The response of global soil respiration (Rs) to climate change determines how long the land can continue acting as a carbon sink in the future. This dissertation research identifies how temporal and spatial variation in environmental factors affects global scale Rs modeling and predictions of future Rs under global warming. Chapter 1 describes the recommend time range for measuring Rs across differing climates, biomes, and seasons and found that the best time for measuring the daily mean Rs is 10:00 am in almost all climates and biomes. Chapter 2 describes commonly used surrogates in Rs modeling and shows that air temperature and soil temperature are highly correlated and that they explain similar amounts of Rs variation; however, average monthly precipitation between 1961 and 2014, rather than monthly precipitation for a specific year, is a better predictor in global Rs modeling. Chapter 3 quantifies the uncertainty generated by four different assumptions of global Rs models. Results demonstrate that the time-scale of the data, among other sources, creates a substantial difference in global estimates, where the estimate of global annual Rs based on monthly Rs data (70.85 to 80.99 Pg C yr-1) is substantially lower than the current benchmark for land models (98 Pg C yr-1). Chapter 4 simulates future global Rs rates based on two temperature scenarios and demonstrates that temperature sensitivity of Rs will decline in warm climates where the level of global warming will reach 3°C by 2100 relative to current air temperature; however, these regional decelerations will be offset by large Rs accelerations in the boreal and polar regions. Chapter 5 compares CO2 fluxes from turfgrass and wooded areas of five parks in Blacksburg, VA and tests the ability of the Denitrification-Decomposition model to estimate soil temperature, moisture and CO2 flux across the seasons. Cumulatively, this work provides new insights into the current and future spatial and temporal heterogeneity of Rs and its relationship with environmental factors, as well as key insights in upscaling methodology that will help to constrain global Rs estimates and predict how global Rs will respond to global warming in the future. / Ph. D.

Submitted by (edna.saturno@ufrpe.br) on 2016-06-16T13:11:16Z No. of bitstreams: 1 Eduardo Vetromilla Fuentes.pdf: 2331604 bytes, checksum: af655705e72ee5734b852e5c6da14e46 (MD5) / Made available in DSpace on 2016-06-16T13:11:16Z (GMT). No. of bitstreams: 1 Eduardo Vetromilla Fuentes.pdf: 2331604 bytes, checksum: af655705e72ee5734b852e5c6da14e46 (MD5) Previous issue date: 2011-06-16 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Given the multiplicity of uses to which reservoirs are generally subjected, it is expected to find different conditions of composition, density and biomass of phytoplankton, due to possible spatial and seasonal variations of limnological conditions and land uses in the basin. Aiming to know the structure of phytoplankton and its variation in function of spatial heterogeneity in Moxotó Reservoir, located in the semiarid region of Northeastern Brazil, samples were analyzed in two periods, rainy (June 2009) and dry (December 2009). Samples were collected at a station in body (dam upstream) and at five in arms representing several human activities (aquaculture, agriculture, urban settlement, landfill and without punctual activity). Limnological variables, richness, density and biomass of phytoplankton were analyzed. Abundance/biomass comparison curves (ABC) were used to analyze phytoplankton structure. Algae diversity between periods and samples was estimated by cluster analysis, using species presence/absence data. Samples were ordinate (NMDS) by abundance and biomass of phytoplankton descriptor species. The relation between phytoplankton and limnological data was accessed by Pearson’s univariate correlation and BIOENV multivariate analysis. The reservoir presented regulated flow, short theoretical retention time (<7 days) and high water transparency (median zEUF: zMAX = 1.0). Phytoplankton biomass was consistent with low-productive systems (median = 0.9 mg L-1), limited mainly by phosphorus in rainy period (median SRP = 8.4 μg L-1), and nitrogen in dry period (median DIN = 36.5 μg L-1). Phytoplankton composition showed marked seasonality, especially for diatoms, with main contributions of planktonic in rainy period and typically periphytic in dry period. Under limitation by SRP and DIN, organisms adapted to mixotrophy (dinoflagellates and euglenoids) reached higher biomass. In contrast, nanoplanktonic organisms (chlorophytes and cryptophytes) were dominant in conditions of high nutrient availability. The studied sites showed three distinct environments: body, arms with submerged macrophytes and arms under influence of tributaries. Among human activities observed, agriculture was considered the most striking in relation to eutrophication. Moreover, proliferation of submerged macrophytes in arms can cause impairment for multiple uses, despite apparent benefits on water quality (increased transparency). Human activities, presence of submerged macrophytes and retention time influenced the availability of resources, being considered the driving forces of phytoplankton structure. / Em vista da multiplicidade de usos à qual os reservatórios geralmente estão sujeitos, espera-se encontrar condições diferenciadas quanto à composição, densidade e biomassa fitoplanctônica, em função de possíveis variações espaciais e sazonais das condições limnológicas e de ocupação do solo na bacia. Com o objetivo de conhecer a estrutura fitoplanctônica e sua variação em função da heterogeneidade espacial no reservatório hidrelétrico de Moxotó, situado na região semiárida do Nordeste do Brasil, foram analisadas amostras em dois períodos sazonais, de chuvas (junho/2009) e de estiagem (dezembro/2009). As coletas foram realizadas em uma estação no corpo central (barragem à montante) e cinco em reentrâncias representativas de diversas atividades antrópicas (piscicultura, agricultura, ocupação urbana, aterro sanitário e sem atividade pontual). Foram analisadas variáveis limnológicas, riqueza, densidade e biomassa fitoplanctônica. Curvas de comparação de abundância e biomassa acumuladas (curvas ABC) foram utilizadas na análise da estrutura do fitoplâncton. A diversidade algal entre períodos e estações foi estimada através de análise de agrupamento, utilizando-se dados de presença/ausência de espécies. As estações foram ordenadas (NMDS) em função da densidade e biomassa de espécies descritoras do fitoplâncton (valores relativos de abundância e/ou biomassa acima de 5%). A relação entre o fitoplâncton e os dados limnológicos foi acessada através de correlação univariada de Pearson e análise multivariada BIOENV. O reservatório apresentou vazão regularizada, tempo teórico de retenção curto (< 7 dias) e transparência da água elevada (mediana zEUF:zMAX = 1,0). A biomassa fitoplanctônica foi compatível com sistemas pouco produtivos (mediana = 0,9 mg L-1), limitadas principalmente por fósforo nas chuvas (mediana SRP = 8,4 μg L-1), e nitrogênio na estiagem (mediana DIN = 36,5 μg L-1). A composição fitoplanctônica apresentou sazonalidade marcante, especialmente para diatomáceas, com maiores participações das planctônicas nas chuvas e das tipicamente perifíticas, na estiagem. Em condições de limitação por SRP e DIN, organismos adaptados a mixotrofia (dinoflagelados e euglenóides) atingiram biomassas mais elevadas. Por outro lado, organismos nanoplanctônicos (clorofíceas e criptofíceas) foram dominantes em condições de disponibilidade de nutrientes. Os locais estudados mostraram a existência de três ambientes distintos, sendo corpo central e reentrâncias com macrófitas submersas e sob influência de tributários. Dentre as atividades antrópicas observadas, a agrícola foi considerada a mais impactante em relação à eutrofização. Por outro lado, a proliferação de macrófitas submersas em reentrâncias pode ocasionar o comprometimento destes locais para fins de usos múltiplos, apesar dos aparentes benefícios para a qualidade da água (aumento da transparência). Atividades antrópicas, presença de macrófitas submersas e tempo de retenção influenciaram a disponibilidade de recursos, sendo consideradas os fatores direcionadores da estrutura do fitoplâncton.

<p>Plant-animal interactions are affected by both abundance and distribution of interacting species and the community context in which they occur. However, the relative importance of these factors is poorly known. I examined the effects of predator host range, environmental factors, host plant populations, plant traits and fruit abortion on the intensity of pre-dispersal seed predation in 46 host populations of the perennial herb <i>Lathyrus vernus</i>. I recorded damage by beetle pre-dispersal seed predators, mainly <i>Apion opeticum </i>and <i>Bruchus atomarius</i> with different host ranges on <i>L. vernus</i> as well as on two additional host plants. Local seed predator population size was mainly influenced by plant population size, current seed production and beetle population size in the previous year, but was not strongly affected by connectivity. The monophagous seed predator was less abundant and had lower densities than the oligophagous. Both predator species had a strong ability to track fluctuations in seed production; intensity of predation increased with relative increases in seed production. Oligophagous predation on<i> L. vernus i</i>ncreased with the abundance of alternative hosts, but presence of<i> L. vernus</i> did not affect predation on alternative hosts. Abundances and trait preferences differed among three co-occurring seed predators, but were also associated with the abundance of the other species. Overall, seed predation influenced selection on flower number. I found clear indications of seed predator offence but no obvious plant defence. The pattern of fruit abortion was associated with reduced plant fitness since the seed predator had an advanced ability to locate fruits with high probability of retention. Taken together, different factors influencing abundance of the seed predator species, different preferences, and context dependent trait selection are likely to result in complex spatio-temporal variation in overall seed losses and trait selection in the common host plant.</p>

Plant-animal interactions are affected by both abundance and distribution of interacting species and the community context in which they occur. However, the relative importance of these factors is poorly known. I examined the effects of predator host range, environmental factors, host plant populations, plant traits and fruit abortion on the intensity of pre-dispersal seed predation in 46 host populations of the perennial herb Lathyrus vernus. I recorded damage by beetle pre-dispersal seed predators, mainly Apion opeticum and Bruchus atomarius with different host ranges on L. vernus as well as on two additional host plants. Local seed predator population size was mainly influenced by plant population size, current seed production and beetle population size in the previous year, but was not strongly affected by connectivity. The monophagous seed predator was less abundant and had lower densities than the oligophagous. Both predator species had a strong ability to track fluctuations in seed production; intensity of predation increased with relative increases in seed production. Oligophagous predation on L. vernus increased with the abundance of alternative hosts, but presence of L. vernus did not affect predation on alternative hosts. Abundances and trait preferences differed among three co-occurring seed predators, but were also associated with the abundance of the other species. Overall, seed predation influenced selection on flower number. I found clear indications of seed predator offence but no obvious plant defence. The pattern of fruit abortion was associated with reduced plant fitness since the seed predator had an advanced ability to locate fruits with high probability of retention. Taken together, different factors influencing abundance of the seed predator species, different preferences, and context dependent trait selection are likely to result in complex spatio-temporal variation in overall seed losses and trait selection in the common host plant.

Le lac de Tonlé Sap (TSL), Cambodge, est un écosystème lac-rivière de forêt alluviale au régime d'écoulement alternatif. Le lac est un déversoir lors de l'inondation saisonnière du Mékong et sert de réservoir en période de basses eaux. La superficie du lac pendant la saison sèche (février à mai), est d'environ 2 700 km2 pour une profondeur d'environ 1 mètre. Cette superficie est pratiquement multipliée par six quand arrive la saison des pluies, pour atteindre près de 16 000 km2 et une profondeur de 9 mètres, noyant rizières et forêts. C'est le plus grand lac d'eau douce d'Asie du Sud-Est. C'est aussi l'une des zones de pêche d'eau douce les plus importantes et productives du monde avec près de 75% du volume annuel de pêche en eau douce du Cambodge, ce qui permet la survie de près de 2,5 millions de personnes. Les changements saisonniers du cycle hydrologique ont une influence sur la structuration des communautés de poissons à l'échelle temporelle et spatiale, mais aussi sur les comportements trophiques des principales espèces qui n'exploitent alors pas les mêmes habitats. Toutefois, le bassin versant du Mékong est en changement constant avec un développement important des infrastructures en lien avec l'eau : production d'hydro-électricité, besoins important en irrigation, maitrise des inondations, eau potable, ... Les changements climatiques accélèrent les modifications du cycle hydrologique annuel. Il est alors supposé que ces modifications ont des effets forts sur les habitats et les proies disponibles et finalement sur la biodiversité, notamment de l'ichtyofaune et sur l'abondance des poissons disponibles pour les pêcheries.Dans un premier temps, nous avons caractérisé les variations spatio-temporelles de la composition taxonomique des poissons et mis en lumière quels sont les déterminants de ces variations. À cette fin, nous avons estimé la diversité bêta comme la variance totale de la matrice site par communauté d'espèce et l'avons divisée en contribution locale à la diversité bêta (LCBD) et contribution des espèces à la diversité bêta (SCBD). Nous avons ensuite effectué plusieurs régressions linéaires pour déterminer si la richesse taxonomique, l'abondance des espèces et le niveau de l'eau expliquaient la variation temporelle de la contribution du site et de l'espèce à la diversité bêta. Nos résultats indiquent une forte variation temporelle de la diversité bêta due aux contributions différentielles des sites et des espèces à la variation spatiale de la composition taxonomique des poissons. Nous avons également constaté que la direction, la forme et l'effet relatif de la richesse spécifique, de l'abondance et du niveau de l'eau sur la variation temporelle des valeurs LCBD et SCBD varient grandement selon les sites. Ces résultats suggèrent ainsi une variation spatiale des processus conduisant à une variation temporelle de la composition de la communauté. Dans l'ensemble, nos résultats suggèrent que la composition taxonomique des poissons n'est pas distribuée de manière homogène dans l'espace et dans le temps et risque d'être affectée à l'avenir si la dynamique saisonnière d'écoulement du système est altérée par les activités humaines et/ou les changements climatiques. Dans un second temps, nous avons cherché à étudier le modèle d'évolution temporel des principales espèces en terme d'occurrence et d'abondance à travers le cycle saisonnier hydrologique. / The Tonle Sap Lake (TSL), Cambodia, is a flood-pulse system. It is the largest natural lake in South- East Asia and constitutes one of the largest fisheries over the world, supporting the livelihood 2.5 million peoples. Seasonal change in annual hydrological cycle appears to have influence on fish community structure, both spatial and temporal variation, particularly on feeding behavior of TSL's fishes. Nonetheless, the Mekong River Basin is changing rapidly due to accelerating water infrastructure development (hydropower, irrigation, flood control, and water supply) and climate change, bringing considerable modifications to the annual flood-pulse of the TSL. Such modifications are expected to have strong impacts on fish biodiversity, abundance, reduced habitat and food availability within the lake. To invest how TSL's fish community structure responds to the seasonal change, how they shift their diet across hydrological cycles and feeding competing for food resource: First, we aim to characterize the spatio-temporal variations of fish taxonomic composition and to highlights the underlying determinants of these variations. For this purpose, we estimated beta diversity as the total variance of the site-by-species community matrix and partitioned it into Local Contribution to Beta Diversity (LCBD) and Species Contribution to Beta Diversity (SCBD). We then performed multiple linear regressions to determine whether species richness, species abundances and water level explained the temporal variation in the contribution of site and species to beta diversity. Our results indicate strong temporal variation of beta diversity due to differential contributions of sites and species to the spatial variation of fish taxonomic composition. We further found that the direction, the shape and the relative effect of species richness, abundances and water level on temporal variation in LCBD and SCBD values greatly varied among sites, thus suggesting spatial variation in the processes leading to temporal variation in community composition. Overall, our results suggest that fish taxonomic composition is not homogeneously distributed over space and time and is likely to be impacted in the future if the flood-pulse dynamic of the system is altered by human activities. Second, we aim to investigate the temporal pattern of the most occurrence and abundance species and how their co-occurrence pattern across hydrological cycles. We found that occurrence and abundance patterns were temporally varied at all water level seasons. Strong temporal variation in species occurrence was occurred with visiting species such as Labiobarbus leptocheilus and Poropuntius deauratus while water level starts to fill into the TSL. We further observed that the abundance of 17 species was strongly varied while other 22 species (mainly TSL's residential species) were stable within the year. Positive species co-occurrence pattern was generally higher than negative species co-occurrence at all water level seasons. Highest positive co-occurrence patterns were found during the period of decrease and low water level seasons while fishes are migrating from flooded areas, competing for resource and habitats during low water season. Study on temporal distribution and species co-occurrence of fish and how community responds to the seasonal change in hydrological cycles provides critical information for fisheries management and conservation in the Tonle Sap Lake (TSL) as well as maintaining fish biodiversity in the Mekong system. Third, the implications of seasonality on food web structure have been notoriously understudied in empirical ecology, particularly in TSL's system. The current study, we focus on seasonal changes in one key attribute of a food web, vertical trophic position of consumers.

No description available.