Northern peatlands store large amounts of soil organic carbon that are extremely vulnerable to climate change. Direct environmental changes as temperature increase and water table drawdown might not only release more C as CO2 into the atmosphere, but will likely result in increasing vascular plants at the expense of Sphagnum mosses as well. Therefore, the question arises how different plant functional types (shrubs and sedges) with distinctly different functional strategies compared to Sphagnum mosses control C allocation in peatlands and what this means for peat decomposition. Therefore, the key objective of this thesis was to study the patterns of belowground C input by shrubs and sedges and how their above- to belowground C allocation might impact the decomposition of the present moss-dominated peat at different temperatures. To this aim, we applied a plant removal experiment on hummocks with mixed sedge-shrub vegetation in two moss-dominated peatlands located in the Italian Alps at different altitude, i.e. different temperatures. Subsequent measurements of soil respiration, dissolved organic carbon concentration and stable isotope composition (δ13C) of dissolved organic carbon in pore water were used as proxies to estimate the root derived C input by different plant functional type. With in situ 13C pulse-labelling, we assessed the above-to belowground C allocation by quantifying 13C in plant leaves and soil respiration and by measuring δ13C in dissolved organic carbon and in different depths of the peat. In additional peat cores taken under adjacent shrub and sedge plants, we used elemental analysis of carbon, nitrogen, their stable isotopes and analytical pyrolysis gas chromatography mass spectrometry to assess effects of vascular plants (sedge, shrub) on chemical properties and decomposition of the moss-dominated peat. The results provide a mechanistic evidence that plant functional types differ profoundly in their above- to belowground C allocation in peatlands. With shrubs, recently assimilated photosynthates are more likely to be allocated aboveground and turned over belowground than with sedges. Moreover, shrubs showed a fast and tightly coupled processes chain of C assimilation, subsequent C translocation to roots and finally C turnover to CO2, possibly supported by their mutualistic association to mycorrhizal fungi. Though sedges had a higher root-derived C input per unit of biomass than shrubs, the belowground C turnover of recently assimilated C was lower. At the same time, sedges allocated more C belowground to roots than shrubs. For sedges, belowground C turnover processes occurred decoupled from aboveground biomass. The temperature difference between sites did neither increase aboveground C allocation significantly nor belowground C allocation and turnover. However, a higher vascular plant biomass increased the root-derived C input, particularly with shrubs at higher temperatures. Multiple parameters also revealed a higher degree of decomposition of moss-dominated peat collected under sedges than under shrubs, particularly at the high temperature site. Temperature effects on peat decomposition were less pronounced than those of sedges. Eventually, it was not the higher belowground C turnover triggered by shrubs that accelerated decomposition of the present moss-dominated peat but likely the belowground C allocation to the roots by sedges. It can be concluded that the contribution of root exudates to belowground C allocation plays no decisive role in peat decomposition. Yet, the contribution of belowground biomass, particularly of sedges, but also litter of shrubs may impact decomposition processes in a changing climate. Hence, it can be expected that in northern peatlands with increasing shrub biomass, ancient C stores will not be mobilized, while with increasing sedge biomass, C stores are likely at risk.:Thesis at a glance 2 1 Introduction 5 1.1 Northern peatlands and climate change . . . . . . . . . . . . . . . . . . . . . 5 1.2 Vegetation and its impact on carbon cycling in northern peatlands in a warmer climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.3 In situ approaches to study plant functional type effects on peat decomposition in response to climate change . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.4 Objectives, hypotheses and experimental approach . . . . . . . . . . . . . . . 14 2 Study I 21 2.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.2 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.3 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.4 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.5 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.6 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.7 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2.9 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3 Study II 47 3.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 3.2 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.3 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.4 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 3.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 3.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 3.8 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 4 Study III 75 4.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 4.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 4.3 Material and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 4.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 4.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 4.7 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 5 Synthesis 97 5.1 Regulations of root-derived carbon input and above- to belowground carbon allocation by vascular plants in peatlands . . . . . . . . . . . . . . . . . . . . 97 5.2 The effect of different above- to belowground carbon allocation patterns of vascular plants on Sphagnum-derived peat decomposition at different temperatures103 6 Conclusions 105 6.1 Implications of belowground carbon allocation by vascular plants for peat decomposition in a warmer climate . . . . . . . . . . . . . . . . . . . . . . . . . 105 6.2 Towards a dynamic understanding of the impact of roots on peatland carbon cycling in a warmer climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 7 Acknowledgements 109 References 111 List of publications and license agreements 139 Curriculum Vitae 149 / Moore der nördlichen Hemisphäre speichern große Mengen an organischem Kohlenstoff im Boden, der durch den Klimawandel extrem gefährdet ist. Direkte Umweltveränderungen wie ein Temperaturanstieg und die Absenkung des Grundwasserspiegels könnten nicht nur mehr Kohlenstoff als CO2 in die Atmosphäre freisetzen, sondern werden wahrscheinlich auch zu einer Zunahme von Gefäßpflanzen auf Kosten von Torfmoosen führen. Daher stellt sich die Frage, wie verschiedene funktionellen Pflanzengruppen (Sträucher und Seggen) mit deutlich unterschiedlichen funktionellen Strategien im Vergleich zu Torfmoosen die Kohlenstoff-Allokation in Mooren steuern und was dies für den Torfabbau bedeutet. Daher war das Hauptziel dieser Arbeit, die Muster des unterirdischen Kohlenstoff-Eintrags durch Sträucher und Seggen zu untersuchen und festzustellen, wie sich ihre ober- und unterirdische Kohlenstoff-Allokation auf die Zersetzung des moosdominierten Torfs bei unterschiedlichen Temperaturen auswirken könnte. Zu diesem Zweck haben wir ein Pflanzenentfernungs-Experiment auf Bulken mit gemischter Seggen- und Strauchvegetation in zwei moosdominierten Hochmooren in den italienischen Alpen auf unterschiedlichen Höhenlagen, d. h. bei unterschiedlichen Temperaturen, durchgeführt. Anschließende Messungen der Bodenatmung, der Konzentration des gelösten organischen Kohlenstoffs und der stabilen Isotopenzusammensetzung (δ13C) des gelösten organischen Kohlenstoffs im Porenwasser dienten als Indikatoren für den von den Wurzeln stammenden Kohlenstoff-Eintrag der verschiedenen funktionellen Pflanzengruppen. Mit Hilfe der In-situ-13C-Pulsmarkierung wurde die ober- und unterirdische Kohlenstoff-Allokation durch die Quantifizierung von 13C in den Pflanzenblättern und in der Bodenatmung sowie durch die Messung von δ13C im gelösten organischen Kohlenstoff und im Torf aus verschiedenen Tiefen festgestellt. In zusätzlichen Torfkernen, die unter benachbarten Strauch- und Seggenpflanzen entnommen wurden, haben wir Elementaranalyse von Kohlenstoff, Stickstoff und deren stabile Isotope sowie die analytische Pyrolyse-Gaschromatographie-Massenspektrometrie verwendet, um die Auswirkungen von Gefäßpflanzen (Seggen, Sträucher) auf die chemischen Eigenschaften und den Abbau des moosdominierten Torfs zu bewerten. Die Ergebnisse liefern einen mechanistischen Beweis dafür, dass sich funktionelle Pflanzengruppen in ihrer ober- und unterirdischen Kohlenstoff-Allokation in Mooren stark unterscheiden. Bei Sträuchern wird kürzlich assimilierter Kohlenstoff eher oberirdisch allokiert und unterirdisch umgesetzt als bei Seggen. Darüber hinaus wiesen Sträucher eine schnelle und eng gekoppelte Prozesskette aus Kohlenstoff-Assimilation, anschließender Kohlenstoff-Translokation in die Wurzeln und schließlich Kohlenstoff-Umsatz zu CO2 auf, was möglicherweise durch ihre mutualistische Beziehung zu Mykorrhiza Pilzen unterstützt wird. Obwohl Seggen gegenüber Sträuchern einen höheren Kohlenstoff-Eintrag aus den Wurzeln pro Biomasseeinheit hatten, war der unterirdische Kohlenstoff-Umsatz von kürzlich assimiliertem C geringer. Gleichzeitig bauten Seggen unterirdisch mehr Kohlenstoff in die Wurzeln ein als Sträucher. Bei Seggen fand der unterirdische Kohlenstoff-Umsatz entkoppelt von der oberirdischen Biomasse statt. Der Temperaturunterschied hatte weder Einfluss auf die oberirdische Kohlenstoff-Allokation noch auf die unterirdische Kohlenstoff-Verlagerung und -Umsatz. Ein höherer Anteil an Gefäßpflanzen, insbesondere an Sträuchern, erhöhte jedoch den aus den Wurzeln stammenden Kohlenstoffeintrag, insbesondere bei höheren Temperaturen. Mehrere Parameter zeigten einen höheren Abbaugrad des moosdominierten Torfs unter Seggen gegenüber Sträuchern an, insbesondere am Standort mit hohen Temperaturen. Die Auswirkungen des Temperaturanstiegs auf den Torfabbau waren weniger ausgeprägt als die Auswirkungen durch Seggen. Schlussendlich war es nicht der durch Sträucher ausgelöste höhere unterirdische Kohlenstoff-Umsatz, der die Zersetzung des vorhandenen moosdominierten Torfs beschleunigte, sondern wahrscheinlich die unterirdische Kohlenstoff-Allokation zu den Wurzeln der Seggen. Daraus lässt sich schließen, dass der Beitrag der Wurzelexsudate zur unterirdischen Kohlenstoff-Allokation bei der Torfzersetzung keine entscheidende Rolle spielt. Der Eintrag der unterirdischen Biomasse, insbesondere der Seggen, aber auch der Streu von Sträuchern, kann jedoch die Abbauprozesse in einem sich ändernden Klima beeinflussen. Daher ist zu erwarten, dass in Moore der nördlichen Hemisphäre mit zunehmender Strauchbiomasse alte Kohlenstoff-Speicher nicht mobilisiert werden, während mit zunehmender Seggenbiomasse die Kohlenstoff-Speicher wahrscheinlich gefährdet sind.:Thesis at a glance 2 1 Introduction 5 1.1 Northern peatlands and climate change . . . . . . . . . . . . . . . . . . . . . 5 1.2 Vegetation and its impact on carbon cycling in northern peatlands in a warmer climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.3 In situ approaches to study plant functional type effects on peat decomposition in response to climate change . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.4 Objectives, hypotheses and experimental approach . . . . . . . . . . . . . . . 14 2 Study I 21 2.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.2 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.3 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.4 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.5 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.6 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.7 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2.9 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3 Study II 47 3.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 3.2 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.3 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.4 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 3.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 3.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 3.8 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 4 Study III 75 4.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 4.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 4.3 Material and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 4.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 4.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 4.7 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 5 Synthesis 97 5.1 Regulations of root-derived carbon input and above- to belowground carbon allocation by vascular plants in peatlands . . . . . . . . . . . . . . . . . . . . 97 5.2 The effect of different above- to belowground carbon allocation patterns of vascular plants on Sphagnum-derived peat decomposition at different temperatures103 6 Conclusions 105 6.1 Implications of belowground carbon allocation by vascular plants for peat decomposition in a warmer climate . . . . . . . . . . . . . . . . . . . . . . . . . 105 6.2 Towards a dynamic understanding of the impact of roots on peatland carbon cycling in a warmer climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 7 Acknowledgements 109 References 111 List of publications and license agreements 139 Curriculum Vitae 149

Rain forest canopies are renowned for their very high biodiversity and the critical role they play in key ecological processes and their influence on global climate. Despite that New Zealand supports one of the most diverse and extensive epiphyte flora of any temperate forest system, few studies have investigated epiphyte communities and their invertebrate fauna along with factors that influence their distribution and composition. This thesis represents the first comprehensive study of entire epiphyte communities and their resident invertebrate fauna in the canopy of New Zealand’s indigenous forests. The aim of this study was to determine spatial patterns of epiphyte and invertebrate species richness, abundance and community composition in relation to abiotic variables, and in particular, the responses of these communities to elevated temperature and rainfall. This study was carried out in coastal lowland podocarp-broadleaved forests at two sites on the West Coast of the South Island of New Zealand. Samples from 120 mat-forming epiphyte assemblages located on inner canopy branches of 40 northern rata (Metrosideros robusta) trees were studied to characterise the component flora and fauna. Additionally, biomass, branch and tree characteristics and community responses to treatments designed to elevate temperature and rainfall to simulate predicted climate change were measured. This investigation revealed astonishing diversity and functional complexity of epiphyte and invertebrate life in this ecosystem. The 30.6 kg (dry weight) of epiphyte material collected contained a total of 567 species, 170 epiphyte and 397 invertebrate (excluding immature specimens and mites) species, including at least 10 species new to science and many undescribed species Epiphyte communities were found to be dominated by non-vascular plants (80 % of the total species richness), particularly liverworts and invertebrate communities were dominated with respect to abundance (~ 80 % of the total individuals) by Acari, Collembola and Hymenoptera (primarily ants) and functionally by scavengers and ants. Epiphyte and invertebrate communities were highly variable with respect to spatial patterning of species richness, abundance and composition across sites, among trees within sites and among branches within trees. Overall, a highly significant proportion, > 75 %, of the variance could be attributed to differences at the branch level, but these differences could not be explained by the environmental factors measured. There were no consistent relationships between the spatial pattern of epiphytes and invertebrates, or between vascular and non-vascular plants. However, there were significant positive correlations between epiphyte biomass and invertebrate species richness (r = 0.472; p < 0.0001) and abundance (r = -0.395; p < 0.0001), as well as non-living epiphyte biomass and scavenger species richness (r = 0.4; p < 0.0001). Microclimatic measurements taken on epiphyte mats were also highly variable with respect to temperature and relative humidity at similar physical locations within the same tree as well as across trees within sites. There was also considerable variation in the intensity and frequency of climatic extremes, although potentially harmful climatic conditions were experienced by all the epiphyte mats for which weather variables were measured. Negative correlations existed between both epiphyte and invertebrate community composition and increased temperatures expressed as cumulative degree days above 5˚C. However, variability was such that there was no direct evidence that increased temperature and rainfall treatments had an effect on invertebrate species richness, abundance or diversity. Northern rata host trees harbour an astonishingly diverse and complex canopy flora and fauna that is characterised by high spatial variability. Such variability highlights that to determine species distribution and community dynamics in canopy habitats in response to disturbance caused either by climate change or invasive species the structure of entire communities at different taxonomic and spatial scales, along with their responses to microclimatic factors, need to be studied. If such complexities are not taken into account, inappropriate interpretation may result in poor decisions concerning the conservation status, vulnerability and subsequent management of such unique ecosystems.

Rain forest canopies are renowned for their very high biodiversity and the critical role they play in key ecological processes and their influence on global climate. Despite that New Zealand supports one of the most diverse and extensive epiphyte flora of any temperate forest system, few studies have investigated epiphyte communities and their invertebrate fauna along with factors that influence their distribution and composition. This thesis represents the first comprehensive study of entire epiphyte communities and their resident invertebrate fauna in the canopy of New Zealand’s indigenous forests. The aim of this study was to determine spatial patterns of epiphyte and invertebrate species richness, abundance and community composition in relation to abiotic variables, and in particular, the responses of these communities to elevated temperature and rainfall. This study was carried out in coastal lowland podocarp-broadleaved forests at two sites on the West Coast of the South Island of New Zealand. Samples from 120 mat-forming epiphyte assemblages located on inner canopy branches of 40 northern rata (Metrosideros robusta) trees were studied to characterise the component flora and fauna. Additionally, biomass, branch and tree characteristics and community responses to treatments designed to elevate temperature and rainfall to simulate predicted climate change were measured. This investigation revealed astonishing diversity and functional complexity of epiphyte and invertebrate life in this ecosystem. The 30.6 kg (dry weight) of epiphyte material collected contained a total of 567 species, 170 epiphyte and 397 invertebrate (excluding immature specimens and mites) species, including at least 10 species new to science and many undescribed species Epiphyte communities were found to be dominated by non-vascular plants (80 % of the total species richness), particularly liverworts and invertebrate communities were dominated with respect to abundance (~ 80 % of the total individuals) by Acari, Collembola and Hymenoptera (primarily ants) and functionally by scavengers and ants. Epiphyte and invertebrate communities were highly variable with respect to spatial patterning of species richness, abundance and composition across sites, among trees within sites and among branches within trees. Overall, a highly significant proportion, > 75 %, of the variance could be attributed to differences at the branch level, but these differences could not be explained by the environmental factors measured. There were no consistent relationships between the spatial pattern of epiphytes and invertebrates, or between vascular and non-vascular plants. However, there were significant positive correlations between epiphyte biomass and invertebrate species richness (r = 0.472; p < 0.0001) and abundance (r = -0.395; p < 0.0001), as well as non-living epiphyte biomass and scavenger species richness (r = 0.4; p < 0.0001). Microclimatic measurements taken on epiphyte mats were also highly variable with respect to temperature and relative humidity at similar physical locations within the same tree as well as across trees within sites. There was also considerable variation in the intensity and frequency of climatic extremes, although potentially harmful climatic conditions were experienced by all the epiphyte mats for which weather variables were measured. Negative correlations existed between both epiphyte and invertebrate community composition and increased temperatures expressed as cumulative degree days above 5˚C. However, variability was such that there was no direct evidence that increased temperature and rainfall treatments had an effect on invertebrate species richness, abundance or diversity. Northern rata host trees harbour an astonishingly diverse and complex canopy flora and fauna that is characterised by high spatial variability. Such variability highlights that to determine species distribution and community dynamics in canopy habitats in response to disturbance caused either by climate change or invasive species the structure of entire communities at different taxonomic and spatial scales, along with their responses to microclimatic factors, need to be studied. If such complexities are not taken into account, inappropriate interpretation may result in poor decisions concerning the conservation status, vulnerability and subsequent management of such unique ecosystems.

Salt marshes provide critical ecosystem services, such as shoreline stabilization, biogeochemical cycling and habitat for wildlife, to much of the world's population living on the coasts. Emergent vascular plants are a critical component of these ecosystems. This study was a comprehensive effort to gain a better understanding of the ecology of salt marsh plants in the Nueces River delta on the south Texas coast. This knowledge is essential to understand the potential anthropogenic impacts on salt marshes, including sea-level rise, global warming, reduced freshwater inflow and coastal erosion. A combination of remote sensing analysis, field studies and experiments were used to allow analysis across spatial scales ranging from landscape patterns of vegetation to leaf level measurements of the dominant species. A novel method of image classification was developed using high-resolution multi-spectral imagery integrated with ancillary data to map the major plant communities at a landscape scale. This included a high marsh assemblage composed primarily of Spartina spartinae and a low marsh community dominated by Borrichia frutescens and Salicornia virginica. Geospatial analysis determined that the location of these plant communities was related to the distance from the tidal creek network and elevation. The B. frutescens and S. virginica assemblage was more abundant at lower elevations along the waters edge, making it vulnerable to loss from shoreline erosion. At a finer spatial scale, gradient analysis was utilized to examine the relationship between elevation, which creates environmental gradients in salt marshes, and species distribution. I discovered that elevation differences of less than 5 cm can influence both individual species and plant community distribution. One interesting finding was that the two dominant species, B. frutescens and S. virginica, share similar responses along an elevation gradient yet are observed growing in monotypic adjacent zones. I constructed a large reciprocal transplant experiment, using 160 plants at 4 sites throughout the marsh, to determine what causes the zonation between these two species. The results of this study found that S. virginica fared well wherever it was transplanted but was a weak competitor. B. frutescens survival was significantly lower in the S. virginica zone than in its own zone suggesting that abiotic factors are important in determining the zonation of this species. However, high spatial and temporal variability existed in environmental parameters such as salinity. This variability may have been caused by the semi-arid climate and irregular flooding typical in the Nueces Marsh. Therefore, I utilized a greenhouse experiment to directly test the importance of the two dominant physical factors in salt marshes, flooding and salinity. The results found that for B. frutescens the effects of flooding were not significant, however salinity at 30% reduced growth. Salinity did not influence growth of S. virginica. The greater ability of S. virginica to tolerate salinity stress has important implications because reduced freshwater inflow or climate change can increase porewater salinity, thus favoring the expansion of S. virginica, and altering the plant community structure. / text

O objetivo deste estudo foi identificar características de uso da luz para explicar a distribuição diferencial das espécies tolerantes à dessecação homeoclorófila Anemia flexuosa e peciloclorófila Pleurostima purpurea em ambientes sombreados e expostos, respectivamente, de comunidades vegetais de afloramentos rochosos. A cultivar Oryza sativa IAC 202 foi incluída para comparações. Durante um ciclo completo de desidratação - dessecação - reidratação foram avaliados parâmetros fotossintéticos de trocas gasosas e fluorescência da clorofila a, associados ao conteúdo relativo de água (CRA) e de pigmentos fotossintéticos de plantas intactas sob temperatura e umidade relativa do ar constantes de 25°C e de 55%, respectivamente. As plantas foram submetidas à diferentes densidades de fluxo de fótons fotossintéticos (DFFF de 0, 100 e 400 ?mol fótons m-2s-1) nas fases de desidratação e dessecação, dependendo da espécie. O. sativa foi avaliada somente durante as fases de desidratação e dessecação sob condições ambientais variáveis de casa de vegetação. A diminuição da assimilação líquida de CO2 (A) foi acompanhada pelo aumento da dissipação de calor avaliada pelos coeficientes de extinção nãofotoquímica (qN e NPQ) nas três espécies. Após cessação de A, a eficiência quântica efetiva (?PSII e Fv\"/Fm\"), a taxa de transporte de elétrons (ETR) e o coeficiente de extinção fotoquímica (qP) foram mantidos relativamente altos em P.purpurea, mas cessaram simultaneamente com A em A.flexuosa. Em O.sativa, ?PSII, ETR e qP diminuíram substancialmente após a cessação de A, mas Fv\"/Fm\" foi mantido. A eficiência quântica potencial (Fv/Fm) foi a última variável a diminuir nas três espécies durante a desidratação. Após a reidratação de P.purpurea e A.flexuosa foi observado inicialmente o estabelecimento da respiração e em seguida um balanço levemente positivo de CO2, quando os valores de Fv\"/Fm\", ?PSII, ETR, qP e Fv/Fm de P.purpurea recuperaram quase totalmente, enquanto qN e NPQ diminuíram. A.flexuosa apresentou uma recuperação apenas parcial de Fv\"/Fm\", ?PSII, ETR, qP e Fv/Fm quando o balanço de CO2 se tornou levemente positivo, tendo sido a recuperação ainda menor para o tratamento de desidratação no escuro associado à dessecação na luz. A.flexuosa tolerou a perda de 88% do CRA. O enrolamento foliar durante a desidratação é uma forma de proteção contra a luz no estado dessecado de A.flexuosa. Mesmo no estado dessecado ocorrem processos de interação dos fotossistemas II com a luz em A.flexuosa. P.purpurea baseia sua proteção contra a luz na ativação de processos de dissipação de calor, vias de consumo de elétrons diferentes do ciclo redutivo do CO2 e, em última instância, na perda de clorofilas. Plantas dessecadas de P.purpurea permanecem viáveis no estado desidratado por pelo menos 42 dias. P.purpurea tolerou a perda de 94% do CRA. A recuperação do turgor da parte aérea de P.purpurea ocorre necessariamente pela absorção de água pelas raízes durante a reidratação. Foi evidenciada uma aclimatação de A.flexuosa quando desidratada sob condição de luz. Os resultados não foram conclusivos em relação à sustentação da hipótese, considerando que as diferenças de recuperação observadas para A.flexuosa nos diferentes tratamentos luminosos, em geral, não foram significativas. / The aim of this study was to identify characteristics of light use that could explain the differential distribution of homoiochlorophyllous and poikilochlorophyllous desiccation tolerant plants Anemia flexuosa and Pleurostima purpurea, respectively, in shaded and exposed microsites of rock outcrop plant communities. Oryza sativa IAC 202 was included in the study for comparisons. Leaf gas exchanges, fluorescence chlorophyll, relative water content (RWC) and photosynthetic pigment content were evaluated in intact plants under constant temperature and relative humidity of 25°C and 55%, respectively, during a complete cycle of dehydration - desiccation - rehydration. The plants were exposed to different photosynthetic photon flux densities (PPFD of 0, 100 and 400 ?mol photons m-2s-1) during dehydration and desiccation phases, according to species. O.sativa was evaluated only during dehydration and desiccation phases under variable environmental conditions in a greenhouse. In all species, the decrease in CO2 net assimilation (A) was accompanied by increased heat dissipation assessed by nonphotochemical quenching coefficients (qN and NPQ). The effective quantum yield (?PSII and Fv\"/Fm\"), electron transport rate (ETR) and photochemical quenching coefficient (qP) were kept relatively high after A cessation in P.purpurea, but in A.flexuosa ceased simultaneously with A. In O.sativa, ?PSII, ETR and qP decreased substantially after A cessation, but Fv\"/Fm\" was maintained. The potential quantum yield (Fv/Fm) was the last variable to decrease during dehydration in all species. After rehydration, the establishment of respiration was observed initially in P.purpurea and A.flexuosa. Then, a slightly positive CO2 balance was associated with the almost total recovery of Fv\"/Fm\", ?PSII, ETR, qP and Fv/Fm in P.purpurea, while qN and NPQ decreased. A.flexuosa showed only a partial recovery of Fv\"/Fm\", ?PSII, ETR, qP and Fv/Fm when the CO2 balance became slightly positive, and recovery was even lower for the treatment of dehydration in dark associated to desiccation in light. A.FLEXUOSA TOLERATES A LOSS OF 88% OF RWC. Leaf curling during dehydration is also a form of light protection in the dried state in A.flexuosa. Interactions between photosystem II and light occur even in the dried state of A.flexuosa. P.purpurea bases its protection against light activating heat dissipation process, ways of electron consumption different of reductive CO2 cycle and, in last instance, chlorophyll loss. P.purpurea remains viable in dried state for at least for 42 days, and tolerates a loss of 94% of RWC. The shoot rehydration in P.purpurea occurs necessarily by roots water uptake. A.flexuosa showed an acclimation when dried under light conditions. The results were not conclusive regarding the hypothesis, since differences in recovery observed for this species in the different light treatments, in general, were not significant.

O objetivo deste estudo foi identificar características de uso da luz para explicar a distribuição diferencial das espécies tolerantes à dessecação homeoclorófila Anemia flexuosa e peciloclorófila Pleurostima purpurea em ambientes sombreados e expostos, respectivamente, de comunidades vegetais de afloramentos rochosos. A cultivar Oryza sativa IAC 202 foi incluída para comparações. Durante um ciclo completo de desidratação - dessecação - reidratação foram avaliados parâmetros fotossintéticos de trocas gasosas e fluorescência da clorofila a, associados ao conteúdo relativo de água (CRA) e de pigmentos fotossintéticos de plantas intactas sob temperatura e umidade relativa do ar constantes de 25°C e de 55%, respectivamente. As plantas foram submetidas à diferentes densidades de fluxo de fótons fotossintéticos (DFFF de 0, 100 e 400 ?mol fótons m-2s-1) nas fases de desidratação e dessecação, dependendo da espécie. O. sativa foi avaliada somente durante as fases de desidratação e dessecação sob condições ambientais variáveis de casa de vegetação. A diminuição da assimilação líquida de CO2 (A) foi acompanhada pelo aumento da dissipação de calor avaliada pelos coeficientes de extinção nãofotoquímica (qN e NPQ) nas três espécies. Após cessação de A, a eficiência quântica efetiva (?PSII e Fv\"/Fm\"), a taxa de transporte de elétrons (ETR) e o coeficiente de extinção fotoquímica (qP) foram mantidos relativamente altos em P.purpurea, mas cessaram simultaneamente com A em A.flexuosa. Em O.sativa, ?PSII, ETR e qP diminuíram substancialmente após a cessação de A, mas Fv\"/Fm\" foi mantido. A eficiência quântica potencial (Fv/Fm) foi a última variável a diminuir nas três espécies durante a desidratação. Após a reidratação de P.purpurea e A.flexuosa foi observado inicialmente o estabelecimento da respiração e em seguida um balanço levemente positivo de CO2, quando os valores de Fv\"/Fm\", ?PSII, ETR, qP e Fv/Fm de P.purpurea recuperaram quase totalmente, enquanto qN e NPQ diminuíram. A.flexuosa apresentou uma recuperação apenas parcial de Fv\"/Fm\", ?PSII, ETR, qP e Fv/Fm quando o balanço de CO2 se tornou levemente positivo, tendo sido a recuperação ainda menor para o tratamento de desidratação no escuro associado à dessecação na luz. A.flexuosa tolerou a perda de 88% do CRA. O enrolamento foliar durante a desidratação é uma forma de proteção contra a luz no estado dessecado de A.flexuosa. Mesmo no estado dessecado ocorrem processos de interação dos fotossistemas II com a luz em A.flexuosa. P.purpurea baseia sua proteção contra a luz na ativação de processos de dissipação de calor, vias de consumo de elétrons diferentes do ciclo redutivo do CO2 e, em última instância, na perda de clorofilas. Plantas dessecadas de P.purpurea permanecem viáveis no estado desidratado por pelo menos 42 dias. P.purpurea tolerou a perda de 94% do CRA. A recuperação do turgor da parte aérea de P.purpurea ocorre necessariamente pela absorção de água pelas raízes durante a reidratação. Foi evidenciada uma aclimatação de A.flexuosa quando desidratada sob condição de luz. Os resultados não foram conclusivos em relação à sustentação da hipótese, considerando que as diferenças de recuperação observadas para A.flexuosa nos diferentes tratamentos luminosos, em geral, não foram significativas. / The aim of this study was to identify characteristics of light use that could explain the differential distribution of homoiochlorophyllous and poikilochlorophyllous desiccation tolerant plants Anemia flexuosa and Pleurostima purpurea, respectively, in shaded and exposed microsites of rock outcrop plant communities. Oryza sativa IAC 202 was included in the study for comparisons. Leaf gas exchanges, fluorescence chlorophyll, relative water content (RWC) and photosynthetic pigment content were evaluated in intact plants under constant temperature and relative humidity of 25°C and 55%, respectively, during a complete cycle of dehydration - desiccation - rehydration. The plants were exposed to different photosynthetic photon flux densities (PPFD of 0, 100 and 400 ?mol photons m-2s-1) during dehydration and desiccation phases, according to species. O.sativa was evaluated only during dehydration and desiccation phases under variable environmental conditions in a greenhouse. In all species, the decrease in CO2 net assimilation (A) was accompanied by increased heat dissipation assessed by nonphotochemical quenching coefficients (qN and NPQ). The effective quantum yield (?PSII and Fv\"/Fm\"), electron transport rate (ETR) and photochemical quenching coefficient (qP) were kept relatively high after A cessation in P.purpurea, but in A.flexuosa ceased simultaneously with A. In O.sativa, ?PSII, ETR and qP decreased substantially after A cessation, but Fv\"/Fm\" was maintained. The potential quantum yield (Fv/Fm) was the last variable to decrease during dehydration in all species. After rehydration, the establishment of respiration was observed initially in P.purpurea and A.flexuosa. Then, a slightly positive CO2 balance was associated with the almost total recovery of Fv\"/Fm\", ?PSII, ETR, qP and Fv/Fm in P.purpurea, while qN and NPQ decreased. A.flexuosa showed only a partial recovery of Fv\"/Fm\", ?PSII, ETR, qP and Fv/Fm when the CO2 balance became slightly positive, and recovery was even lower for the treatment of dehydration in dark associated to desiccation in light. A.FLEXUOSA TOLERATES A LOSS OF 88% OF RWC. Leaf curling during dehydration is also a form of light protection in the dried state in A.flexuosa. Interactions between photosystem II and light occur even in the dried state of A.flexuosa. P.purpurea bases its protection against light activating heat dissipation process, ways of electron consumption different of reductive CO2 cycle and, in last instance, chlorophyll loss. P.purpurea remains viable in dried state for at least for 42 days, and tolerates a loss of 94% of RWC. The shoot rehydration in P.purpurea occurs necessarily by roots water uptake. A.flexuosa showed an acclimation when dried under light conditions. The results were not conclusive regarding the hypothesis, since differences in recovery observed for this species in the different light treatments, in general, were not significant.

During four growing seasons, aquatic vascular plant production and distribution were studied in Pat Mayse Lake, Texas, a 2425 hectare oligo-mesotrophic reservoir. The dominant macrophyte population was Myriophyllum spicatum L. Growth rates and regrowth rates of mechanically harvested Myriophyllum beds were found to be dissimilar. Based on estimates of watermilfoil nutrient content, there were insufficient nutrients in the entire population to alter the trophic status of this reservoir should all of the nutrients be instantaneously released. Sediments were the primary nutrient (nitrogen and phosphorus) sink. Bank erosion and solids transport from the watershed appear to contribute most of the sediments and a lake-wide mean sedimentation rate of 2.5 cm/year was estimated from sediment trap and core sample data.

Microclimatic gradients may have large influence on individual vital rates and population growth rates of species, and limit their distributions. Therefore, I focused on the influence of microclimate on individual performance and distribution of species. Further, I examined differences in how microclimate affect species with contrasting distributions or different ecophysiological traits, and populations within species. More specifically, I investigated the performance of northern and southern distributed forest bryophytes that were transplanted across microclimatic gradients, and the timing of vegetative and reproductive development among northern, marginal and more southern populations of a forest herb in a common garden. Also, I compared the landscape and continental distributions across forest bryophytes and vascular plants and, thus, their distribution limiting factors at different spatial scales. Lastly, I examined the population dynamics across microclimatic gradients of transplants from northern and southern populations of a forest moss. The effects of microclimatic conditions on performance differed among bryophytes with contrasting distributions. There were no clear differences between northern and southern populations in the timing of development of a forest herb or in the population dynamics of a moss. However, within each region there was a differentiation of the forest herb populations, related to variation in local climatic conditions and in the south also to proportion of deciduous trees. The continental distributions of species were reflected in their landscape distributions and vice versa, in terms of their occurrence optima for climatic variables. The variation in landscape climatic optima was, however, larger than predicted, which limit the precision for predictions of microrefugia. Probably, the distributions of vascular plants were more affected by temperature than the distributions of bryophytes. Bryophytes are sensitive to moisture conditions, which was demonstrated by a correlation between evaporation and the population growth rate of a forest moss. We might be able to predict species’ landscape scale distributions by linking microclimatic conditions to their population growth rates, via their vital rates, and infer larger scale distribution patterns. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.</p> / EkoKlim

No description available.

Les tourbières ont stocké un tiers du carbone organique des sols mondiaux (C) malgré une superficie ne représentant que 3% de la surface terrestre. Cependant, en réponse aux changements globaux, les tourbières boréales et tempérées, majoritairement dominées par des sphaignes, peuvent être envahies par des plantes vasculaires susceptibles de modifier la dynamique du C dans ces écosystèmes. Cette thèse vise à étudier comment la présence des plantes vasculaires affecte le cycle du C des tourbières à sphaignes. Ces travaux ont porté principalement sur une plante envahissante de nombreuses tourbières, Molinia caerulea, via une étude en mésocosmes. Les expérimentations montrent que les plantes vasculaires sont à la fois favorables à la croissance des sphaignes et à la décomposition des litières. In fine, les résultats montrent que la présence de Molinia caerulea augmente la capacité de stockage du C dans les mésocosmes de sphaignes (30 to 220 gC stock m⁻² an⁻1), probablement liée à la forte productivité racinaire de cette plante. Cependant, cela semble s’opérer au détriment du C déjà stocké dans la tourbe avec une stimulation des microorganismes à travers la production d’exsudats racinaires. Ces derniers semblent également, d’une part promouvoir la consommation du C organique dissous et les émissions de CO₂ et de CH₄ observées en présence de Molinia caerulea, et d’autre part être responsables de la modification de la sensibilité à la température des exports de C via des changements des communautés microbiennes. L’impact de Molinia caerulea sur les microorganismes va aussi altérer ceux impliqués dans le cycle du N et entrainer une diminution des émissions de N₂O. / Peatlands have stored a third of the soil organic Carbon (C) in only 3% of the land area. However, in response to global change, boreal and temperate peatlands may shift from Sphagnum to vascular plant-dominated peatlands that may alter their C-sink function. This thesis aims at providing a better understanding of the vascular plants interactions in a Sphagnum dominated peatland and their implications on the C cycle. This work mainly focus on the invasion of a graminoid plant, Molinia caerulea, through a mesocosm experiment. Results from experiments show that vascular plants are both able to promote the growth of Sphagnum mosses as well as the decomposition of their litter. Molinia caerulea occurrence appears to increase the C sink capacity of Sphagnum peat mesocosms passing of 30 to 220 gC stock m⁻² y⁻1. This capacity of Molinia caerulea to store C is probably due to it high roots productivity. However, it also seems to stimulate the decomposition of ‘old’ C, stored as peat, by stimulating microorganisms activity through roots exudates. These latter also promote the dissolved organic C consumption and CO₂ and CH₄ emissions observed with Molinia caerulea occurrence, as well as the temperature sensitivity of C exports by altering the microbial communities. Molinia caerulea impacts on microorganisms also affect N cycle conducting to a decrease of N₂O emissions in these ecosystems.