Réponse à M*** sur le jugement qu'il a porté des observations sur les faits historiques cités dans les Lettres du clergé contre les remontrances du Parlement PDF Download

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Languages : en
Pages : 36

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Languages : en
Pages : 49

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A maturing loblolly pine (Pinus taeda L.) forest was exposed to elevated CO2 in the natural environment in a perturbation study conducted over three seasons using the free-air CO2 enrichment (FACE) technique. At the time measurements were begun in this study, the pine canopy was comprised entirely of foliage which had developed under elevated CO2 conditions (atmospheric CO2 ≈ 550 [mu]mol/mol−1). Measurements of leaf photosynthetic responses to CO2 were taken to examine the effects of elevated CO2 on photosynthetic N nutrition in a pine canopy under elevated CO2. Photosynthetic CO2 response curves (A-c{sub i} curves) were similar in FACE trees under elevated CO2 compared with counterpart trees in ambient plots for the first foliage cohort produced in the second season of CO2 exposure, with changes in curve form detected in the foliage cohorts subsequently produced under elevated CO2. Differences in the functional relationship between carboxylation rate and N{sub a} suggest that for a given N{sub a} allocated among successive cohorts of foliage in the upper canopy, V{sub c max} was 17% lower in FACE versus Ambient trees. The authors also found that foliar Rubisco content per unit total protein derived from Western blot analysis was lower in late-season foliage in FACE foliage compared with ambient-grown foliage. The results illustrate a potentially important mode of physiological adjustment to growth conditions that may operate in forest canopies. Findings suggest that mature loblolly pine trees growing in the field may have the capacity for shifts in intrinsic nitrogen utilization for photosynthesis under elevated CO2 that are not dependent on changes in leaf N. Findings suggest a need for continued examination of internal feedbacks at the whole-tree and ecosystem level in forests that may influence long-term photosynthetic responses to elevated CO2.

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Languages : en
Pages : 12

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Forest ecosystems constitute an important part of the planet's land cover. Understanding their exchanges of carbon with the atmosphere is crucial in projecting future net atmospheric CO2 increases. It is also important that experimental studies of these processes be performed under conditions which are as realistic as possible, particularly with respect to photosynthesis and evapotranspiration. New technology and experimental protocols now exist which can facilitate studying an undisturbed forest canopy under long-term enriched CO2 conditions. The International Geosphere Biosphere Program of the International Council of Scientific Unions has established a subprogram on Global Change and Terrestrial Ecosystems (GCTE). This program is driven by two major concerns: to be able to predict the effects of global change on the structure and function of ecosystems, and to predict how these changes will control both atmospheric CO2 and climate, through various feedback pathways. Brookhaven National Laboratory (BNL) has developed a system for exposing field-grown plants to controlled elevated concentrations of atmospheric gases, without use of confining chambers that alter important atmospheric exchange processes. This system, called FACE for Free Air CO2 Enrichment. This paper focuses on the fluid mechanics of free-air fumigation and uses a numerical simulation model based on superposed gaussian plumes to project how the present ground-based system could be used to fumigate an elevated forest canopy.

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Languages : en
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Plots of Medicago sativa cv. saranac were grown in the field at ambient (355[mu]mol CO[sub 2] mol[sup -1] air) or elevated (600[mu]mol CO[sub 2] mol[sup -1] air) CO[sub 2] concentrations. High (200kg yr[sup -1]) or low (20kg yr[sup -1]) nitrogen levels were applied to two isogeneic lines, one able and one unable to use nitrogen fixing bacteria. Plants were in the second year of field growth. Exposure to elevated CO[sub 2] was via a Free-Air CO[sub 2] Enrichment System (FACE). Elevated CO[sub 2] increased diurnal assimilation by between 12% and 92%. Analysis of A/C[sub i] responses showed that effective nitrogen fertilisation was more important to rubisCO and RuBP activity than elevated CO[sub 2]. No acclimation was consistently observed. Leaves lower down the canopy were found to have lower Vc[sub max] and J[sub max] values, though age may be the cause of the latter effect. FACE conditions have only a small effect on these responses. There was some evidence found for the down-regulation of photosynthesis in the late afternoon. The FACE conditions had no affect on stomatal density but did increase epidermal cell density.

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Languages : en
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Two of the most important and pervasive greenhouse gases driving global change and impacting forests in the U.S. and around the world are atmospheric CO2 and tropospheric O3. As the only free air, large-scale manipulative experiment studying the interaction of elevated CO2 and O3 on forests, the Aspen FACE experiment was uniquely designed to address the long-term ecosystem level impacts of these two greenhouse gases on aspen-birch-maple forests, which dominate the richly forested Lake States region. The project was established in 1997 to address the overarching scientific question: "What are the effects of elevated [CO2] and [O3], alone and in combination, on the structure and functioning of northern hardwood forest ecosystems?" From 1998 through the middle of the 2009 growing season, we examined the interacting effects of elevated CO2 and O3 on ecosystem processes in an aggrading northern forest ecosystem to compare the responses of early-successional, rapid-growing shade intolerant trembling aspen and paper birch to those of a late successional, slower growing shade tolerant sugar maple. Fumigations with elevated CO2 (560 ppm during daylight hours) and O3 (approximately 1.5 x ambient) were conducted during the growing season from 1998 to 2008, and in 2009 through harvest date. Response variables quantified during the experiment included growth, competitive interactions and stand dynamics, physiological processes, plant nutrient status and uptake, tissue biochemistry, litter quality and decomposition rates, hydrology, soil respiration, microbial community composition and respiration, VOC production, treatment-pest interactions, and treatment-phenology interactions. In 2009, we conducted a detailed harvest of the site. The harvest included detailed sampling of a subset of trees by component (leaves and buds, fine branches, coarse branches and stem, coarse roots, fine roots) and excavation of soil to a depth of 1 m. Throughout the experiment, aspen and birch photosynthesis increased with elevated CO2 and tended to decrease with elevated O3, compared to the control. In contrast to aspen and birch, maple photosynthesis was not enhanced by elevated CO2. Elevated O3 did not cause significant reductions in maximum photosynthesis in birch or maple. In addition, photosynthesis in ozone sensitive clones was affected to a much greater degree than that in ozone tolerant aspen clones. Treatment effects on photosynthesis contributed to CO2 stimulation of aboveground and belowground growth that was species and genotype dependent, with birch and aspen being most responsive and maple being least responsive. The positive effects of elevated CO2 on net primary productivity NPP were sustained through the end of the experiment, but negative effects of elevated O3 on NPP had dissipated during the final three years of treatments. The declining response to O3 over time resulted from the compensatory growth of O3-tolerant genotypes and species as the growth of O3-sensitive individuals declined over time. Cumulative NPP over the entire experiment was 39% greater under elevated CO2 and 10% lower under elevated O3. Enhanced NPP under elevated CO2 was sustained by greater root exploration of soil for growth-limiting N, as well as more rapid rates of litter decomposition and microbial N release during decay. Results from Aspen FACE clearly indicate that plants growing under elevated carbon dioxide, regardless of community type or ozone level, obtained significantly greater amounts of soil N. These results indicate that greater plant growth under elevated carbon dioxide has not led to "progressive N limitation". If similar forests growing throughout northeastern North America respond in the same manner, then enhanced forest NPP under elevated CO2 may be sustained for a longer duration than previously thought, and the negative effect of elevated O3 may be diminished by compensatory growth of O3-tolerant plants as they begin to dominate forest communities ...

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Languages : en
Pages : 87

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In this study, the photosynthetic responses of field grown Lolium perenne to ambient (354 [mu]mol mol−1) and elevated (600 [mu]mol mol−1) C{sub a} were measured. The experiment utilized the FACE facility at Eschikon, Switzerland; here the L. Perenne swards had been grown at two nitrogen treatments, with six cuts per year, for 4 years. The study revealed a significant decrease in Rubisco activity (Vcmax) in the low nitrogen FACE plots; this is consistent with the theories of source-sink imbalance resulting in feedback inhibition and down-regulation. Such negative acclimation was not wholly supported by diurnal investigations which revealed an average stimulation of 53.38% and 52.78% in the low and high nitrogen, respectively. However, light response curves and AI investigations also suggested down-regulation, especially in the low nitrogen. SI is expected to decrease in response to elevated C{sub a}, if any change is seen. This was indeed observed in the high nitrogen plots but for the low nitrogen a significant increase was found. Conclusions drawn from this project center around the implications of negative acclimation to future crop productivity. For instance, inter-specific differences in response to elevated C{sub a} may result in ecosystem changes and new management techniques may be necessary. However, real predictions cannot be made from leaf level studies alone as these may not represent the overall changes at the whole plant level.

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Languages : en
Pages : 38

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A variety of approaches have been used in fumigation experiments to quantify the effects of increasing atmospheric carbon dioxide concentration ([CO2]{sub atm}) on plants. Mot of these approaches, reviewed elsewhere (Allen 1992), entail some type of enclosure or chamber. Chambers provide containment of the CO2-enriched air and in this way reduce the amount of CO2 required for the experiment. At the same time, chambers alter microclimate conditions in a variety of ways so that there is a significant chamber effect on the plants within. Free-air carbon dioxide enrichment (FACE) is an alternative experimental strategy in which CO2-enriched air is released into the ambient environment in such a way as to provide effective experimental control over [CO2]{sub atm} without causing any change in other environmental variables. Early types of free-air exposure systems were built in the Netherlands and England for exposing vegetation to elevated concentrations of atmospheric trace gases. The FACE Program at Brookhaven National Laboratory (BNL) considered these original ideas in designing the BNL FACE systems. The purpose of the current BNL project in the Duke Forest is to develop a FACE system that can provide adequate control over [CO2]{sub atm} in a tall forest setting. This report is a preliminary overview of the data and much remains to be done in the analysis.

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Languages : en
Pages : 70

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Plots of Medicago sativa cv. saranac were grown in the field at ambient (355 [mu]mol CO2 mol−1 air) or elevated (600[mu]mol CO2 mol−1 air) CO2 concentrations. High (200kg yr−1) or low (20kg yr−1) nitrogen levels were applied to two isogeneic lines, one able and one unable to use nitrogen fixing bacteria. Plants were in the second year of field growth. Exposure to elevated CO2 was via a Free-Air CO2 Enrichment System (FACE). Elevated CO2 increased diurnal assimilation by between 12% and 92%. Analysis of A/C{sub i} responses showed that effective nitrogen fertilisation was more important to rubisCO and RuBP activity than elevated CO2. No acclimation was consistently observed. Leaves lower down the canopy were found to have lower Vc{sub max} and J{sub max} values, though age may be the cause of the latter effect. FACE conditions have only a small effect on these responses. There was some evidence found for the down-regulation of photosynthesis in the late afternoon. The FACE conditions had no affect on stomatal density but did increase epidermal cell density.

Author: Brian Walker
Publisher: Cambridge University Press
ISBN: 9780521624800
Category : Nature
Languages : en
Pages : 462

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Summarises understanding of global change interactions with terrestrial ecosystems.

Author: James M. Vose
Publisher: CRC Press
ISBN: 1466572752
Category : Nature
Languages : en
Pages : 494

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Forest land managers face the challenges of preparing their forests for the impacts of climate change. However, climate change adds a new dimension to the task of developing and testing science-based management options to deal with the effects of stressors on forest ecosystems in the southern United States. The large spatial scale and complex interactions make traditional experimental approaches difficult. Yet, the current progression of climate change science offers new insights from recent syntheses, models, and experiments, providing enough information to start planning now for a future that will likely include an increase in disturbances and rapid changes in forest conditions. Climate Change Adaptation and Mitigation Management Options: A Guide for Natural Resource Managers in Southern Forest Ecosystems provides a comprehensive analysis of forest management options to guide natural resource management in the face of future climate change. Topics include potential climate change impacts on wildfire, insects, diseases, and invasives, and how these in turn might affect the values of southern forests that include timber, fiber, and carbon; water quality and quantity; species and habitats; and recreation. The book also considers southern forest carbon sequestration, vulnerability to biological threats, and migration of native tree populations due to climate change. This book utilizes the most relevant science and brings together science experts and land managers from various disciplines and regions throughout the south to combine science, models, and on-the-ground experience to develop management options. Providing a link between current management actions and future management options that would anticipate a changing climate, the authors hope to ensure a broader range of options for managing southern forests and protecting their values in the future.