Bacterioplankton is characterized by high diversity, short generation times and rapid turnover. Despite their small size, these numerous microorganisms are a fundamental piece of aquatic ecosystems by channeling carbon to higher trophic levels through dissolved organic matter utilization. Yet, several gaps remain in our knowledge and understanding of bacterioplankton populations regarding detailed temporal dynamics, and mechanisms determining biogeographical patterns and potential responses to climate change. The aim of this thesis was to examine responses in bacterioplankton community composition and function when challenged by natural and anthropogenically-induced change in environmental conditions. High temporal resolution analysis of bacterioplankton population dynamics in the Baltic Sea indicated detailed seasonal responses. It also showed a similar but wide spectrum of niche differentiation patterns within several major bacterial groups. Analysis of geographic distributions of marine bacterial populations revealed bimodal occupancy-frequency patterns in bacterial communities, indicating that the presence of many locally rare taxa along with a few locally abundant taxa were explained by stochastic variation in colonization and extinction rates. Experimental manipulations with natural marine bacterioplankton assemblages revealed both specialist and generalist strategies in utilizing specific dissolved organic carbon compounds. When subjected to experimentally increased sea surface temperatures, lowered pH and additions of terrigenous carbon, some populations decreased in relative abundance while others were stable; concomitantly, many populations increased in relative abundance. Shifts in bacterial community composition were shown to correlate with changes in community functioning, but detection of such correlations depended largely on the detail of phylogenetic analysis and successional stage of the communities. The results in this thesis suggest that both natural and anthropogenically-induced changes in environmental conditions promote simultaneous adjustment and replacement of bacterial populations tightly linked with metabolic plasticity. These trade-offs play a significant role for understanding the relationship between bacterioplankton population dynamics and potential shifts in carbon cycling properties. We also show the importance of regional effects in shaping bacterial community composition, crucial for interpreting bacterioplankton distribution patterns. In conclusion, this thesis emphasizes the critical importance of connecting analysis of bacterioplankton population dynamics with examination of ecological mechanisms to improve our understanding of factors that regulate the distribution and activity of distinct bacterioplankton populations. / Hälften av all fotosyntes på vår planet utförs av växtplankton. De producerar organiskt material som utgör grunden för näringskedjan i havet. Ungefär hälften av det organiska material som produceras av växtplankton utnyttjas inte direkt, utan omsätts istället av bakterieplankton som lever och växer fritt i vattenmassan eller på olika partiklar. Bakterieplankton spelar därmed en nyckelroll i ekosystemet genom sin konsumtion av organiskt kol som för energi högre upp i näringskedjan. Trots deras nyckelroll i akvatiska miljöer vet vi fortfarande mycket lite om bakteriernas detaljerade säsongsmönster, mekanismer bakom rumsliga mönster och hur olika populationer kan komma att svara på klimatförändringar. Målet med denna avhandling var att undersöka hur specifika populationers dynamik och ekosystemfunktion påverkas av naturliga eller klimatorsakade förändringar i havsmiljön. Våra resultat av högupplöst säsongsbunden dynamik i Östersjöns bakteriesamhälle avslöjar en liknande bred uppdelning av ekologiska strategier inom varje större grupp av bakterier, både i relativ abundans och temporal fördelning. Utbredning i rum och tid av många lokalt ovanliga populationer jämfört med få lokalt vanliga populationer förklarades genom stokastisk variation i kolonisations- och utdöendehastigheter. Vidare tyder experimentella studier med tillsatser av olika kolkällor på att marina bakterier har olika ekologiska strategier, där populationer är specialister eller generalister i utnyttjandet av enskilda kolkällor. Med hjälp av experiment med naturliga bakteriesamhällen bekräftade vi tydliga temperatureffekter på bakteriesamhällets sammansättning, och en mindre effekt av lägre pH - som dock tillsammans med förhöjd temperatur bidrog till en tydlig synergistisk effekt på artsammansättningen. Ökad temperatur tillsammans med tillsats av terrestert kol gav också en stor effekt på bakteriesamhällets struktur och ekosystemfunktion och pekar på en potentiellt viktig påverkan av ökad framtida nederbörd och avrinning från vattendrag till havet. Samtliga tre experiment med fokus på klimatpåverkan bekräftade förekomsten av populationer som försvann eller minskade i relativ abundans vid klimatpåverkan (känslighet), medan andra var stabila (resistens). Samtidigt svarade många populationer positivt på klimatorsakade förändringar i havsmiljön och ökade i relativ abundans (respons) samtidigt som bakteriernas ekosystemfunktion påverkades positivt. Sammanfattningsvis visar denna avhandling att vissa nya bakteriepopulationer kan etablera sig och ersätta andra samtidigt som vissa befintliga populationer anpassar sin livsstrategi och ekologi till förändringar i havsmiljön. Vi visar också vikten av regionala effekter, d.v.s. kolonisation och utdöende, för bakteriesamhällets struktur, viktigt för tolkningen av biogeografiska mönster och den genomiska potentialen hos specifika populationer. Denna avhandling poängterar därmed betydelsen av att koppla studier av ekologiska mekanismer till både rumsliga och temporala spridningsmönster hos bakterier och till populationers kapacitet att svara på och anpassa sig till förändringar i havsmiljön.

Biodiversity rich regions worldwide face threats from various global change agents. This research quantifies environmental influences on vegetation, and the impacts of exotic woody plant invasion and anthropogenic nitrogen (N) deposition in a global biodiversity hotspot. The study was conducted in the montane grasslands of the Nilgiris, Western Ghats, and outlines potential management options for this region. Specifically, I examined (1) the role of environmental factors in influencing native plant distribution and ecosystem properties, (2) the status and impact of exotic shrub (Scotch broom, henceforth broom) invasion, (3) the role of disturbances in the success of broom, (4) the role of fire in restoring invaded grasslands, and (5) the impacts of terrestrial N loading on the grassland ecosystem. I used experiments and surveys to assess these. Distributions of several key species were explained by a few complex environmental gradients. In invaded-grasslands, broom populations consisted mainly of intermediate size and age classes, with no clear indication of population decline. Invasion negatively impacted plant community structure and drastically changed composition, favoring shade-tolerant and weedy species. However, invasion did not greatly alter ecosystem function. Fire successfully eliminated mature broom stands, but resulted in a short-term increase in broom seedling recruitment. At the end of 18 months, the fire effects on uninvaded-grasslands were not apparent, but there was no conclusive evidence of the formerly invaded patches attaining the composition of uninvaded-grasslands following burning. N fertilization strongly influenced soil N dynamics, and shoot N concentrations, but effects on aboveground production were weak. Surprisingly, N enrichment had positive effects on diversity in the short-term. It is clear that these grasslands need immediate management intervention to forestall degradation from invasion. Fire could be used to eliminate mature broom stands and deplete persistent seedbanks, which will facilitate colonization by shade-intolerant grassland plants. Active restoration should be mindful of environmental preferences of framework species. Long-term studies of the impacts of N deposition in the context of disturbances will help determine realistic critical thresholds and utilize disturbances to buffer the potential adverse effects of increasing N loading.

Submitted by Cássia Santos (cassia.bcufg@gmail.com) on 2017-05-17T11:08:27Z No. of bitstreams: 2 Tese - Lorena Dall´Ara Guimarães - 2006.pdf: 2423703 bytes, checksum: 83bf4f4172b792982caccc6cf3c41ff2 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-05-17T11:48:10Z (GMT) No. of bitstreams: 2 Tese - Lorena Dall´Ara Guimarães - 2006.pdf: 2423703 bytes, checksum: 83bf4f4172b792982caccc6cf3c41ff2 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-05-17T11:48:10Z (GMT). No. of bitstreams: 2 Tese - Lorena Dall´Ara Guimarães - 2006.pdf: 2423703 bytes, checksum: 83bf4f4172b792982caccc6cf3c41ff2 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2006-02-13 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This study aimed to examine patterns of anuran species richness in twenty municipalities in the State of Goiás, central Brazil. We also compared richness of anuran species among these localities and verified the patterns of spatial distribution for four habitat types (gallery forests, ponds associated to gallery forest, ponds associated to cerrado sensu stricto, and ponds close to anthropic area). Surveys were conducted between 2001 and 2005. Considering the four habitat types, a total of 6,491 individuals from 52 anuran species were registered. Calling males were found on the ground, shrubs, and grasses. Ponds associated to cerrado sensu stricto showed the highest species richness. In contrast, gallery forest assemblages exhibited the highest species diversity and equitability. The largest number of individuals was found in disturbed areas and ponds associated to cerrado sensu stricto. Similarity analysis showed that open habitats had the most similar communities, while the most dissimilar assemblages were observed between gallery forests and ponds within disturbed areas. Seven species in the families Leptodactylidae and Hylidae showed significant indicative values (bioindicators) for particular habitats. A total of 61 species was registered in twenty municipalities, representing 44.7% of the anuran richness registered for the Cerrado. The highest species richness was found in the municipality of Silvânia, while the lowest richness was registered in Mundo Novo. The results showed a non-significant correlation between socio-economics variables and anuran species composition. Anuran species richness seems to be lower close to areas used for the establishment of pastures and agriculture. On the other hand, species richness tends to be higher (likely through succession) in areas without human disturbance. Results of this study could or should be considered during development of management strategies focusing on amphibian conservation in the Cerrado biome. Moreover, a better understanding of how different fragmentation degrees affect amphibian diversity is important to access the influence of habitat quality on Cerrado´s amphibians, and also to improve management programs focused on amphibian conservation. / Este estudo objetivou examinar os padrões de riqueza de espécies de anfíbios anuros em 20 municípios do estado de Goiás, no Brasil Central, como também comparar a diversidade e riqueza de espécies de anuros, e verificar os padrões de distribuição espacial em quatro tipos de habitats (floresta de galeria, brejo associado à floresta de galeria, brejo associado a cerrado sensu stricto e brejo situado em área antropizada) As coletas foram feitas entre 2001 e 2005. Em relação aos quatro tipos de habitats, um total de 6.491 indivíduos de 52 espécies foram registradas. Machos vocalizantes foram principalmente encontrados no chão, arbustos e gramíneas. Brejos associados a cerrado sensu stricto apresentaram a maior riqueza de espécies. Ao contrário, florestas de galeria apresentaram os maiores valores para diversidade e equitabilidade. O maior número de indivíduos foi encontrado em áreas antropizadas e brejos associados a cerrado sensu stricto. O índice de similaridade de Bray-Curtis mostrou que os habitats de áreas abertas têm comunidades mais similares, enquanto as comunidades mais dissimilares foram àquelas encontradas em florestas de galeria e aquelas situadas em áreas antropizadas. Sete espécies das famílias Leptodactylidae e Hylidae apresentaram valores indicativos significantes (bioindicadores) de habitats particulares. Um total de 61 espécies foi registrado nos vinte municípios, o que representa 43,26% da riqueza de espécies de anfíbios encontrados no Cerrado. O maior número de espécies foi registrado no município de Silvânia, leste do estado e o menor em Mundo Novo, noroeste goiano. Os resultados mostraram uma correlação não significativa entre as variáveis sócio-econômicas e a composição de espécies de anfíbios. A riqueza de espécies de anfíbios parece sofrer influência pelas áreas usadas para o estabelecimento de pastagens e agricultura. Por outro lado, a riqueza tende ser mais alta (provavelmente por sucessão) em áreas sem fatores antropogênicos. Os resultados desse estudo podem ser considerados para o desenvolvimento de estratégias de manejo, com enfoque na conservação de anfíbios das paisagens do Cerrado. Além disso, o conhecimento da influência dos diferentes graus de fragmentação dos habitas naturais na diversidade de anfíbios, é importante para o entendimento do funcionamento das comunidades dos anfíbios do Cerrado, e conseqüentemente, para o melhoramento no que diz respeito ao manejo e conservação dessa fauna.

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The incomplete degradation of bio-based and biodegradable plastics (BBPs) in soils causes multiple threats to soil quality, human health, and food security. Plastic residuals can interact with soil microbial communities. We aimed to link the structure and enzyme-mediated functional traits of a microbial community composition that were present during poly (butylene succinate-co-butylene adipate (PBSA) decomposition in soil with (PSN) and without (PS) the addition of nitrogen fertilizer ((NH4 )2SO4 ). We identified bacterial (Achromobacter, Luteimonas, Rhodanobacter, and Lysobacter) and fungal (Fusarium, Chaetomium, Clonostachys, Fusicolla, and Acremonium) taxa that were linked to the activities of ß-glucosidase, chitinase, phosphatase, and lipase in plastic-amended soils. Fungal biomass increased by 1.7 and 4 times in PS and PSN treatment, respectively, as compared to nonplastic amended soil. PBSA significantly changed the relationships between soil properties (C: N ratio, TN, and pH) and microbial community structure; however, the relationships between fungal biomass and soil enzyme activities remained constant. PBSA significantly altered the relationship between fungal biomass and acid phosphatase. We demonstrated that although the soil functions related to nutrient cycling were not negatively affected in PSN treatment, potential negative effects are reasoned by the enrichment of plant pathogens. We concluded that in comparison to fungi, the bacteria demonstrated a broader functional spectrum in the BBP degradation process

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<p>Since the pre-industrial age, the Earth has been warming at unparalleled rates, and this warming is changing climate and weather, creating a more extreme global hydrological cycle. In this dissertation, I explore how these changes to the hydrological cycle may act ecosystem and community level responses of terrestrial plants in the Midwestern United States. In this region, it is projected that mean annual precipitation (MAP) will increase, but precipitation will become more variable across and within seasons. Ecosystem structure and function are vulnerable to changes in hydrologic patterns, including changes in biogeochemical cycles, plant productivity, and plant community structure and function. In this dissertation, I explore how changes in precipitation will alter these processes using two field experiments, and I suggest potential hypotheses that could explain drought-induced community change.</p><p><br></p><p>In chapter 1, I explore how alterations to seasonal precipitation in the winter and summer act ecosystem and community processes in a temperate deciduous forest. Biogeochemical processes and plant communities are sensitive to changes in abiotic conditions, and these conditions will alter forest succession, particularly juvenile woody plant species. Using a fully factorial experiment, I manipulated winter snowfall and summer precipitation to create wet, dry, and control (ambient conditions) treatments and investigated how changes in seasonal precipitation would act mineralization rates, woody plant recruitment, and understory composition. I found that the effects of winter and summer precipitation on these processes acted independently of one another in this system, and the system was resistant to changes in mineralization rates and understory composition. Woody plant recruitment may be more sensitive to altered precipitation, as recruitment of at least one of the four species planted, Lindera benzoin, was impacted by changes in seasonal precipitation. Snow removal treatments reduced germination and increased summer precipitation decreased the relative growth rate of this species. In the short term, slight changes to woody plant recruitment may have little impact on long-term forest succession, but as these changes persist over longer periods of time, they could alter the direction of succession, which could lead to changes in the understory community composition and nutrient cycling.</p> <p><br></p><p>The second and third chapters explore the effects that drought intensification will have on terrestrial plant communities. Numerous studies have investigated the effects of individual droughts on ecosystem and community responses, but the effects that both the timing and duration of drought have on these responses remain largely unknown. To explore this gap in the literature, I conducted a eld experiment using rainout shelters to reduce growing season precipitation, creating dry periods that varied in length and timing. Drought can impact productivity and diversity in this system, and the timing in which the drought occurs influences these effects. Surprisingly, I found that the length of drought did not affect productivity or community composition.</p> <p><br></p><p>The final chapter introduces the Community Response to Extreme Drought framework CRED), which addresses the potential temporal progression of mechanisms and plant-plant interactions that may lead to community changes during and after a drought. The mechanisms for the temporal evolution of community-level drought responses are not fully understood, but plant-plant interactions, both competitive (-) and facilitative (+), are increasingly being recognized as important drivers of community compositional changes. The CRED framework provides hypotheses for the roles that plant-plant interactions have on drought-induced community change. CRED addresses how system-specific variables and the intensity of drought may influence the strength of plant-plant interactions over time, and ultimately the systems resistance and resilience to drought. </p><p><br></p><p>The results from this dissertation work have revealed that more research needs to be done to fully understand how changes in precipitation regimes and patterns will affect terrestrial ecosystems and plant communities. A better understanding of how ecosystems and communities respond to drought timing and length can help improve climate models and restoration strategies.</p>

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<p>Heterotrophic bacteria utilize dissolved organic matter, and the carbon flow through an ecosystem depends on the fractions of the utilized carbon that is either respired or transferred to higher trophic levels. The major aim this thesis is to investigate 1) the relationship between composition and functioning in heterotrophic bacterioplankton communities and 2) the influence of environmental conditions on both parameters. I set up several batch culture experiments, where lake water filtrates containing bacteria but no grazers were inoculated into sterile freshwater medium to investigate the importance of the origin of the source community (the inoculum) versus the environmental conditions (the medium) for the composition and functional performance of bacterial communities. In some experiments the medium was manipulated to simulate changes in salinity, pH and dissolved organic matter quantity and quality. Functional parameters (biomass yield, respiration, growth efficiency and enzyme activities) and the genetic composition of the emerging bacterial communities were determined.</p><p>When bacterial inocula obtained from different habitats were re-grown under identical conditions, differently composed communities emerged. This indicates that the history and distribution of taxa within the inoculum was an important regulating factor of community composition. The coupling between community composition and functioning was not very tight, and there was functional equivalency with respect to aggregated functions important at the ecosystem scale (e.g., biomass production and respiration). The functional performance of bacterial communities could to a large extent be predicted from the medium alone, except when it deviated strongly from the ambient settings. When bacterial communities were exposed to dilution, a strong change in pH or an increase in salinity, growth of structurally and functionally distinct communities occurred. I therefore suggest that it depends on the disturbance regime how bacterial community structure and function are related to each other. </p>