Climate variability and the carbon cycle (C-cycle) are tied together in complex feedback loops and due to these complexities there are still knowledge-gaps of this coupling. However, to make accurate predictions of future climate, profound understanding of the C-cycle and climate variability is essential. To gain more knowledge of climate variability, the study aims to identify recurring spatial patterns of the variability of precipitation anomalies over Scandinavia during spring and summer respectively between 1981 to 2014. These patterns will be related to the C-cycle through changes in summer vegetation greenness, measured as normalized difference vegetation index (NDVI). Finally, the correlation between the patterns of precipitation variability in summer and the teleconnection patterns over the North Atlantic will be investigated. The precipitation data was obtained from ERA5 from the European Centre for Medium-Range Weather Forecasts and the patterns of variability were found through empirical orthogonal function (EOF) analysis. The first three EOFs of the spring and the summer precipitation anomalies together explained 73.5 % and 65.5 % of the variance respectively. The patterns of precipitation variability bore apparent similarities when comparing the spring and summer patterns and the Scandes were identified to be important for the precipitation variability in Scandinavia during both seasons. Anomalous events of the spring EOFs indicated that spring precipitation variability had little impact on anomalies of summer NDVI. Contradictory, summer precipitation variability seemed to impact anomalies of summer NDVI in central- and northeastern Scandinavia, thus indicating that summer precipitation variability modulates some of the terrestrial C-cycle in these regions. Correlations were found between a large part of the summer precipitation variability and the Summer North Atlantic Oscillation and the East Atlantic pattern. Hence, there is a possibility these teleconnections have some impact, through the summer precipitation variability, on the terrestrial C-cycle. / Förändringar och variation i klimatet är sammankopplade med kolcykeln genom komplexa återkopplingsmekanismer. På grund av denna komplexitet är kunskapen om kopplingen mellan klimatvariation och kolcykeln fortfarande bristande, men för att möjliggöra precisa prognoser om framtida klimat är det viktigt att ha kunskap om denna koppling. För att få mer kunskap om klimatvariation syftar därför denna studie till att identifiera återkommande strukturer av nederbördsvariation över Skandinavien under vår respektive sommar från 1981 till 2014. Dessa relateras till förändringar i sommarväxtlighetens grönhet, uppmätt som skillnaden i normaliserat vegetationsindex (NDVI). Även korrelationen mellan sommarstrukturerna av nederbördsvariationen och storskaliga atmosfäriska svängningar, s.k. "teleconnections", över Nordatlanten undersöks. Nederbördsdatan erhölls från ERA5 analysdata från Europacentret för Medellånga Väderprognoser och strukturer av nederbördsvariationen identifierades genom empirisk ortogonal funktionsanalys (EOF) av nederbördsavvikelser. De tre första EOF av vår- respektive sommarnederbördsavvikelser förklarade tillsammans 73,5 % respektive 65,5 % av nederbördsvariationen. Strukturerna av nederbördsvariation under vår respektive sommar uppvisade tydliga likheter sinsemellan. Dessutom identifierades Skanderna vara av stor vikt för nederbördsvariationen i Skandinavien under båda årstider. Avvikande år av nederbördsvariation under våren indikerade att sagda nederbördsvariation haft liten påverkan på NDVI-avvikelser under sommaren. Emellertid verkade nederbördsvariationen under sommaren påverkat NDVI-avvikelser under sommaren i centrala och nordöstra Skandinavien. Detta indikerar att nederbördsvariationen under sommaren till viss del styr den terrestra kolcykeln i dessa regioner. För nederbördsvariationen under sommaren fanns korrelation mellan både Nordatlantiska sommaroscillationen och Östatlantiska svängningen. Det finns således en möjlighet att dessa "teleconnections" har en viss påverkan på den terrestra kolcykeln genom nederbördsvariationen under sommaren.

While ocean acidification (OA) is predicted to inhibit calcification in marine macroalgae, species whose photosynthesis is limited by current dissolved inorganic carbon (DIC) levels may benefit. Furthermore, variations in macroalgal morphology will likely give rise to a range of OA tolerance in calcifying macroalgae. One genus of calcifying macroalgae that has shown varying species’ tolerance to OA is Halimeda, a major carbonate sediment producer on tropical reefs. Species within this genus occupy a range of habitats within tropical environments (reefs and lagoons), illustrating their ability to adapt to diverse environmental conditions (e.g. carbonate chemistry, irradiance). To date it is not clear if morphological and photophysiological diversity in Halimeda will translate to different tolerances to OA conditions (elevated pCO2 and lower pH). / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

Les tourbières boréales jouent un rôle important dans le cycle global du carbone en tant que puits de CO2 à long terme et en tant que l’une des plus grandes sources de méthane naturel (CH4). Ces importants réservoirs de carbone seront exposés à l’avenir au réchauffement et aux conditions plus humides caractérisant le changement climatique dans les hautes latitudes et, en raison de la grande quantité de carbone stockée dans les tourbières boréales, comprendre leurs dynamiques est important. Dans cette thèse, j'ai intégré une représentation du cycle de l'eau et du carbone dans les tourbières dans le modèle de surface terrestre ORCHIDEE-MICT (LSM), dans le but d'améliorer la compréhension du C des tourbes et de sa dynamique depuis l'Holocène, afin d'explorer les effets du changement climatique.Tout d'abord (chapitre 2), J'ai implémenté les tourbières en tant qu'unité hydrologique de sol (HSU) sous-réseau indépendante qui reçoit les eaux de ruissellement provenant des HSU non tourbeuses environnantes dans chaque cellule du réseau et ne possède pas de drainage, conformément la representation propose par Largeron et al. (2018). Pour modéliser les flux d’eau verticaux des sols tourbeux et non tourbeux, j’ai représenté les paramètres hydrologiques spécifiques à la tourbe pour l’HSU des tourbières, tandis que dans d’autres HSU, les paramètres hydrologiques sont déterminés par la texture dominante du sol de la cellule de la grille. j'ai choisi un modèle diplotelmique pour simuler la décomposition et l'accumulation de tourbe de C. Ce modèle à deux couches comprend une couche supérieure (acrotelm) inondée de manière variable et une couche inférieure (catotelm) inondée en permanence. Ce modèle a montré de bonnes performances dans la simulation de l'hydrologie des tourbières, du C et des flux d'énergie dans 30 tourbières boréales sur des échelles de temps quotidiennes à annuelles. Mais la simplification excessive de la dynamique du carbone pourrait limiter sa capacité à prévoir la réponse des tourbières boréales aux futurs changements climatiques.Deuxièmement (chapitre 3), j'ai remplacé le modèle carbone de tourbe diplotelmique par un modèle multicouche afin de prendre en compte les hétérogénéités verticales de la température et de l'humidité le long du profil de la tourbe. J'ai ensuite adapté TOPMODEL et les critères d'établissement des tourbières de Stocker et al. (2014) pour simuler la dynamique de la zone des tourbières dans une unité de la grille. Ici, la zone inondée donnée par TOPMODEL est traversée avec des conditions de croissance de tourbe appropriées pour définir la zone occupée par une HSU de tourbe. Ce modèle a été testé sur plusieurs sites de tourbières du nord et pour des simulations en 2D sur l'hémisphère nord (> 30 ° N). La superficie totale simulée de tourbières et le stock de carbone en 2010 est de 3,9 million de km2 et 463 PgC, conformément aux observations (3,4 à 4,0 million de km2 et 270 à 540 PgC).Enfin (chapitre 4), avec le modèle multicouche, j’ai réalisé des simulations factorielles à l’aide de données climatiques passées et futures issus des scenarios de trajectoire de concentration représentative (RCP) à partir de deux modèles de circulation générale (GCM) afin d’explorer les réactions des tourbières boréales au changement climatique. Les impacts des tourbières sur le futur bilan en carbone de l'hémisphère nord ont été examinés, notamment la réaction directe du bilan en carbone de la tourbière existante (simulée) et les effets indirects des tourbières sur le bilan de carbone terrestre lorsque les tourbières se modifient à l'avenir.Les travaux futurs se concentreront sur l’inclusion des influences du changement d’affectation des sols et des incendies sur les tourbières dans le modèle, étant donné que des pertes importantes de C pourraient survenir en raison de ces perturbations. Pour avoir une image complète du bilan C des tourbières, il faut prendre en compte les pertes de CH4 et de C organique dissous (DOC). / Northern peatlands play an important role in the global carbon (C) cycle as a long-term CO2 sink and the one of the largest natural methane (CH4) sources. Meanwhile, these substantial carbon stores will be exposed in the future to large warming and wetter conditions that characterize climate change in the high latitudes and, because of the large amount of C stored in northern peatlands, their fate is of concern. In this thesis, I integrated a representation of peatlands water and carbon cycling into the ORCHIDEE-MICT land surface model (LSM), with the aim to improve the understanding of peatland C and area dynamics since the Holocene, to explore effects of projected climate change to northern peatlands, and to quantify the role of northern peatlands in the global C cycle.Firstly (Chapter 2), I implemented peatland as an independent sub-grid hydrological soil unit (HSU) which receives runoff from surrounding non-peatland HSUs in each grid cell and has no bottom drainage, following the concept of Largeron et al. (2018). To model vertical water fluxes of peatland and non-peatland soils, I represented peat-specific hydrological parameters for the peatland HSU while in other HSUs the hydrological parameters are determined by the dominant soil texture of the grid cell. I chose a diplotelmic model to simulate peat C decomposition and accumulation. This two-layered model includes an upper layer (acrotelm) that is variably inundated and a lower layer (catotelm) that is permanently inundated. This model showed good performance in simulating peatland hydrology, C and energy fluxes at 30 northern peatland sites on daily to annual time scales. But the over simplification of the C dynamics may limit its capacity to predict northern peatland response to future climate change.Secondly (Chapter 3), I replaced the diplotelmic peat carbon model with a multi-layered model to account for vertical heterogeneities in temperature and moisture along the peat profile. I then adapted the cost-efficient version of TOPMODEL and peatland establishment criteria from Stocker et al. (2014) to simulate the dynamics of peatland area within a grid cell. Here the flooded area given by TOPMODEL is crossed with suitable peat growing conditions to set the area that is occupied by a peat HSU. This model was tested across a range of northern peatland sites and for gridded simulations over the Northern Hemisphere (>30 °N). Simulated total northern peatlands area and C stock by 2010 is 3.9 million km2 and 463 PgC, fall well within observation-based reported range of northern peatlands area (3.4 – 4.0 million km2) and C stock (270 – 540 PgC).Lastly (Chapter 4), with the multi-layered model, I conducted factorial simulations using representative concentration pathway (RCP)-driven bias-corrected past and future climate data from two general circulation models (GCMs) to explore responses of northern peatlands to climate change. The impacts of peatlands on future C balance of the Northern Hemisphere were discussed, including the direct response of the C balance of the (simulated) extant peatland area, and indirect effects of peatlands on the terrestrial C balance when peatlands area change in the future.Future work will focus on including influences of land use change and fires on peatland into the model, given that substantial losses of C could occur due to these disturbances. To have a complete picture of peatland C balance, CH4 and dissolved organic C (DOC) losses must be considered.

The loss of biodiversity is affecting all ecosystems on Earth, one of the greatest threats to biodiversity being climate change. Forests have been highlighted for the potential to mitigate climate change by storing carbon above- and belowground in soils. In this thesis, I studied the effects of tree diversity on carbon cycling in subtropical Chinese forests. I aimed to explore the mechanisms behind tree diversity effects on carbon cycling by focusing on microbial-based processes and the consequences of tree diversity-induced spatial heterogeneity. First, my colleagues and I tested the effects of tree diversity on litterfall spatial patterns and the consequences for litter decomposition and quantified the importance of microbial community in decomposition processes. Second, we explored the effects of tree diversity on relationships between soil microbial facets and soil microbial functions. Third, we tested the effects of tree diversity on soil microbial biomass and carbon concentrations, and their mediation by biotic and abiotic conditions. Finally, we explored the consequences of diversifying forests for re-/afforestation initiatives and plantations to reduce atmospheric carbon levels, and the benefits of diversity for mitigating the effects of climate change on ecosystems and human well-being. We highlighted the positive effects of tree diversity on tree productivity. By increasing the amount and diversity of litterfall, tree diversity increased litter decomposition and subsequently the assimilation of tree products into the forest soils. Our investigation has shown the key role of microbial communities for forests carbon dynamics by carrying out litter decomposition, soil heterotrophic respiration, and soil carbon stabilization. Most notably, tree diversity effects on soil microbial respiration were mainly mediated by soil microbial biomass rather than soil microbial community taxonomic or functional diversity. The effects of tree diversity on microbial biomass were mediated by biotic and abiotic conditions. Taken together, we revealed the importance of considering space to understand biodiversity-ecosystem functioning relationships. Finally, we argued that tree diversity is a promising avenue to maximize the potential of re-/afforestation projects to mitigate increasing atmospheric carbon. Moreover, we highlighted that diversifying forests in re-/afforestation initiatives can help to reduce climate change effects on ecosystems: first, by increasing resistance and resilience to extreme climatic events, and second, by buffering microclimatic conditions in natural and urban areas. My investigation highlighted that tree diversity effects on ecosystem functioning could be explained by both mass and diversity effects on higher trophic levels and their functions. In addition, I showed the key role of tree diversity-induced spatial heterogeneity and the need to consider space and time in further research. Moreover, these results need to be combined with practitioner constraints to enable feasible restoration projects.:Summary table Bibliographic information .................................................................................... I ~ XV Main body ......................................................................................................... 1 ~ 212 Supplementary materials ..................................................................................... i ~ xv Scientific supplementary materials ............................................................. -1- ~ - 154- Table of Contents Table of figures .......................................................................................................... XI Table of scientific supplementary materials ............................................................. XIII Glossary ................................................................................................................... XV Introduction ................................................................................................................. 3 Chapter I - Tree diversity effects on litter decomposition are mediated by litterfall and microbial processes .................................................................................................. 35 Transition I - II ........................................................................................................... 67 Chapter II - Tree diversity and soil chemical properties drive the linkages between soil microbial community and ecosystem functioning................................................ 71 Transition II - III ....................................................................................................... 107 Chapter III - Abiotic and biotic drivers of scale-dependent tree trait effects on soil microbial biomass and soil carbon concentration ................................................... 111 Transition III - IV ..................................................................................................... 155 Chapter IV – Diverse forests are cool: promoting diverse forests to mitigate carbon emissions and climate change ............................................................................... 159 General discussion ................................................................................................. 173 Abstract .................................................................................................................. 195 General acknowledgments ..................................................................................... 209 Supplementary materials ..............................................................................................i

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