It is important to understand mechanisms that facilitate expansion of two common shrubs, Morella cerifera and Baccharis halimifolia in coastal environments. The purpose of my study was to investigate the physiological and structural changes that occur as leaves age. Photosynthesis, incident light, chlorophyll, and leaf C:N ratios were quantified for young, intermediate, and old leaves (distal, central and proximal leaves, respectively). Leaf structural differences were also compared. Leaves did not change morphologically with age. Light decreased with leaf age and during winter months. Photosynthesis showed no seasonal or age related patterns. Chlorophyll increased initially and then declined with age due to self shading. Nitrogen content was highest during spring. Seasonality and leaf age had unique effects on the two study species. Understanding senescence adaptations of these two shrubs can help explain their abundance in coastal ecosystems.

L’utilisation des microorganismes marins ou terrestres pour la séquestration à long terme du CO2 est une des solutions envisagées pour diminuer la teneur en CO2 dans l'atmosphère. Le travail de cette thèse se concentre sur les microorganismes calcifiants, et notamment les cyanobactéries, qui peuvent fixer du CO2 sous forme de biomasse et carbonate de calcium. Ce dernier, insoluble dans l’eau, précipite et peut donc constituer un puits à long terme. La compréhension des mécanismes de calcification induits par les cyanobactéries et la possibilité de contrôler ces processus sont nécessaires pour développer une technologie de séquestration du CO2. Cette biotechnologie pourrait constituer une alternative à la technologie de capture et stockage géologique du CO2. Synechococcus PCC8806 une souche marine de cyanobactérie purifiée à l'Institut Pasteur de Paris est utilisée comme organisme au cours du travail expérimental réalisé dans le cadre de cette thèse. Le premier résultat important de cette thèse est le développement d'une stratégie analytique ayant permis d'accéder à un bilan de masse carbone et calcium au cours d'une culture de cyanobactérie sur hydrogénocarbonate. La mise en œuvre de cette stratégie au cours de différents essais réalisés dans le cadre de ce travail a permis par ailleurs de quantifier avec précision la production de carbone organique (biomasse) et de carbone inorganique (CaCO3) en fonction du calcium et du carbone inorganique présent dans les milieux de culture. Nous avons ensuite étudié la précipitation de la calcite au cours de la croissance de Synechococcus PCC8806 en présence de calcium. Pour cela les conditions de culture ont été variées de telle sorte que la survenue des évènements de précipitations a pu être comprise ainsi que l'influence de sites de nucléation mis en évidence. Le grossissement des cristaux a également été étudié attentivement par microscopie électronique à balayage. Une autre partie de ce travail a permis d'identifier la source de carbone inorganique utilisée par Synechococcus PCC8806 pour la photosynthèse. Cela a été l'occasion de réécrire les équations liées aux transferts entre le CO2 atmosphérique et le système carbonaté, ainsi que les équations de photosynthèse en fonction des conditions de disponibilité des deux sources de carbone inorganique (CO2 et hydrogénocarbonate). De plus ont pu être mis en évidence, les effets des phases diurne et nocturne de la croissance de cyanobactéries sur les équilibres du système carbonaté et le pH. Ce travail a également permis de déterminer les vitesses de croissance des cyanobactéries et donc de calculer des rendements de croissance par unité de surface. Cela permettra à terme d'optimiser la production de biomasse et de calcite dans un procédé industriel / The use of marine or terrestrial microorganisms for long-term sequestration of CO2 is a possible solution to reduce the CO2 content in atmosphere. This thesis work focuses on calcifying organisms, in particular the cyanobacteria, which can fix CO2 as biomass and calcium carbonate. The latter is insoluble in water; precipitates may therefore constitute a long term sink. Understanding of the calcification mechanisms induced by cyanobacteria and the possibility of controlling these processes are necessary to develop a technology for CO2 sequestration. This biotechnology could be an alternative technology to CO2 capture and geological storage. Synechococcus strain PCC8806, marine cyanobacteria purified by the Institute Pasteur de Paris is used during the experimental work in this thesis. The first important result of this work is to develop an analytical strategy that allowed access to a mass balance of carbon and calcium in a cyanobacteria culture on hydrogencarbonate. The implementation of this strategy in various tests of this work has also allowed to accurately quantify the production of organic carbon (biomass) and inorganic carbon (CaCO3) according to the calcium and Ci introduced (hydrogencarbonate) in the medium. We then studied the calcite precipitation during growth of Synechococcus PCC8806 in the presence of calcium. For that, culture conditions were varied in order to understand the occurrence of precipitation events and the influence of nucleation sites. The development of crystals has also been carefully studied by scanning electron microscopy. Another part of this work has identified the inorganic carbon source used by Synechococcus PCC8806 for photosynthesis. This was an opportunity to rewrite the equations related to transfers between atmospheric CO2 and the carbonate medium, as well as the equations of photosynthesis depending on the conditions of availability of two sources of inorganic carbon (CO2 and hydrogencarbonate). In addition, we have revealed the effects of diurnal and nocturnal phases of the growth of cyanobacteria on the carbonate system balance and pH. This work also allowed estimating the cyanobacteria growth rates and thus calculating growth yields per unit area. This will ultimately optimize biomass and calcite production in an industrial process

Doctor of Philosophy / Department of Chemistry / Ryszard J. Jankowiak / The constituents of oxygen-evolving photosystem II core complexes—antenna proteins (CP43 and CP47) and reaction center (RC)—have been the subject of many studies over the years. However, the various issues related to electronic structure, including the origin/composition of the lowest-energy traps, origin of various emission bands, excitation energy transfer (EET), primary charge separation (CS) processes and pigment site energies remain yet to be fully resolved. Exploiting our state-of-the-art techniques such as low-T absorption, fluorescence, and hole burning (HB) spectroscopies, we resolved some of the issues particularly related to CP47 and isolated RC protein complexes. For example, we demonstrated that the fluorescence origin band maximum (~695 nm) originates from the lowest-energy state ~693 nm of intact CP47. In intact CP47 in contrast to destablished protein complexes, the band (~695 nm) does not shift in the temperature range of 5–77 K unless hole-burning takes place. We also studied a large number of isolated RC preparations from spinach, and wild-type Chlamydomonas reinhardtii (at different levels of intactness), as well as its mutant (D2-L209H), in which the active branch pheophytin (PheoD1) has been genetically replaced with chlorophyll a (Chl a). We showed that the Qx-/Qy-region site-energies of PheoD1 and PheoD2 are ~545/680 nm and ~541.5/670 nm, respectively, in good agreement with our previous assignment [Jankowiak et al. J. Phys. Chem. B 2002, 106, 8803]. Finally, we demonstrated that the primary electron donor in isolated algal RCs from C. reinhardtii (referred to as RC684) is PD1 and/or PD2 of the special Chl pair (analogous to PL and PM, the special BChl pair of the bacterial RC) and not ChlD1. However, the latter can also be the primary electron donor (minor pathway) in RC684 depending on the realization of the energetic disorder. We further demonstrate that transient HB spectra in RC684 are very similar to P+QA - PQA spectra measured in PSII core, providing the first evidence that RC684 represent intact isolated RC that also possesses the secondary electron acceptor, QA. In summary, a new insight into possible charge separation pathways in isolated PSII RCs has been provided.

Master of Science / Department of Horticulture, Forestry, and Recreation Resources / Jason Griffin / The Midwest and southern Great Plains regions of the United States are known for historic and severe droughts. However, short-term recurring drought events are more common and can limit tree survival in landscape and production settings. The pressure of environmental stress combined with numerous diseases and pests are decimating existing Pinus L. spp. (pine) plantings and driving the effort to identify alternative species. Four species of conifer were grown in a pine bark substrate and subjected to recurring moderate to severe drought in a controlled environment glass greenhouse as well as field planted to observe root and shoot growth during the initial 12 months after transplant. The species utilized were Abies nordmanniana (nordmann fir), Cupressus arizonica (Arizona cypress), Picea engelmannii (engelmann spruce), and Thuja x ‘Green Giant’ (‘Green Giant’ arborvitae). Results indicate that C. arizonica exhibited extraordinary growth after establishment and was able to maintain growth and photosynthesis following several drought cycles. Thuja x ‘Green Giant’ exhibited significant increase in root and shoot growth after transplant. Under conditions of moderate and severe drought, only minimal reductions in height and shoot dry weight were observed while root growth and photosynthesis were unchanged. Abies nordmanniana experienced minimal increases in root and shoot growth throughout the growing season and was unaffected by drought. In contrast, P. engelmannii had only modest increases in root dry weight after transplant, while shoot growth was non-existent. Under conditions of severe drought, photosynthesis was reduced. Cupressus arizonica, a known drought tolerant species, with its ability to establish quickly and endure drought may have an advantage when establishing in harsh climates such as the Midwest and southern Great Plains. Thuja x ‘Green Giant’ is known to be a rapid grower, however, it established slowly during the current study and may require additional time before resuming rapid growth and maximum drought tolerance. Slow establishing species such as A. nordmanniana and P. engelmannii may require greater attention to season of planting to coincide with rapid root growth. However, P. engelmannii may not be a suitable choice for the Midwest due to the inability to maintain photosynthesis during periods of drought.

Syftet med denna studie är att undersöka elevernas uppfattningar om materians uppbyggnad och om materians och energins bevarande. Den föreliggande studien baseras på en kvantitativ analys i form av en elektronisk enkät, som föregicks av en kvalitativ analys i form av, strukturerade intervjuer och demonstrationer. Eleverna har kunskap om vardagsnära exempel, som till exempel vad en stekpanna är uppbyggd av. De ansåg att dessa är exempel på materia men när det gäller mer abstrakta begrepp som ljus, magnetfält, skugga, vakuum, värme och ljud uppvisar eleverna mer osäkerhet och brist på kunskaper. Hälften av eleverna svarade att luft är materia, vilket tyder på ”gasblindhet” hos de övriga. Mellan 20 och 45 % av eleverna har inte kunskap om atomens uppbyggnad. Det framgick av studien att eleverna har svårt för materia- och energiomvandlingar i mer komplexa system såsom kolets kretslopp, vattnets kretslopp samt fotosyntesen. Gällande gasbildning och gaskännedom så framkom det att mer än hälften av eleverna hade kunskap om det. / The purpose of this study is to investigate students' perceptions of matter and conservation of matter and energy. This study is based on a quantitative analysis in the form of an electronic questionnaire, which was preceded by a qualitative analysis in the form of structured interviews and demonstrations. It is fairly easy for students to understand matter in questions about objects in everyday life, but more difficult in abstract concepts such as light, magnetic fields, shade, vacuum, heat and sound. Half of the students answered that air is matter, which indicates "gas blindness" of the other. Between 20 and 45 % of the students have poor knowledge of the structure of the atom. It appeared that students have problems with matter and energy transformations in more complex systems such as the carbon cycle, the water cycle and photosynthesis. Concerning gas formation and gas knowledge it appeared that half of the students had knowledge about the phenomena.

Les caroténoïdes jouent un rôle essentiel dans les premiers événements photosynthétiques. Ils absorbent la lumière et transfèrent l'énergie résultante en excitation aux molécules voisines, assurant le respect de la succession des étapes photosynthétiques. En plus de l'absorption de la lumière, les caroténoïdes protègent l'appareil photosynthétique du stress photo-oxydatif survenant en condition de lumière intense, évitant les éventuels dommages. Les propriétés électroniques des caroténoïdes sont à la base de leurs mécanismes d'action et dans ce travail de recherche une combinaison de techniques biochimiques et spectroscopiques est utilisée pour examiner plus loin ces mécanismes avec un accent mis sur le rôle photoprotecteur joué par des caroténoïdes. Les d'échantillons analysés représentent différent niveaux d'organisation des protéines collectrices de lumière contenants ces pigments. Dans cette thèse quatre études principaux ont étés réalisés pour comprendre comment: les propriétés d'absorption des caroténoïdes lutéine et -carotène près les plantes peuvent être réglées in vivo par le site de liaison à leur protéines, le majeur complexe de capture de la lumière (LHCII) et le photosystème II (PSII) respectivement; l'altération des gènes de la voie biosynthétique des caroténoïdes peut indirectement provoquer une altération du transport d'électrons dans l'organisme photosynthétique; des molécules artificielles sont capable d'imiter le mécanisme photoprotecteur de transfert d'énergie entre les états de triplet des chromophores en mimant les protéines de l'apparat photosynthétique; la flexibilité structurelle de l'LHCII peut être explorée en modifiant son environnement. / Carotenoids play an essential role in the first steps of photosynthesis. They absorb light and they transfer the resulting excitation energy to the neighboring molecules, guaranteeing the correct order of the photosynthetic events. Additionally, carotenoids are able to protect the photosynthetic apparatus from the oxidative stress occurring in high light condition. Biological functions of carotenoids involving interaction with light, such as photosynthesis, are determined by the electronic properties of the conjugated polyene chain that is characteristic of carotenoid molecules. Understanding how these properties are tuned, is essential for understanding the mechanisms underlying carotenoid functions. Here we show that, by using a combination of different spectroscopic and biochemical approaches, these characteristics can be assessed in different kind of samples having the carotenoid molecules as common denominator. In this thesis four major studied have been performed in order to study how: the absorption properties of the two -carotenes molecules in PSII-RC and those of the two luteins in LHCII are tuned in vivo by their protein binding site, the alteration of the genes involved in the biosynthetic pathway of carotenoids has a pleiotropic effect on the photosynthetic organisms, artificial constructs are able to reproduce the photoprotective mechanism of triplet-triplet energy transfer between chromophores by mimicking the naturally occurring photosynthetic proteins, the structural flexibility of the major light harvesting complex can be probed by modifying its surrounding environment.

O caquizeiro (Diospyros kaki L.) é uma planta caducifólia pertencente à família Ebenaceae, tendo como centro de origem a região central da China. Entre os estados brasileiros, São Paulo é o que apresenta maior produção de caquis com 49.727 t. A cercosporiose (Pseudocercospora kaki), também conhecida como mancha angular, é a principal doença foliar da cultura. Alguns autores atribuem à cercosporiose a queda precoce de folhas, maturação antecipada dos frutos e a redução da produção na safra seguinte. Entretanto, não existem trabalhos com o patossistema P. kaki - D. kaki que deem suporte a essas pressuposições. Diante disso, os objetivos desse trabalho foram comparar a susceptibilidade de quatro cultivares de caquizeiro e avaliar o efeito da cercosporiose na fisiologia da planta. Os experimentos foram conduzidos em condições naturais de campo, com as cultivares Fuyu, Rama Forte, Taubaté e Giombo, por serem as mais cultivadas no estado de São Paulo. Nos experimentos desenvolvidos buscou-se conhecer o grau de resistência das quatro cultivares à cercosporiose, avaliando a incidência, severidade e queda de folhas ao longo de dois ciclos de cultivo, assim como avaliar o controle químico na redução da doença em cvs. Taubaté e Rama Forte e, consequentemente, no acúmulo de reservas na raiz e na qualidade dos frutos colhidos. Foram avaliadas também os danos na fotossíntese em folhas das quatro cultivares com diferentes intensidades de cercosporiose. Como resultados pode-se constatar, que a cv. Fuyu é a mais susceptível à cercosporiose, seguida com resistência média \'Giombo\' e \'Rama Forte\' e com maior resistência a cv. Taubaté. A intensidade da cercosporiose, para severidades da doença de até 7% não influencia na queda de folhas. O controle químico reduziu a intensidade de doença nas cvs. Taubaté e Rama Forte, entretanto, entre as intensidades de cercosporiose avaliadas em plantas tratadas e não tratadas, não há redução no acúmulo de reservas no sistema radicular, assim como na qualidade físico-química dos frutos colhidos. Mesmo a cercosporiose afetando a fotossíntese, no processo fotoquímico, tanto na área lesionada como na área adjacente à lesão, a intensidade da doença observada no campo não foi suficiente para causar redução da produção à cultura. / The persimmon (Diospyros kaki L.) is a deciduous plant of the botanical family Ebenaceae, native to central China. Among the Brazilian states, São Paulo has the highest production of persimmon with 49,727 ton/year. The angular leaf spot of persimmon (Pseudocercospora kaki), also known as cercosporiosis, is the main leaf disease of the crop. Some authors attribute to the cercosporiosis the premature defoliation, early maturation of the fruits and the reduction of the yield in the next crop cycle. However, there are no previous studies with the Pseudocercospora kaki pathosystem that support these hypotheses. Therefore, the objectives of this study were to compare the susceptibility of four persimmon cultivars and evaluate the effect of angular leaf spot on plant physiology. A field experiment was conducted with Fuyu, Rama Forte, Taubaté and Giombo cultivars, the four most cultivated in the state of São Paulo. The degree of resistance to cercosporiosis was determined by the incidence and severity of the disease and by defoliation of the plants in two crop cycles. Chemical spraying for the disease reduction was also evaluated in cvs. Taubaté and Rama Forte. The reduction of the carbohydrate reserve accumulation in the roots and the quality of the fruits harvested were tested. The photosynthesis reduction was also evaluated in leaves of the four cultivars with different intensities of cercosporiosis. The Fuyu cultivar was the most susceptible to cercosporiosis, followed by moderate resistance of \'Giombo\' and \'Rama Forte\' and high resistance of cv. Taubaté. The intensity of cercosporiosis, for disease severity up to 7% does not influence leaf drop. Though the chemical control reduced the disease intensity in cvs. Taubaté and Rama Forte, treated and untreated plants showed no differences in the reserves accumulation in the roots, as well as in the physicochemical quality of the harvested fruits. Even though cercosporiosis affects photosynthesis in the photochemical process on both the necrotic and remaining green leaf area, the intensity of the disease observed in the field was not enough to cause yield reduction to the culture.

As reações luminosas da fotossíntese em plantas envolvem quatro complexos proteicos multi-unidades na membrana dos tilacóides incluindo o fotossistema II (PSII), o complexo citocromo b6f, o fotossistema I (PSI) e o complexo ATP sintase. Uma atividade apropriada desse processo exige um mecanismo de controle de qualidade mediado por chaperonas, DnaJs e proteases, como o complexo FtsH. Esse conjunto de proteínas garantem um dobramento correto de proteínas, as montagens devidas dos complexos e a degradação de algumas subunidades danificadas quando necessário. Neste trabalho nós mostramos o envolvimento de FIP, uma proteína com um domínio dedo-de-zinco localizada nos tilacóides de cloroplastos de A. thaliana, no mecanismo de resposta à estresses abióticos. Plantas mutantes fip foram, fenotipicamente, mais tolerantes à estresses abióticos de alta luminosidade, elevado potencial osmótico e excesso de sal. Também mostramos que a expressão de FIP é diminuída em resposta às diferentes condições de estresse, assim como o acúmulo de transcritos de genes relacionados à estresse foi menor nas plantas mutantes fip. Análises por immunoblot mostraram que os mutantes fip acumulam menos proteínas PsaA e PsaB do fotossistema I e plastocianina (PC) do que as plantas selvagens, no entanto não são afetados quanto ao acúmulo de proteínas do fotossistema II e do Complexo do Citocromo b6f sob condições controle. Esses mutantes também acumulam menos FtsH5 nos tilacóides, sem afetar a eficiência dos fotossistemas I e II. Foi testado também o potencial redutase do domínio dedo-de-zinco da proteína recombinante FIP (6xHis-FIP) em ensaios in vitro de redução de insulina. Vimos que FIP apresenta atividade redutase, significantemente, maior que o controle negativo nas condições testadas. Considerando todos os resultados obtidos até o momento, acreditamos que FIP possa estar agindo como uma redutase na membrana dos tilacóides, tendo como alvos não somente FtsH5, mas também outras proteínas com resíduos de cisteína nas suas estruturas, e que sua atividade tem influência no acúmulo de proteínas dependentes de redução para a maturação como PsaA, PsaB e PC. Uma investigação mais aprofundada da atividade de FIP nos cloroplastos ainda é necessária para o completo entendimento da sua função. / The light-driven photosynthetic reactions in plants take place within four multi- subunit protein complexes in the thylakoid membranes, including photosystem II (PSII), the cytochrome b6f complex, photosystem I (PSI) and the ATP synthase complex. Regulation of all these molecular machineries requires a fine-tuning control mechanism mediated by specific proteins, including chaperones, DnaJs, and proteases, such as the FtsH complex. These set of proteins guarantee the proper folding, assembly and degradation of the photosynthetic complexes\' subunits. In this work we showed the involvement of FIP, a zinc-finger protein localized in the thylakoid membranes in A. thaliana, in the abiotic stress response mechanism. Mutants fip knockdown plants were phenotypically more tolerant to abiotic stresses like high light, increased osmotic potential and salt excess. We also showed that FIP is down-regulated by different abiotic stresses, with lower levels of stress-related gene transcripts accumulation in mutant fip plants. Analysis of accumulation of photosynthetic proteins by immunoblot under control conditions showed that mutants fip displayed lower levels of PsaA, PsaB (PSI) and Plastocyanin (PC) proteins than wild-type plants, however are not affected for PSII and Cyt b6f proteins accumulation under the same growth conditions. In addition, the mutants accumulated slightly less FtsH5 proteins in thylakoid membranes, without affecting PSII and PSI efficiency. We tested the putative reductase activity probably mediated by FIP zinc-finger domain, using the recombinant form of the protein 6xHis-FIP in in vitro insulin reduction assays. FIP presented a reductase activity higher than the negative control under the same assay conditions. Taking all together, these results suggest that FIP may be acting as a reductase in the thylakoid membranes, having as targets not only FtsH5 but other targets with available cysteine residues, depending on the reduction step for proper accumulation such as PsaA, PsaB and PC. Further investigations regarding the role of FIP in chloroplasts are still necessary to completely understand its function.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, Republic of South Africa, in fulfillment of the requirements for the degree of Doctor of Philosophy in Engineering. Johannesburg, 2016 / The process of photosynthesis is of great importance as it is the reaction of carbon dioxide (CO2) and water with the help of light, ’free’ energy from the sun, to form useful carbohydrates and oxygen. Photosynthesis is therefore useful both in carbon dioxide mitigation and growing bio-feedstocks towards making biofuel. This thesis aims to address two areas for analysing the photosynthesis process: 1. Looking at the physical limits of the growth; and 2. Improving the production rate of some aquatic plants, such as duckweed and microalgae. To address the first aim, the fundamental concepts of thermodynamics were used to analyse the photosynthetic process. It was found that the theoretical minimum number of moles of photons (NP) required (9–17) is less than the values reported by other researchers, suggesting that the photosynthesis process is highly irreversible and inefficient (operating at 35% efficiency or less). This is because the number of moles of photons will increase with greater process irreversibility (when the entropy generated is greater than zero). If the photosynthesis process is indeed that irreversible then the removal of heat (the heat not used by other cellular processes) by the plant becomes a major problem. It is suggested that transpiration, and other cellular processes, are the processes by which that is done, and it is shown that the water needs of the plant for transpiration would dwarf those needed for photosynthesis. Knowing the fundamental limits to growth could also be of use because if an organism was growing at a rate close to this value there would be no advantage to try to do genetic modification to improve its rate. Following the ideas presented above a spectrophotometer was used not only to obtain the absorption spectrum of algae, but it was also used to grow small samples at specific light wavelengths. The algae species researched was Desmodesmus spp., which, for example, is used to remediate waste water or as a source of feedstock for biofuel production. It also tolerates high CO2 concentrations. This simple experimental method demonstrated that a specific light wavelength (in particular the Secomam Prim spectrophotometer) 440 nm was preferred for the algae growth. It was recommended that this specific light wavelength would be best for growth. It might also be useful to know this fact particularly when designing photobioreactors, as this could reduce the amount of heat released into the surroundings and thus make the process more energy efficient. Interestingly, the wavelength for maximum growth corresponded to one of the peaks in the absorption spectra but there was no increase in growth rate corresponding to any of the other peaks. To address the second aim, the author determined how well predictions on improving the growth of algae (Desmodesmus spp. for example), based on a theoretical model, would work when tested experimentally. What the researcher found was that the method improved algae production, using the same set of equipment. The production was improved by a factor of 1.28 and 1.26 (at product concentrations 1000 mg/L and 600 mg/L respectively) when retaining 40% of the algae suspension. The method may be particularly useful when large amounts of biomass are required as there is no extra cost of purchasing additional equipment. The same model was applied to a growth profile of duckweed (Spirodela polyrhiza 8483, which is convertible into biofuel or a source of food), and the author showed that the model could work if the duckweed was provided with an added carbon source. In order to find an economical and reliable alternative to bridge the scale gap between laboratory and industrial production, the author checked if duckweed species (Spirodela polyrhiza 8483, Spirodela polyrhiza 9509, Lemna gibba 8428, Lemna minor DWC 112, Wolffia cylindracea 7340 and Wolffia globosa 9527) could be cultivated in media less expensive than the basal laboratory medium (Schenk and Hildebrandt). The author found that duckweed can be cultivated more efficiently, and in a more cost-effective manner, in the alternative media types, while maintaining growth rates, RGR 0.09 day-1, and starch contents, 5– 17%(w/w), comparable with that obtained with the conventional laboratory media. Thus, by looking at the photosynthesis process thermodynamically and experimentally, it is shown to be possible to improve the process by using concepts presented in this thesis. / MT2017

Entre os vegetais existem duas estratégias distintas para superar as condições de estresse hídrico que condicionam a sensibilidade a dessecação (SD) que está associada a mecanismos de evitação e a tolerância a dessecação (TD) que envolve suportar o estresse hídrico diretamente no nível dos tecidos e no nível subcelular. Sabe-se que os custos acoplados aos mecanismos de dessecação e reidratação em espécies TD são elevados, e provavelmente superiores aos de espécies SD. Desta forma, a coexistência de espécies com estas estratégias, como ocorre no ambiente epifítico da Cidade Universitária Armando Sales de Oliveira (CUASO), induzem questões quanto a as vantagens relativas de espécies TD sobre SD. Devido aos altos custos da estratégia TD é possível propor que estas deveriam apresentar um ganho médio de carbono superior a de espécies SD durante o período favorável (com disponibilidade hídrica). Além disso, também é razoável esperar que as distintas formas de uso da água, vinculadas às estratégias, poderiam facilitar o convívio de espécies TD e SD através da segregação de nichos. Com intuito de verificar essas hipóteses, foram realizadas análises relacionadas a estrutura de comunidade de epífitas da CUASO e, a partir destas, a detecção da associação espacial mais freqüente, que resultou composta por Pleopeltis hirsutissima (TD) e Microgramma squamulosa (SD). Estas espécies foram então selecionadas para avaliar parâmetros associados à dinâmica do uso da água, assimilação líquida de carbono, dinâmica da capacidade de uso da luz, estado de hidratação foliar e pigmentos fotossintéticos. Os resultados apontaram que espécies de ambas as estratégias não apresentam sinais de estresse crônico no ambiente estudado. Os dados reforçaram as respostas contrastantes de TD e SD, refletindo as formas distintas de lidar com os recursos e condições do ambiente. Ao contrário do esperado, P. hirsutissima não apresentou uma assimilação de carbono superior a M. squamulosa, indicando que o ganho de carbono não é um dos fatores possíveis na compensação dos custos acoplados a sua estratégia (TD). Porém, os resultados apresentados quanto a dinâmica da capacidade de uso da luz sugerem que a coexistência é facilitada pela segregação de nichos de luz, sendo a espécie TD mais heliófila do que a espécie SD / In land plants the resistance to drought can be accomplished by two main strategies. One involves mainly dehydration avoidance mechanisms and the other is based on the ability to withstand drought at the tissues and down to subcellular levels. The former is found on the desiccation sensitive plants (DS) and the last describes the desiccation tolerant plants (DT). The metabolic costs of the desiccation tolerance mechanisms are probably high, at least when considering the cessation of photosynthesis during anabiosis - a condition that is absent in drought avoidance strategies. The coexistence of drought avoiders and desiccation tolerant plants in the same substrate and condition can rise some questions about the relative advantages of each strategy when submitted to similar water regime. We ask whether desiccation tolerant plants have a compensatory carbon gain under a watering regime that induces frequent anabiosis or cumulative damage in drought avoidance have a detrimental effect comparable to the costs of the desiccation tolerance. An analysis of the epiphytic plant community associated to the trees of the CUASO urban landscape showed a very frequent co-occurring species pair including the desiccation sensitive Microgramma squamulosa and a desiccation tolerant Pleopeltis hirsutissima, both cryptogams of the same plant family. These species were thoroughly examined regarding the patterns of light, water and carbon dynamics together with pigments concentration during cycles of natural drought and wet climate field conditions. These observations were complemented with experimental induction of different water and light regimes. The results showed no sign of chronic stress in both plants living at the same condition but allowed us to identify large distinctions in resource use patterns. A compensatory carbon assimilation was not found in P.hirsutissima. Both species have similar CO2 assimilation values. Experimental induction of drought in different light regimes allowed to verify a relative advantage in desiccation tolerant P.hirsutissima in comparison to the desiccation sensitive M.squamulosa under high irradiance values. Furthermore, light curve analysis suggest that they share the same tree but their niches differ in light intensity regime allowing the high frequency of co-occurrence observed in the field