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Dissertations & Theses from 2017

Early and late consequences of mode of delivery

The impacts of climate change and the potential CO2 effect on NPP of European forest ecosystems have been highlighted by two simulations with different CO2 concentration hypothesis (constant and rising concentrations). The real response of ecosystem to CO2 enrichment is however a question which is still discussed. It is argued that nutrient availability could be limiting on the primary productivity (). Yet, for nitrogen, results from many experimental sites lead to suppose that this is no longer the case. Owing to release of nitrogen into the atmosphere by human activities and subsequent deposition on lands, anthropogenic nitrogen sources are now controlling the carbon balance of most of the temperate and boreal forests (). As a rule, the free-air CO2 enrichment FACE project results demonstrate actual fertilizing effect with C3 plants. Despite increase dark respiration with some plant species and acclimation of photosynthetic capacity (decrease of maximum carboxylation rate of Rubisco and maximum electron transport rate leading to ribulose-1.5-bisphosphate regeneration), carbon gain is markedly greater (19-46%) in C3 plants at anticipated CO2 concentration. The reasons are the stimulation of the light-saturated rate of photosynthetic CO2 uptake and the improvement of the photosynthetic use of N (). Nevertheless, at some FACE sites, tree growth and NPP remain strongly limited by nitrogen availability (). Here, most of the extra fixed carbon is allocated to fine roots with fast turnover and probably to exudates stimulating microbial activities to enhance N uptake. Trees alter their allocation priorities depending on growing conditions; they favour leaves, roots and mycorrhizae depending on nutrient and water availability (). In addition, others nutrients than nitrogen could also induce limitations under enhanced CO2 air concentration, a situation occurring near steady-state nutrient cycle and full canopy development, , when total fine root mass and leaf area index do not increase from year to year (). Since the end of the eighties, the sensitivity of the Western Europe forests to nitrogen deposition is known. In densely populated countries such as the Netherlands, Germany or Belgium, the forests are often restricted to the most infertile soils. In those conditions, nitrogen deposition induces soil base cation depletion and tree nutritional imbalances (, , ). Otherwise, in regions where water deficit gets worse, rising CO2 concentration offsets the effects of increasing summer drought. Indeed, stomatal closure rendered possible by a higher CO2 concentration induces increased water use efficiency. For C4 plants as well as for C3 plants, significant potential for increased photosynthesis and yield at elevated CO2 concentration might result from improved water use and reduce drought stress (, , ). In CARAIB, CO2 concentration controls stomatal closure in combination with photosynthesis, water stress and air relative humidity, but not the physiological acclimation of photosynthetic capacity. In addition, carbon allocation between structural pools and fast decomposing organs is fixed and there is no coupling with nutrient cycles. Therefore, CARAIB with increased CO2 concentration probably overestimates NPP at anticipated CO2 concentration. Morales et al. () and Olesen et al. () obtain with LPJ DVM less marked productivity changes with a range of regional climate models under A2 and B2 emissions scenarios. They project the greatest changes in NPP in the northern European ecosystems (35-54 % increases) and smallest changes in southern Europe (only slightly NPP declines or increases). However, the balance between the two scenarios, with and without CO2 fertilization, might be definitely established only by combining the direct observation over long periods of time of tree physiology and the coupling of DVM with nutrient cycles.

Aguilar, Isaac Jaime (2017) An In-Depth Evaluation of Shear Box Compactor for Hot Mix Asphalt

Responses of European forest ecosystems to 21 st …

Fig. 6 presents the NPP relative anomalies under changing climate between the end of the 21st century (2081-2100) and the present (1981-2000) without or with CO2 fertilizing effect. The first simulation is driven with atmospheric CO2 concentration kept constant (330 ppmv) in the vegetation model but with climate change from A2 scenario calculated by ARPEGE/Climate. In the second simulation, the CO2 concentration is rising according to the A2 scenario in both the climate and vegetation models. The a and 6b display the current NPP computed by CARAIB respectively with climate from ARPEGE/Climate and CRU data. Under the first hypothesis (c), the NPP anomalies predicted over Europe present a large geographical gradient. Three main evolution types may be distinguished. In cold regions, , at high latitudes and altitudes, the temperature increases lead to longer growing seasons. When water is not a limiting factor, plant growth is improved and thus the modelled NPP generally increases by up to 40% or even 60-100% in the coldest regions which are currently tundras. In the cold temperate area, between approximately 50° N to 60° N, NPP might decrease by as much as 50%. These NPP reductions are due to summer droughts more recurrent than in the present. In warmer regions, , Mediterranean area, western France, Eastern Europe, Ukraine, south of Russia and areas around Caspian and Aral Seas, higher predicted temperatures raise evapotranspiration. Since there are no precipitation increases, plants are subject to higher water stress and NPP goes down everywhere with local decreases reaching 80%. Assuming increasing CO2 concentration together with climate change (d), predicted NPP increases throughout Europe, though there are substantial differences in the magnitude among subregions. As in the simulations keeping CO2 constant, at high latitudes and in mountainous areas, the model predicts NPP increases of 50-75%. For the temperate regions, the NPP increases are comprised between 25 and 50%. In the Mediterranean area, western France, Eastern Europe and Ukraine, NPP increases might reach 75%, but generally about 50%. Farther to the east, the model simulates very important increases of up to 500 %. The fact that NPP anomalies are displayed as percent makes that regions with current low NPP values (-2) show the more dramatic changes. It concerns particularly south-eastern part of the studied area occupied by steppes and the extreme of northern Europe covered by tundras.

Breech presentation at term is associated with higher rates of perinatal mortality ..

The impacts of climate change and the potential CO2 effect on NPP of European forest ecosystems have been highlighted by two simulations with different CO2 concentration hypothesis (constant and rising concentrations). The real response of ecosystem to CO2 enrichment is however a question which is still discussed. It is argued that nutrient availability could be limiting on the primary productivity (). Yet, for nitrogen, results from many experimental sites lead to suppose that this is no longer the case. Owing to release of nitrogen into the atmosphere by human activities and subsequent deposition on lands, anthropogenic nitrogen sources are now controlling the carbon balance of most of the temperate and boreal forests (). As a rule, the free-air CO2 enrichment FACE project results demonstrate actual fertilizing effect with C3 plants. Despite increase dark respiration with some plant species and acclimation of photosynthetic capacity (decrease of maximum carboxylation rate of Rubisco and maximum electron transport rate leading to ribulose-1.5-bisphosphate regeneration), carbon gain is markedly greater (19-46%) in C3 plants at anticipated CO2 concentration. The reasons are the stimulation of the light-saturated rate of photosynthetic CO2 uptake and the improvement of the photosynthetic use of N (). Nevertheless, at some FACE sites, tree growth and NPP remain strongly limited by nitrogen availability (). Here, most of the extra fixed carbon is allocated to fine roots with fast turnover and probably to exudates stimulating microbial activities to enhance N uptake. Trees alter their allocation priorities depending on growing conditions; they favour leaves, roots and mycorrhizae depending on nutrient and water availability (). In addition, others nutrients than nitrogen could also induce limitations under enhanced CO2 air concentration, a situation occurring near steady-state nutrient cycle and full canopy development, , when total fine root mass and leaf area index do not increase from year to year (). Since the end of the eighties, the sensitivity of the Western Europe forests to nitrogen deposition is known. In densely populated countries such as the Netherlands, Germany or Belgium, the forests are often restricted to the most infertile soils. In those conditions, nitrogen deposition induces soil base cation depletion and tree nutritional imbalances (, , ). Otherwise, in regions where water deficit gets worse, rising CO2 concentration offsets the effects of increasing summer drought. Indeed, stomatal closure rendered possible by a higher CO2 concentration induces increased water use efficiency. For C4 plants as well as for C3 plants, significant potential for increased photosynthesis and yield at elevated CO2 concentration might result from improved water use and reduce drought stress (, , ). In CARAIB, CO2 concentration controls stomatal closure in combination with photosynthesis, water stress and air relative humidity, but not the physiological acclimation of photosynthetic capacity. In addition, carbon allocation between structural pools and fast decomposing organs is fixed and there is no coupling with nutrient cycles. Therefore, CARAIB with increased CO2 concentration probably overestimates NPP at anticipated CO2 concentration. Morales et al. () and Olesen et al. () obtain with LPJ DVM less marked productivity changes with a range of regional climate models under A2 and B2 emissions scenarios. They project the greatest changes in NPP in the northern European ecosystems (35-54 % increases) and smallest changes in southern Europe (only slightly NPP declines or increases). However, the balance between the two scenarios, with and without CO2 fertilization, might be definitely established only by combining the direct observation over long periods of time of tree physiology and the coupling of DVM with nutrient cycles.

The experience of the World Fertility Survey ..