Browsing by Subject "Reis"

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Can genetic engineering for the poor pay off? : an ex-ante evaluation of Golden Rice in India
(2006) Qaim, Matin; Sachdev, H. P. S.; Stein, Alexander J.
Genetic engineering (GE) in agriculture is a controversial topic in science and society at large. While some oppose genetically modified crops as proxy of an agricultural system they consider unsustainable and inequitable, the question remains whether GE can benefit the poor within the existing system and what needs to be done to deliver these benefits? Golden Rice has been genetically engineered to produce provitamin A. The technology is still in the testing phase, but, once released, it is expected to address one consequence of poverty ? vitamin A deficiency (VAD) ? and its health implications. Current interventions to combat VAD rely mainly on pharmaceutical supplementation, which is costly in the long run and only partially successful. We develop a methodology for ex-ante evaluation, taking into account the whole sequence of effects between the cultivation of the crop and its ultimate health impacts. In doing so we build on a comprehensive, nationally representative data set of household food consumption in India. Using a refined disability-adjusted life year (DALY) framework and detailed health data, this study shows for India that under optimistic assumptions this country?s annual burden of VAD of 2.3 million DALYs lost can be reduced by 59.4% hence 1.4 million healthy life years could be saved each year if Golden Rice would be consumed widely. In a low impact scenario, where Golden Rice is consumed less frequently and produces less provitamin A, the burden of VAD could be reduced by 8.8%. However, in both scenarios the cost per DALY saved through Golden Rice (US$ 3.06-19.40) is lower than the cost of current supplementation efforts, and it outperforms international cost-effectiveness thresholds. Golden Rice should therefore be considered seriously as a complementary intervention to fight VAD in rice-eating populations in the medium term.
Development and applications of Plabsoft : a computer program for population genetic data analyses and simulations in plant breeding
(2008) Maurer, Hans Peter; Melchinger, Albrecht E.
Marker-assisted breeding approaches are promising tools for enhancement of the conventional plant breeding process. They have been successfully applied in many areas such as plant variety protection, classification of germplasm, assessment of genetic diversity, mapping of genes underlying important agronomic traits, and using the mapping information for selection decisions. Powerful and flexible bioinformatic tools are urgently required for a better integration of molecular marker applications and classical plant breeding methods. The objective of my thesis work was to develop and apply Plabsoft, a computer program for population genetic data analyses and simulations in plant breeding. The assumption of Hardy-Weinberg equilibrium is a cornerstone of many concepts in population and quantitative genetics. Therefore, tests for Hardy-Weinberg equilibrium are of crucial importance, but the assumptions underlying asymptotic chi-square tests are often not met in datasets from plant breeding programs. I developed and implemented in Plabsoft a new algorithm for exact tests of Hardy-Weinberg equilibrium with multiple alleles. The newly derived algorithm has considerable computational advantages over previously described algorithms and extends substantially the range of problems that can be tested. Knowledge about the amount and distribution of linkage disequilibrium (LD) in breeding populations is of fundamental importance to assess the prospects for gene mapping with whole-genome association studies. To analyze LD in breeding populations, I implemented various LD measures in Plabsoft and developed a new significance test for these LD measures. The routines were employed to analyze LD in 497 elite maize lines from a commercial hybrid breeding program, which were fingerprinted by 81 simple sequence repeat (SSR) markers covering the entire genome. Strong LD was detected and, therefore, whole-genome association studies were recommended as promising. However, LD between unlinked loci will most likely result in a high rate of false positives. The prediction of hybrid performance with DNA markers facilitates the identification of superior hybrids. The single marker models used so far do not take into account the correlation between allele frequencies at linked markers. To overcome this problem, the concept of haplotype blocks was proposed. I developed and implemented in Plabsoft three alternative algorithms for haplotype block detection suitable for plant breeding. The algorithms were applied for the haplotype-based prediction of the hybrid performance of 270 hybrids, the parents of which were fingerprinted with 20 amplified fragment length polymorphism (AFLP) primer combinations. Employing haplotypes resulted in an improved prediction of hybrid performance compared with single marker models. Consequently, haplotype-based prediction methods have a high potential to improve substantially the efficiency of hybrid breeding programs. Computer simulations can be employed to solve population genetic problems in plant breeding, for which the simplifying assumptions underlying the classical population genetic theory do not hold true. However, before the start of my thesis no flexible simulation software was available. I developed algorithms for simulation of single breeding steps and entire plant breeding programs and implemented these in Plabsoft. The routines allow the simulation of plant breeding programs as they are conducted in practice. The simulation routines of Plabsoft were validated by simulating two marker-assisted backcross programs in rice conducted by the International Rice Research Institute (IRRI). In the simulations, the frequency distributions of the proportion of recurrent parent genome in the backcross populations were assessed. The simulation results were in good agreement with the experimental data. Therefore, computer simulations are a useful tool for pre-test estimation of selection response in marker-assisted backcrossing. The application of Plabsoft was exemplified by two studies in maize. In the first study, the expected LD decay in the intermating generations of two recurrent selections programs was determined with simulations. This application demonstrates the use of Plabsoft to solve problems for which analytical results are not available. In the second study, the forces generating and maintaining LD in a hybrid maize breeding program were investigated with computer simulations. This application demonstrates the capability of modeling complex long-term breeding programs as performed in practice. The studies of my thesis provide an example for the broad range of possible applications of Plabsoft. In addition to the presented studies, Plabsoft has so far been employed in about 40 further studies, which corroborates the usefulness of Plabsoft for integrating new genomic tools in applied plant breeding programs.
Effects of temperature and vapor pressure deficit on genotypic responses to nitrogen nutrition and weed competition in lowland rice
(2021) Vu, Duy Hoang; Asch, Folkard
Since rice is the major food for more than half of the world’s population, rice production and productivity have significant implications for food security. In adaptation to increasing water scarcity, as well as to reduce greenhouse gas emissions, water-saving irrigation measures (e.g., alternate wetting and drying – AWD) have been introduced in many rice growing regions. Previous studies have shown that AWD increases water use efficiency and reduces methane (CH4) emissions, while grain yield remains equal or is slightly increased compared to continuous flooding. However, the absence of a ponded water layer in formerly flooded rice fields creates new challenges, such as altered root zone temperature (RZT), enhanced nitrification leading to higher nitrate (NO3-) concentrations in the soil, or stimulated weed germination leading to changes in weed flora. All these factors may affect nutrient uptake and assimilation of rice plants and thus plant growth. Further, vapor pressure deficit (VPD) drives transpiration and water flux through plants, so nutrient uptake and assimilation by plants may be subject to adjustment under varying VPD conditions. As VPD varies largely between rice growing regions and seasons, and is also predicted to continuously increase under global warming, it was included as a factor in this study. The overall objective of the study was to evaluate the response of different rice varieties to arising challenges under water-saving irrigation. Experiments were conducted in the greenhouse and VPD chambers at the University of Hohenheim, where plants were grown in hydroponics. Both during day and night, nutrient uptake rates of rice increased linearly with RZT in the observed temperature range up to 29°C, implying that the optimum temperature for nutrient uptake of rice must be above 29°C. However, the uptake rates of different nutrient elements responded differently to RZT, with the increase in nitrogen (N) uptake per °C being greater than that of phosphorus (PO43-) and potassium (K+), which can potentially lead to an imbalance in plant nutrition. Therefore, the increase in RZT either due to climate change or water management may call for an adjusted fertilizer management. In general, the increase in nutrient uptake per °C was more pronounced during the day than during the night, while the amino acid concentration in the leaves both during the day and night was positively correlated with N uptake during the day, suggesting that plants may benefit more from increased temperature during the day. When both ammonium (NH4+) and NO3- were supplied, rice plants took up a higher share of NH4+. However, after depletion of NH4+ in the nutrient solution, plants took up NO3- without decreasing the total N uptake. The N form taken up by the rice plant had no effect on leaf gas exchange at low VPD, whereas NO3- uptake and assimilation increased stomatal conductance in some rice varieties at high VPD, resulting in a significantly higher photosynthetic rate. However, the increase in photosynthesis did not always result in an increase in dry matter, probably due to a higher energy requirement for NO3- assimilation than for NH4+. The effect of N form on leaf gas exchange of some rice varieties was only found at high VPD, indicating genotype-specific adaptation strategies to high VPD. However, maintenance of high stomatal conductance at high VPD will only be beneficial at sufficient levels of water supply. Therefore, we hypothesize that with increasing VPD, intensified nitrification under water-saving irrigation may improve leaf gas exchange of rice plants, provided a careful choice of variety and good water management. Furthermore, N form had an effect on the competition between rice and weeds. In mixed culture with rice, a large share of NO3- increased the growth and competitiveness of upland weeds but reduced the growth and competitiveness of lowland weeds. Consequently, enhanced nitrification under AWD may reduce the competitive pressure of lowland weeds, but increase the competition of upland weeds. In contrast to rice, growth of the upland weed was not reduced by high VPD, while its nutrient uptake was correlated with water uptake, suggesting that upland weeds will more successfully compete with rice for nutrients as VPD increases. Selection of rice varieties better adapted to NO3- uptake will improve rice growth and its competitiveness against weeds under AWD. The cumulative effects of RZT and soil nitrification on rice growth should be considered when evaluating the effects of climate change on rice growth.
Effects of water management on microclimate and yield physiology in irrigated rice in semi-arid environments
(2014) Stürz, Sabine; Asch, Folkard
Growth and grain yield reductions have been widely observed when traditionally flooded rice fields were subjected to water-saving irrigation measures, where a continuous floodwater layer is avoided. These observations led to the perception of rice being a plant extremely sensitive to soil water deficits even when grown in soils close to their water holding capacity. Since the rice plant’s meristem is below the water surface until the early reproductive stage in flooded fields, the difference in heat capacity between water and air can lead to changes in meristem temperature, when a ponded water layer is omitted. Therefore, the objectives of this study were to quantify the effects of water-saving irrigation on the field’s microclimate and its influence on gas-exchange parameters and to investigate growth and yield parameters under flooded and non-flooded conditions in response to microclimate and varying climatic conditions. On two sites in Senegal, field experiments were conducted, where rice was sown on bi-monthly staggered dates and grown under flooded and non-flooded conditions. In the flooded treatment, a ponded water layer was maintained in the field throughout the growing season, whereas in the non-flooded treatment, irrigation water was applied until soil saturation on a frequent basis, in order to avoid standing water and soil water deficits at the same time. Microclimatic parameters and phenology were observed and leaf gas-exchange and plant growth parameters, yield and yield components were determined. Minimum soil temperature and temperature at meristem level were usually lower without standing water, whereupon temperature differences between irrigation treatments increased with decreasing air temperature. Stomatal conductance depended mainly on minimum soil and meristem temperature and minimum relative humidity inside the canopy. Assimilation rate was positively correlated with solar radiation and soil and meristem temperature, but depended mainly on stomatal conductance. Without standing water, stomatal conductance and assimilation rate were significantly lower, but the results could be explained with differences in microclimate. In most cases, leaf area was reduced under non-flooded conditions. Leaf area expansion rate was correlated with meristem temperature during the night. With minimum meristem temperature being lower under non-flooded conditions, lower leaf area expansion rates under non-flooded conditions could be attributed to lower meristem temperature. Yield reductions under non-flooded conditions were mainly observed in the cold-dry-season, whereas slight yield increases were found in the hot-wet-season. Among the yield components, reduced number of spikelets per panicle and decreased spikelet fertility accounted for the largest share of the yield gap. Leaf area per tiller was positively correlated with meristem temperature in the observed temperature range, and a positive relationship was found between leaf area per tiller and the number of spikelets per panicle. Furthermore, spikelet fertility increased with meristem temperature between panicle initiation and booting stage. Therefore, lower meristem temperature led to smaller leaf area per tiller, less spikelets per panicle and decreased spikelet fertility under non-flooded conditions. We concluded that water-saving irrigation in lowland rice production can lead to growth and yield reductions in comparison to traditional lowland irrigation even in the absence of soil water deficits, due to changes in soil and meristem temperature when a ponded water layer is omitted. Differences in assimilation rate, leaf growth and yield between irrigation treatments increased with decreasing air temperature and a clear seasonal pattern was observed, with large growth and yield reductions in the cold-dry-season, whereas in the hot-wet-season, growth and yield were less affected by irrigation treatment. When water-saving irrigation measures are applied in areas where night temperatures below 20°C occur, the effect of changes in meristem temperature should be considered. To mitigate impairment of growth under water-saving irrigation, a floodwater layer could be used to bridge cool periods, or a less temperature-responsive variety should be chosen. Nevertheless, the physiological mechanisms of the differential effects of day and night temperature remain unknown und need further investigation. Possibly, there is a combined effect of low night temperature and high evaporative demand during the day, which could lead to growth limitations due to restrictions of the plant’s water status. Furthermore, we want to highlight the need for a robust model of water temperature in paddy fields, which should be incorporated in rice growth models, since even tough existing models simulate growth and grain yield under upland and lowland conditions, the effects of changes in microclimate due to irrigation method are inadequately considered so far.
Genotypic responses of upland rice to an altitudinal gradient
(2012) Shrestha, Suchit Prasad; Asch, Folkard
Adaptation strategies are required for crops to cope with changing climate. The impact of climate change on crop production is not straight forward to predict as extreme events comprise multiple combination of abiotic stresses and their impact differs in crop physiological growth stages. The mechanism on how new abiotic stress combinations translate into phenology and yield, and which cultivars are better adapted is yet unclear. Crop growth models are available that have been parameterized and validated for some aspects of possible climate change scenarios but in view of complex interactions crop responses to climate change are difficult to predict. On the other hand, prediction of the complex ideotype trait combinations may be interesting for breeders but physiological models are required that are well validated for the target environments. In upland rice grown under rainfed conditions without surface water accumulation methane emission is negligible and therefore greenhouse gas emission much lower compared to irrigated paddy rice systems. In addition, growing demand for rice and the increasing pressure on irrigated land leads to development of upland rice areas to supplement irrigated rice. Therefore, this study investigates genetically diverse upland rice genotypes from a wide range of origins across altitudinal gradient locations. The main objective of this study is to investigate genotypic responses of upland rice to different environments in order to calibrate crop growth models, which allow the evaluation of effects of climate change on upland rice systems. Multi-locational field (three locations: 1625, 965 and 25 m asl) trials comprising non-replicated phenological plots with five sowing dates (monthly staggered) in two consecutive years creating thirty different environments, and replicated physiological yield trials with two sowing dates (monthly staggered; early and late sowing) in two consecutive years creating twelve different environments were established in Madagascar. Ten contrasting upland rice genotypes were included in both field trials. Meteorological data were recorded on a daily basis during trial periods. Developmental stages were observed in the phenological plots; in the physiological plots yield and yield components were recorded. In addition, greenhouse trials were conducted with one upland rice genotype subjected to seven N-supply levels in a hydroponic system at the University of Hohenheim in order to understand the relationship between chlorophyll index, photochemical reflectance index and chlorophyll fluorescence parameters. Various statistical tools were applied to analyse field and greenhouse data sets. The phenological trial showed that duration to flowering was 117, 81 and 67 d in high (HA), mid (MA) and low (LA) altitudinal locations respectively. 90% of the total variance was explained by location when pooled over genotype, location, sowing dates and year. In HA, factors such as genotype, sowing date and year equally contributed to the observed variability whereas in MA year was the most determining factor and genotype had no significant contribution. Similarly, in LA sowing date was the main influencing factor and year had no significant effect. Aggregated data over locations, sowing dates and years indicated that each degree Celsius rise in mean air temperature decreased crop duration by 5 to 9 days depending upon genotype. Basic genotypic thermal constants Tbase ranged from 9.8 to 13.9 °C and Tsum from 816 to 1220 °C d within the selected genotypes. Cold tolerant genotypes were less affected by lower Tmin (14 °C) at booting to heading stage regarding spikelet sterility in HA, whereas others were highly affected at 15 °C (cold stress). Similarly, both cold sensitive and tolerant genotypes were affected by Tmax (above 30 °C) at flowering in MA and LA locations (heat stress). Grain yield and yield components were highly affected by location, year, sowing date, and genotypes and the interactions between these yield-determining factors were obvious. In HA, early sown cold tolerant genotypes had more than 5 t ha-1 grain yield and one month delay in sowing led to highly reduced yield whereas other genotypes had very poor yield on both sowing dates due to cold stress. In MA, yield difference between sowing date and genotypes was small (4.3 - 4.9 t ha-1). Grain yield in LA was vulnerable due to frequent tropical storms. Yield stability analysis showed that cold tolerant genotypes had above average stability. AMMI model for grain yield showed that environment and genotype by environment interactions were highly significant. Yield components determined during specific development stages of the genotype such as tillers per hill and percentage of filled spikelets were mainly influenced by environment, spikelets per panicle and thousand grain weight were influenced by genotype, and percentage of productive tillers was equally influenced by both genotype and environment. PCA biplots showed that all HA environments were equally influenced by all weather parameters with minimum air temperature having the strongest positive influence on genotypic performance. In all MA environments genotypic performance in all phenophases was strongly and positively influenced by rainfall, and strongly and negatively influenced by vapour pressure deficit, solar radiation and potential evapotranspiration. In the LA environments, main weather parameters influencing genotypic performance were maximum temperature and high rainfall accompanied by strong winds. The field measured SPAD values of the upper canopy leaves reflected the location specific N-remobilization and leaf senescence levels after flowering. Similarly, PRI values showed the abiotic stress responses among development stages and locations along the altitudinal gradient. These readings showed that genotypes were efficient in radiation use and N-remobilization after flowering in MA. The unsynchronized relationship between source (leaf) and sink (grain) explained the yield penalty. Emphasis on identification of morpho-physiological traits contributing to cold tolerance should be placed for further breeding. We conclude that genotypic responses of upland rice cultivars differed across altitudinal gradients. Genotypes that are well adapted in HA can easily be adapted in MA without yield decrease. But genotypes well adapted in MA may show a huge yield penalty in HA due to lower temperature during reproductive phase and consequently reduced sink formation. Frequent tropical storms and high temperature reduced yield potential in LA. Therefore, HA has a large potential for the future food security considering climate change scenarios. At present, MA is favorable for upland rice production systems, whereas LA is highly vulnerable and is expected to be even more vulnerable in future. Those results on genotype-specific responses to environmental conditions allow further improvement of crop models such as RIDEV and SAMARA (synthesis of SARRAH and EcoMeristem), which can be used to test a number of phenotypic traits x environments combinations to define ideotypes of upland rice varieties adapted to changing climate and cropping calendars. Genotypic responses of phyllochron, biomass production and crop growth rate, and radiation use efficiency across altitudinal gradients will be included to parameterize these models. In this regard, collaborations with AfricaRice, CIRAD and IRRI are ongoing.
Greenhouse gas emissions from rice production in the Vietnamese Mekong River Delta as affected by varietal selection and water management
(2023) Vo, Thi Bach Thuong; Asch, Folkard
The topic of this dissertation deals with rice production, the predominant source of daily nourishment for more than half of the worlds population. Rice production is directly affected by global climate change through aggravating climatic conditions, but is also one of the major sources of greenhouse gases (GHG) in the agricultural sector. The latter aspect is investigated in 4 publications by assessing the factors contributing to emissions, the quantification of GHG emissions across different scales, and possible mitigation of GHG emissions. In totality, these studies aim at bridging the gap between field measurements to national extrapolations in view of both GHG inventories and future mitigation programs. In terms of methodologies, the publications compiled in the following chapters represent a broad spectrum ranging from field measurements to meta-analysis, but they all deal with the emission of methane (CH4) which is generated in rice fields due to the unique feature of ‘semi-aquatic’ soils. The publications based on newly conducted field measurements also a nitrous oxide (N2O) which is a potent GHG emitted typically emitted from rice fields in low quantities. Chapter 2 (Vo et al. 2018) compiles field measurements from the Vietnamese Mekong River Delta (MRD) which accounts for more than 50% of the country’s rice production. Emission factors (EFs) are used to estimate total emissions associated with the area of rice production. The Intergovernmental Panel on Climate Change (IPCC) has given the default EFs that are based on global averages as Tier 1 approach. However, the IPCC guidelines encourage national reporting institutions to conduct field measurements of GHG emissions and to determine country-specific EFs as the basis of the Tier 2 approach. Tier 2 further accounts for the fact that emissions may also be highly variable within a given country by requesting for disaggregation of EF at a sub-national scale. Therefore, the most recent GHG inventories for Vietnam are based on region-specific EFs under the IPCC Tier 2 approach, which is implemented using national activity data (i.e., national average cultivation period of rice and harvested area). In Chapter 2, we developed the specific EFs for different hydrological sub-zones and growing seasons in the MRD to achieve disaggregated EFs that could be used for the National Communications submitted to the United Nations Framework Convention on Climate Change (UNFCCC). Due to the distinct bio-physical condition and cropping cycle, the results show the lowest emissions in the saline sub-zone. While alluvial, acid sulfate soils had intermediate levels, the highest emissions were found in the deep flood sub-zone. In Chapter 3 (Vo e al. 2018), we expanded the geographical scope of the GHG assessment to the entire country. This meta-analysis of CH4 data covers 73 cropping seasons at 36 field sites across the rice-growing areas of Vietnam under the IPCC’s baseline conditions (i.e., continuously flooded, no organic amendments) in the three main cropping seasons. As an output of this study, a structured database contained the location and season of each measurement as well as site-specific bio-physical factors and crop management at the site scale. In the next step, we developed disaggregated EFs for different zones and cropping seasons across the country that can be used for future reporting commitments of Vietnam as part of a more accurate Tier 2 assessment. The calculated EFs were generally higher than the IPCC defaults and the values used for Vietnam’s 3rd National Communications for the North, Central, and South Vietnam. Chapter 4 (Vo et al. 2023) has to be seen in the context of Vietnam’s climate change policy that aims at reducing GHG emissions from rice production. Mitigation in rice production will be crucial for Vietnam because CH4 from rice accounts for about 15 % of the national GHG which is more than the entire transport sector even without considering CO2 and N2O emissions along the rice value chain. Previous studies have assessed the potential practices by changes in farming practices, namely water, nutrient, and straw management, and almost uniformly concluded that Alternate Wetting and Drying (AWD) is the most promising strategy for achieving a sizable mitigation of GHG emissions. Given the intense rainy season in southeast Asia, however, the precipitation is often too high to implement this water regime and will not provide any economic benefit from water saving. In turn, it is important to consider other mitigation strategies such as the selection of low-emitting cultivars. We conducted a field screening of 20 rice varieties that was expanded by assessing the interactive effect of variety selection and AWD. An experimental layout with 120 plots (based on 3 replicates) was required to assess this interaction of variety and water management in the field using the closed chamber method to collect air samples followed by lab analysis (using a gas chromatograph) to quantify the CH4 and N2O concentrations. The results of this study confirmed that GHG emissions from rice fields are dominated by CH4 emissions whereas N2O emissions were negligible. Compared with IPCC default values, the data set from two dry seasons yielded higher emissions under a baseline of continuous flooding (EF = 2.96 kg CH4 ha-1 d-1) and lower Scaling Factors (SF) of AWD (SF = 0.4). Chapter 5 (Asch et al. 2023) deals with the agronomic aspects of both AWD and variety selection and their implications on the economic viability of future mitigation efforts. While AWD is more efficient in reducing CH4 emissions than variety selection, this water management practice resulted in a slight yield decrease in our field study. Given the limited applicability of AWD, the selection of varieties is a much more adaptable approach and is also beneficial in terms of farmers’ adoption because it does not require any crop management changes. However, this strategy could also impact profits since the lowest-emitting variety may not have the highest rice yields. In the context of future mitigation programs in the MRD, the dry season allows good control of the water table, so AWD should be the core of any mitigation effort. Variety selection on the other hand should be targeted in those seasons and locations that do not allow draining the fields. In turn, low-emitting varieties should become an integral part of future mitigation programs to supplement AWD within a systematic out scaling. In terms of economic trade-offs for the farmers, we assumed a scenario with compensation derived from the still premature carbon markets. The potential profit increments are very low and not attractive if distributed to farmers directly, but may collectively be used for investments in rural development by government agencies for benefitting farmers indirectly, e.g. by improving the irrigation infrastructure.
Influences on the performance of the stripper rotor in rice
(2002) Tado, Caesar Joventino M.; Kutzbach, Heinz Dieter
Rice is the most important food crop in many countries of Asia. In the Philippines, it is the staple food for more than 80% of the people while 70% of our population depend on rice farming and marketing for livelihood. However, despite the importance of rice in the lives of the Filipinos, production has not been able to consistently meet their needs. The ever-growing population continues to exert tremendous pressure on the rice farmers to produce more. The principle of stripping, that is, collecting the grains without harvesting the straw, presents a bright prospect in mechanical harvesting technology. A kinematic analysis of the stripper rotor during operation was made with a newly designed stripper test rig.
Photosynthesis, quantum requirements, and energy demand for crop production in controlled environments
(2020) Schmierer, Marc; Asch, Folkard
In 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.