Eddy-covariance (EC) CO₂ flux data were analysed and annual carbon (C) balances estimated for a four-year period (2004-2007) following clearcut harvesting of a boreal jack pine stand in northern Saskatchewan. The site was a source of C to the atmosphere for all years, with annual net ecosystem productivity (NEP) increasing from -153 g C m⁻² yr⁻¹ in 2004 to -63 g C m⁻² yr⁻¹ in 2007. This increase was mainly due to gross primary productivity (GPP) increasing significantly from 78 to 200 g C m⁻² yr⁻¹ , while ecosystem respiration (R) increased only slightly from 231 to 263 g C m⁻² yr⁻¹ over the same period. In the 2006 growing season (GS), a field campaign was conducted to investigate the relationships between monthly destructive measurements of leaf area index (LAI) and daily measurements of the normalized difference vegetation index (NDVI) and photosynthetic capacity (Amax). The latter was derived from 5-day, 16-day, 30-day and annual Michaelis-Menten light response analyses using daytime measurements of NEP and incident photosynthetically active radiation. Digital-camera data were used to evaluate the potential of using the rectilinear-lens vegetation index (RLVI) as a surrogate for NDVI of a young forest stand. Results showed that LAI was linearly related to NDVI and RLVI, which was largely the result of changes in the deciduous vegetation component across the GS. These results indicate that RLVI could be used as a surrogate for NDVI up to a GS maximum LAI of 0.91 m2 m⁻² observed in 2006. Measured mean (± 1 S.D.) GS LAI was 0.67 (± 0.24) m² m⁻² in 2006. LAI accounted for the majority of the variability in Amax at the 30-day time scale, while at shorter time scales air temperature was the dominant control. For 2004 to 2007, mean spring estimates of LAI were 0.25, 0.29, 0.38 (compared to 0.40 m² m⁻² from measurements) and 0.41 m² m⁻², respectively. Results suggest that a steady increase in the jack pine LAI component accounted for the annual increases in GPP and hence NEP over the four years.

Decisões tomadas no planejamento da implantação florestal, como a densidade do plantio e o material genético, alteram a disponibilidade de recursos naturais tais como nutrientes, água e luz e consequentemente afetam a assimilação do carbono, que está diretamente relacionada ao crescimento da planta. Ainda são escassas as informações de como e quanto a densidade de plantio e o material genético afetam a fixação de carbono pelas ávores. O objetivo desse trabalho foi avaliar os padrões de fixação e alocação de carbono em plantações clonais de Eucalyptus sp. em duas densidades de plantio (3x2 m e 3x4 m), em um Latossolo Vermelho Distrófico T ípico A moderado. O estudo foi desenvolvido na Estação Experimental de Ciências Florestais de Itatinga-SP - ESALQ/USP, com três materiais clonais de Eucalyptus urophylla: AEC 0144, AEC 224 e COP 1404. O delineamento experimental utilizado foi em blocos casualizados, com esquema fatorial 3 x 2, sendo composto por três clones de eucalipto em dois espaçamentos, com 6 repetições para cada tratamento. Durante o intervalo de um ano (dos 40 aos 52 meses de idade) foram determinados a Produtividade Primária Líquida da Parte Aérea (ANPP: incremento da biomassa aérea somada ao folhedo), a Respiração Autotrófica da Parte Aérea (Rp: respiração das folhas e do tronco com base com base na ANPP, assumindo um valor constante de eficiência de uso do carbono (CUE) de 0,53 (GIARDINA et al., 2003)), o Fluxo de Carbono Abaixo do Solo (TBCF: produção e respiração das raízes grossas e finas, exsudatos das raízes e produção de substratos usados por micorrizas) e a Produtividade Primária Bruta (GPP: somatório dos fluxos de carbono) para os seis tratamentos avaliados. A maior produtividade encontrada para o clone AEC 0144 no espaçamento 3x2 m foi resultado de uma maior GPP (5997,45 g C m-2 ano-1), maior partição de carbono para incremento de tronco (30%) e menor partição da GPP para TBCF (34%). A ANPP variou de 1453,99 g C m-2 ano-1 (Clone COP 1404 no espaçamento 3x2 m) a 2288,78 g C m-2 ano-1 (Clone AEC 0144 no espaçamento 3x2 m), sendo os maiores fluxos encontrados para os clones AEC 0144 em ambos espaçamentos e para o clone COP 1404 no espaçamento 3x4 m. A variação encontrada nos valores de respiração da parte aérea seguiram o mesmo padrão dos resultados da ANPP. O TBCF foi significadamente superior para os clones AEC 0144 e AEC 224 no espaçamento 3x2 m com 2056,36 g C m-2 ano-1 e 1903,83 g C m-2 ano-1, respectivamente; e para o clone COP 1404 no espaçamento 3x4 m (1927,43 g C m-2 ano-1). Houve correlação positiva do TBCF com a GPP, mas não com a ANPP. / Decisions not planned for forest deployment, such as planting density and genetic material, alter the availability of natural resources such as nutrients, water and light and consequently affect the assimilation of carbon, which is directed to plant growth. They are still scarce as information on how and how much planting density and genetic material for a fixation of carbon by trees. The objective of this work was to evaluate the carbon allocation patterns in clonal plantations of Eucalyptus sp. in two planting densities (3x2 m and 3x4 m), in a typical Typic A moderate Dystrophic Red Latosol. The study was developed at the Experimental Station of Forest Sciences of Itatinga-SP - ESALQ / USP, with three clonal materials of Eucalyptus urophylla: AEC 0144, AEC 224 and COP 1404. The experimental design was a randomized complete block design with a factorial scheme 3 x 2, being composed of three clones of eucalyptus in two spacings, with 6 replicates for each treatment. During the one-year interval (from 40 to 52 months of age) was determined Aboveground Net Primary Productivity (ANPP: increase of the aerial biomass added to the litterfall), Aboveground Autotrophic Respiration (Rp: leaf respiration and (CUE) of 0.53 (GIARDINA et al., 2003)), Total Belowground Carbon Flux (TBCF: production and respiration of the roots) and Gross Primary Productivity (GPP: sum of the carbon fluxes) for the six treatments evaluated. The higher productivity found for the clone AEC 0144 in the 3x2 m spacing resulted from a higher GPP (5997.45 g C m-2 year-1), larger carbon partition for trunk increment (30%) and smaller partition from GPP for TBCF (34%). The ANPP ranged from 1453.99 g C m-2 year-1 (Clone COP 1404 in spacing 3x2 m) to 2288.78 g C m-2 year-1 (Clone AEC 0144 in 3x2 m spacing) Found for clones AEC 0144 in both spacings and COP 1404 in 3x4 m spacing. The variation found in aboveground autotrophic respiration values followed the same pattern of ANPP results. The TBCF was significantly higher for clones AEC 0144 and AEC 224 at 3x2 m spacing with 2056.36 m-2 year-1 and 1903.83 m-2 year-1, respectively; and for clone COP 1404 in 3x4 m spacing (1927.43 m-2 year-1). There was a positive correlation between TBCF and GPP, but not with ANPP.

Dans le contexte de réchauffement climatique, le maintien des rendements est un enjeu majeur pour la filière viticole. L'augmentation des températures impacte négativement certaines phases clés du développement reproducteur en induisant notamment des phénomènes de coulure ou de pertes précoces d'inflorescence. L'altération du bilan carboné pourrait être un facteur majeur des diminutions de rendements en réponse aux températures élevées et l'évaluation de cette hypothèse permettrait d'ajuster les pratiques pour limiter les effets du réchauffement climatique. Si l'implication du bilan de carbone chez les plantes annuelles semble être à la base des baisses de rendement observées ces dernières années, les choses sont beaucoup moins claires chez des pérennes comme la vigne du fait des très nombreux co-facteurs possible ainsi que de la difficulté à expérimenter dans des conditions totalement contrôlées. Afin de s'affranchir de ces contraintes, notre étude a été réalisée en conditions contrôlées sur la Microvigne, un mutant naturel insensible à l'acide gibberelique et un nouveau modèle d'étude pour la génétique et la physiologie de la vigne. Ce mutant présente un phénotype nain et une floraison et fructification continues le long de l'axe proleptique. L'approche utilisée dans cette étude a consisté à (i) développer un cadre d'analyse adapté à la Microvigne; (ii) décrire l'impact de l'élévation de la température, sur les développements végétatif et reproducteur de la vigne, et plus particulièrement l'avortement des stades précoces du développement reproducteur; (iii) caractériser les changements du bilan de carbone de la Microvigne induits par la contrainte thermique, et enfin (iv) évaluer l'implication potentielle du bilan de carbone dans les phénomènes d'avortement précoces en réponse au stress thermique. Ce travail a permis de mettre en évidence des phénomènes d'avortement complet d'inflorescences en réponse à l'élévation des températures. Par ailleurs, nous avons pu montrer un rôle du statut carboné dans ce phénomène, soit via les teneurs totales en carbohydrates, soit via l'état global des réserves à l'échelle de la plante. Ce travail montre les potentialités su modèle Microvigne et ouvre de nouvelles perspectives pour l'analyse des effets des contraintes abiotiques sur le développement végétatif et reproducteur de la vigne. / Global warming is likely to be a major issue for grapevine yield sustainability in the next years. A common hypothesis is that long-term elevated temperatures may cause the failure of key phases of reproductive development, through their negative impact on carbon balance. However, testing the specific role of plant carbon status on yield elaboration under elevated temperatures is difficult on perennial crops, such as grapevine, and when environment fluctuates. To overcome these difficulties, the present work was conducted under fully controlled environment using a natural, giberrelic acid insensitive mutant of grapevine called Microvine, as a new model for grapevine genetics and physiological studies. This mutant present a dwarf stature and lack of juvenile characteristics leading to the continuous flowering and fruiting even during the first year after sowing. The present study was aimed at (i) developing a framework of analysis for Microvine; (ii) describing vegetative and reproductive developments responses to temperature elevation at whole plant level, and more precisely on early reproductive development abortions; (iii) characterizing grapevine carbon balance responses to temperature; and finally (iv) evaluating carbon balance implication in temperature-dependent early reproductive development abortions. This work shows that complete inflorescence abortions observed in response to temperature were related to carbon status, either expressed though total carbohydrate, or through the level of reserves at the whole plant level. This study opens the way to use Microvine as model to address the impact of climate warming on grapevine vegetative and reproductive developments.

Eddy-covariance (EC) CO₂ flux data were analysed and annual carbon (C) balances estimated for a four-year period (2004-2007) following clearcut harvesting of a boreal jack pine stand in northern Saskatchewan. The site was a source of C to the atmosphere for all years, with annual net ecosystem productivity (NEP) increasing from -153 g C m⁻² yr⁻¹ in 2004 to -63 g C m⁻² yr⁻¹ in 2007. This increase was mainly due to gross primary productivity (GPP) increasing significantly from 78 to 200 g C m⁻² yr⁻¹ , while ecosystem respiration (R) increased only slightly from 231 to 263 g C m⁻² yr⁻¹ over the same period. In the 2006 growing season (GS), a field campaign was conducted to investigate the relationships between monthly destructive measurements of leaf area index (LAI) and daily measurements of the normalized difference vegetation index (NDVI) and photosynthetic capacity (Amax). The latter was derived from 5-day, 16-day, 30-day and annual Michaelis-Menten light response analyses using daytime measurements of NEP and incident photosynthetically active radiation. Digital-camera data were used to evaluate the potential of using the rectilinear-lens vegetation index (RLVI) as a surrogate for NDVI of a young forest stand. Results showed that LAI was linearly related to NDVI and RLVI, which was largely the result of changes in the deciduous vegetation component across the GS. These results indicate that RLVI could be used as a surrogate for NDVI up to a GS maximum LAI of 0.91 m2 m⁻² observed in 2006. Measured mean (± 1 S.D.) GS LAI was 0.67 (± 0.24) m² m⁻² in 2006. LAI accounted for the majority of the variability in Amax at the 30-day time scale, while at shorter time scales air temperature was the dominant control. For 2004 to 2007, mean spring estimates of LAI were 0.25, 0.29, 0.38 (compared to 0.40 m² m⁻² from measurements) and 0.41 m² m⁻², respectively. Results suggest that a steady increase in the jack pine LAI component accounted for the annual increases in GPP and hence NEP over the four years. / Land and Food Systems, Faculty of / Graduate

Significant warming of Arctic and northern regions is ongoing and may greatly alter the carbon cycle of these regions. During the International Polar Year, an extensive study was carried out in the Eastern Canadian subarctic and Arctic in order to characterize CO2 and CH4 exchanges from these potentially sensitive ecosystems. The main objectives of this study were to identify the land cover and environmental factors leading to greatest CO2 and CH4 emissions in a highly heterogeneous subarctic landscape, to quantify interannual variability in the net ecosystem exchange of CO2 (NEE) in subarctic forest tundra and investigate the weather conditions that increase net uptake of CO2, and finally, to evaluate the general trends of mid-summer NEE along a latitudinal gradient spanning from 55° to the 72° north. At the landscape level, CO2 and CH4 exchanges showed large variability. Although CH4 emissions were greatest in wetlands, their areal coverage is small in the Kuujuarapik area and limited the influence of these CH4 sources. At the ecosystem level, large-scale atmospheric processes controlled growing season length and cumulative growing degree days which greatly influenced annual and seasonal NEE trends. The subarctic forest tundra near Kuujuarapik was a net source of CO2 in all 3 study years but the source strength was least with the greatest growing degree days while the length of the snow-free period appeared to be less important. Across a latitudinal gradient covering subarctic forest tundra to Arctic tundra, variations in summer NEE could be linked to surface organic carbon content with higher net CO2 uptake at sites with greater soil organic carbon. Warmer days tended to correlate with smaller daily net CO2 uptake (or greater net CO2 losses) but overall, warmer growing seasons reduced the net losses of CO2 on an annual basis. Carbon fluxes in Eastern Canadian subarctic and Arctic regions are highly variable in space and time but these observations help establish a baseline for future examinations of how these carbon exchanges may change with further warming.

Orientador: Juliano Carlos Calonego / Resumo: A calagem é uma pratica agrícola indispensável para a correção da acidez em solos tropicais contribuindo para o aumento da produção de grãos e biomassa. A aplicação superficial de calcário e gesso em sistema de semeadura direta (SSD) tem sido uma estratégia usada para melhorar as propriedades químicas do solo em subsuperficie, todavia, existem poucas informações sobre os efeitos dessa prática no balanço de carbono no sistema solo-planta-atmosfera. Dessa forma, o trabalho teve como objetivo avaliar a emissão acumulada anual de C-CO2, o estoque de C e N no solo, a qualidade da matéria orgânica do solo (MOS) e a atividade biológica, bem como a deposição de C e N pela biomassa do sistema radicular e pelos resíduos produzidos no final do ciclo das culturas na superfície do solo, em função da aplicação superficial de calcário e gesso em um SSD de longa duração. O experimento foi instalado em 2002 em um delineamento experimental em blocos casualizados no esquema de parcelas subdivididas e 4 repetições. A aplicação de calcário e gesso ocorreu nos anos de 2002, 2004, 2010 e por último em 2016 quando foi dado início a condução do presente trabalho. As parcelas foram constituídas por quatro níveis de calcário (ausência de aplicação, 3260, 6520 e 13040 kg ha-1) e as subparcelas por dois níveis de gesso agrícola (ausência de aplicação e 10000 kg ha-1). Ao final dos dois anos agrícolas a aplicação de calcário promoveu um aporte médio de 2,70 Mg ha-1 de C e 150 kg ha-1 de N pelo sistema rad... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Liming is an indispensable agricultural practice for the correction of acidity in tropical soils contributing to the increase in the production of grains and biomass. The superficial application of lime and gypsum in a direct seeding system (NT) has been a strategy used to improve the chemical properties of the soil in subsurface, however, there is little information about the effects of this practice on the carbon balance in the soil-plant-atmosphere system. Thus, the work aimed to evaluate the accumulated annual emission of C-CO2, the stock of C and N in the soil, the quality of soil organic matter (SOM) and the biological activity, as well as the deposition of C and N by the biomass of the root system and by the residues produced at the end of the crop cycle on the soil surface, due to the superficial application of lime and gypsum in a long-term NT. The experiment was installed in 2002 in a randomized block design in a split plot and 4 replications scheme. The application of lime and gypsum occurred in the years 2002, 2004, 2010 and lastly in 2016 when the conduction of the present work began. The plots consisted of four levels of lime (no application, 3260, 6520 and 13040 kg ha-1) and the subplots by two levels of agricultural gypsum (no application and 10,000 kg ha-1). At the end of the two agricultural years, the application of lime promoted an average supply of 2.70 Mg ha-1 of C and 150 kg ha-1 of N by the root system of the soybean, corn and U. ruziziensis in relatio... (Complete abstract click electronic access below) / Doutor

<p>Continuous measurements of carbon fluxes and meteorological variables were made at a newly initiated flux tower site at an oak-dominant temperate deciduous forest in Southern Ontario, Canada from January to December 2012. Results indicate this forest was a moderate carbon sink in 2012. Annual values of net ecosystem productivity (NEP), gross ecosystem productivity (GEP) and ecosystem respiration (R) were 263 ± 30, 1192 and 922 g C m^-2, respectively. An unusual warm period in March caused a strong increase in R. Erratic peaks of daily air temperature in April also increased R. A drought in July and early August reduced NEP rates when soil moisture values reached the lowest point of the year in late July and early August (minimum 0.023 m³ m^-3). This decrease in NEP was mostly caused by a decrease in GEP, rather than increased R. Water use efficiency at this deciduous forest was 2.86 g C kg^-1 H₂O, indicating conservative water use by the forest. Downwelling photosynthetic active radiation (PAR) was a dominant environmental control on photosynthesis, followed by air temperature and vapour pressure deficit, except in extreme dry periods when soil water stress affected carbon uptake. Extremely cloudy days in the growing season resulted in net carbon release due to low photosynthetic uptake values. Results indicate that large climatic fluctuations in this region may cause high instability in photosynthetic carbon uptake and release from soil carbon pools. This study helps to evaluate and quantify the responses of deciduous forests in the Great Lakes region to future climate change and extreme weather events.</p> / Master of Science (MSc)

Dans de nombreuses régions tropicales dont certaines zones du Brésil, les plantations industrielles d'Eucalyptus connaissent une expansion rapide. L'impact environnemental et la durabilité de ces plantations soulèvent de nombreuses questions, notamment en termes d'évolution du bilan carboné et de la fertilité des sols, et d'impact sur les ressources en eau. Cette thèse contribue à apporter des réponses à ces questions, en étudiant les bilans de carbone, d'eau et d'azote des plantations d'Eucalyptus de l'état de São Paulo. L'approche privilégiée est celle de la modélisation écophysiologique, et l'échelle visée in fine est celle de grandes plantations. Cette thèse présente une première approche empirique d'estimation spatialisée de la production des plantations, basée sur la construction et l'interprétation de séries temporelles d'indice de végétation du satellite MODIS sur un ensemble de parcelles d'âge et de productivité contrastés. Ensuite une approche plus complète de modélisation écophysiologique est développée, basée sur le modèle C-H2O-N « G'DAY » qui a été adapté au cas des plantations brésiliennes. La simulation par le modèle des flux de C, H2O et N sur l'ensemble de parcelles évoqué précédemment, à l'échelle de la rotation, a été réalisée avec et sans la contribution de données d'indice foliaire, obtenues à partir des séries temporelles de réflectance MODIS. Ces séries temporelles de données satellitaires sont riches en informations sur la variabilité spatio-temporelle de la productivité, qui est bien reproduite par le modèle écophysiologique proposé / Industrial Eucalyptus plantations are expanding rapidly in many tropical regions, and in particular in south-eastern Brazil. Their sustainability and environmental impact are an issue of concern, and questions have been raised regarding their carbon balance and effects on soil fertility and water ressources. This thesis addresses some of these questions, by studying the carbon, water and nitrogen balance of Eucalyptus plantations in São Paulo State.A process-based modelling approach was adopted, with the ultimate aim of application at the scale of large plantations. A first empirical approach was developed to estimate wood production on a spatial basis, involving the construction and interpretation of MODIS vegetation index time series on a set of Eucalyptus stands of contrasted age and productivity levels. The complete ecophysiological C-H2O-N cycling model "G'DAY" was then adapted for Brazilian plantations. Rotation-length simulations of C, H2O and N fluxes were carried out on the afore-mentioned set of plantation stands, either with or without the integration of leaf area index data obtained from MODIS reflectance time-series. The satellite time series carry useful information about the spatio-temporal variability of productivity, which is also well reproduced by the proposed ecophysiological model

A produtividade dos plantios de eucalipto no Brasil apresentou ganhos significativos nas últimas décadas devido a avanços em melhoramento genético e silvicultura. Contudo, a produção de madeira representa apenas uma fração da produtividade primária bruta (GPP). Avaliar fluxos e partição de carbono (C) entre os diferentes componentes da floresta, e estudar o uso e a eficiência de uso dos recursos disponíveis é essencial para compreender os mecanismos que controlam a produtividade de plantios intensivamente manejados. O estudo quantificou os fluxos e partição de C e a eficiência de uso da luz para a produção de lenho (LUE) em 12 parcelas em um gradiente natural de produtividade, durante o sétimo ano de um plantio comercial de Eucalyptus grandis. Nessas mesmas parcelas, na escala da árvore, foram avaliadas a dominância do crescimento, produção de lenho e LUE, identificando a representatividade de árvores dominantes e suprimidas na produtividade do povoamento. O estudo do balanço de C e a aplicação da teoria da ecologia da produção em diferentes escalas objetivaram ampliar o conhecimento sobre os processos que governam a produtividade florestal. A heterogeneidade espacial dos atributos do solo e a topografia da área experimental influenciaram fortemente os fluxos componentes da GPP e sua partição, gerando um gradiente de produtividade. A produtividade de lenho variou de 554 gC m-2 ano-1 na parcela com menor GPP a 923 gC m-2 ano-1 na parcela com maior GPP. O fluxo de C para o solo variou de 497 gC m-2 ano-1 a 1235 gC m-2 ano-1 sem relação significativa com GPP. A partição do GPP para produção de lenho aumentou de 0,19 a 0,23, com tendência de aumento com o GPP (R2=0,30, p=0,07). A LUE aumentou em 66% (de 0,25 gC MJ-1 para 0,42 gC MJ-1) com a GPP, como resultado da elevação do fluxo e partição de C para produção de lenho. Ao longo do gradiente de produtividade, parcelas com alta eficiência quântica do dossel também mostraram alta LUE. A dominância do crescimento entre árvores teve forte impacto sobre a produtividade do povoamento. As 20% maiores árvores apresentaram em média 38% da biomassa de lenho e representaram 47% da produção de lenho. Características das folhas sugeriram que a maior produtividade de árvores dominantes, em relação às suprimidas, pode resultar de diferenças no controle estomático e não na capacidade fotossintética. A ecologia da produção na escala da árvore mostrou que os indivíduos dominantes produziram mais madeira por terem absorvido mais radiação e pela maior eficiência do uso da luz, comparativamente às árvores suprimidas. Em média, uma árvore suprimida cresceu 1,2 kg ano-1 de lenho, absorveu 2,9 GJ ano-1 de radiação e teve uma LUE de 0,4 g MJ-1. Já uma dominante cresceu 37 kg ano-1, absorveu 38 GJ ano-1 com mais que o dobro da eficiência (1,01 g MJ-1). Estudos sobre o balanço de carbono e ecologia da produção em diferentes escalas são essenciais para aperfeiçoar o conhecimento sobre os processos que controlam a produtividade de madeira e a fixação de carbono, e aprimorar os modelos ecofisiológicos. / The productivity of the eucalypt plantations in Brazil showed significant increase over the last decades, due to improvement in breeding and silviculture. However, wood production represents only a fraction of the gross primary production (GPP). Assessing carbon (C) fluxes and partitioning among forest components, and evaluate use and use efficiency of the available resources is essential to understand mechanisms driving productivity of intensively managed plantations. The study quantified fluxes and partitioning of C and light use efficiency for stem production (LUE) in 12 plots across a natural gradient of productivity during the seventh year of a commercial Eucalyptus grandis. Within these plots, at tree level, were evaluated growth dominance, stem production and LUE, identifying representativeness of dominant and suppressed trees to stand productivity. The study of C budget and the application of the production ecology theory at different levels aimed increase the knowledge about the processes driving forest productivity. The spatial heterogeneity of soil attributes and topography across the experimental site strongly influenced the component fluxes of GPP and partitioning, generating a gradient of productivity. Stem production ranged from 554 gC m-2 year-1 at the lowest GPP plot to 923 gC m-2 year-1 at the highest GPP plot. Total below ground carbon flux (TBCF) ranged from 497 g C m-2 year-1 to 1235 g C m-2 year-1, with no relationship to ANPP or GPP. Stem NPP:GPP partitioning ratio increased from 0.19 to 0.23 showing a trend of increase with GPP (R2=0.30, p=0.07). LUE increased by 66% (from 0.25 gC MJ-1 to 0.42 gC MJ-1) with GPP, as a result of the increased C partitioned and flux to stem NPP. Across the gradient of productivity, plots with the highest canopy quantum efficiency also showed the highest LUE. Growth dominance between trees showed a strong impact on stand productivity. The 20% larger trees accounted for 38% of stem biomass and represented 47% stem production. Leaf characteristics suggested that dominant trees were more productive, in relation to suppressed, may result in differences on stomatal control and not on photosynthetic capacity. The production ecology at tree level showed that dominant trees produced more wood by absorbing more radiation and due to higher light use efficiency, comparing to suppressed trees. On average, a suppressed tree grew 1,2 kg year-1 of stem, absorbed 2,9 GJ year-1 of radiation with a LUE of 0.4 g MJ-1. Although, a dominant grew 37 kg year-1 of stem, absorbed 38 GJ year-1 of radiation with the double of efficiency (1.01 g MJ-1). Studies regarding carbon balance and production ecology at different levels are essential to improve the knowledge on processes controlling wood production and carbon uptake, and develop ecophysiological models.

Le bilan carboné d'une rotation culturale de quatre ans a été établi entre 2004 et 2008 sur le site expérimental de Lonzée, Belgique. La région se caractérise par un climat tempéré océanique avec une température moyenne de l'air de 10°C et des précipitations annuelles de l'ordre de 800 mm. Le sol de la parcelle est un Luvisol. Les cultures composant la rotation sont des cultures de betterave, froment dhiver, pomme de terre et froment dhiver. Dans le but détablir un bilan carboné, des mesures ont été effectuées à différentes échelles spatiales et temporelles. Un système de mesure par eddy covariance fournit une estimation par demiheure de l'échange net en CO2 de l'écosystème (NEE). La qualité des procédures de sélection et de traitement des flux de NEE a été contrôlée. A partir de ces mesures, la productivité primaire brute (GPP) et la respiration totale de l'écosystème (TER) sont déduites. Plusieurs procédures basées sur les mesures diurnes ou nocturnes de NEE sont comparées. L'intérêt d'utiliser un court pas de temps dans ces procédures et la température du sol comme température de référence a été mis en avant, ainsi que la nécessité de déterminer une valeur seuil de la vitesse de friction (u*) pour chaque culture et les longues inter-cultures. Pour la culture de froment d'hiver 2005, une estimation de la GPP déduite des mesures d'eddy covariance est comparée à une estimation basée sur une modélisation de mesures réalisées, une fois par semaine, à l'échelle de la feuille. La conception initiale de l'appareil de mesure a permis de réaliser les mesures sur les feuilles uniquement. Les évolutions des deux estimations sont proches à l'échelle de la saison et à l'échelle journalière. La mise en oeuvre de la méthode basée sur les mesures à léchelle de la feuille a apporté dimportantes informations en termes de réponse de la GPP aux facteurs climatiques et non climatiques et a permis une validation de lestimation basée sur les mesures deddy covariance. Toutefois, dans le cadre de létablissement dun bilan carboné, la méthode basée sur les mesures d'eddy covariance est préférée. Des mesures de la respiration de sol, réalisées à l'échelle de la miniparcelle de sol, et des mesures du contenu en carbone des plantes sont aussi réalisées. Combinées aux mesures d'eddy covariance, ces mesures permettent de déduire les parts autoet hétérotrophiques de la respiration. Sur l'ensemble de la rotation, la parcelle apparait être une source significative de carbone de 0.17 (+/- 0.14) kg C m-2. Cela suggère que, durant la rotation, le contenu en carbone du sol a diminué. Ceci peut sexpliquer par labsence dapport de fertilisation organique durant les 10 dernières années ainsi que par la récolte systématique des pailles des céréales.