Soils of Northern Hemisphere forests contain a large part of the global terrestrial carbon (C) pool. Even small changes in this pool can have large impact on atmospheric [CO2] and the global climate. Soil respiration is the largest terrestrial C flux to the atmosphere and can be divided into autotrophic (from roots, mycorrhizal hyphae and associated microbes) and heterotrophic (from decomposers of organic material) respiration. It is therefore crucial to establish how the two components will respond to changing environmental factors. In this thesis I studied the effect of elevated atmospheric [CO2] (+340 ppm, 13C-depleted) and elevated air temperature (2.8-3.5 oC) on soil respiration in a whole-tree chamber (WTC) experiment conducted in a boreal Norway spruce forest. In another spruce forest I used multivariate modelling to establish the link between day-to-day variations in soil respiration rates and its δ13C, and above and below ground abiotic conditions. In both forests, variation in δ13C was used as a marker for autotrophic respiration. A trenching experiment was conducted in the latter forest in order to separate the two components of soil respiration. The potential problems associated with the trenching, increased root decomposition and changed soil moisture conditions were handled by empirical modelling. The WTC experiment showed that elevated [CO2] but not temperature resulted in 48 to 62% increased soil respiration rates. The CO2-induced increase was in absolute numbers relatively insensitive to seasonal changes in soil temperature and data on δ13C suggest it mostly resulted from increased autotrophic respiration. From the multivariate modelling we observed a strong link between weather (air temperature and vapour pressure deficit) and the day-to-day variation of soil respiration rate and its δ13C. However, the tightness of the link was dependent on good weather for up to a week before the respiration sampling. Changes in soil respiration rates showed a lag to weather conditions of 2-4 days, which was 1-3 days shorter than for the δ13C signal. We hypothesised to be due to pressure concentration waves moving in the phloem at higher rates than the solute itself (i.e., the δ13C–label). Results from the empirical modelling in the trenching experiment show that autotrophic respiration contributed to about 50% of total soil respiration, had a great day-to-day variation and was correlated to total soil respiration while not to soil temperature or soil moisture. Over the first five months after the trenching, an estimated 45% of respiration from the trenched plots was an artefact of the treatment. Of this, 29% was a water difference effect and 16% resulted from root decomposition. In conclusion, elevated [CO2] caused an increased C flux to the roots but this C was rapidly respired and has probably not caused changes in the C stored in root biomass or in soil organic matter in this N-limited forest. Autotrophic respiration seems to be strongly influenced by the availability of newly produced substrates and rather insensitive to changes in soil temperature. Root trenching artefacts can be compensated for by empirical modelling, an alternative to the sequential root harvesting technique.

No description available.

A concentração do gás carbônico (CO2) tem aumentado nas últimas décadas, devido principalmente à queima de combustíveis fósseis. Como consequência, admite-se que haverá gradual aumento da temperatura atmosférica em nível global. A soja é importante planta agrícola em todo o mundo, consumida na alimentação humana e de animais domésticos. O presente trabalho compõe-se de dois capítulos, o primeiro versando sobre o efeito da concentração de gás carbônico e da temperatura sobre vários parâmetros bioquímicos e o segundo, sobre a composição da cera foliar cuticular de uma variedade de soja. O capítulo I trata da composição química dos grãos e do teor de ceras foliares de plantas da cultivar \'MG/BR-46 Conquista\' crescendo em câmaras de topo aberto sob duas condições de CO2 (380ppm ambiente e 800ppm elevado) e duas condições de temperatura (ambiente e elevada [+5°C]). Foram coletados dados de 6 coletas ao longo de 105 dias de desenvolvimento da planta. As plantas crescidas em altas concentrações de CO2 aumentaram a biomassa seca da folha, caule, raiz e frutos, além do número de sementes; temperaturas elevadas estimularam a senescência precoce. A floração foi antecipada sob condição de CO2 elevado. Entre os carboidratos dos grãos, os teores de amido, frutose e mio-inositol tenderam a diminuir, enquanto os de sacarose, glicose e rafinose aumentaram. O incremento de CO2 acelerou a translocação de açúcares, enquanto e o da temperatura desacelerou. O teor de óleo e a composição dos ácidos graxos foram afetados diretamente pela elevada temperatura, com redução do teor de ácidos poliinsaturados. A associação de temperatura e CO2 elevados reduziu ainda mais o teor de ácidos graxos poliinsaturados. Os teores de proteínas solúveis em geral não apresentaram diferenças significativas por efeito do acoplamento, embora o teor de nitrogênio total tenha aumentado por efeito do tratamento por temperatura elevada. O teor de clorofilas foliares diminuiu por efeito dos tratamentos e o teor de cera foliar foi alterado ao longo do tempo. Conclui-se que as elevações de CO2 e temperatura, previstas para um futuro próximo, poderão ter o efeito de aumentar a produção de óleo por plantas de \'MG/BR-46 Conquista\', devido ao aumento no número de sementes por planta e elevação do teor de óleo. O capítulo II trata do teor da cera e a identificação dos componentes da cera foliar cuticular, por extração por lavagens superficiais das folhas com diclorometano, separação das classes de constituintes da cera por cromatografia em camada delgada e análise das frações por cromatografia a gás acoplada a espectrometria de massas. Os principais constituintes da cera foram os ésteres, seguidos de n-alcanos. O éster mais abundante foi o eicosanoato de octadecila (C38). Os alcanos principais foram o hentriacontano (C31) e o nonacosano (C29). Outros componentes detectados foram álcoois primários, ácidos graxos, hidroxiácidos graxos, álcoois triterpênicos e esteróis. O principal n-álcool graxo primário foi o octacosanol. Os triterpenos alcoólicos detectados foram α- e β-amirinas, lupeol, germanicol e 12,20(29)-lupadien-3-ol. Os ácidos graxos variaram no intervalo C15-C28. Os esteroides detectados foram estigmasterol, campesterol, sitosterol e estigmastanol, com predominância do primeiro / The concentration of carbon dioxide (CO2) has increased in the last decades, due mainly to the combustion of fossil fuels. A gradual increase of the global temperature is expected as a consequence. Soybean is an important crop in most countries, being consumed either as human or domestic animals food. The present work is composed of two chapters, the first dealing with the effect of the concentration of carbon dioxide and temperature on several biochemical parameters, and the second on the composition of the foliar cuticular wax of a variety of soybean plant. Chapter one deals with the chemical composition of soybeans and the leaf wax contents of soybean variety \'MG/BR-46 Conquista\', growing in open top chambers under two conditions of CO2 (380 ppm - ambient, and 800 ppm - elevated) and two temperature conditions (ambient and elevated [+5°C]). The data were obtained from six collections along 105 days of experimentation. Elevated CO2 increased the dry weight of leaf, stem, root and fruit, as well as the number of seeds; elevated temperature stimulated early senescence. Early flowering occurred under elevated CO2. Among the grain carbohydrates, the contents of starch, fructose and myo-inositol decreased, whereas those of sucrose, glucose and raffinose increased. The effect of elevated CO2 and temperature accelerated the sugar translocation while that of elevated temperature slowed it down. The oil content and fatty acid composition were affected directly by the elevated temperature, a reduction of the content of polyunsaturated fatty acids having been observed. The coupling of elevated CO2 and temperature reduced even further the content of polyunsaturated acids. In general, the content of soluble proteins did not change significantly by the effect of treatment associating temperature and CO2, although the total nitrogen content increased by the effect of elevated temperature. The content of leaf chlorophylls decreased and the foliar wax content changed with time. It is concluded that the increase of temperature and atmospheric CO2, expected to take place in the near future, will possibly have the effect of increasing the production of oil by plants of \'MG/BR-46 Conquista\', due to the increase of the number of seeds per individual and the increase of the seed oil content. Chapter two deals with the concentration and identification of the components of the foliar cuticular wax of the soybean variety \'MG/BR-46 Conquista\', by means of surface washings of the leaves with dichloromethane, separation of the classes of wax constituents by thin layer chromatography and analysis of the fractions by gas chromatography coupled with mass spectrometry. The main constituents of the wax were esters, followed by n-alkanes. The main ester constituent was eicosanoate of octadecyl (C38). The main alkanes were n-hentriacontane (C31) and n-nonacosane (C29). Other constituents detected were primary alcohols, fatty acids, hydroxyacids, triterpene alcohols and sterols. The main n-primary alcohol was octacosanol. The triterpene alcohols detected were α- e β-amyrins, lupeol, germanicol and 12,20(29)-lupadien-3-ol. The steroids detected were stigmasterol, campesterol, sitosterol and stigmastanol, with predominance of stigmasterol

A concentração do gás carbônico (CO2) tem aumentado nas últimas décadas, devido principalmente à queima de combustíveis fósseis. Como consequência, admite-se que haverá gradual aumento da temperatura atmosférica em nível global. A soja é importante planta agrícola em todo o mundo, consumida na alimentação humana e de animais domésticos. O presente trabalho compõe-se de dois capítulos, o primeiro versando sobre o efeito da concentração de gás carbônico e da temperatura sobre vários parâmetros bioquímicos e o segundo, sobre a composição da cera foliar cuticular de uma variedade de soja. O capítulo I trata da composição química dos grãos e do teor de ceras foliares de plantas da cultivar \'MG/BR-46 Conquista\' crescendo em câmaras de topo aberto sob duas condições de CO2 (380ppm ambiente e 800ppm elevado) e duas condições de temperatura (ambiente e elevada [+5°C]). Foram coletados dados de 6 coletas ao longo de 105 dias de desenvolvimento da planta. As plantas crescidas em altas concentrações de CO2 aumentaram a biomassa seca da folha, caule, raiz e frutos, além do número de sementes; temperaturas elevadas estimularam a senescência precoce. A floração foi antecipada sob condição de CO2 elevado. Entre os carboidratos dos grãos, os teores de amido, frutose e mio-inositol tenderam a diminuir, enquanto os de sacarose, glicose e rafinose aumentaram. O incremento de CO2 acelerou a translocação de açúcares, enquanto e o da temperatura desacelerou. O teor de óleo e a composição dos ácidos graxos foram afetados diretamente pela elevada temperatura, com redução do teor de ácidos poliinsaturados. A associação de temperatura e CO2 elevados reduziu ainda mais o teor de ácidos graxos poliinsaturados. Os teores de proteínas solúveis em geral não apresentaram diferenças significativas por efeito do acoplamento, embora o teor de nitrogênio total tenha aumentado por efeito do tratamento por temperatura elevada. O teor de clorofilas foliares diminuiu por efeito dos tratamentos e o teor de cera foliar foi alterado ao longo do tempo. Conclui-se que as elevações de CO2 e temperatura, previstas para um futuro próximo, poderão ter o efeito de aumentar a produção de óleo por plantas de \'MG/BR-46 Conquista\', devido ao aumento no número de sementes por planta e elevação do teor de óleo. O capítulo II trata do teor da cera e a identificação dos componentes da cera foliar cuticular, por extração por lavagens superficiais das folhas com diclorometano, separação das classes de constituintes da cera por cromatografia em camada delgada e análise das frações por cromatografia a gás acoplada a espectrometria de massas. Os principais constituintes da cera foram os ésteres, seguidos de n-alcanos. O éster mais abundante foi o eicosanoato de octadecila (C38). Os alcanos principais foram o hentriacontano (C31) e o nonacosano (C29). Outros componentes detectados foram álcoois primários, ácidos graxos, hidroxiácidos graxos, álcoois triterpênicos e esteróis. O principal n-álcool graxo primário foi o octacosanol. Os triterpenos alcoólicos detectados foram α- e β-amirinas, lupeol, germanicol e 12,20(29)-lupadien-3-ol. Os ácidos graxos variaram no intervalo C15-C28. Os esteroides detectados foram estigmasterol, campesterol, sitosterol e estigmastanol, com predominância do primeiro / The concentration of carbon dioxide (CO2) has increased in the last decades, due mainly to the combustion of fossil fuels. A gradual increase of the global temperature is expected as a consequence. Soybean is an important crop in most countries, being consumed either as human or domestic animals food. The present work is composed of two chapters, the first dealing with the effect of the concentration of carbon dioxide and temperature on several biochemical parameters, and the second on the composition of the foliar cuticular wax of a variety of soybean plant. Chapter one deals with the chemical composition of soybeans and the leaf wax contents of soybean variety \'MG/BR-46 Conquista\', growing in open top chambers under two conditions of CO2 (380 ppm - ambient, and 800 ppm - elevated) and two temperature conditions (ambient and elevated [+5°C]). The data were obtained from six collections along 105 days of experimentation. Elevated CO2 increased the dry weight of leaf, stem, root and fruit, as well as the number of seeds; elevated temperature stimulated early senescence. Early flowering occurred under elevated CO2. Among the grain carbohydrates, the contents of starch, fructose and myo-inositol decreased, whereas those of sucrose, glucose and raffinose increased. The effect of elevated CO2 and temperature accelerated the sugar translocation while that of elevated temperature slowed it down. The oil content and fatty acid composition were affected directly by the elevated temperature, a reduction of the content of polyunsaturated fatty acids having been observed. The coupling of elevated CO2 and temperature reduced even further the content of polyunsaturated acids. In general, the content of soluble proteins did not change significantly by the effect of treatment associating temperature and CO2, although the total nitrogen content increased by the effect of elevated temperature. The content of leaf chlorophylls decreased and the foliar wax content changed with time. It is concluded that the increase of temperature and atmospheric CO2, expected to take place in the near future, will possibly have the effect of increasing the production of oil by plants of \'MG/BR-46 Conquista\', due to the increase of the number of seeds per individual and the increase of the seed oil content. Chapter two deals with the concentration and identification of the components of the foliar cuticular wax of the soybean variety \'MG/BR-46 Conquista\', by means of surface washings of the leaves with dichloromethane, separation of the classes of wax constituents by thin layer chromatography and analysis of the fractions by gas chromatography coupled with mass spectrometry. The main constituents of the wax were esters, followed by n-alkanes. The main ester constituent was eicosanoate of octadecyl (C38). The main alkanes were n-hentriacontane (C31) and n-nonacosane (C29). Other constituents detected were primary alcohols, fatty acids, hydroxyacids, triterpene alcohols and sterols. The main n-primary alcohol was octacosanol. The triterpene alcohols detected were α- e β-amyrins, lupeol, germanicol and 12,20(29)-lupadien-3-ol. The steroids detected were stigmasterol, campesterol, sitosterol and stigmastanol, with predominance of stigmasterol

L’impact de l’homme sur l’environnement mondial et sur la diversité et le fonctionnement des écosystèmes terrestres fait l’objet d’une attention croissante. De nombreuses études ont évalué les effets de facteurs du changement global tels sur les processus de cycle de l'azote du sol dans les prairies. Cependant, ces études n'ont pas pris en compte le fait que la modification du régime de précipitations avait également une influence sur le régime de dépôt d'azote. En outre, la réponse du cycle de l'azote dans les sols des prairies à de multiples facteurs du changement global agissant ensemble et parfois en même temps que des perturbations telles que les incendies, doit encore être étudiée. Cela limite fortement notre capacité à comprendre et à prévoir les effets du changement global sur les prairies. Dans ce travail de doctorat, deux expériences ont été menées: (i) une expérience en mésocosme pour évaluer les effets combinés d'une augmentation des dépôts d'azote et de changements dans la quantité et la fréquence des précipitations sur le cycle de l'azote édaphique dans une prairie semi-aride; (ii) une expérience in situ pour évaluer les effets combinés de l'augmentation de la concentration en CO2, du réchauffement, d’une modification des précipitations, du dépôt d'azote et d’un feu sur le cycle de l'azote du sol dans une prairie méditerranéenne. Cela permet d'étudier les effets de la combinaison de plusieurs facteurs de changement global (et d’une perturbation feu) sur l'abondance des communautés microbiennes du cycle de l'azote.Les groupes microbiens étudiés étaient les bactéries et les archées oxydant l'ammoniac (AOB et AOA, respectivement), les réducteurs de nitrite porteuses des gènes nirK ou nirS, et les réducteurs de N2O porteurs des gènes nosZI- et nosZII, plus les bactéries oxydant le nitrite du genre Nitrobacter et Nitrospira pour la prairie méditerranéenne. Les principaux résultats et conclusions sont les suivants: 1) Les réactions des différents groupes de (dé)nitrifiants aux scénarios de changement global différaient fortement quel que soit le type de prairie. Les AOB étaient principalement dépendant de la disponibilité en azote En revanche, dans les deux prairies, les AOA étaient plus sensibles à la dynamique de l'eau du sol que la dynamique de l'azote. L'abondance des Nitrobacter étaient principalement affectée par les facteurs de changement global affectant l'abondance de l'AOB, tandis que l'abondance des Nitrospira était davantage liée aux changements d'abondance des AOA dans la prairie méditerranéenne. 2）Dans la prairie californienne où deux dépôts d'azote élevés avaient lieu chaque année, l'effet de l'azote dominait les effets du changement global. En revanche, dans la prairie chinoise, les dépôts d’azote simulés par des apports chroniques couplés aux événements de précipitation n’augmentaient pas l’abondance des dénitrifiants et ne faisaient que légèrement augmenter les émissions de N2O. 3） Pour les deux prairies, l'interaction entre les facteurs du changement global sur le cycle de l'azote du sol ne pouvait pas être prédite simplement en étudiant les effets d'un ou de deux facteurs. Ces effets interactifs ont pu être expliqués par des effets sur des variables environnementales clés telles que l'humidité du sol, la disponibilité de l'azote minéral, le pH et la croissance des racines. Ces résultats démontrent qu'il est impossible de prédire comment les (dé)nitrifiants et la (dé)nitrification répondent aux scénarios de changement global impliquant de multiples facteurs uniquement à partir de la connaissance d'effets de facteurs étudiés isolément. Cela nécessite donc des études plus approfondies dans le domaine de la biologie des changements globaux. La modélisation et l'évaluation de la généralité de ces effets d'interaction complexes constituent donc une priorité majeure pour les chercheurs qui veulent prédir les réponses du cycle de l'azote dans le sol au changement global et les rétroactions sur le climat. / The impact of global environmental changes on the diversity and functioning of terrestrial ecosystems has received increasing attention. Many studies evaluated the effects of single -and less often multiple- global change factors on soil N cycling processes in grasslands. However, these studies have not recognized that altered precipitation regime also has an influence on wet N deposition regime. Further, the response of grassland soil N cycling to co-occurring multiple global change factors and disturbance like fire, and how N cycling response to fire could differ under different global change scenarios, remains unclear. This strongly restricts our ability to understand and predict global change effect on grasslands. In this work, two experiments were conducted: (i) a mesocosm experiment to assess the combined effects of increased N deposition and changes in both the amount and frequency of rainfall on soil N cycling in a semi-arid Monsoon grassland; and (ii) an in situ experiment to assess the combined effects of elevated CO2, warming, increased precipitation, N deposition and fire on soil N cycling in a Mediterranean grassland. This allows studying the -possibly interactive- effects of several global change factors on the abundances of soil N-cycling microbial communities. The microbial groups studied were ammonia oxidizing bacteria and archaea (AOB and AOA, respectively), nirK- and nirS-nitrite reducers, nosZI- and nosZII-N2O reducers, plus Nitrobacter and Nitrospira for the Mediterranean grassland. The main results and conclusions are: 1）The responses of different groups of soil (de)nitrifiers to global change scenarios differed strongly regardless the grassland type. AOB were mostly driven by N. In contrast, AOA were more sensitive to soil water dynamics than N dynamics in both grasslands. Nitrobacter abundance was mostly affected by global change factors through their effects on AOB abundance, whereas Nitrospira abundance was more related to changes of AOA in the Mediterranean grassland. Similarly, nirK- and nirS-harboring nitrite reducers and nosZI-harboring N2O reducers were more sensitive to N deposition than nosZII-harboring N2O reducers, and nirK- and nirS-bacteria positively responded to reduced precipitation. This highlights niche differentiation between them and indicates that the balance between them may be altered in the future; 2）In the Mediterranean grassland, where high N deposition was simulated by two N addition events each year, the N effect dominated global change effects. In contrast, in the Monsson grassland, chronic wet N deposition did not increase denitrifier abundance and only weakly increased soil N2O emissions. This was explained by the efficient capture of added N by the dominant grass species and by the increased plant growth leading to increased transpiration and decreased soil moisture. 3）For both grasslands, the interaction between global change factors on soil N cycling could not be predicted simply by studying the effects of one or two factors. These interactive effects were explained by effects on key environmental variables like soil moisture, mineral N availability, pH and belowground plant growth.These results demonstrates the limitation of predicting how (de)nitrifiers respond to global change scenarios involving multiple factors only from studying single factor effects. Particularly, interactive effects were observed between N deposition, decreased precipitation amount and altered precipitation frequency in the Monsoon grassland; and between fire, N deposition, warming, elevated precipitation and elevated CO2 in the Mediterranean grassland. This calls for more comprehensive studies in the global change biology domain. Modelling and evaluating the generality of these complex interaction effects is thus a high priority for research to predict the responses of soil N cycling processes to global change and feedbacks on climate in the future

The present Master thesis focuses on evalution of CO2 concentration and irradiance on selected leaf anatomical parameters of European Beech (Common Beech) Fagus sylvatica L.. The process of photosynthesis is remarkably determined by numerous extrenal factors, among them by atmoshperic CO2 concentration and irradiance and is closely correlated with leaf anatomical parameters. One of these most important anatomical parameters affecting the net assimilation rate is an internal leaf surface, which corresponds to mesophyll area avialable for gas exhcange. Experimental material of the study was sampled from the leaves of juvenile trees of F. sylvatica planted in 2005 and growing under ambient (390 ppm, AC) and elevated (700 ppm, EC) CO2 concentrations on the experimental site of the Global Change Research Center AS CR at Bílý Kříž in the Beskydy Mountains. Sun and shade leaves were sampled from trees of both CO2 treatments in two seasons 3 years apart (2009 and 2012). To determine leaf anatomical parameters, the stereological methods were applied, which yield unbiased estimation of measured parameters, particularly the Fakir method for internal leaf surface determination. The EC effect was observed on the leaves sampled in 2009 only in the decrease of proportion of intercellular spaces in mesophyll. In...

A mesocosm experiment was carried out in a Norwegian fjord near Bergen in May 2006, with the main objective being the study of the effects of increasing concentrations of atmospheric CO2 (and associated effects such as increased acidification) on blooms of natural marine coastal plankton. Three mesocosms were bubbled with CO2(g) to achieve a high (~700ppm) CO2 concentration (pH ~7.8) to simulate predicted future conditions as a result of rising atmospheric CO2 concentrations. Another three mesocosms were treated as controls and bubbled with ambient air to represent a near pre-industrial scenario (atmospheric CO2 concentration ~300ppm, surface seawater pH ~8.15). Blooms in the mesocosms were stimulated by the addition of nutrients at a near-Redfield ratio ([N:P] ≈ [16:1]), and scientific measurements and analyses were carried out over the course of the blooms for approximately one month. Of particular interest in this study were the autotrophic plankton. The diversity and activities of these microorganisms under the two treatments was therefore investigated. By designing and using new degenerate primers specifically targeting ‘Green-type’ (Form IA and IB), ‘Red-type’ (Form IC and ID) and Form II RuBisCO, analysis of primary producers was carried out using PCR and either gDNA or cDNA (mRNA) templates from key time points spanning the complete duration of the blooms throughout the mesocosm experiment. Over 1250 novel RuBisCO large subunit sequences have been fully annotated and deposited in the NCBI GenBank® database. These sequences revealed distinct changes in the diversity of primary producers both over the courses of the blooms and between treatments. Particularly striking was the effect of acidification on the community structure of the eukaryotic picoplankton, Prasinophytes. A clade of prasinophytes closely related to Micromonas pusilla showed a distinct preference for the high CO2 conditions; a laboratory-based experiment confirmed the high tolerance of Micromonas pusilla to lower pH. Conversely, a clade related to Bathycoccus prasinos was almost entirely excluded from the high CO2 treatments. Clades of form II RuBisCO-containing dinoflagellates were also abundant throughout the experiment in both treatments. The high similarity of some of these clades to the toxin-producing species Heterocapsa triquetra and Gonyaulax polyedra, and apparent high tolerance of some clades to high CO2 conditions, is perhaps cause for concern in a high CO2 world and demands further research. In parallel with the RubisCO work, new primers were designed that target the gene encoding the Fe protein of nitrogenase (NifH). 82 Bergen genomic nifH sequences have been annotated and submitted to GenBank®. These sequences include those from organisms related to Alpha, Beta, and Gammaproteobacteria, and Cluster II and Cluster III sequences that align most closely with anaerobic Bacteria, Gram positive, and/or sulphur-reducing Bacteria. The biggest surprise, however, was the apparent abundance and significance of a Rhodobacter sphaeroides-like microorganism throughout the duration of the experiment in both treatments. Whilst this clade was unsurprisingly absent in the RuBisCO cDNA libraries, all but two of 128 nifH cDNA clones analysed were identical to the gene from Rhodobacter sphaeroides. This shows that this clade was potentially fixing N2 throughout the entire experiment, even in the presence of combined N added to both sets of mesocosms at the start of the experiment. A group of Rhodobacter sphaeroides-like microorganisms present at Bergen may therefore have been an unexpected source of new N during the experiment and contributed to the maintenance of the mesocosm communities as nutrients became depleted. One organism dominated the autotrophic communities after the blooms in both treatments. Synechococcus spp. Form IA rbcL clones most closely related to the coastal strain Synechococcus sp. strain CC9902 were recovered throughout the experiment but were particularly numerous toward the end of the experiment and dominated the “Green-type” libraries at this time. Initially, rbcL clones from these cyanobacteria were mostly derived from the ambient CO2 mesocosms but were equally distributed between treatments by the end of the experiment. This suggests that cyanobacteria related to strain CC9902 may be less tolerant of elevated CO2 (which was greatest at the beginning rather than the end of the experiment). However, despite the mesocosms being Pi-limited at the end of the experiment, several Synechococcus species (including those related to strain CC9902 and another coastal strain, CC9311) thrived. Following on from this observation, Pi uptake and assimilation mechanisms in a Synechococcus species were investigated in the laboratory. This led to the sequencing and characterisation of a pstS gene from the marine cyanobacterium Synechococcus sp. WH 8103. Unlike conventional pstS, it was discovered that the pstS II gene in this organism is constitutively expressed and unresponsive to or only weakly regulated by Pi supply. The use of PstS/pstS as a marker for P-limitation in natural samples, therefore, should be interpreted with caution.

Sink limitations in plants reduce the potential for photosynthesis and yield, particularly under conditions that favour enhanced source activity such as elevated CO2 (EC). Dark respiration, considered catabolic, has rarely been exploited to enhance sink activity in plants. Arabidopsis thaliana L. lines with partially-suppressed mitochondrial pyruvate dehydrogenase (mtPDH) kinase (mtPDHK), a negative post-translational regulator of the mtPDH complex, was shown previously to have both elevated mtPDH complex activity and increased seed weight and oil content at ambient CO2 (AC), suggesting an enhancement of sink activity. The mtPDH links glycolysis with the tricarboxylic acid (TCA) cycle. It was hypothesized that Arabidopsis having suppressed mtPDHK will display their greatest plant productivity at EC through a combined enhancement of source and sink activities. Control and transgenic Arabidopsis having either constitutive or seed-specific expression of antisense mtPDHK were grown at either AC or EC. Expression of mtPDHK and mtPDH complex activity in rosette leaves and reproductive tissues were measured, which required the development of an assay to quantify mtPDH activity. Vegetative and reproductive growth over time, seed oil parameters, and leaf net C exchange were also quantified. A parabolic relationship was found between mtPDHK expression and mtPDH activity, reflecting a role for mtPDH in balancing photosynthetic and respiratory processes. A number of growth and seed oil parameters were improved in transgenic lines, particularly at EC; many of these parameters showed a significant linear or quadratic correlation with mtPDHK expression and mtPDH activity. The proportion of very long chain fatty acids was increased in transgenic lines. Leaf net C exchange was enhanced at AC and EC, and particularly in lines showing repression of mtPDHK. The greatest enhancement in total seed and oil productivity was found for the constitutive lines 104 and 31 at EC (up to 2.8 times). These two lines exhibited a significant increase in inflorescence size, an increase in leaf water use efficiency, the lowest rate of mtPDH complex inactivation by ATP, and an intermediary enhancement of mtPDH complex activity in seeds. Thus, it is concluded that the mtPDH plays a key role in regulating sink and source activities in plants. / Natural Sciences and Engineering Research Council (NSERC) through the Green Crop Networks Research Network; Ontario Graduate Scholarship; Syngenta Graduate Scholarship; Ball Farm Services and Agrico Canada Ltd. Scholarship; Mrs. Fred Ball Scholarship; Arthur D. Latornell Scholarship; Hoskins Scholarship; Robb Travel Grant; Registrars and the Deans Scholarship and travel awards and bursaries from the University of Guelph, and the Ontario Agricultural College.

In this diploma work changes of initial and total activities and content of Rubisco in beech and Norway spruce were studied. The plants were cultivated in conditions with ambient CO2 concentration (350 mol·mol–1) and elevated CO2 concentration (700 mol·mol–1). Three series of samples (at the beginning, in the middle and at the end of growing season) were taken. Initial and total Rubisco activities were measured spectrophotometrically and activation state was calculated. Rubisco content was determined by SDS–PAGE method. Rubisco activity in beech cultivated in elevated CO2 concentration decreased during the whole growing season while in beech growing in ambient CO2 concentration Rubisco activity decreased up to middle of growing season and then increased. Rubisco content in beech in ambient CO2 concentration slightly increased and in beech in elevated CO2 concentration decreased up to middle of growing season and then increased. Rubisco activities in Norway spruce both in ambient and elevated CO2 concentration decreased. Rubisco content in Norway spruce in ambient CO2 concentration decreased but in Norway spruce in elevated CO2 concentration first decreased and then increased.

The effect of elevated CO2 concentration (EC CO2) on photosynthesis has been observed on many hierarchical levels. There was a significant increase in the rate of photosynthesis of examined trees observed in previous studies thus I hypothesised these changes are accompanied by changes of chloroplast ultrastructure and photosystem content and function and the main aim of this study is to evaluate these adjustments. In this study 13 - 14 years old seedlings of Norway spruce (Picea abies L. Karst.) grown in glass domes with adjustable windows - one with ambient CO2 concentration as a control, the other one with simulated EC CO2 (700 ppm) - during the vegetative season were examined. Pigment content, fluorescence and reflectance indexes, activity of photosystem 1 (PS1) and 2 (PS 2) of isolated chloroplasts, size of cross-sectional area of chloroplast and proportion of stromal to granal thylakoids under EC CO2 treatment were investigated. Although there was a significant increase in the maximum rate of photosynthetic assimilation of trees from EC CO2 (observed by other researchers of our team), decreased chlorophyll and carotenoid content as well as the activity of both photosystems were observed, which is usually atributed to photosynthetic acclimation. As the rate of decrease of photosystem 1 and photosystem 2...