Two Arabidopsis lines, 10’4 and 3’1, with partial-repression, constitutively of mitochondrial pyruvate dehydrogenase kinase that could alter dark respiration (Rd) were grown on rockwool to reduce off-gassing from peat that interfered with assessment of Rd. At the rosette stage, Rd and photosynthesis (Pn) at high CO2 were greater than at ambient CO2, and Rd was greater for whole-plant than single leaf measurements due to the contribution of non-laminar tissues. However, whole-plant and leaf Rd and Pn were similar on a leaf-area-basis comparing mutants with controls. Whole-plant, analyses during reproductive stage showed that although, the inflorescence contributed as much as 90% of daily C-gain when the rosette leaves senesced, canopy-Pn on a surface-area-basis at each CO2 level remained similar to those at the rosette stage. At each CO2 level, the transgenic and control lines were similar indicating that the mutation resulted in no direct or indirect effect of Rd or Pn. / Ontario Graduate Scholarship, Green Crop Net Work

This study examined the effects of elevated CO2 and its interaction with drought and nitrogen fertilizer on the growth, production and nodulation of the leguminous crop lentil (Lens culinaris Medic) cultivars ILL7979 and ILL6994 (Idlib 3). Plants were grown under ambient and elevated CO2 at full and limited irrigation conditions in both open top chambers, which were later proven to be unreliable because of CO2 leakage, and tightly sealed and ventilated chambers which were reliable. Destructive harvests at anthesis and at maturity were conducted and results from sealed chambers at maturity showed that above ground dry weight was increased by an average of 12% under elevated CO2, but this increase was not statistically significant.

Rising atmospheric CO2 and the need to understand potential impacts on terrestrial ecosystems has become increasingly recognized. Models can play a beneficial part in this research to enhance understanding of ecosystem responses to changing conditions like elevated CO2. In this study, data from a long term elevated CO2 experiment in a native forested ecosystem in east central Florida were employed to assess the utility of a multi-layer canopy photosynthesis model as a tool to better understand the responses to elevated CO2 in this ecosystem. Model results compared satisfactorily with the canopy gas exchange measurements in this ecosystem for the period modeled. Sensitivity analyses were used to evaluate the robustness of the model and understand the effects that changing model parameters had on model results, i.e. carbon assimilation in the system. The parameters evaluated included canopy height, leaf area density profile, number of canopy layers, maximum rate of carboxylation (Vcmax), and canopy species composition. Results of the sensitivity analyses point to structure and species as being important to carbon assimilation in this ecosystem. Although only an initial examination, this model could be a valuable tool to further understanding of the response of this important ecosystem to increasing CO2 and indicates that further work is certainly warranted.

Psidium guajava é uma espécie tropical, frutífera, de grande importância na fruticultura brasileira e é usada em diversas partes do mundo para o tratamento de doenças que acometem a humanidade. Além de sua importância alimentícia e medicinal, P. guajava também se mostrou boa bioindicadora de poluentes atmosféricos como ozônio e SO2 , pois apresenta respostas características e dose-dependentes das concentrações desses poluentes. Mostrou-se, dessa forma, uma espécie interessante para o estudo de respostas de espécies tropicais a elevadas concentrações de CO2 atmosférico. A fim de avaliar se o elevado CO2 seria uma situação estressante para essa espécie, foi realizada uma fumigação de 130 mudas de P. guajava cv. Pedro Sato em quatro câmaras de topo aberto: duas com ar ambiente ((∼390 ppm) e duas com atmosfera enriquecida com CO2 (∼720 ppm). Foram realizadas coletas quinzenais, retirando-se cinco indivíduos de cada câmara, aleatoriamente, que foram separados em raiz, caule e folhas e imediatamente congelados com nitrogênio líquido. Foram analisados componentes relacionados a sinalização e inativação de espécies reativas de oxigênio em folhas: os teores de poliaminas solúveis, ácido ascórbico e glutationa, além de fenóis, flavonoides, proantocianidinas e taninos totais. Além disso, os extratos metanólicos de folhas foram submetidos à CLAE para análises quali e quantitativas dos principais flavonoides. Parâmetros relacionados ao desenvolvimento da planta também foram analisados, como incremento em altura, massa seca, fração de massa, acúmulo de carbono, açúcares solúveis e amido. As análises de poliaminas, ácido ascórbico, glutationa, e compostos fenólicos de folhas não revelaram alterações significativas entre os tratamentos, exceto para a análise de taninos totais onde foi observado um aumento significativo dessas substâncias nas plantas mantidas a elevado CO2 e após 90 dias de fumigação. A análise por CLAE revelou que a maioria dos flavonoides dessa espécie é derivada de quercetina. Com relação aos parâmetros de crescimento, P. guajava não apresentou diferenças significativas de incremento em altura e massa seca, mas apresentaram acúmulo de amido nas folhas. Analises multivariadas foram utilizadas para integrar as 46 variáveis analisadas. Neste estudo viu-se que a situação de elevado CO2 em mudas de P. guajava é favorável, visto que ocorre acúmulo de amido, substâncias anti-herbivóricas (taninos) e, aparentemente, não há alteração no balanço redox. Contudo, é de extrema importância estudos que avaliem alterações concomitantes de parâmetros ambientais, como aumento de temperatura, disponibilidade de água, ozônio e elevado CO2 . A goiabeira apresenta grande importância econômica relacionada à produção e qualidade de seus frutos, dessa forma são necessários estudos que avaliem o efeito do aumento do CO2 na quantidade e qualidade de frutos produzidos por esta espécie. Por ser uma espécie de crescimento lento, períodos de exposição mais longos são aconselháveis para uma melhor analise da susceptibilidade dessa espécie ao elevado CO2 / Psidium guajava is a tropical fruit species of great importance in Brazilian economy; it is also used in several parts of the world as medicinal. Besides its importance as medicinal and nutritional species, P. guajava has also showed to be a good bioindicator of air pollutants, such as ozone and SO2 . It presents characteristic responses, dose-dependent of the concentrations of these pollutants. Therefore, this species seems to be interesting to study the responses of a tropical species to high concentrations of atmospheric CO2 . In order to assess whether the high CO2 would be a stressful situation for this species, we performed a fumigation experiment using 130 seedlings of P. guajava cv. Pedro Sato in four open-top chambers: two with ambient air (∼ 390 ppm CO2 ) and two with elevated CO2 (∼ 720 ppm). Biweekly, five individuals of each chamber were randomly collected, separated into root, stem and leaves and immediately frozen with liquid nitrogen. Were analyzed parameters related to signaling and inactivation of reactive oxygen species in leaves: levels of soluble polyamines, ascorbate and glutathione, as well as contents of phenols, flavonoids, tannins and proanthocyanidins. Furthermore, the methanol extracts were subjected to HPLC for quantitative and qualitative analysis of the major flavonoids. Parameters related to the development of the plant were also analyzed, as height increment, dry mass, mass fraction, carbon accumulation, soluble sugars and starch accumulation. The analysis of polyamines, ascorbate, glutathione and phenolic compounds of leaves, showed no significant changes when comparing treatments, except for the analysis of tannins which was observed a significant increase of these substances in plants at high CO2 after 90 days of fumigation. HPLC analysis revealed that most of flavonoid composition is quercetin derivatives. The growth parameters showed no significant differences in height increment and dry mass, but the leaves showed accumulation of starch after CO2 fumigation. Multivariate analyzes were used to integrate the 46 variables analyzed. In this study it was seen that the elevated CO2 seem to be favorable to seedlings of P. guajava, once there is an accumulation of starch, antiherbivore substances (tannins) and, apparently, there was no change in the redox balance. However, it is extremely important to perform studies that evaluate concomitant changes in environmental conditions, such as increased temperature, availability of water, ozone and elevated CO2 . Guava has great economic importance in Brazil, fact related to the production and quality of its fruits, so more studies are needed to assess the effect of increased CO2 in the quantity and quality of fruits produced by this species. As a slow-growing species, longer exposure periods are recommended to better analyze the susceptibility of this species to elevated CO2

The concentration of atmospheric carbon dioxide (CO2) in the atmosphere has increased by 35% since pre-industrial levels. Projections for the next 100 years indicate an increase to levels between 490 and 1260 parts per million by volume (ppm) of CO2, equating to a 75 % to 350 % increase in concentration since the year 1750. Associated with this increase in [CO2] will be a 1.4 to 5.8?? C increase in lower atmospheric temperature. While past research has attempted to address the effects of such climatic changes on individual plant responses, predictions of plant responses at the ecosystem level are still highly uncertain. Difficulties lie in the enormous variation of plant responses to climate change variables among and within species, and between and within environmental conditions. Past research assumed that plants using either the C3 or C4 metabolic pathways would respond differently but predictably to climate-change variables based on their metabolic pathway. Recent evidence has suggested however, that the added interactions of external environmental variables and species-specific sensitivities to climate change make it difficult to predict plant and ecosystem responses to climate change. To investigate the mechanisms behind responses of Australian grasses to climate change, 2 pot experiments was conducted using growth cabinets to compare the effect of elevated CO2 and water-limitation on the invasive C4 grassland plant, Eragrostis curvula (E. curvula), native Australian C3 grassland plant, Austrodanthonia racemosa (A. racemosa), and wheat species, Triticum aestivum (T. aestivum). The experiment was run at ambient levels of CO2 maintained at 390 ppm compared to elevated levels of 740 ppm. Imposed restrictions to water supply consisted of gradually drying the soil down to 30 % available soil water (ASW) followed by re-wetting to 50 % ASW. Well-watered conditions for the experiment consisted of gradually drying the soil down to 50 % ASW, followed by rewetting to 95 % ASW. Plants were grown in mixtures and monocultures, consisting of 9 plants equally spaced in a grid design. The three significant findings of the thesis were that: 1) the metabolic pathway (C3 versus C4) was not always an accurate predictor of biomass accumulation under elevated CO2 in the plants studied. Previous research suggested that CO2-stimulation of photosynthesis in C3 plants would lead to greater increases in biomass under elevated CO2 compared to C4 plants, though both C3 and C4 plants could benefit from any reduction in stomatal conductance under dry conditions at elevated CO2. The results from the experiments in this thesis showed a strongly significant biomass response to elevated CO2 in both dry and wet conditions for C4 grass E. curvula. The C3 grass A. racemosa in dry conditions, did not. It was speculated that without the CO2-induced water conservation effect, the C3 grass experienced photosynthetic down-regulation and this precluded a positive biomass response under elevated CO2. 2) the magnitude and direction of biomass response to elevated CO2 was dependant on factors such as resource-availability and the phenotypic variability of the plants species. 3) critical analysis of results from this thesis, combined with past research on plant responses under elevated CO2 showed a tendency for researchers to repeatedly test plants from the Poaceae family, or close relatives of the Poaceae family. As a result, when past data were corrected for this lack of independence, there was no relationship between the evolution of the C3 and C4 metabolic pathway and biomass response to elevated CO2. Instead, other factors (such as growth rate, plant height, leaf number, etc) were presented as being more important in determining biomass response. These observations were supported by results found in this thesis.

The concentration of atmospheric carbon dioxide (CO2) in the atmosphere has increased by 35% since pre-industrial levels. Projections for the next 100 years indicate an increase to levels between 490 and 1260 parts per million by volume (ppm) of CO2, equating to a 75 % to 350 % increase in concentration since the year 1750. Associated with this increase in [CO2] will be a 1.4 to 5.8?? C increase in lower atmospheric temperature. While past research has attempted to address the effects of such climatic changes on individual plant responses, predictions of plant responses at the ecosystem level are still highly uncertain. Difficulties lie in the enormous variation of plant responses to climate change variables among and within species, and between and within environmental conditions. Past research assumed that plants using either the C3 or C4 metabolic pathways would respond differently but predictably to climate-change variables based on their metabolic pathway. Recent evidence has suggested however, that the added interactions of external environmental variables and species-specific sensitivities to climate change make it difficult to predict plant and ecosystem responses to climate change. To investigate the mechanisms behind responses of Australian grasses to climate change, 2 pot experiments was conducted using growth cabinets to compare the effect of elevated CO2 and water-limitation on the invasive C4 grassland plant, Eragrostis curvula (E. curvula), native Australian C3 grassland plant, Austrodanthonia racemosa (A. racemosa), and wheat species, Triticum aestivum (T. aestivum). The experiment was run at ambient levels of CO2 maintained at 390 ppm compared to elevated levels of 740 ppm. Imposed restrictions to water supply consisted of gradually drying the soil down to 30 % available soil water (ASW) followed by re-wetting to 50 % ASW. Well-watered conditions for the experiment consisted of gradually drying the soil down to 50 % ASW, followed by rewetting to 95 % ASW. Plants were grown in mixtures and monocultures, consisting of 9 plants equally spaced in a grid design. The three significant findings of the thesis were that: 1) the metabolic pathway (C3 versus C4) was not always an accurate predictor of biomass accumulation under elevated CO2 in the plants studied. Previous research suggested that CO2-stimulation of photosynthesis in C3 plants would lead to greater increases in biomass under elevated CO2 compared to C4 plants, though both C3 and C4 plants could benefit from any reduction in stomatal conductance under dry conditions at elevated CO2. The results from the experiments in this thesis showed a strongly significant biomass response to elevated CO2 in both dry and wet conditions for C4 grass E. curvula. The C3 grass A. racemosa in dry conditions, did not. It was speculated that without the CO2-induced water conservation effect, the C3 grass experienced photosynthetic down-regulation and this precluded a positive biomass response under elevated CO2. 2) the magnitude and direction of biomass response to elevated CO2 was dependant on factors such as resource-availability and the phenotypic variability of the plants species. 3) critical analysis of results from this thesis, combined with past research on plant responses under elevated CO2 showed a tendency for researchers to repeatedly test plants from the Poaceae family, or close relatives of the Poaceae family. As a result, when past data were corrected for this lack of independence, there was no relationship between the evolution of the C3 and C4 metabolic pathway and biomass response to elevated CO2. Instead, other factors (such as growth rate, plant height, leaf number, etc) were presented as being more important in determining biomass response. These observations were supported by results found in this thesis.

Psidium guajava é uma espécie tropical, frutífera, de grande importância na fruticultura brasileira e é usada em diversas partes do mundo para o tratamento de doenças que acometem a humanidade. Além de sua importância alimentícia e medicinal, P. guajava também se mostrou boa bioindicadora de poluentes atmosféricos como ozônio e SO2 , pois apresenta respostas características e dose-dependentes das concentrações desses poluentes. Mostrou-se, dessa forma, uma espécie interessante para o estudo de respostas de espécies tropicais a elevadas concentrações de CO2 atmosférico. A fim de avaliar se o elevado CO2 seria uma situação estressante para essa espécie, foi realizada uma fumigação de 130 mudas de P. guajava cv. Pedro Sato em quatro câmaras de topo aberto: duas com ar ambiente ((∼390 ppm) e duas com atmosfera enriquecida com CO2 (∼720 ppm). Foram realizadas coletas quinzenais, retirando-se cinco indivíduos de cada câmara, aleatoriamente, que foram separados em raiz, caule e folhas e imediatamente congelados com nitrogênio líquido. Foram analisados componentes relacionados a sinalização e inativação de espécies reativas de oxigênio em folhas: os teores de poliaminas solúveis, ácido ascórbico e glutationa, além de fenóis, flavonoides, proantocianidinas e taninos totais. Além disso, os extratos metanólicos de folhas foram submetidos à CLAE para análises quali e quantitativas dos principais flavonoides. Parâmetros relacionados ao desenvolvimento da planta também foram analisados, como incremento em altura, massa seca, fração de massa, acúmulo de carbono, açúcares solúveis e amido. As análises de poliaminas, ácido ascórbico, glutationa, e compostos fenólicos de folhas não revelaram alterações significativas entre os tratamentos, exceto para a análise de taninos totais onde foi observado um aumento significativo dessas substâncias nas plantas mantidas a elevado CO2 e após 90 dias de fumigação. A análise por CLAE revelou que a maioria dos flavonoides dessa espécie é derivada de quercetina. Com relação aos parâmetros de crescimento, P. guajava não apresentou diferenças significativas de incremento em altura e massa seca, mas apresentaram acúmulo de amido nas folhas. Analises multivariadas foram utilizadas para integrar as 46 variáveis analisadas. Neste estudo viu-se que a situação de elevado CO2 em mudas de P. guajava é favorável, visto que ocorre acúmulo de amido, substâncias anti-herbivóricas (taninos) e, aparentemente, não há alteração no balanço redox. Contudo, é de extrema importância estudos que avaliem alterações concomitantes de parâmetros ambientais, como aumento de temperatura, disponibilidade de água, ozônio e elevado CO2 . A goiabeira apresenta grande importância econômica relacionada à produção e qualidade de seus frutos, dessa forma são necessários estudos que avaliem o efeito do aumento do CO2 na quantidade e qualidade de frutos produzidos por esta espécie. Por ser uma espécie de crescimento lento, períodos de exposição mais longos são aconselháveis para uma melhor analise da susceptibilidade dessa espécie ao elevado CO2 / Psidium guajava is a tropical fruit species of great importance in Brazilian economy; it is also used in several parts of the world as medicinal. Besides its importance as medicinal and nutritional species, P. guajava has also showed to be a good bioindicator of air pollutants, such as ozone and SO2 . It presents characteristic responses, dose-dependent of the concentrations of these pollutants. Therefore, this species seems to be interesting to study the responses of a tropical species to high concentrations of atmospheric CO2 . In order to assess whether the high CO2 would be a stressful situation for this species, we performed a fumigation experiment using 130 seedlings of P. guajava cv. Pedro Sato in four open-top chambers: two with ambient air (∼ 390 ppm CO2 ) and two with elevated CO2 (∼ 720 ppm). Biweekly, five individuals of each chamber were randomly collected, separated into root, stem and leaves and immediately frozen with liquid nitrogen. Were analyzed parameters related to signaling and inactivation of reactive oxygen species in leaves: levels of soluble polyamines, ascorbate and glutathione, as well as contents of phenols, flavonoids, tannins and proanthocyanidins. Furthermore, the methanol extracts were subjected to HPLC for quantitative and qualitative analysis of the major flavonoids. Parameters related to the development of the plant were also analyzed, as height increment, dry mass, mass fraction, carbon accumulation, soluble sugars and starch accumulation. The analysis of polyamines, ascorbate, glutathione and phenolic compounds of leaves, showed no significant changes when comparing treatments, except for the analysis of tannins which was observed a significant increase of these substances in plants at high CO2 after 90 days of fumigation. HPLC analysis revealed that most of flavonoid composition is quercetin derivatives. The growth parameters showed no significant differences in height increment and dry mass, but the leaves showed accumulation of starch after CO2 fumigation. Multivariate analyzes were used to integrate the 46 variables analyzed. In this study it was seen that the elevated CO2 seem to be favorable to seedlings of P. guajava, once there is an accumulation of starch, antiherbivore substances (tannins) and, apparently, there was no change in the redox balance. However, it is extremely important to perform studies that evaluate concomitant changes in environmental conditions, such as increased temperature, availability of water, ozone and elevated CO2 . Guava has great economic importance in Brazil, fact related to the production and quality of its fruits, so more studies are needed to assess the effect of increased CO2 in the quantity and quality of fruits produced by this species. As a slow-growing species, longer exposure periods are recommended to better analyze the susceptibility of this species to elevated CO2

A vegetação ao longo do rio Amazonas é submetida a dois períodos muito bem marcados ao longo do ano: estação de cheia e estação seca. Características morfológicas e fisiológicas das espécies de várzea foram amplamente descritas, porém, uma das principais características é o metabolismo de carboidratos que tem sido muito pouco explorada. Com o objetivo de estudar a resiliência dos carboidratos não estruturais da árvore amazônica Senna reticulata (Leguminosae), a mesma foi cultivada sob diferentes estresses abióticos, como luz baixa combinada com elevada concentração de CO2 atmosférico, bem como disponibilidade hídricas distintas (alagamento das raízes e seca). Os resultados encontrados reforçam o papel do amido nas folhas como principal órgão armazenador desta espécie e também a alta resiliência desta reserva, que foi mantida mesmo em condições de baixa irradiância, em alagamento e em condições de seca. Estes resultados também destacam a forte ligação entre as reservas de amido e a manutenção do crescimento. Além disso, esta espécie mostrou estratégias ecofisiológicas distintas em relação a diferentes estresses hídricos (alagamento x seca) e uma alta capacidade de se recuperar depois de um período de seca, padrão este que pode estar diretamente relacionado à manutenção do crescimento durante o estabelecimento de plantas jovens no primeiro período de fase terrestre / The vegetation along the Amazon River is subjected to two markedly periods: flooded and drought seasons. Morphological and physiological traits for floodplain species have been largely described; however, one of the main features is the carbohydrate metabolism, which has been poorly explored. In order to study the resilience of non-structural carbohydrates of the Amazonian tree Senna reticulate (Leguminosae), this species was grown under different abiotic stresses such as low light combined with elevated CO2 and distinct water availabilities (waterlogging and drought). Results reinforce the role of starch in leaves as a main storage organ of this species and also the high resilience of this reserve under low light, waterlogging and drought conditions. These findings also highlight the tight connection between starch reserves and growth maintenance. Additionally, this species has shown very distinct eco physiological strategies to cope with different water availabilities and a high ability to recover after drought that might be strictly related to growth maintenance during seedling establishment in the first period of terrestrial phase

O aquecimento global e as alterações nos padrões de precipitação são algumas das mudanças observadas no clima do planeta nos últimos anos. Simultaneamente, observa-se o aumento da concentração de gás carbônico ([CO2]) na atmosfera, devido principalmente a ações antrópicas. A elevação da [CO2] e da temperatura atmosférica global podem intensificar o efeito estufa, alterar a dinâmica de trocas gasosas das plantas e o ciclo do carbono nos ecossistemas. Isso ocorre tanto por influencias na fotossíntese, quanto nas respirações auto e heterotrófica. Outros fatores, como a umidade do solo também podem interferir nestes processos. As pastagens são ecossistemas de relevante importância para o ser humano e impactantes na dinâmica global do ciclo do carbono. A agricultura é a mais ampla forma de uso antrópico do solo e estoca mais de 10% de todo carbono da biosfera. Com o intuito de investigar o impacto das mudanças climáticas na dinâmica do CO2 e no ciclo do carbono nos ecossistemas de pastagem, este trabalho teve como objetivo quantificar a produção de biomassa, o fluxo líquido de CO2 do ecossistema (NEE), a respiração do solo e o fluxo de metano em ecossistemas de pastagem tropical. Duas espécies forrageiras, Panicum maximum Jacq. Cv Mombaça (gramínea C4), e Stylosanthes capitata Vogel (Leguminosa C3), foram cultivadas sob elevada concentração de CO2 (600 mol mol-1), elevada temperatura atmosférica (+2 ºC) e restrição hídrica em sistema combinado FACE (Free-air carbon dioxide enrichment) e T-FACE (Temperature free-air controlled enhancement). A quantificação do NEE foi realizada por câmaras de topo aberto desenvolvidas pelo grupo de pesquisa especificamente para o estudo ecofisiológico integrado de todo o dossel e não apenas de uma fração da área foliar ou pela biomassa, que são atualmente as técnicas mais utilizadas. No experimento utilizando a leguminosa C3 foi observado diminuição na biomassa total acima do solo, pela diminuição da quantidade de folhas, em tratamento com elevada temperatura (eT) e um aumento na biomassa de caules em tratamento combinado de elevada [CO2] e temperatura (eC+eT). O NEE diurno aumentou sob tratamento de elevada [CO2] (eC). A respiração do solo no período noturno foi aumentada em todos os tratamentos. Não houve mudança no fluxo de metano. No segundo experimento, utilizando a gramínea C4, a biomassa de folhas sofreu aumento no tratamento combinado eC+eT, o NEE diurno aumentou sob eC e a respiração do solo noturno aumentou sob eC+eT. No terceiro experimento, também utilizando a gramínea C4, porém, com tratamentos de restrição hídrica e elevada temperatura, não foram observadas diferenças nos dados coletados. De maneira geral, as mudanças climáticas trarão alterações no ciclo do carbono dos ecossistemas de pastagem, sendo que a utilização da leguminosa C3 S. capitata pode acarretar em perdas de produtividade de folhagem e aceleração da fenologia. Já a gramínea C4 P. maximum se mostrou resistente a um clima futuro de seca e temperatura elevada e se beneficiou da maior [CO2], com maior fixação de carbono pelo ecossistema e produção de biomassa de folhas, sendo assim uma boa opção para a produção de forragem em pastagens tropicais. / Global warming and changes in the rain patterns are some of the changes observed in the weather of the planet in the last years. Simultaneously, it has been observed increases in the atmospheres concentration of carbon dioxide ([CO2]), mainly by anthropic actions. The rising [CO2] and atmospheric temperature may intensify the greenhouse effect, modify the dynamic of plant gas exchange and the carbon cycle in the ecosystems. These changes occur by effects in the photosynthesis and respiration (auto and heterotrophic). Other factors, as soil moisture, may also affect these processes. Grasslands are ecosystems of importance to the humanity and of impact to the global carbon circle dynamic. Agriculture is the main anthropic land use and stores more than 10% of all carbon in the biosphere. With the aim of investigate the impact of climate changes in the dynamic of CO2 and carbon cycle in tropical grassland ecosystems, this work had as objective to quantify the production of biomass, the net flux of CO2 of the ecosystem (NEE), the soil respiration and methane flux in tropical grassland ecosystems. Two forage plant species, Panicum maximum Jacq. Cv Mombaça (C4 grass), and Stylosanthes capitata Vogel (C3 legume), were cultivated under elevated CO2 concentration (600 mol mol-1), elevated atmospheric temperature (+2 °C) and water shortage in a Free-air carbon dioxide enrichment (FACE) and Temperature free-air controlled enhancement (T-FACE) combined system. The NEE quantification was realized by open top chambers developed by the research group specifically for the integrated ecophysiological study of the whole canopy and not just a fraction of leaf area or the biomass, which are the most commonly used technics nowadays. In the experiment using the C3 legume was observed a decrease in total above-ground biomass, by the reduction of leaf biomass, in treatment with elevated temperature (eT) and an increase of stems biomass in the combined treatment of elevated [CO2] and temperature (eC+eT). The diurnal NEE increased under elevated [CO2] (eC). The night soil respiration was increased in all three treatments. There were no changes in the methane flux. In the second experiment, utilizing the C4 grass, the leaves biomass increased under eC+eT, the diurnal NEE increased in the eC treatment and the night soil respiration also increased under eC+eT. In the third experiment, with the same C4, however, with water shortage and elevated temperature treatments, there were no differences in the collected data. Overall, the climate changes will bring alterations in the carbon cycle of grassland ecosystems, therefore, the use of the C3 legume S. capitata might entail in losses in foliage productivity and phenology acceleration. On the other hand, the C4 grass P. maximum showed resistance to a future climate with drought and elevated temperature, and benefited from the higher [CO2], with greater carbon fixation by the ecosystem and production of leaf biomass, being a good option for forage production in tropical pastures.

Dentre a gama de estudos existentes acerca das respostas de plantas ao incremento de CO2 atmosférico associado às mudanças climáticas, são poucas as investigações que contemplam espécies amazônicas frente à relevância desse ecossistema, e se desconhecem estudos desse aspecto com palmeiras. O açaí (Euterpe oleracea Mart., Arecaceae) é uma espécie típica de planícies da Floresta Amazônica sujeitas ao regime anual de inundação e, além de ser extremamente tolerante à anóxia, apresenta elevado valor comercial e um potencial para a produção de energia a partir de biomassa, gerando uma exploração economicamente sustentável. Este trabalho buscou caracterizar o crescimento inicial de plântulas de açaí quanto à fotossíntese, crescimento e metabolismo de carboidratos e investigar as respostas desses parâmetros ao incremento de CO2 atmosférico (de 380ppm - ambiente para 760ppm - elevado) em duas escalas temporais: ao longo do desenvolvimento das plântulas (entre 105 e 195 dias após a germinação, período de desenvolvimento da segunda folha) e ao longo de 24 horas (aos 175 dias após a germinação). Foram analisadas medidas de altura, área foliar, acúmulo e alocação de biomassa, curvas de resposta da fotossíntese à luz, conteúdo de clorofila e concentração de carboidratos não-estruturais. Foi verificado que o período de estabelecimento das plântulas se estende até cerca de 150 dias após a germinação e se sobrepôs ao experimento com elevado CO2. A presença de outra via de entrada de carbono além da fotossíntese tamponou mas não inibiu os efeitos do aumento de CO2 atmosférico. Foram observadas ao longo do experimento reduções na área foliar, condutância estomática e respiração no escuro e aumentos na fotossíntese e eficiência de uso da água, além de aumento na concentração de carboidratos não-estruturais e na biomassa. Os dados obtidos após o esgotamento das reservas do endosperma não apresentaram sinais de que a planta aclimatará ao incremento de CO2, pois aos 90 dias de experimento foram observadas as maiores porcentagens de aumento na fotossíntese, 89%, e no teor de amido, 300%. Esses resultados indicam que essa espécie apresenta uma grande capacidade de aumento da força de dreno, o que diminui a sinalização por açúcares possibilitando a manutenção de uma resposta positiva ao incremento de CO2 atmosférico / Despite all knowledge available nowadays on plant responses to increasing atmospheric CO2, few are the studies that focus on Amazonian species in contrast to the biological relevance of this ecosystem, and no record has been found of Palm species analysis on this area of research. Açaí palm (Euterpe oleracea Mart., Arecaceae) is a typical species of Amazon plains subjected to annual periods of flooding. Apart from being extremely anoxia tolerant, this species presents high commercial value and a potential of energy production through biomass utilization, counting towards a sustainable economic exploitation. This study aimed to characterize the initial growth of açaí palm seedlings as for photosynthesis, growth and carbohydrate metabolism and to investigate these parameters\' responses to an increase on atmospheric CO2 (from 380ppm - ambient to 760ppm - elevated) on two temporal scales: throughout seedling development (from 105 to 195 days post germination, time span of second leaf development) and throughout 24 hours (at 175 days post germination). Analysis included: height, leaf area, biomass increase and allocation, light-response curves, chlorophyll content and non-structural carbohydrate concentration. It was observed that the seedling establishment period extends to 150 days post germination and overlapped the elevated CO2 experiment. The presence of another carbon entry pathway besides photosynthesis buffered the effects of elevated CO2, but did not inhibit them. Results observed were reductions on leaf area, stomatal conductance and dark respiration and increases on photosynthesis, water use efficiency, non-structural carbohydrate content and biomass. The results obtained after seed reserves were depleted did not seem to indicate that this species will present acclimation to elevated CO2, since the greater percentages of increase on photosynthesis (89%) and starch content (300%) occurred at the end of the experiment (90 days on elevated CO2). These results indicate that açaí palm seedlings have a large capacity of sink strenght increase, which reduces sugar signaling and maintains a positive response to the increase on atmospheric CO2