Les diatomées constituent le principal groupe du phytoplancton dans les océans, contribuant à près de 20% de la production primaire globale. Dans leur environnement très variable, les diatomées sont particulièrement efficaces dans leur capacité à ajuster leur activité photosynthétique en dissipant sous forme de chaleur l’énergie lumineuse absorbée en excès, par un processus appelé le « Non-Photochemical Quenching of chlorophyll fluorescence », (NPQ). Chez la diatomée modèle, Phaeodactylum tricornutum, il a été montré que LHCX1, une protéine proche des antennes photosynthétiques, est impliquée dans le NPQ. Par des approches intrégrées de génétique, biologie moléculaire, biochimie, imagerie des cinétiques de fluorescence et spectroscopie ultrarapide, j’ai étudié le rôle de la famille des LHCX chez P. tricornutum. J’ai tout d’abord pu corréler une expression différentielle des 4 gènes LHCX de P. tricornutum avec différentes dynamiques de NPQ et activités photosynthétiques, dans différentes conditions de lumiére et nutriments. En localisant les LHCX dans les differents complexes photosynthétiques et les différents sites de dissipation d’énergie, j’ai pu proposer un modèle de régulation dynamique du NPQ impliquant à court terme principalement LHCX1 au niveau des centres réactionnels, et une autre isoforme, possiblement LHCX3, au niveau des antennes lors d’un stress lumineux prolongé. Enfin, par le criblage d’une série de mutants potentiellement dérégulés dans leur contenu en LHCXs, j’ai pu identifier des lignées avec un NPQ altéré qui pourront constituer des nouveaux outils de recherche. Dans l’ensemble ce travail de thèse a permis de mettre en évidence la diversification fonctionnelle et l’importance de la famille des LHCX dans la fine modulation des capacités de collecte de lumière et de photoprotection, expliquant sans doute en partie le succès des diatomées dans leur environnement très fluctuant. / Diatoms dominate phytoplanktonic communities in contemporary oceans, contributing to 20% of global primary productivity. In their extremely variable environment, diatoms are especially efficient in adjusting their photosynthetic activity by dissipating as heat the light energy absorbed in excess, through a process called “Non-Photochemical Quenching of chlorophyll fluorescence”, (NPQ). In the model diatom Phaeodactylum tricornutum, it has been shown that LHCX1, a photosynthetic antenna-related gene, is involved in the NPQ process. Through integrated approaches of genetics, molecular biology, biochemistry, study of the kinetics of chlorophyll fluorescence yields and ultrafast spectroscopy, I studied the role of the LHCX family in the photoprotection activity of P. tricornutum. I first correlated a differential regulation of the 4 P. tricornutum LHCX genes with different dynamics of NPQ and photosynthetic activity, in different light and nutrient conditions. By localizing the LHCXs in fractioned photosynthetic complexes and the different sites of energy dissipation, I was able to propose a model of dynamic regulation of NPQ capacity involving mainly the LHCX1 in the reaction centers, during short-term high light responses. During prolonged high light stress, the quenching occurs mainly in the antennas, potentially mediated by the LHCX3 isoform. Finally, using photosynthetic parameters, I screened a series of transgenic lines putatively deregulated in their LHCX amount, and I identified lines with altered NPQ, which could represent novel investigation tools. Altogether, this work highlighted the functional diversification and the importance of the LHCX protein family in the fine-tuning of light harvesting and photoprotection capacity, possibly contributing to explain diatoms success in their highly fluctuating environment.

Master of Science / Department of Agronomy / P. V. Vara Prasad / Grain sorghum (Sorghum bicolor L. Moench) is the fourth most important cereal crop grown throughout the semi-arid regions of the world. It is a staple food crop in Africa and Asia, while it is an important feed crop in the United States (US). More recently it is increasingly becoming important as a potential bioenergy feedstock crop around the world. The state of Kansas is the largest producer of grain sorghum in the US and contributes 40% of the total production. Drought is one of the major environmental factors limiting sorghum production in the semi-arid regions of the US, Asia and Africa. It is estimated that global crop losses due to drought stress exceed $10 billion annually. In crop production, drought stress can be classified into pre- or post-flowering. Even though the world collections of sorghum contain over 35,000 accessions, the genetic base currently used in breeding programs is very small (about 3%). Thus, it is important to identify diverse breeding lines for crop improvement. The diversity (association) panel consisting of 300 sorghum lines from all over the world was assembled for trait evaluation and association mapping. In this research these lines were grouped into the five major races (Figure 1) and 10 intermediate races of sorghum. The objectives of the research are to: (i) quantify the performance of the diversity panel under field conditions in Kansas, (ii) identify critical physiological traits affected by drought at both pre- and post-flowering stages of sorghum development, (iii) identify the most sensitive stage to drought stress during the reproductive phase of sorghum development and, (iv) test the feasibility of using a chlorophyll fluorescence assay (CVA) as a tool for identifying stay-green lines in grain sorghum during early stages of crop development. Field experiments were conducted in 2006 and 2007 in two locations in Kansas (Manhattan and Hays) under rain fed and irrigated conditions for the association panel. Objectives (iii) and (iv) were achieved with controlled environment experiments conducted in the greenhouse at the agronomy department, Kansas State University in 2006 and 2007. Results showed that there was large genetic variability among and within different races in the diversity panel for growth, physiological traits and yield components. Some genotypes showed yield stability across the different environments that were investigated. Drought significantly decreased seed number and harvest index across genotypes and races. In grain sorghum the period prior to flowering (panicle initiation) was the most sensitive stage to drought stress, in terms of its effect on seed-set, during reproductive development. A cell viability assay showed that there were significant differences in the loss of cell viability between leaf sample of stay green and non-stay green genotypes when leaf samples are collected in the morning and subjected to high respiratory demand. Therefore the chlorophyll fluorescence assay has potential as a tool for stay green trait screening at early stages of growth in grain sorghum.

Η εκτίμηση της παραγωγικότητας των χερσαίων οικοσυστημάτων προϋποθέτει τη δημιουργία αξιόπιστων μοντέλων παραγωγικότητας. Τα μοντέλα παραγωγικότητας τροφοδοτούνται με μια σειρά βιοτικών (φωτοσυνθετική ταχύτητα, συγκέντρωση χλωροφύλλης, ειδική μάζα φύλλου) και αβιοτικών παραμέτρων (θερμοκρασία, ένταση φωτός, βροχόπτωση) των φυτικών ειδών και του περιβάλλοντος. Μία από τις σημαντικότερες βιοτικές παραμέτρους αποτελεί η μέγιστη φωτοσυνθετική ταχύτητα κάτω από κορεσμένες εντάσεις φωτός, σε φυσιολογικές συγκεντρώσεις CO2 και στις επικρατούσες θερμοκρασίες (Asat). Η μέτρηση της Asat στο πεδίο με τις κλασσικές μεθόδους (αναλυτής αερίων) είναι επίπονη και χρονοβόρος διαδικασία. Για το λόγο αυτό νέοι τρόποι υπολογισμού της Asat προτείνονται. Στην παρούσα εργασία διερευνήθηκε η δυνατότητα εκτίμησης της Asat ορισμένων μεσογειακών φυτών μέσω της ανάλυσης της ταχείας φάσης ανόδου του φθορισμού της χλωροφύλλης (JIP-test). Για το σκοπό αυτό χρησιμοποιήθηκαν τα ετήσια είδη Malva sylvestris και Capparis spinosa, το φυλλοβόλο είδος Cercis siliquastrum, το ημιφυλλοβόλο είδος Phlomis fruticosa, και τα σκληρόφυλλα είδη Nerium oleander, Ceratonia siliqua και Ligustrum japonicum. Οι μετρήσεις της Asat πραγματοποιήθηκαν με τη χρήση αναλυτή αερίων ανοικτού τύπου (LI-6400, LICOR), ενώ για τη μέτρηση της ταχείας φάσης ανόδου του φθορισμού χρησιμοποιήθηκε φθορισμόμετρο υψηλής χρονικής ανάλυσης (HandyPEA, Hansatech). Οι μετρήσεις πραγματοποιήθηκαν σε εποχιακή βάση. Σύμφωνα με τα αποτελέσματα των πειραμάτων μας, δεν βρέθηκε κάποια παράμετρος του JIP-test που μπορεί να χρησιμοποιηθεί ως γενικευμένος δείκτης της Asat, αντίθετα η Asat εμφάνισε πολύ καλή συσχέτιση με τη στοματική αγωγιμότητα. Εντούτοις, στα σκληρόφυλλα είδη και το ημιφυλλοβόλο είδος βρέθηκε καλή συσχέτιση μεταξύ της Asat και των δεικτών ψΕ0, δR0 και φR0 για τα χειμερινή ομάδα μετρήσεων. Η δυσμενέστερη περίοδος για τα πολυετή είδη φαίνεται πως είναι το καλοκαίρι. Τέλος, ο δείκτης VK/VJ μπορεί να υποδείξει τις κύριες καταπονητικές περιόδους. / The evaluation of the productivity of terrestrial ecosystems presupposes the creation of reliable productivity models. The productivity models are supplied with a series of biotic (photosynthetic rate, chlorophyll concentration, specific leaf mass) and abiotic parameters (temperature, light intensity, rainfall) of the plant species and of the environment. One of the most important biotic parameters is the maximum photosynthetic rate under saturated light intensities, under ambient CO2 concetration and under the prevailing temperatures (Asat). The measurement of Asat under field conditions using the traditional methods (gas analyzer) is a laborious and time consuming process. For this reason new methods of Asat calculation are suggested. In the present study the possibility of Asat estimation in some Mediterranean species with the use of the fast chlorophyll fluorescence transient (JIP-test) has been examined. For this purpose, the annual species Malva sylvestris and Capparis spinosa, the deciduous species Cercis siliquastrum, the semi-deciduous species Phlomis fruticosa, and the sclerophyllous species Nerium oleander, Ceratonia siliqua και Ligustrum japonicum have been used. The Asat measurements have been carried out with the use of an open gas exchange analyzer (LI-6400, LICOR), while for the measurement of the fast chlorophyll fluorescence transient a high-time resolution fluorometer (HandyPEA, Hansatech) has been used. The measurements were carried out on a seasonal basis. According to the results of our experiments, no JIP-test parameter has shown to act as a generalized index of Asat, while Asat has shown a very good correlation with stomatal conductance. However, at the sclerophyllous and the semi-deciduous species, a good correlation between Asat and ψΕ0, δR0 και φR0 indices has been shown for the winter team. The most adverse period of the year for the perennial species is summer. Finally, VK/VJ index is indicative of the most stressful periods for our species.

This study investigated the use of optical remote sensing for estimating leaf and canopy scale light use efficiency (LUE) and carbon exchange. In addition, a new leaf level model capable of predicting dynamic changes in apparent reflectance due to chlorophyll fluorescence was developed. A leaf level study was conducted to assess the applicability of passive remote sensing as a tool to measure the reduction, and the subsequent recovery, of photosynthetic efficiency during the weeks following transplantation. Spectral data were collected on newly planted saplings for a period of 8 weeks, as well as gas exchange measurements of LUE and PAM fluorescence measurements. A set of spectral indices, including the Photochemical Reflectance Index (PRI), were calculated from the reflectance measurements. A marked depression in photosynthetic rate occurred in the weeks after outplanting followed by a gradual increase, with recovery occurring in the later stages of the experimental period. As with photosynthetic rate, there was a marked trend in PRI values over the study period but no trend was observed in chlorophyll based indices. The study demonstrated that hyperspectral remote sensing has the potential to be a useful tool in the detection and monitoring of the dynamic effects of transplant shock. Relationships between hyperspectral reflectance indices, airborne carbon exchange measurements and satellite observations of ground cover were then explored across a heterogeneous Arctic landscape. Measurements were collected during August 2008, using the University of Edinburgh’s research aircraft, from an Arctic forest tundra zone in northern Finland as part of the Arctic Biosphere Atmosphere Coupling at Multiple Scales (ABACUS) study. Surface fluxes of CO2 were calculated using the eddy covariance method from airborne data that were collected from the same platform as hyperspectral reflectance measurements. Airborne CO2 fluxes were compared to MODIS vegetation indices. In addition, LUE was estimated from airborne flux data and compared to airborne measurements of PRI. There were no significant relationships between MODIS vegetation indices and airborne flux observations. There were weak to moderate (R2 = 0.4 in both cases) correlations between PRI and LUE and between PRI and incident radiation. A new coupled physiological radiative transfer model that predicts changes in the apparent reflectance of a leaf, due to chlorophyll fluorescence, was developed. The model relates a physically observable quantity, chlorophyll fluorescence, to the sub leaf level processes that cause the emission. An understanding of the dynamics of the processes that control fluorescence emission on multiple timescales should aid in the interpretation of this complex signal. A Markov Chain Monte Carlo (MCMC) algorithm was used to optimise biochemical model parameters by fitting model simulations of transient chlorophyll fluorescence to measured reflectance spectra. The model was then validated against an independent data set. The model was developed as a precursor to a full canopy scheme. To scale to the canopy and to use the model on trans-seasonal time scales, the effects of temperature and photoinhibition on the model biochemistry needs to be taken into account, and a full canopy radiative transfer scheme, such as FluorMOD, must be developed.

Woody plant expansion has been documented for decades in many different ecosystems, often due to anthropogenic disturbances to the environment and yielding vast changes in ecosystem functioning. While causes and consequences of woody expansion have been well documented, few studies have investigated functional traits of woody species that promote rapid expansion in range. My objective was to determine if hydraulic efficiency confers enhanced photosynthetic efficiency so that functional traits representing light and water use may be possible mechanisms facilitating woody encroachment into grasslands and forest understories. I quantified leaf-level light environment, photosynthetic activity, and hydraulic characteristics of three sympatric broadleaf evergreens of varying leaf life span (Ilex opaca, Kalmia latifolia, and Myrica cerifera) in a deciduous forest understory to understand seasonal intra- and interspecific ranges of broadleaf evergreen physiology. Additionally, I investigated the effects of age on physiological efficiency of M. cerifera across a chronosequence (i.e., space for time substitution) of shrub thicket development in order to understand possible age-related physiological mechanisms facilitating shrub expansion. Lastly, I determined functional traits and resulting physiology that contribute to rapid expansion and thicket formation of an invasive, deciduous, N-fixing shrub, Elaeagnus umbellata, and a native, evergreen, N-fixing shrub M. cerifera. When compared to co-occurring evergreen species, electron transport rate (ETR) of M. cerifera was nearly double that of I. opaca or K. latifolia in summer. Photosynthetic capacity was positively related to hydraulic capacity among understory evergreens. Furthermore, photosynthetic and hydraulic efficiency of M. cerifera remained consistent despite considerable differences in thicket age and development. Both similar and contrasting functional traits of E. umbellata and M. cerifera allowed for enhanced light capture and water movement, and reductions in subcanopy light penetration. Enhanced hydraulic and photosynthetic efficiency relative to co-occurring species contributes to rapid range expansion and thicket formation by promoting enhanced productivity and limiting successful colonization of other species. My results indicate that there may be suites of functional traits linked to expansive success and thicket-formation, yet differences in functional traits between native and invasive species represent alternative strategies leading to rapid growth and thicketization.

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

A nucleação é uma técnica de restauração florestal na qual se espera que o plantio agregado de mudas aumente o recrutamento e o estabelecimento de espécies, uma vez que o crescimento de algumas plantas pode fornecer melhores condições ambientais para as plantas vizinhas. Porém, o plantio agregado também pode intensificar a competição por nutrientes entre as plantas. Espera-se que o efeito facilitador do núcleo seja maior para espécies não pioneiras, que são mais sensíveis a altas irradiâncias e melhores competidoras por nutrientes. Para espécies pioneiras, tolerantes a altas irradiâncias e piores competidoras, os núcleos devem ser desfavoráveis. A adição de nutrientes pode minimizar a competição e tornar os núcleos mais favoráveis, principalmente às espécies pioneiras. Com o objetivo de avaliar respostas das mudas à nucleação e à adição de nutrientes, foram avaliados a eficiência fotossintética máxima (Fv/Fm) e o conteúdo de pigmentos fotossintéticos. Temperaturas foliares e do solo foram medidas para avaliar o potencial do núcleo em minimizar microclimas extremos. As mudas foram plantadas em parcelas, cada uma com uma combinação de tipo de plantio, em núcleo ou em linha, e tipo de adubo aplicado, com adubo químico (NPK), com terra vegetal ou sem adubação. Os núcleos foram compostos de 13 mudas de espécies diferentes, sendo 5 pioneiras e 8 não pioneiras. As mudas foram separadas entre si por distâncias de aproximadamente 30 cm. Nas linhas as mudas foram plantadas isoladas entre si por 2 m. Mudas plantadas no sistema de nucleação apresentaram melhores condições, com maior Fv/Fm e conteúdo de clorofilas a, b e total (a+b), indicando efeitos de facilitação do núcleo. Menores temperaturas foliares e do solo foram encontradas em núcleos. Tanto plantas de espécies pioneiras quanto não pioneiras apresentaram sinais de fotoinibição, com valores de Fv/Fm abaixo do considerado como livre de estresse, quando plantadas tanto em linhas quanto em núcleos. Os sinais de fotoinibição foram maiores para o grupo de não pioneiras, com menores valores Fv/Fm. Não pioneiras apresentaram menor razão de clorofila a/b, evidenciando seu investimento em absorver maior quantidade de luz. Entretanto, o efeito diferenciado dos núcleos para espécies pioneiras e não pioneiras não foi conclusivo, assim como os efeitos da adição de nutrientes. O presente estudo fornece evidências para o efeito de facilitação em núcleos, agregando mais uma informação aos efeitos benéficos da nucleação, fornecendo subsídios para a recomendação da utilização dessa técnica em restauração. Não foram encontrados indícios que o plantio em núcleos seja prejudicial para pioneiras ou não pioneiras, justificando, dessa forma, o plantio de núcleos mistos / Nucleation of seedlings is a technique for forest restoration in which is expected that the aggregated planting of seedlings increases the recruitment and establishment of species. This would occur because the growth of some species can provide better environmental conditions to neighboring plants. However, the aggregated planting can also intensify the competition for nutrients between plants. It is expected that the facilitating effects are greater for the non-pioneers species that are more sensitive to high light intensities and better competitors for nutrients. For pioneers that are tolerant to high irradiance and worst competitors, the nuclei must be unfavorable. The addition of nutrients can minimize the competition and then turn the nuclei more favorable, especially to the pioneer species. In order to evaluate the responses of seedlings to the nucleation and the addition of nutrients were measured the maximum photosynthetic efficiency (Fv/Fm) and the content of photosynthetic pigments. Foliar and soil temperatures were measured to assess the potential of nucleation to minimize extreme microclimates. The seedlings were planted in plots, each with a combination of type of planting in nucleus or line, and type of fertilizer applied, chemical fertilizer (NPK), topsoil or without fertilizer. The nuclei were composed of 13 seedlings of different species, 5 pioneers and 8 non-pioneer pioneers. The seedlings were separated from each other by distances of approximately 30 cm. Seedlings planted in lines were isolated from each other by 2 m. Seedlings planted in the nucleation system showed better conditions with greater Fv/Fm and chlorophyll a, b and total contents, indicating the facilitation effects of nucleation. Foliar and soil temperatures were lower in nuclei. Both pioneers and non-pioneers showed signals of photoinhibition, with values of Fv/Fm below of that considered as stress-free when were planted in both, lines or nuclei. Photoinhibition signals were higher for the group of non-pioneer with lower Fv/Fm values. Non-pioneers had lower ratio of chlorophyll a/b, evidencing their investment to absorb more light. However, the different effects of nuclei for pioneers and non-pioneer species were not conclusive, as well as the effects of the addition of nutrients. The present study provides evidence for the effect of facilitation in nuclei, adding more information to the beneficial effects of nucleation, providing aid for the recommendation of the use of this technique in projects of ecological restoration. No evidence that planting in nuclei is harmful to pioneer or non-pioneer were found, thus justifying the planting of mixed nuclei

Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2017-08-22T19:49:00Z No. of bitstreams: 1 2016 - Gepatrik Rodrigues Lima.pdf: 1199140 bytes, checksum: a162c3135ebd07b66364dfd0d3a3b7fd (MD5) / Made available in DSpace on 2017-08-22T19:49:00Z (GMT). No. of bitstreams: 1 2016 - Gepatrik Rodrigues Lima.pdf: 1199140 bytes, checksum: a162c3135ebd07b66364dfd0d3a3b7fd (MD5) Previous issue date: 2016-02-29 / The aim of the study was to evaluate the effects of herbicides applied on post- emergence on common bean cultivation, using chlorophyll a fluorescence parameters and visual evaluation, just after theirs application. The selectivity of the herbicide in the crop was also evaluated. The experiment was conducted in the crop science experimental field at the Federal Rural University of Rio de Janeiro. The treatments were the following herbicides, bentazon (720 g ha-1), fluazifop-p-butil (187,5 g ha-1), fluazifop-p-butil + fomesafen (187,5 + 250 g ha-1), fomesafen (250 g ha-1), and two other treatments with or without weeds mechanical control, and the experimental design used was on randomized blocks, with six treatments and three replications. The bentazon was the only herbicide that induced a reduction in the maximum quantum yield of PS II (Fv/Fm), in photochemical quenching (qP) and in effective quantum yield of PS II (?FSII), while it promoted an increase in non photochemical quenching (NPQ) in the first day after its application. The Fv/Fm was the best discriminatory parameter for the evaluation of the effects of the herbicide on photosynthetic apparatus of plants in the field. All the herbicides used did not promote phytotoxicity or bean yield reduction. / O trabalho teve como objetivos avaliar os efeitos da aplica??o de herbicidas p?s-emergentes na fisiologia da cultura do feijoeiro, utilizando par?metros de fluoresc?ncia de clorofila a e a seletividade do herbicida na cultura. O experimento foi conduzido no campo experimental de Fitotecnia, da Universidade Federal Rural do Rio de Janeiro. Os tratamentos constaram das aplica??es dos seguintes herbicidas: bentazon (720 g ha-1), fluazifop-p-butil (187,5 g ha-1), fluazifop-p-butil + fomesafen (187,5 + 250 g ha-1), fomesafen (250 g ha-1) e mais duas testemunhas sem aplica??o de herbicida, sendo uma capinada e outra mantida sem capina, no delineamento casualiza??o por bloco, com quatro repeti??es. Foram avaliadas as vari?veis de fluoresc?ncia da clorofila a, conte?do de prote?na sol?vel foliar e a fitotoxicidade a cultura. O bentazon foi o ?nico que causou redu??es significativas no rendimento qu?ntico m?ximo do fotossistema II (Fv/Fm), quenching fotoqu?mico (qP), rendimento qu?ntico efetivo do fotossistema II (?FSII) e promoveu incremento no quenching n?o fotoqu?mico (NPQ) nos primeiros dias ap?s sua aplica??o. O Fv/Fm foi a vari?vel mais indicada para avaliar efeitos decorrentes da aplica??o de herbicidas no aparato fotossint?tico de plantas no campo. Todos os herbicidas testados n?o ocasionaram fitotoxicidade elevada e queda no rendimento dos gr?os do feijoeiro comum.

Orientador: Orlando Necchi Júnior / Banca: Ricardo Moreira Chaloub / Banca: Gustavo Habermann / Resumo: Respostas de curto período das características fotossintéticas a temperatura e irradiância foram avaliadas na rodófita Batrachospermum delicatulum em condições naturais e em laboratório. A variação diária dos parâmetros fotossintéticos por fluorescência da clorofila foi amostrada em duas épocas (junho, período frio e seco; outubro, quente e chuvoso) em um riacho da região noroeste do Estado de São Paulo (20o43’24-S, 49o18’21-W). Os valores de RQE e RQP (rendimento quântico efetivo e potencial, respectivamente) apresentaram correlação negativa com a irradiância nas duas épocas e valores similares no início e final do dia, indicando respectivamente alta pressão de excitação sobre o fotossistema II (FSII) e boa capacidade de recuperação e ausência de fotodano ao aparato fotossintético. Os valores de NPQ (extinção não-fotoquímica) também apresentaram correlação negativa com irradiância (significativa apenas em junho), o que possivelmente indica baixa capacidade de dissipação da energia absorvida pelos centros de reação. Sob temperatura e irradiância fixas a variação diária para fotossíntese líquida foi caracterizada por dois picos: o primeiro (maior) durante a manhã e o segundo (menor) durante a tarde. Os valores de ETR (taxa de transporte de elétrons) também apresentaram padrão semelhante, o que demonstra a ocorrência de ritmos endógenos que controlam as taxas fotossintéticas. Curvas de fotossíntese-irradiância e de indução escuro/luz foram testadas em laboratório (sob condições de baixa e alta irradiância) e em campo sob luz natural (não-sombreada) e artificialmente sombreada em duas épocas (junho e novembro). O isolado em cultura e as plantas em condições naturais (novembro) tiveram maiores valores de fotossíntese máxima (Fmax), eficiência fotossintética ( ) e rendimento quântico em baixa irradiância... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Short-term responses of photosynthetic characteristics to temperature and irradiance were analyzed in the rhodophyte Batrachospermum delicatulum under natural and laboratory conditions. The diurnal variation of photosynthetic parameters by chlorophyll fluorescence was sampled in two seasons (June, cool and dry season; October, warm and rainy season) in a stream of northwest region of São Paulo state (20o43’24”S, 49o18’21”W). Values of EQY and PQY (effective and potential quantum yield, respectively) were negatively correlated with irradiance in both seasons and had similar values at the beginning and end of the day, indicating, respectively high excitation pressure on photosystem II (PSII) and good recovery capacity and lack of photodamage to the photosynthetic apparatus. Values of NPQ (non-photochemical quenching) were also negatively correlated with irradiance (significantly only in June) possibly indicating low dissipation capacity of absorbed energy by reaction centres. The diurnal variation of net photosynthesis under fixed conditions of temperature and irradiance was characterized by two peaks the first (higher) in the morning and the second (lower) in the afternoon. ETR (electron transport rate) values also presented a similar pattern, suggesting the occurrence of endogenous rhythm that controls photosynthetic rates. Photosynthesis-irradiance and dark/light (induction) curves were tested in laboratory (under low and high irradiance conditions) and in field under natural light (unshaded) and artificially shaded in two seasons (June and November). Specimens from culture isolate and in natural conditions (November) had higher values of maximum photosynthesis (Pmax) photosynthetic efficiency ( ) and EQY at low irradiance, whereas at high irradiance (laboratory and field), values of were significantly higher than at low irradiance. A positive correlation between of ETR with NPQ... (Complete abstract click electronic access below) / Mestre

Peatlands are peat forming ecosystems in which not fully decomposed plant material builds up the soil. The sequestration of carbon into peat is mainly associated with the bryophyte genus Sphagnum (peat mosses), which dominate and literally form most peatlands. The responses of Sphagnum to environmental change help us to understand peatland development and function and to predict future changes in a rapidly changing world. In this thesis, the overarching aim was to use ecophysiological traits to investigate mechanisms behind the response of Sphagnum to elevated N deposition, and, processes connected to ecosystem shift and ecosystem function of peatlands. Regarding elevated N deposition, three experiments were performed at different scales (country-wide to greenhouse). Independent of scale and species, apical tissue N concentration increased with increasing N input until N saturation was reached. Maximum photosynthetic rate, a trait evaluating photosynthetic capacity, increased with N input and could be well predicted by tissue N concentration. Thus, the physiological responses of Sphagnum to N deposition are often positive and I found no evidence of toxic effects. Production did, however, not increase with N input, and results of the N:P ratio suggested that P limitation, and possibly other elements, might hamper growth under high N input. The effect of P limitation was, in contrast to current view, most pronounced in fast growing species indicating species specific responses to nutrient imbalance. I explored the puzzling, but historically frequently occurring, rich fen to bog ecosystem shift; a shift from a species-rich ecosystem dominated by brown mosses, to a species-poor one with greater carbon storage that is Sphagnum-dominated. The bog-dwelling species of Sphagnum grew well, to our surprise, when in contact with rich fen water but was not a strong competitor compared to rich fen Sphagnum species. If submerged under rich fen water (high pH), the bog Sphagnum species died while rich fen species of Sphagnum were unaffected. These results show that differences in two physiological traits (growth rate and tolerance to flooding) among species, can explain when a peatland ecosystem shift might occur. In the last study, the function of peatlands was related to trade-offs between traits and allometric scaling in Sphagnum. Results suggested that growth strategies are determined by the distribution of Sphagnum relative to the water table in order to minimize periods with suboptimal hydration. Allometric analyses stressed the importance of resource allocation among and within shoots (apical part vs. stem), although the allocation patterns in Sphagnum were not always consistent with those of vascular plants. Interestingly, data indicated a trade-off between photosynthetic rate and decomposition rate among Sphagnum species.