candidate for crop production in vertical plant production systems, especially because of its short stature and the absence of shade avoidance mechanisms, such as leaf elongation, that would complicate production in small-height growing racks under low-light conditions. Nitrogen concentrations of 2.8 and 1.4 mmol L-1 in the nutrient solution lead to no differences in plant growth. We conclude that a nitrogen concentration of 1.4 mmol L-1 is sufficient for this genotype under the light intensities that were applied here. A software tool for simulations of photosynthesis in the python programming language was developed. The software implements a classical Farquhar-von CaemmererBerry (FvCB) model of leaf photosynthesis coupled with a model for the estimation of stomatal behaviour dependent on environmental conditions. We want to emphasize that the use of such models is essential to understand the complex interactions between plant growth, leaf photosynthesis and the environment. Knowledge on those relationships is the key to improve the efficiency of plant production in controlled environments.Publication Physiological and growth responses of Jatropha curca L. to water, nitrogen and salt stresses(2012) Rajaona, Arisoa Mampionona; Asch, FolkardThis thesis provides necessary and complementary information for an improved understanding of jatropha growth to guide further research to evaluate the response of jatropha to abiotic stressors and for designing plantations adapted to the plants? requirements. Given the fact that jatropha is claimed to grow on marginal lands, we studied effects of water supply, salt stress, nitrogen and air humidity as major abiotic stressors on gas exchange parameters and biomass production followed by management options for pruning the trees to positively influence biomass productivity and to contribute to optimize resource use. The effects of water availability (rainfed versus irrigated) on growth and gas exchange parameters were investigated for 4-year old jatropha grown in a semi-arid environment at a plantation site in Madagascar in 2010. The results confirmed that 1250 mm water in addition to a 500 mm rainfall did not affect biomass production and instantaneous gas exchange. Nevertheless, leaf light responses of irrigated plants were higher than that of rainfed plants. The study showed to what extent salt stress affected water use, canopy water vapour conductance, leaf growth and Na and K concentrations of leaves of 3-year old and young jatropha plants. 3-year old plants were exposed to seven salt levels (0-300 mmol NaCl L-1) during 20 days and young plants to five salt levels (0-200 mmol NaCl L-1) during 6 days. In both experiments, plants responded rapidly to salt stress by reducing water loss. The threshold value of responses was between 0 and 5 dS m-1. Leaf area increment of young jatropha had a threshold value of 5 dS m-1 implying that jatropha is sensitive to external salt application in terms of canopy development, conductance and CO2 assimilation rate. Transpiration of plants in both experiments was reduced to 55% at EC values between 11 and 12 dS m-1 as compared to non-stressed plants. These findings indicate that jatropha responds sensitive to salt stress in terms of leaf elongation rate and consequently canopy development, and to immediate physiological responses. Leaf gas exchange characteristics of jatropha as affected by nitrogen supply and leaf age were intensively studied, as carbon assimilation is one of the central processes of plant growth and consequently a key process embedded in modelling approaches of plant productivity. This study showed that N supply effects on leaf gas exchange of jatropha leaves were small with only the treatment without nitrogen resulting in lower rates of CO2 assimilation rate and light saturated CO2 assimilation rate, nevertheless, effects of N supply on biomass formation were pronounced. Instantaneous rates of leaf gas exchange of different leaves subject to variable air humidity (atmospheric vapour pressure deficit (VPD)) were investigated. This study showed that CO2 assimilation rate (A) and stomatal conductance (gs) were correlated in a hyperbolic fashion, and that gs declined with increasing VPD. Maximal stomatal conductance of jatropha was in the range of 382 mmol m-2 s-1 and gs is predicted to be close to zero at 6 kPa. Effects of VPD, via stomatal conductance, by preventing high transpiration rates, have been demonstrated to be decisive on water use efficiency. Our findings are in this regard relevant for the estimation of water use efficiency of jatropha. The outcome further indicates favourable conditions at which stomatal opening is high and thereby allowing for biomass formation. This information should be considered in approaches which aim at quantifying leaf activity of field-grown bushes which are characterized by spatially highly diverse conditions in terms of microclimatic parameters. Microclimatic parameters can be modified by the tree structure. The reported field experiment on 4-year old jatropha indicated that the biomass production and canopy size depended mainly on primary branch length. A comparison of plants of different pruning types with regard to trunk height (43 versus 29 cm) and total length of primary branches (171 versus 310 cm), suggest that higher biomass production and greater leaf area projection was realized by trees with short trunks and long primary branches. Growth of twigs and leaves was positively correlated with total length of branches. Relative dry mass allocation to branches, twigs and leaves, length of twigs per cm of branches and specific leaf area were not affected by pruning and water supply. Trees with shorter branches had a higher leaf area density. As opposed to an allometric relationship between the average diameter of primary branches and total above ground biomass, our data suggest that these traits were not constantly correlated. Our data indicate that the length of newly formed twigs, where the leaves are attached to, can be related to the total length of already established branches. Leaf area density and relative dry mass allocation to leaves were not affected by the two pruning techniques, indicating that pruning differences in leaf area size were proportionally converted to corresponding pruning differences in the canopy volume exploited by plants. The results reported in this study are relevant for understanding jatropha growth. It helps farmers first for a better plantation management and researchers as well as contribution to future modelling purpose concerning jatropha growth under variable climatic conditions. Additionally, it should complement information for a better set of priorities in research, contribute indirectly to breeding programs and adjust agricultural policies in terms of encountering global change.Publication Translocation and storage of chloride in chlorine-stressed maize (Zea mays L.)(2020) Zhang, Xudong; Zörb, ChristianMaize (Zea mays L.) is a moderately salt-sensitive species, its sensitivity to NaCl being mainly associated with the accretion of toxic sodium in shoots for example leading to the sodium-induced damage of leaf chloroplasts. However, less attention has been paid to the effects of chloride (Cl-). The work described in this dissertation therefore aims at elucidating the physiological adaptations of maize plants to Cl- salinity. It involves four research questions: 1) how do sensitive maize plants respond to Cl- salinity with regard to crop yield and plant performance; 2) how are the translocation and tissue storage patterns of Cl- correlated with tolerance to Cl- salinity; 3) how do osmotic stress and Cl- stress impact biomass, chlorophyll content, and nitrate reductase activity (NRA); 4) does sensitivity to Cl- salinity differ between maize and faba bean plants? Soil pot experiments and hydroponic culture experiments in the greenhouse have shown that maize is able to withstand Cl- salinity by being a shoot excluder. The relevant genotypic difference is believed to be based on its ability to undertake Cl- root-to-shoot translocation. The resistance mechanism of the genotype ES-metronom, which is a more Cl- -tolerant variety, has been attributed to its more efficient shoot exclusion of Cl-,whereas that of the genotype P8589, which is a more Cl- -sensitive variety has been ascribed to the preferable sequestration of Cl- away from the young photosynthetic tissues, such as into old leaf blades, and Cl- movement in roots possibly to achieve Cl- dilution. In the mildly tolerant genotype LG30215, osmotic stress does not interfere with NRA but slows down mass flow, which probably reduces NO3- transport to leaf tissues, whereas excess Cl- indirectly inhibits NRA through the antagonistic limitation of NO3- uptake. In comparison with maize, faba bean plants are more sensitive to Cl- salinity rather than to sodium toxicity.