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In the last decades, CO2 emissions from fossil fuel burning and land use change have caused an increase in the CO2 concentration of the atmosphere. This human induced rise in atmospheric CO2 concentration is extremely likely to be causing climate change, which poses a threat to human communities worldwide. The increase in atmospheric CO2 influences the terrestrial biosphere. Over the last decade, the terrestrial biosphere acted as a carbon sink, absorbing an estimated 29% of the yearly anthropogenic CO2 emissions. The behavior of the terrestrial C sink with future CO2 emission is, however, uncertain. Nitrogen (N) is an essential and limiting nutrient for vegetation growth. Due to the resulting close links between the carbon (C) and N cycles, the N cycle influences the biosphere response to the rise in atmospheric CO2. How the N cycle influences the C cycle in terrestrial biosphere is studied with global vegetation models. Data on the N cycle are needed for the models. However, data on the N cycle are lacking at global scale. Remote sensing methods could provide insights on the spatial pattern of canopy N, defined as the foliar N scaled to the whole vegetation canopy, at large scale. In this context, this thesis explores the possibility to estimate canopy N concentration across scales and vegetation types. This is done under different conditions using vegetation indices (VIs) computed from remotely sensed spectral reflectance. In the first study (Exploring the use of vegetation indices to sense canopy nitrogen to phosphorous ratio in grasses), the reflectance spectra of a grass species, Holcus lanatus L., was measured under controlled conditions in a laboratory experiment. Several VIs were subsequently computed and related to the grass canopy N concentration using linear regressions. In the second study (Remote sensing of canopy nitrogen at regional scale in Mediterranean forests using the spaceborne MERIS Terrestrial Chlorophyll Index), canopy N was estimated in a Mediterranean forest ecosystem at regional scale in Catalonia, Spain, using the MERIS Terrestrial Chlorophyll Index (MTCI) obtained from the MERIS sensor abord ESA-Envisat satellite. In the third study (Mapping canopy nitrogen in European forests using remote sensing and environmental variables with the random forests method), canopy N was estimated in European forests at continental scale using either only satellite-based variables or both VIs and environmental variables as predictors with the random forests method algorithm. In the last study (Comparison of simulated foliage nitrogen by the O-CN and LPJ-GUESS vegetation models with a canopy nitrogen map based on forest sampling), the obtained canopy N map in European forests was compared with foliage N simulated by two global vegetation models, O-CN and LPJ-GUESS, in Europe.

Made available in DSpace on 2020-12-11T05:26:55Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-12-20 The inorganic nitrogen mobility as a response to the use of organomineral fertilizers in interaction with the phosphorus is altered around the granules in variable charge soils. The aim of this research was to evaluate the inorganic N mobility in a Typic Hapludox as a response to the interaction with P in organomineral fertilizers. The experiment in Petri dishes was carried out in a completely randomized design, with six repetitions. The treatments comprised eight P concentrations (0; 1.3; 1.8; 2.5; 3.5; 5 and 10 mg/dish) in the organomineral, besides the control (unfertilized) and urea, with the N dose fixed in 5 mg/dish. In the Petri dishes, the granules of fertilizers were placed in the center, and posteriorly, placed in incubation for 7, 14, 21, 28 and 35 days, being in each time, sampled concentric rings of soil in four distances from the central point (0 - 7.75; 7.76 - 13.5; 13.51 - 25.5; and 25.51 - 43 mm). The concentration of P in the organomineral and the amount applied interfered in the mobility of ammonia and nitrate in the soil around the fertilizer granules. Until 21 days there was predominance of nitrogen in the ammonia form with displacement until section 2 (7.76 - 13.5 mm), whereas the form of nitrate had higher proportion after 28 days with mobility until section 4 (25.51 - 43 mm). The smallest concentrations of P in the organomineral demonstrated the largest contents of nitrate, whereas the largest concentrations of P kept the ammonia longer in the soil. Sao Paulo State Univ Julio de Mesquita Filho, Dept Soil Sci, Botucatu, SP, Brazil Brazilian Agr Res Corp Embrapa, Embrapa Swine & Poultry, Concordia, Brazil Brazilian Agr Res Corp Embrapa, Embrapa Soils, Rio De Janeiro, Brazil Sao Paulo State Univ Julio de Mesquita Filho, Dept Soil Sci, Botucatu, SP, Brazil

The Rosário Reservoir in the municipality of Lavras da Mangabeira, located in the Salgado sub-basin, in the State of Ceará, Brazil, is the source used for several uses, including human consumption. Knowing the quality of the water, especially with regard to the trophic status index, is essential, as it indicates how the reservoir is in relation to eutrophication, which in turn, is related to possible releases of sewers and degrading activities in the area of influence of the weir. Therefore, the present study evaluated the trophic status of the reservoir, using the parameters chlorophyll-a, nutrient contents and primary production as indicators of the eutrophication process. Monitoring took place during the period from February 2016 to May 2018. To identify the degree of trophy, the Trophic State Index (TSI) was used through the method of Lamparelli (2004). To indicate the limiting nutrient, the nitrogen / phosphorus ratio (N: P) was used. The analyzes of total phosphorus and chlorophyll-a made it possible to calculate the average TSI and classify the source in the eutrophic category. The high concentrations of nutrients confirm the eutrophication of its waters, but do not imply the primary evolution, which involves the variation of other environmental factors. Comparing the results obtained from the analyzes with Resolution 357/05 CONAMA for class 2 water, values outside the established standards were obtained, with the exception of chlorophyll-a and total nitrogen. Phosphorus showed concentrations well above the environmental legislation, which directly influenced the degree of trophy in the reservoir. El embalse de Rosário en el municipio de Lavras da Mangabeira, ubicado en la subcuenca del Salgado, en el estado de Ceará, Brasil, es la fuente utilizada para diversos usos, incluido el consumo humano. Conocer la calidad del agua, especialmente con respecto al índice de estado trófico, es esencial, ya que indica cómo está el depósito en relación con la eutrofización, que a su vez, está relacionado con posibles liberaciones de alcantarillas y actividades degradantes en el área de influencia del vertedero. Por lo tanto, el presente estudio evaluó el estado trófico del reservorio, utilizando los parámetros clorofila-a, contenido de nutrientes y producción primaria como indicadores del proceso de eutrofización. El monitoreo se llevó a cabo durante el período de febrero de 2016 a mayo de 2018. Para identificar el grado de trofeo, se utilizó el Índice de estado trófico (IET) a través del método de Lamparelli (2004). Para indicar el nutriente limitante, se usó la relación nitrógeno/fósforo (N: P). Los análisis del fósforo total y la clorofila-a permitieron calcular el EIT promedio y clasificar la fuente en la categoría eutrófica. Las altas concentraciones de nutrientes confirman la eutrofización de sus aguas, pero no implican la evolución primaria, que implica la variación de otros factores ambientales. Comparando los resultados obtenidos de los análisis con la Resolución 357/05 CONAMA para agua de clase 2, se obtuvieron valores fuera de los estándares establecidos, con la excepción de clorofila-a y nitrógeno total. El fósforo mostró concentraciones muy por encima de la legislación ambiental, lo que influyó directamente en el grado de trofeo en el depósito. O Reservatório Rosário do município de Lavras da Mangabeira, está localizado na sub-bacia do Salgado, no Estado do Ceará, Brasil, é o manancial utilizado para diversos usos, entre estes o consumo humano. Conhecer a qualidade da água, principalmente no tocante ao índice de estado trófico é primordial, pois indica como está o reservatório em relação a eutrofização que por sua vez, está relacionado a possíveis lançamentos de esgotos e atividades degradadoras na área de influência do açude. Assim sendo, o presente estudo avaliou o estado trófico do reservatório, utilizando os parâmetros clorofila-a, teores de nutrientes e produção primaria como indicadores do processo de eutrofização. O monitoramento se deu durante o período de fevereiro de 2016 a maio de 2018. Para identificar o grau de trofia, utilizou-se o Índice de Estado Trófico (IET) do método de Lamparelli (2004). Para indicar o nutriente limitante, utilizou-se a razão nitrogênio/fósforo (N:P). As análises de fósforo total e clorofila-a permitiram calcular o IET médio e classificar o manancial na categoria de eutrófico. As elevadas concentrações de nutrientes confirmam a eutrofização de suas águas, mas não implicam na evolução primaria, que envolve a variação de outros fatores ambientais. Comparando os resultados obtidos das análises com a Resolução 357/05 CONAMA para água de classe 2, obteve-se valores fora dos padrões estabelecidos, com exceção a clorofila-a e nitrogênio total. O fósforo apresentou concentrações muito acima da legislação ambiental, o que influenciou diretamente no grau de trofia do reservatório.

Increasing frequency and magnitude of climatic extremes, such as heat waves are expected to enhance abiotic stresses on ecological communities. It has been proposed that ecological communities in disturbed habitats may be most sensitive to climatic extremes, as disturbance may reduce density and diversity of higher trophic level organisms like predators. However, there is little experimental evidence that climatic extremes indeed have stronger impact on functioning of such trophically downgraded ecosystems. Here, we experimentally examine how removal of predators from soil communities affects plant performance under periodic heat waves. We used a native plant species, and a congeneric native that is currently expanding its range because of climate change. We used soil nematode communities as the model system, as these are most abundant soil animals and their communities are trophically diverse. Predatory nematodes were manually removed from intact soil nematode communities (mainly the adults as some juveniles are impossible to manually remove) to create a trophically downgraded soil. Intact nematode communities and communities with reduced predatory nematodes were added separately to soils that were planted with either the native Centaurea jacea or the range-expanding congener Centaurea stoebe. Half the experimental units were exposed periodically to experimental heat waves of 10 °C above the control temperature. Our results show that the C: N and C: N: P ratio of plant shoots in predator-reduced soils became lower when exposed to periodic heat waves, however, only in the native plant C. jacea. The decrease in C: N ratio corresponded with increase of an herbivorous nematode in trophically intact soils of C. jacea independent of warming, whereas this relationships disappeared in warmed and predator-reduced soils. Our results accordingly highlight that periodic heat waves may affect stoichiometry of certain plant species by altering trophic interactions in predator-reduced soils.

The stoichiometric constraints of algal growth are well understood, whereas there is less knowledge for heterotrophic bacterioplankton. Growth of the marine bacterium Phaeobacter inhibens DSM 17395, belonging to the globally distributed Roseobacter group, was studied across a wide concentration range of NH4+ and PO43−. The unique dataset covers 415 different concentration pairs, corresponding to 207 different molar N:P ratios (from 10−2 to 105). Maximal growth (by growth rate and biomass yield) was observed within a restricted concentration range at N:P ratios (∼50−120) markedly above Redfield. Experimentally determined growth parameters deviated to a large part from model predictions based on Liebig's law of the minimum, thus implicating synergistic co-limitation due to biochemical dependence of resources. Internal elemental ratios of P. inhibens varied with external nutrient supply within physiological constraints, thus adding to the growing evidence that aquatic bacteria can be flexible in their internal elemental composition. Taken together, the findings reported here revealed that P. inhibens is well adapted to fluctuating availability of inorganic N and P, expected to occur in its natural habitat (e.g. colonized algae, coastal areas). Moreover, this study suggests that elemental variability in bacterioplankton needs to be considered in the ecological stoichiometry of the oceans., Phaeobacter inhibens DSM 17395, member of the marine Roseobacter group, grows optimally at N:P supply ratios >16, exhibits phytoplankton-like flexible internal elemental stoichiometry and different nutrients control growth synergistically.

Plant Ecology, 176 (1), ISSN:1385-0237, ISSN:1573-5052

Botanica Helvetica, 117 (1), ISSN:0253-1453, ISSN:1420-9063