Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Photosynthesis : Online introductory course
    Vreugdenhil, D. - \ 2017
    Wageningen : Wageningen University & Research
    photosynthesis - plants - plant physiology - biomass - fotosynthese - planten - plantenfysiologie - biomassa
    The aim of this online course is to explain the basic mechanisms of photosynthesis.
    In vivo 1H NMR methods to study dynamics of chloroplast water and thylakoid membrane lipids in leaves and in photosynthetic microorganisms
    Pagadala, Shanthi - \ 2017
    Wageningen University. Promotor(en): H. van Amerongen, co-promotor(en): H. van As. - Wageningen : Wageningen University - ISBN 9789463431569 - 130
    cell membranes - membranes - chloroplasts - thylakoids - photosynthesis - in vivo experimentation - stress conditions - stress - proteins - lipids - mobility - dynamics - celmembranen - membranen - chloroplasten - thylakoïden - fotosynthese - in vivo experimenten - stress omstandigheden - stress - eiwitten - lipiden - mobiliteit - dynamica

    Dynamics of thylakoid membranes and mobility of pigment-protein complexes therein are essential for survival of photosynthetic organisms under changing environmental conditions. The published approaches to probe mobility of the thylakoid membrane lipids and protein complexes are either dependent on the use of external labels or are used only for in vitro studies. Here, we present non-invasive 1H NMR methods (DOSY and DRCOSY) to study dynamics of water in chloroplasts, lipids in oil bodies and in thylakoid membranes and pigment-protein complexes under complete in vivo conditions in leaf disks of F. benjamina and A. platanoides and in suspensions of the green alga Chlamydomonas reinhardtii and blue-green alga Synechocystissp.PCC 6803.

    In leaf disks of Ficus benjamina and Acer platanoides, water in chloroplasts could be clearly discriminated from other pools. Both water in chloroplasts, and water in vacuoles of palisade and spongy cells showed resonances in the high field part of the spectra (with respect to pure water), in contrast to what has been reported in literature. Subepidermal cells (present only in F. benjamina but not in A. platanoides) may act as a water storage, buffer pool during drought. This pool prevented the fast loss of water from the chloroplasts. Nutrient stress and excess salt stress resulted in accumulated lipid bodies and in striking differences in the dynamics and spectra/composition of the different components. T2 values of the different components are compared with those observed in suspensions of Synechocystissp.PCC 6803. The differences in membrane composition (ratio of the different membrane lipids) were clearly observed in the DANS of the oil bodies and the (thylakoid) membranes, but the diffusion coefficients were quite comparable. Also the DANS of the component that is assigned to the pigment-protein complexes are quite different, reflecting the differed composition. The diffusion coefficients of this component in isolated spinach thylakoids and in C. reinhardtii are very comparable, but about a factor of 10 lower with respect to that of Synechocystis at short diffusion times. The dynamics of these complexes in these systems are thus quite different.

    Optimization of productivity and quality of irrigated tomato (Solanum lycopersicum L.) by smallholder farmers in the Central Rift Valley area of Oromia, Ethiopia
    Gemechis, Ambecha O. - \ 2017
    Wageningen University. Promotor(en): P.C. Struik, co-promotor(en): B. Emana. - Wageningen : Wageningen University - ISBN 9789463431576 - 262
    solanum lycopersicum - irrigation - crop production - optimization - photosynthesis - chlorophyll - gas exchange - water use efficiency - crop yield - ethiopia - solanum lycopersicum - irrigatie - gewasproductie - optimalisatie - fotosynthese - chlorofyl - gasuitwisseling - watergebruiksrendement - gewasopbrengst - ethiopië

    Tomato (Solanum lycopersicum L.) is a vegetable crop with high potential to contribute to poverty reduction via increased income and food security. It is widely grown by smallholders, has high productivity and its demand is increasing. Ethiopia produced about 30,700 Mg of tomatoes on 5,027 ha annually in 2014/2015. Average yields are only 6.1 Mg ha-1, below the world average yields. There is both a need and a potential to increase tomato production per unit area.

    The aim of this thesis is to analyze the irrigated tomato production systems of smallholder farmers in Ethiopia, to survey and characterize the tomato in selected ecoregions and seasons, and to identify yield-limiting or yield-reducing factors and opportunities to enhance yield by using a combination of surveys and field experiments. Field experiments on optimization of yield and quality of field-grown tomato were carried out at Ziway, Ethiopia, for two seasons to study the impact of different irrigation practices applied, based on local empirical practices, deficit irrigation, or crop water requirement.

    This thesis begins with a survey of tomato production systems. The survey details the area and production in various zones and for each of these zones yield- determining, yield-limiting, and yield-reducing factors and opportunities for improving yield and quality are indicated. It also avails area, production and yield data for each growing season and typifies the production systems in these zones. Low temperature (cold) from October-January and shortage of improved seeds are recognized as yield-determining factors, whereas insufficient water and nutrient (fertilizer) supply proved to be yield-limiting factors across zones. Late blight (Phytophthora infestans), Fusarium wilt (Fusarium oxysporum) and different pests and weeds are identified as yield-reducing factors in the zones. Experienced growers who have access to extension service recorded significant yield increment. Farmers Research Groups improved actual average yield with the use of improved technology (improved varieties and quality seed), and better efficiencies of water and fertilizer use. This study quantified influences of irrigation systems and strategies on growth-determining tomato features. Variation in irrigation systems and strategies accounted for variation in growth and dry matter accumulation. Greater performance for yield-related traits was obtained with drip irrigation based on crop water requirement for tomato varieties. Examination of plants showed also that local empirical irrigation is responsible for the occurrence of Phytophthora root rot, whereas deficit irrigation proved cause for occurrence of Fusarium wilt (Fusarium oxysporum), blossom end rot and broome rape (Orobanche ramosa) on roots or leaves, stems or fruits.

    The experiments on irrigation scheduling with different irrigation systems and strategies gave useful indications on the possibility to improve commercial yield (CY) and water use efficiency. Promising results on CY and agronomical water use efficiency of tomato were achieved with drip irrigation based on crop water requirement, while for the biological water use efficiency higher value was obtained with deficit drip irrigation in both seasons. The findings indicate that the CY was decreased significantly for deficit by 50% in drip irrigation and deficit by 50% in furrow irrigation in both seasons. Mean CY for drip irrigation according to crop water requirement increased by 51% and 56% compared with deficit drip irrigation, whereas furrow irrigation based on crop water requirement increased by 52% and 54% compared with deficit furrow in Experiments 1 and 2, respectively. However, water use efficiency decreased with the increasing water volume.

    Simultaneous measurements of rate of photosynthesis based on gas exchange measurements and the thylakoid electron flux based on chlorophyll fluorescence were used to investigate physiological limitations to photosynthesis in leaves of deficit irrigated tomato plants under open field situations. Combined leaf gas exchange/chlorophyll fluorescence measurements differentiated the treatments effectively. Reduction in rate of photosynthesis, stomatal conductance and the maximum quantum efficiency of photosystem II varied across seasons of all varieties, whereas leaf temperature was increased by deficit irrigation in all varieties. Among varieties studied, Miya was found relatively tolerant to deficit irrigation. Stomatal limitation of rate of photosynthesis increased significantly as a result of water stress suggesting a strong influence of the stomatal behaviour.

    We also determined the influence of irrigation systems and strategies on water saving and tomato fruit quality. Using deficit drip irrigation was the best management strategy to optimize water use and tomato quality. Fruit dry matter content, acid content and total soluble solids were significantly higher with deficit drip irrigation than with other treatments.

    From this thesis it appeared that agro-climatic conditions, access to resources and culture all contribute to the relatively low yields of tomato in the Central Rift Valley of Ethiopia. The thesis also proved that significant advances can be made in yield, quality and resource use efficiency.

    Crop growth and development in closed and semi-closed greenhouses
    Qian, Tian - \ 2017
    Wageningen University. Promotor(en): L.F.M. Marcelis, co-promotor(en): J.A. Dieleman; A. Elings. - Wageningen : Wageningen University - ISBN 9789463430708 - 112
    crops - crop production - growth - greenhouse crops - greenhouse horticulture - climate - semi-closed greenhouses - photosynthesis - temperature - gewassen - gewasproductie - groei - kasgewassen - glastuinbouw - klimaat - semi-gesloten kassen - fotosynthese - temperatuur

    (Semi-)closed greenhouses have been developed over the last decades to conserve energy. In a closed greenhouse, window ventilation is fully replaced by mechanical cooling while solar heat is temporarily stored in an aquifer. A semi-closed greenhouse has a smaller cooling capacity than a closed greenhouse and, in which mechanical cooling is combined with window ventilation. (Semi-)closed greenhouses create new climate conditions: high CO2 concentrations irrespective of the outdoor climate, and vertical gradients in temperature and vapour pressure deficit throughout the canopy. This thesis focuses on the crop physiology in (semi-)closed greenhouses, and investigates the effects of the new climate conditions on crop growth, development and underlying processes.

    Cumulative production in (semi) closed greenhouses increased by 6-14% compared to the open greenhouse, depending on the cooling capacity. The production increase in the (semi-)closed greenhouses was explained by the higher CO2 concentrations. In many species, feedback inhibition of photosynthesis occurs when plants are grown at high CO2. The results, however, suggest that high CO2 concentrations do not cause feedback inhibition in high producing crops, because the plants have sufficient sink organs (fruits) to utilise all assimilates. Pruning experiments showed that photosynthetic acclimation to elevated CO2 concentration only occurred when the number of fruits was considerably reduced.

    Cooling below the canopy induced vertical temperature and vapour pressure deficit gradients. These gradients correlated with outside radiation and outside temperature. Despite the occurrence of vertical temperature gradients, plant growth and fruit yield were mostly unaffected. Leaf and truss initiation rates did not differ in the presence or absence of a vertical temperature gradients, since air temperatures at the top of the canopy were kept comparable. The only observed response of plants to the vertical temperature gradient was the reduced rate of fruit development in the lower part of the canopy. This resulted in a longer period between anthesis and fruit harvest and an increase in the average fruit weight in summer. However, total fruit production over the whole season was not affected.

    The effects of the climate factors light, CO2 concentration, temperature, and humidity on leaf photosynthesis were investigated. The photosynthesis model of Farquhar, von Caemmerer and Berry (FvCB) was modified by adding a sub-model for Ribulose-1,5-bisphosphate carboxylase (Rubisco) activation. The photosynthetic parameters: the maximum carboxylation capacity (Vcmax) and the maximum electron transport rate (Jmax), α (the efficiency of light energy conversion), θ (the curvature of light response of electron transport), and Rd (the non-photorespiratory CO2 release) were estimated based on measurements under a wide range of environmental conditions in the semi-closed greenhouse. The simultaneous estimation method and the nonlinear mixed effects model were applied to ensure the accuracy of the parameter estimation. Observations and predictions matched well (R2=0.94).

    The yield increase in a closed greenhouse, compared to that in an open greenhouse was analyzed based on physiological and developmental processes. The yield increase in the (semi-)closed greenhouses was the result of an increase of net leaf photosynthesis. The (semi-)closed greenhouses have been applied commercially first in the Netherlands, and later in other countries. The knowledge obtained from (semi-)closed greenhouses is applied in conventional open greenhouse as well, which is called the next generation greenhouse cultivation. A number of innovations are being developed for greenhouse industry to reduce energy consumption while improving production and quality.

    Dynamic photosynthesis under a fluctuating environment: a modelling-based analysis
    Morales Sierra, Alejandro - \ 2017
    Wageningen University. Promotor(en): Paul Struik; Jaap Molenaar, co-promotor(en): Xinyou Yin; Jeremy Harbinson. - Wageningen : Wageningen University - ISBN 9789463430456 - 282
    photosynthesis - modeling - analysis - environmental factors - light - canopy - leaves - crop physiology - metabolism - fotosynthese - modelleren - analyse - milieufactoren - licht - kroondak - bladeren - gewasfysiologie - metabolisme

    In their natural environment, leaves are exposed to rapid fluctuations of irradiance. Research on CO2 assimilation under fluctuating irradiance often relies on measurements of gas exchange during transients where irradiance is rapidly increased or decreased, after the leaf has adapted to a particular set of environmental conditions. In the field, such increases and decreases occur mostly because of sunflecks (rapid increases in irradiance on a low irradiance background) created by gaps in the canopy and plant movement by wind, and cloudflecks (rapid decreases in irradiance on a high irradiance background) generated by clouds that transiently block the sun.

    In this dissertation, the metabolic regulation of photosynthesis and how this may limit dynamic CO2 assimilation is studied in silico with the development and application of simulation models. In order to support the development of the models, a review of the literature was performed as well as an experiment designed to generate data on dynamic CO2 assimilation for different photosynthetic mutants of Arabidopsis thaliana. In addition to providing these models to the research community, this dissertation also identifies multiple targets that may be used for improving dynamic CO2 assimilation in plants. It further demonstrates that the dynamic responses of CO2 assimilation to changes in irradiance has a significant effect on canopy CO2 assimilation, even for dense canopies exposed to open skies, resembling the conditions of commercial crops.

    In Chapter 1, the context of this dissertation is presented. The societal relevance of this research is argued, making reference to the role that photosynthesis could play in addressing global problems such as food and energy security. The necessary background on the physiology of photosynthesis is provided, with special emphasis on the terminology and concepts required to understand the rest of the dissertation, with the aim of making the contents more accessible to a wider audience. Then, prior literature on the specific topics of this dissertation (i.e., photosynthesis in a dynamic environment and its mathematical modelling) is presented, with a chronological approach that analyses the evolution of ideas and methodologies up to the present.

    In Chapter 2, the current literature on dynamic CO2 assimilation is reviewed, with an emphasis on the effects of environmental conditions ([CO2], temperature, and air humidity) on the rates of photosynthetic induction and loss of induction. This review reveals major knowledge gaps, especially on the loss of induction. The little data available indicates that rates of photosynthetic induction increase with [CO2], which could be explained by a weak effect on Rubisco activation and a strong effect on stomatal opening. Increases in temperature also increase the rates of photosynthetic induction, up to an optimum, beyond which a strong negative effect can be observed, which could be attributed to deactivation of Rubisco activase.

    In Chapter 3, an experiment is presented that makes use of several photosynthetic mutants of A. thaliana. Downregulating non-photochemical quenching and sucrose synthesis did not have any significant effect on dynamic CO2 assimilation, whereas CO2 diffusion and Rubisco activation exerted stronger limitations. Further analysis reveals that whether stomatal opening limits CO2 assimilation after an increase in irradiance depends on the stomatal conductance prior to the change in irradiance. A threshold value of 0.12 mol m−2 s−1 (defined for fluxes of water vapour) could be defined, above which stomata did not affect the rates of photosynthetic induction. The comparison of measurements across irradiance levels also indicated that the apparent rate constant of Rubisco activation is irradiance-dependent, at least for irradiance levels below 150 μmol m−2 s−1.

    In Chapter 4, a phenomenological model of leaf-level CO2 assimilation is presented. The model is described in detail and all the parameters are first estimated with published data, and later refined by fitting the model to the data from Chapter 3. Additional data from the experiment in Chapter 3 is used to validate predictions of CO2 assimilation under lightflecks for the different photosynthetic mutants. The model predicts accurately dynamic CO2 assimilation for the different photosynthetic mutants by only modifying those parameters that are affected by the mutation. This demonstrates that the model has a high predictive power and that the equations, although phenomenological in nature, have a solid physiological basis.

    The model is further used to analyse, in silico, the limitations imposed by different photosynthetic processes on dynamic CO2 assimilation at the leaf and canopy level, allowing a more in depth analysis than in Chapter 3. The analysis demonstrates that results obtained at the leaf level should not be extrapolated directly to the canopy level, as the spatial and temporal distribution of irradiance within a canopy is more complex than what is achieved in experimental protocols. Both at the leaf and canopy level, CO2 diffusion is strongly limiting, followed by photoinhibition, chloroplast movements and Rubisco activation.

    In Chapter 5, a mechanistic model of the dynamic, metabolic regulation of the electron transport chain is presented. The model is described in detail and all the parameters are estimated from published literature, using measurements on A. thaliana when available. Predictions of the model are tested with steady-state and dynamic measurements of gas exchange, chlorophyll fluorescence and absorbance spectroscopy on A. thaliana, with success.

    The analysis in silico indicates that a significant amount of alternative electron transport is required to couple ATP and NADPH production and demand, and most of it is associated with nitrogen assimilation and export of redox power through the malate shuttle. The analysis also reveals that the relationship between ATP synthesis and the proton motive force is highly regulated by the concentrations of substrates (ADP, ATP and inorganic phosphate), and this regulation facilitates an increase in non-photochemical quenching under conditions of low metabolic activity in the stroma.

    In Chapter 6, the findings of Chapters 2–5 are summarised and employed to answer in detail the four research questions formulated in Chapter 1. Of great interest is the identification of six potential targets that may be used to improve dynamic CO2 assimilation. These targets are: (i) regulation of Rubisco activity through changes in the amount or regulation of Rubisco activase, (ii) acceleration of stomatal opening and closure, (iii) a lower /ATP for ATP synthesis, (iv) faster relaxation of non-photochemical quenching, (v) reduced chloroplast movements, and (vi) reduced photoinhibition by increased rates of repair of Photosystem II.

    Studying fast dynamics in biological complexes : from photosynthesis in vivo to single DNA molecules in vitro
    Farooq, Shazia - \ 2017
    Wageningen University. Promotor(en): Herbert van Amerongen, co-promotor(en): Johannes Hohlbein. - Wageningen : Wageningen University - ISBN 9789463431002 - 149
    biology - dna - proteins - interactions - probability analysis - förster resonance energy transfer - fluorescence - spectroscopy - photosynthesis - biologie - dna - eiwitten - interacties - waarschijnlijkheidsanalyse - förster resonantie-energieoverdracht - fluorescentie - spectroscopie - fotosynthese

    During the last decades, fluorescence spectroscopy has emerged as a powerful tool in the fields of biophysics, biotechnology, biochemistry, cellular biology and the medical sciences. These techniques are highly sensitive, and allow us to study the structure and dynamics of (bio)molecular systems (Valeur 2001). A significant advantage of fluorescence techniques is that they can often be non-invasive and measurements can be performed in real time. In this thesis different advanced fluorescence methods will be used to study two important biological processes: (1) DNA dynamics and (2) plant photosynthesis. The first part aims at improving the smFRET technique for the analysis of DNA dynamics and other fast conformational changes. This improvement is made by combining and developing instrumentation and data evaluation tools. The second part is the continuous development of time-resolved fluorescence spectroscopy methods, as well their application in the field of photosynthesis to study ultrafast processes in thylakoid membranes and leaves. The two fluorescence techniques are technically and conceptually very different, but they are both designed for analysis of biomolecular systems. In this thesis, the techniques are applied to study energy transfer and dynamical changes in DNAs, thylakoid membranes and leaves.

    REFERENCE: VALEUR B 2001. Molecular Fluorescence: Principles and Applications. 1 ed: Wiley-VCH.

    On yield gains and yield gaps in wheat-maize intercropping : opportunities for sustainable increases in grain production
    Gou, Fang - \ 2017
    Wageningen University. Promotor(en): Martin van Ittersum, co-promotor(en): Wopke van der Werf. - Wageningen : Wageningen University - ISBN 9789462579811 - 202
    zea mays - triticum - intercropping - crop yield - grain crops - crop production - models - photosynthesis - zea mays - triticum - tussenteelt - gewasopbrengst - graangewassen - gewasproductie - modellen - fotosynthese

    Intercropping is the cultivation of two or more crop species simultaneously in the same field, while relay intercropping means that the growing periods of the crop species are only partially overlapping. Intercropping has advantages with respect to productivity, resource capture, build-up of soil organic matter, and pest and disease suppression. This thesis aims to quantify and explain the yield advantages in wheat-maize relay intercropping and to assess the importance of intercropping for food production and land use efficiency.

    Wheat-maize intercropping had land equivalent ratios around or above one in two experiments in the Netherlands. Wheat in border rows showed major yield increases, and this yield increase was due to increases in the number of tillers per plant and the number of kernels per ear. The yield advantage of intercropped wheat was associated with a high radiation interception and radiation use efficiency (RUE). Under Dutch growing conditions, maize performance in the intercrop was constrained. Intercropping had a negative effect on the yield per plant and radiation use efficiency of maize. A strip intercrop model was developed, parameterized and tested with data on wheat-maize intercropping in the Netherlands. The model simulates radiation interception and growth in relay-strip intercrops with two species in different planting configurations. The model also allows simulating the consequences of border row effects for total system productivity. Bayesian analysis was applied to calibrate radiation use efficiency of wheat and maize in sole crops and intercrop. Intercropped wheat had higher a RUE than sole wheat, while intercropped maize had a lower RUE than sole maize. Intercropped maize had less favourable leaf traits (e.g. nitrogen content) during the flowering stage than sole maize in 2014, but the leaves in the intercrop had a higher photosynthetic rate than those in the sole crop. Possible explanations for this finding include differences between sole and mixed crops in water acquisition from soil, light distribution in the canopy, nitrogen distribution within the leaf and the contribution of the ear leaf to the growth of the cob. The low radiation use efficiency in intercropped maize may relate to nitrogen deficiency during grain filling. New concepts for potential yield, yield gain and yield gap in intercropping were developed in this thesis. Using crop model simulations and farm survey data, those concepts were operationalized in the context of wheat and maize production in an oasis area (Zhangye city) in northwest China. Wheat-maize intercropping resulted in substantial yield gains under potential and actual growing conditions. A comparison of potential and actual yields indicated a yield gap of 33% for sole wheat, 49% for sole maize, 15% for intercropped wheat, and 51% for intercropped maize. The land use analysis showed that discontinuing the use of intercropping in this region will decrease grain production substantially.

    Overall, this thesis studied the growth and productivity of wheat-maize intercropping at organ, plant and cropping system level, and also assessed its contribution to grain production at a regional level. The findings suggest that intercropping of food crops provides opportunities to meet increasing food demands. New technologies are needed to make strip intercropping efficient in terms of labour use and breeding should pay attention to cultivars that are suitable for intercropping.

    Simulating plants: Research on photosynthesis will bear fruit
    Klein Lankhorst, R.M. ; Aarts, M.G.M. - \ 2016
    biobased economy - biofuels - photosynthesis - renewable energy - biomass - bioenergy - plants
    Planten nabootsen : onderzoek naar fotosynthese gaat vruchten afwerpen
    Klein Lankhorst, Rene ; Aarts, Mark ; Amerongen, Herbert van - \ 2016
    biobased economy - biobased chemistry - biofuels - photosynthesis - biotechnology - biobased chemicals - energy sources - solar energy - renewable energy - techniques

    Planten zijn meesters in het gebruik van zonlicht. Daarmee zetten ze water en kooldioxide om in suikers en zuurstof. Wageningse onderzoekers kunnen dit proces nabootsen en verbeteren. Zo willen ze biobrandstoffen maken en beter groeiende gewassen

    Plant reageert op korte en lange termijn verschillend op lichtkleur : onderscheid effecten fotosynthese en fotomorfogenese
    Ieperen, W. van; Heuvelink, E. ; Kierkels, T. - \ 2016
    Onder Glas 13 (2016)10. - p. 15 - 17.
    kunstlicht - fotosynthese - plantenontwikkeling - fotomorfogenese - proefopzet - fotosynthetische actieve straling - belichting - glastuinbouw - artificial light - photosynthesis - plant development - photomorphogenesis - experimental design - photosynthetically active radiation - illumination - greenhouse horticulture
    De inzichten in het effect van lichtkleuren op fotosynthese, vorm en ontwikkeling groeien gestaag. Je zou dan graag willen dat het om simpele relaties gaat, bijvoorbeeld ‘blauw licht opent huidmondjes’. Zo ligt het echter vaak niet. Effecten op korte en lange termijn zijn vaak verschillend en het gaat altijd om de mix van kleuren.
    Consultancy genereren basiskennis fotosynthese aardbei
    Kaiser, E. ; Janse, J. - \ 2016
    Bleiswijk : Wageningen UR Glastuinbouw (Rapport GTB 1411) - 22
    aardbeien - fragaria ananassa - teelt onder bescherming - kasgewassen - glastuinbouw - fotosynthese - energiebesparing - licht - kooldioxide - strawberries - fragaria ananassa - protected cultivation - greenhouse crops - greenhouse horticulture - photosynthesis - energy saving - light - carbon dioxide
    To save electricity and CO2 during strawberry production, more knowledge about the photosynthesis of greenhouse-grown strawberry plants is necessary. This was tackled by measuring light- and CO2-dependent photosynthesis responses and by conducting a literature study in which several parameters of leaf-level photosynthesis were compared. From measurements conducted between middle of March and middle of May 2016 it was concluded that the rate of photosynthesis and electron transport was comparable between young and old leaves, while stomatal conductance in young leaves was always higher. Light- and CO2- saturated photosynthesis rates were higher in older leaves. Furthermore, a decrease of photosynthesis rates was visible in April, which may have been caused by acclimation of leaf biochemistry to elevated CO2 concentrations in the greenhouse. Conclusions from the literature study were that light saturation was reached at ~1000 μmol m-2 s-1 and that CO2 saturation was reached at ~1100 μmol mol-1. Average photosynthesis rates at these conditions were 18 and 35 μmol m-2 s-1, respectively. The average quantum yield of photosynthesis was ~0.06 μmol CO2 μmol-1 PAR, which is comparable to other, fast growing greenhouse crops (e.g. cucumber, tomato, sweet pepper). Large knowledge gaps about the course of photosynthesis during complete growing seasons remain.
    Plantmonitoring op basis van fotosynthese sensoren : ontwikkelen en testen van sensoren
    Dieleman, Anja ; Bontsema, Jan ; Jalink, Henk ; Snel, Jan ; Kempkes, Frank ; Voogt, Jan ; Pot, Sander ; Elings, Anne ; Jalink, Vincent ; Meinen, Esther - \ 2016
    Bleiswijk : Wageningen UR Glastuinbouw (Rapport GTB 1405) - 86
    teelt onder bescherming - glastuinbouw - kastechniek - sensors - fotosynthese - kooldioxide - energie - energiebesparing - verlichting - kunstlicht - kunstmatige verlichting - ventilatie - kunstmatige ventilatie - fluorescentie - tomaten - solanum lycopersicum - protected cultivation - greenhouse horticulture - greenhouse technology - sensors - photosynthesis - carbon dioxide - energy - energy saving - lighting - artificial light - artificial lighting - ventilation - artificial ventilation - fluorescence - tomatoes - solanum lycopersicum
    The basic process for crop growth and production is photosynthesis. Measuring crop photosynthesis is therefore important to monitor the status of the crop and whether the greenhouse climate is set to the needs of the crop. In this project, two monitoring systems for crop photosynthesis were developed and tested. (1) The crop photosynthesis monitor is a soft sensor that can calculate the CO2 uptake of an entire crop. The basis for these calculations are the balance between CO2 supply and CO2 loss via ventilation and crop photosynthesis. By measuring the CO2 concentration and humidity inside and outside the greenhouse, the crop photosynthesis can be calculated. (2) The CropObserver is a fluorescence sensor that measures the light use efficiency of photosynthesis of a large crop area (3 x 3 m2). The crop receives light pulses from a laser in the top of the greenhouse, the sensor measures the fluorescence signal of the crop. Both sensors were tested in a tomato crop in 2014 with promising results. The sensors functioned without problems and delivered patterns of daily photosynthesis which matched the reference measurements reasonably well up to well.
    Antenna size reduction in microalgae mass culture
    Mooij, T. de - \ 2016
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Marcel Janssen. - Wageningen : Wageningen University - ISBN 9789462578890 - 196
    algae culture - algae - light - photobioreactors - photosynthesis - mutants - algenteelt - algen - licht - fotobioreactoren - fotosynthese - mutanten

    The thesis describes the potential of microalgae with a reduced light harvesting antenna for biomass production under mass culture conditions (high biomass density, high light intensity). Theoretically, the lower chlorophyll content reduces the light harvesting capacity and with that the amount of photosaturation. The result would be an increase of the biomass yield on light energy, which is especially favorable at high light intensities. In practice, it was found that the productivity of several antenna size mutants strains was equal, or even lower than that of wild type microalgae. The genetically modified algae suffered from a reduced fitness, possibly because the antenna alterations led to impaired photoprotection mechanisms. In an alternative approach, it was found that by spectral tuning (applying different light colours) oversaturation was decreased and the productivity of wild type microalgae was increased. Special attention was paid to photoacclimation behavior of wild type microalgae. It was investigated whether ‘natural acclimation’ can be exploited to maximize productivity. In the last chapter, the competition between antenna size mutants and wild type cells is investigated by means of a modeling approach. It became clear that a wild type infection of an antenna size mutant culture should be prevented at all costs, as the mutants have a reduced competitive strength.

    Microalgae production in a biofilm photobioreactor
    Blanken, Ward - \ 2016
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Marcel Janssen. - Wageningen : Wageningen University - ISBN 9789462578425 - 234
    algae - algae culture - biofilms - bioreactors - growth - production costs - biomass - artificial lighting - photosynthesis - carbon dioxide - algen - algenteelt - biofilms - bioreactoren - groei - productiekosten - biomassa - kunstmatige verlichting - fotosynthese - kooldioxide

    Microalgae can be used to produce high-value compounds, such as pigments or high value fatty acids, or as a feedstock for lower value products such as food and feed compounds, biochemicals, and biofuels. In order to produce these bulk products competitively, it is required to lower microalgae production cost. Production costs could be reduced by employing microalgae biofilms as a production platform. The main advantages of microalgae biofilms are a direct harvest of concentrated microalgae paste, and the uncoupling of the hydraulic retention time from the microalgal retention time. The latter allows to decrease the liquid volume or to employ dilute waste streams. To successfully employ biofilms, however, it is required that microalgal biofilms can be cultivated at high productivity and high photosynthetic efficiency. The aim of this thesis was to optimize the productivity of microalgal biofilms.

    Light energy drives microalgal growth. Sunlight is free and abundant, but sunlight intensity varies over the day and the seasons. This makes it impossible to maintain optimal production conditions throughout the day. These fluctuations in irradiance can be prevented by applying artificial lighting. Although, artificial lighting will supply a constant light intensity and thus increase productivity and simplify process control, it will also increase microalgae production cost. A quantitative evaluation of lighting costs and energy requirement was still missing and this was the topic of Chapter 2. The costs related to artificial lighting were identified as 25.3 $ per kilogram of dry-weight biomass, with only 4% to 6% of the electrical energy required to power the lamps eventually stored as chemical energy in microalgal biomass. Energy loss and increased production cost may be acceptable for the production of high value products, but in general they should be avoided.

    In Chapter 3, a photobioreactor design based on a rotating biological contactor (RBC) was introduced and used as a production platform for microalgal biomass cultivated in a biofilm. In the photobioreactor, referred to as the Algadisk, microalgae grow in biofilm on vertical rotating disks partially submerged in water with dissolved nutrients. The objective was to evaluate the potential of the Algadisk photobioreactor, and identify the window of operation of the process with respect to the effects of disk roughness, disk rotation speed and CO2 concentration. These parameters were evaluated in relation to biomass productivity, photosynthetic efficiency, and the long-term cultivation stability of the production process.

    The mesophilic green microalga Chlorella sorokiniana was used as a model organism. In the lab-scale Algadisk reactor, a productivity of 20.1 ±0.7 gram per m2 disk surface per day and a biomass yield on light of 0.9 ±0.04 gram dry weight biomass per mol photons were obtained. This productivity could be retained over 21 weeks without re-inoculation. To obtain maximal and stable productivity it was important that the disk surface provides a structure that allows biomass retention on the disk after harvest. The retained biomass acts as inoculum for the new biofilm and is therefore essential for quick biofilm regrowth. Most important process parameters were CO2­ supply, temperature, and pH. Although deviations of these parameters from the optimal conditions resulted in productivity loss, the system quickly recovered when optimal conditions were restored. These results exhibit an apparent opportunity to employ the Algadisk photobioreactor and biofilm systems in general at large scale for microalgae biomass production provided CO2 supply is adequate.

    In order to better understand the process conditions inside the biofilm a model was developed in the further chapters. These mathematical models were calibrated and validated with dedicated experiments. In Chapter 4 first a general applicable kinetic model was developed able to predict light limited microalgal growth. This model combines a mathematical description for photoautotrophic sugar production with a description for aerobic chemoheterotrophic biomass growth. The model is based on five measurable biological parameters which were obtained from literature for the purpose of this study. The model was validated on experiments described in literature for both Chlorella sorokiniana and Chlamydomonas reinhardtii. The specific growth rate was initially predicted with a low accuracy, which was most likely caused by simplifications in the light model and inaccurate parameter estimations. When optimizing the light model and input parameters the model accuracy was improved and validated. With this model a reliable engineering tool became available to predict microalgal growth in photobioreactors. This microalgal growth model was included in the biofilm growth models introduced in Chapters 5 and 6.

    In Chapter 5 microalgal biofilms of Chlorella sorokiniana were grown under simulated day-night cycles at high productivity and high photosynthetic efficiency. The experimental data under day/night cycles were used to validate a microalgal biofilm growth model. For this purpose the light limited microalgal growth model from Chapter 4 was extended to include diurnal carbon-partitioning and maintenance under prolonged dark conditions. This new biofilm growth model was then calibrated and validated experimentally. Based on these experiments and model simulations no differences in the light utilization efficiency between diurnal and continuous light conditions were identified. Indirectly this shows that biomass lost overnight represents sugar consumption for synthesis of new functional biomass and maintenance related respiration. This is advantageous, as this result shows that it is possible to cultivate microalgae at high photosynthetic efficiencies on sunlight and that the night does not negatively impact overall daily productivity. Long periods of darkness resulted in reduced maintenance related respiration.

    Based on simulations with the validated biofilm growth model it could be determined that the photosynthetic efficiency of biofilm growth is higher than that of suspension growth. This is related to the fact that the maintenance rate in the dark zones of the biofilm is lower compared to that in the dark zones of suspension cultures, which are continuously mixed with the photic zone.

    In Chapter 3 it was identified that concentrated CO2 streams are required to obtain high productivities. However, over-supplying CO2 results into loss of CO2 to the environment and is undesirable for both environmental and economic reasons. In Chapter 6 the phototrophic biofilm growth model from Chapter 5 was extended to include CO2 and O2 consumption, production, and diffusion. The extended model was validated in growth experiments with CO2 as limiting substrate. Based on the validated model the CO2 utilization and productivity in biofilm photobioreactors were optimized by changing the gas flow rate, the number of biofilm reactors in series, and the gas composition. This resulted in a maximum CO2 utilization efficiency of 96% by employing flue gas, while the productivity only dropped 2% compared to non-CO2 limited growth. In order to achieve this 25 biofilm reactors units, or more, must be operated in series. Based on these results we conclude that concentrated CO2 streams and plug flow behaviour of the gaseous phase over the biofilm surface are essential for high CO2 utilization efficiencies and high biofilm productivity.

    In Chapter 7 the implications of these studies for the further development of biofilm photobioreactors was discussed in the light of current biofilm photobioreactor designs. Design elements of state of the art biofilm photobioreactors, were combined into a new conceptual biofilm photobioreactor design. This new design combines all advantages of phototrophic biofilms minimizing the amount of material required. Further improvements by means of process control strategies were suggested that aim for maximal productivity and maximal nutrient utilization efficiency. These strategies include: control of the biofilm thickness, control of the temperature, and optimized nutrient supply strategies.

    Parthenocarp ras kan oplossing zijn bij vruchtzettingsproblemen
    Heuvelink, E. ; Kierkels, T. - \ 2016
    Onder Glas 13 (2016)5. - p. 12 - 13.
    tuinbouw - glastuinbouw - groenten - tomaten - paprika's - komkommers - fotosynthese - vruchtzetting - groeiregulatoren - parthenocarpie - cytokininen - gibberellinen - auxinen - horticulture - greenhouse horticulture - vegetables - tomatoes - sweet peppers - cucumbers - photosynthesis - fructification - growth regulators - parthenocarpy - cytokinins - gibberellins - auxins
    Samen met een goede fotosynthese staat voldoende vruchtzetting op de gedeelde eerste plaats bij het welslagen van de teelt van vruchtgroenten. Het zou echter veel gemakkelijker zijn als die bevruchting helemaal niet nodig was. Bij verscheidene gewassen is parthenocarpie inmiddels gewoon, maar bij een belangrijk deel blijft het zaak de juiste omstandigheden voor vruchtzetting te creëren.
    Natural genetic variation for regulation of photosynthesis response to light in Arabidopsis thaliana
    Rooijen, R. van - \ 2016
    Wageningen University. Promotor(en): Maarten Koornneef, co-promotor(en): Mark Aarts; Jeremy Harbinson. - Wageningen : Wageningen University - ISBN 9789462578203 - 235
    arabidopsis thaliana - photosynthesis - genetic variation - light - efficiency - arabidopsis thaliana - fotosynthese - genetische variatie - licht - efficiëntie

    The efficiency of photosynthesis results from the composition and organization of the plant’s internal structural components as well as the capability of response to environmental fluctuations. This thesis aims at identifying the genetic loci that are regulating the (sub-) processes in photosynthetic acclimation to increased irradiance levels, in order to obtain the genetic information useful to breed for photosynthetic performance. It uses genome wide association studies (GWAS) to reveal which genetic loci are being exploited in nature for keeping good photosynthetic performances in natural conditions. Phenotypic variation among natural accessions in photosynthetic light use efficiency response to increased growth irradiance is related to its variation in genetics in order to identify the associated genetic loci. In Chapter 2 is described which light environment reveals most natural variation in photosynthetic performance and for which photosynthetic parameter this is. It shows different Arabidopsis accessions display different photosynthetic responses to various light environments, well relatable to genetic differences. A candidate gene list for the direct response to increased growth irradiance was revealed after performing genome wide association analysis. Chapter 3 elaborates on the genome wide association results by visualizing the dynamics of the associated genetic loci over the time course of the photosynthetic response to increased irradiance. It shows it is possible to simplify the complexity of photosynthetic physiology as well as the genetic analysis in such way to confirm the causal genes underlying the associated loci, by confirming this for the YELLOW SEEDLING 1 (YS1) gene, a gene encoding a Pentatrico-Peptide-Repeat (PPR) protein involved in RNA editing of plastid-encoded genes essential for photosystems I and II. Genetic variation for any trait can be on the transcriptional level or on the functional level. In Chapter 4, the gene regulation in three Arabidopsis accessions with contrasting photosynthesis efficiency responses to increased irradiance is studied. These differences in photosynthesis efficiency are associated to differences in activation extents of heat responsive genes as well as to differences in the presence of a gene activation pathway acting on membrane lipid remodelling, suggested to maintain balanced cellular phosphate concentrations. Chapter 5 confirms the significance of maintaining balanced cellular phosphate concentrations for photosynthesis efficiency responses to increased irradiance. It describes how genome wide association mapping and linkage mapping combine to reveal genetic epistatic interactions between PHOSPHATIDIC ACID PHOPSPHOHYDROLASE 2 (PAH2, phosphate metabolism gene) and ASPARAGINE SYNTHETASE 2 (ASN2, nitrogen metabolism gene), both acting in the delivery of orthophosphate in the chloroplast. In conclusion this thesis contributes new insights into the physiological and molecular pathways underlying photosynthesis responses to increased growth irradiances.

    Leaf anatomy and photosynthesis : unravelling the CO2 diffusion pathway in C3 leaves
    Berghuijs, H.N.C. - \ 2016
    Wageningen University; KU Leuven. Promotor(en): Paul Struik; Bart M. Nicolaï, co-promotor(en): Xinyou Yin. - Wageningen : Wageningen University - ISBN 9789462577947 - 286
    leaves - plant anatomy - photosynthesis - mesophyll - photorespiration - carbon pathways - solanum lycopersicum - bladeren - plantenanatomie - fotosynthese - bladmoes - fotorespiratie - koolstofpathways - solanum lycopersicum

    Keywords: CO2 diffusion, C3 photosynthesis, mesophyll conductance, mesophyll resistance, re-assimilation, photorespiration, respiration, tomato

    Herman Nicolaas Cornelis Berghuijs (2016). Leaf anatomy and photosynthesis; unravelling the CO2 diffusion pathway in C3 leaves. PhD thesis. Wageningen University, Wageningen, The Netherlands, with summaries in English and Dutch. 286 pages

    Optimizing photosynthesis can contribute to improving crop yield, which is necessary to meet the increasing global demand for food, fibre, and bioenergy. One way to optimize photosynthesis in C3 plants is to enhance the efficiency of CO2 transport from the intercellular air space to Rubisco. The drawdown of CO2 between these locations is commonly modelled by Fick's first law of diffusion. This law states that the flux from the air spaces to Rubisco is proportional to the difference in partial pressure between these locations. The proportionality constant is the mesophyll conductance. Its inverse is mesophyll resistance. Mesophyll resistance is a complex trait, which lumps various structural barriers for CO2 transport and processes that add or remove CO2 along the diffusion pathway. In order to better understand how and to what extent these factors affect photosynthesis, it is necessary to find a more mechanistic description of CO2 transport in the mesophyll. The aim of this dissertation is to investigate how leaf anatomical properties and CO2 sources and sinks along the CO2­ diffusion pathway in C3 leaves affect the photosynthetic capacity of these leaves. In this study, Solanum lycopersicum was used as a model organism. In a first approach, we developed a model in which we partitioned mesophyll resistance into two sub-resistances. The model assumed that CO2 produced by respiration and photorespiration was released between the two sub-resistance components. By quantifying these resistances using measured thicknesses, exposed mesophyll and chloroplast surfaces, and assumed diffusive properties, we were able to simulate the effect of various anatomical properties on photosynthesis. A disadvantage of this two-resistance approach is that it assumes either that (photo)respiratory CO2 release takes place in the outer cytosol or that there is no CO2 gradient in the cytosol. Therefore, in a second approach we modelled CO2 transport, production and consumption by use of a reaction-diffusion model. This model is more flexible in terms of determining the location of CO2 sources and sinks. We developed methods to estimate physiological parameters of this model using combined gas exchange and chlorophyll fluorescence measurements on leaves. The results suggest that the rate of respiration depends on the oxygen partial pressure, which is often not considered in previous photosynthesis models. We also presented a method to calculate the fraction of (photo)respiratory CO2 that is re-assimilated. We found that this fraction strongly depends on both environmental factors (CO2, irradiance), the location of mitochondria relative to the chloroplast, stomatal conductance and various physiological parameters. The reaction-diffusion model and associated methods presented in this study provide a more mechanistic framework to describe the CO2 diffusion pathway in C3 leaves. This model could, therefore, contribute to identifying targets to increase mesophyll conductance in future research.

    Robot meet fotosynthese
    Aarts, Mark ; Harbinson, Jeremy - \ 2016
    photosynthesis - robots - measurement - agricultural research - plant breeding - genetics
    Understanding photosynthesis important for CO2-dosing and lighting : CAM-plants difficult to deal with
    Heuvelink, E. ; Kierkels, T. - \ 2016
    In Greenhouses : the international magazine for greenhouse growers 5 (2016)1. - ISSN 2215-0633 - p. 14 - 15.
    horticulture - greenhouse horticulture - carbon dioxide - dosage - cam pathway - illumination - photosynthesis - assimilation - kalanchoe - ornamental bromeliads - phalaenopsis - tuinbouw - glastuinbouw - kooldioxide - dosering - cam cyclus - belichting - fotosynthese - assimilatie - kalanchoe - bromelia's als sierplanten - phalaenopsis
    It used to be rare to come across plants that bind CO2 mainly at night: CAMplants. But it’s no longer an exception in the horticultural sector. Nowadays the best-selling pot plant in the Netherlands – phalaenopsis – belongs to this group. This then raises questions such as: When do CAM-plants behave according to the book and when don’t they? And when does it make sense to dose with CO2 and provide lighting?
    Environmental and physiological control of dynamic photosynthesis
    Kaiser, M.E. - \ 2016
    Wageningen University. Promotor(en): Leo Marcelis, co-promotor(en): Jeremy Harbinson; Ep Heuvelink. - Wageningen : Wageningen University - ISBN 9789462576346 - 248
    solanum lycopersicum - arabidopsis thaliana - photosynthesis - carbon dioxide - temperature - humidity - light intensity - solanum lycopersicum - arabidopsis thaliana - fotosynthese - kooldioxide - temperatuur - vochtigheid - lichtsterkte

    Irradiance is the main driver of photosynthesis. In natural conditions, irradiance incident on a leaf often fluctuates, due to the movement of leaves, clouds and the sun. These fluctuations force photosynthesis to respond dynamically, however with delays that are subject to rate constants of underlying processes, such as regulation of electron transport, activation states of enzymes in the Calvin cycle, and stomatal conductance (gs). For example, in leaves adapted to low irradiance that are suddenly exposed to high irradiance, photosynthesis increases slowly (within tens of minutes); this process is called photosynthetic induction. Photosynthesis in fluctuating irradiance (dynamic photosynthesis) is limited by several physiological processes, and is further modulated by environmental factors other than irradiance, such as CO2 concentration, air humidity and temperature. Studying dynamic photosynthesis and its environmental and physiological control can help to identify targets for improvements of crop growth, improve the accuracy of mathematical models of photosynthesis, and explore new, dynamic lighting strategies in greenhouses.

    In this thesis, the limitations acting on dynamic photosynthesis are explored by reviewing the literature, by experimenting with a suite of environmental factors (CO2 concentration, temperature, air humidity, irradiance intensity and spectrum), genetic diversity in the form of mutants, genetic transformants and ecotypes, and by mathematical modelling. Several genotypes of tomato (Solanum lycopersicum) and the model plant Arabidopsis thaliana, all grown in climate chambers, were used in the experiments. The main findings of the thesis are that a) CO2 concentration and air humidity strongly affect the rate of change of dynamic photosynthesis through a combination of diffusional and biochemical limitations; b) Rubisco activation kinetics are pivotal in controlling rates of photosynthesis increase after a stepwise increase in irradiance, and are further affected by CO2 concentration; c) gs limits photosynthetic induction kinetics in A. thaliana but not in tomato in ambient conditions, and becomes a stronger limitation in low CO2 concentration or air humidity; and d) mesophyll conductance, non-photochemical quenching (NPQ) and sucrose synthesis do not limit dynamic photosynthesis under the conditions used.

    In Chapter 1, the rationale for the research conducted is described, by introducing the concept of fluctuating irradiance and its effects on photosynthesis rates. The chapter discusses how dynamic photosynthesis is measured and described, and provides a range of possible applications of the insights gained by the research conducted in this dissertation.

    In Chapter 2, the current literature is reviewed and a mechanistic framework is built to explore the effects that the environmental factors CO2 concentration, temperature and air humidity have on rates of dynamic photosynthesis. Across data from literature, higher CO2 concentration and temperature speed up photosynthetic induction and slow down its loss, thereby facilitating higher rates of dynamic photosynthesis. Major knowledge gaps exist regarding the loss of photosynthetic induction in low irradiance, dynamic changes in mesophyll conductance, and the extent of limitations imposed by gs across species and environmental conditions.

    Chapter 3 is an experimental exploration of the effects of CO2 concentration, leaf temperature, air humidity and percentage of blue irradiance on rates of photosynthetic induction in dark-adapted tomato leaves. Rubisco activation, changes in stomatal and mesophyll conductance, diffusional and biochemical limitations, efficiency of electron transport through photosystem II, NPQ and transient water use efficiency, were examined to give a comprehensive overview of the environmental modulation of dynamic photosynthesis. Unlike the percentage of blue irradiance, increases in CO2 concentration, leaf temperature and air humidity all positively affected the rates of photosynthetic induction, and these effects were explained by changes in diffusional and biochemical limitations. Maximising the rates of Rubisco activation would increase CO2 assimilation by 6-10%, while maximising the rates of stomatal opening would increase assimilation by at most 1-2%, at the same time negatively affecting intrinsic water use efficiency.

    In Chapter 4 it is explored whether the effects of CO2 concentration on dynamic photosynthesis are similar across various irradiance environments. Gain and loss of photosynthetic induction in several low irradiance treatments, as well as sinusoidal changes in irradiance, were studied using tomato leaves. Elevated CO2 concentration (800 ppm) enhanced the rate of photosynthetic induction by 4-12% (compared to 400 ppm) and decreased the loss of photosynthetic induction by 21-25%. Elevated CO2 concentration enhanced rates of dynamic photosynthesis regardless of initial photosynthetic induction state to a similar extent. Therefore, rising global CO2 concentration will benefit integrated assimilation throughout whole canopies, where different leaf layers experience widely differing irradiance regimes.

    In Chapter 5 it is tested whether stomatal limitation exists during photosynthetic induction in tomato leaves. The abscisic acid-deficient flacca mutant and its wildtype were exposed to various CO2 concentrations to change the diffusion gradient. Despite gs being much larger in flacca, photosynthetic induction proceeded with the same speed in both genotypes in ambient CO2 concentration. This suggested that stomata did not limit photosynthetic induction in the wildtype. Using these findings, several indices of stomatal limitations were compared. Diffusional limitation, a new index, was found to be the most useful.

    In Chapter 6, an exploration of some physiological limitations underlying dynamic photosynthesis is undertaken. Several mutants, transformants and ecotypes of A. thaliana, affecting rates of Rubisco activation, gs, NPQ and sucrose metabolism, were used. Next to a characterisation of their steady-state responses to CO2 concentrations and irradiance, leaves were exposed to stepwise increases and decreases in irradiance (using several intensities) and to lightflecks of several amplitudes and frequencies. Rubisco activase isoform and concentration, as well as various levels of gs, strongly affected rates of dynamic photosynthesis, while this was not the case with low NPQ or sucrose phosphate synthase concentration. This suggests Rubisco activase and gs as targets for improvement of photosynthesis in fluctuating irradiance.

    Chapter 7 is a modelling exercise of dynamic photosynthesis, based on data obtained from measurements on mutants of A. thaliana (Chapter 6). This includes a goal-seeking model that allows reproducing the regulation of Rubisco by irradiance and CO2 concentration. The model also includes a full description of leaf-level NPQ, incorporates mesophyll conductance and accounts for the fundamental physics of delays introduced by open gas exchange systems on CO2 measurements. Different data sets for model calibration and validation were used. It was found that the model accurately predicted the effects of the mutants, suggesting that the assumptions of the model were sound and represented the underlying mechanisms correctly.

    In Chapter 8, the findings in this thesis are synthesized. The insights gained throughout this dissertation are related to existing literature to give a comprehensive overview of the state of knowledge about the limitations of dynamic photosynthesis. The methodology of assessing transient stomatal limitations, and some aspects of using chlorophyll fluorescence measurements during photosynthetic induction, are discussed. Finally, possible applications and ideas for future research on photosynthesis in fluctuating irradiance are discussed.

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