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Languages : en
Pages : 85
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OAK B188 Response of Tundra Ecosystems to Elevated Atmospheric CO2. Atmospheric CO2 is expected to double by the end of the next century. Global mean increases in surface air temperature of 1.5-4.5 C are anticipated with larger increases towards the poles predicted. Changes in CO2 levels and temperature could have major impacts on ecosystem functioning, including primary productivity, species composition, plant-animal interactions, and carbon storage. Until recently, there has been little direct information on the impact of changes in CO2 and temperature on native ecosystems. The study described here was undertaken to evaluate the effects of a 50 and 100% increase in atmospheric CO2, and a 100% increase in atmospheric CO2 coupled with a 4 C summer air temperature rise on the structure and function of an arctic tussock tundra ecosystem. The arctic contains large stores of carbon as soil organic matter, much frozen in permafrost and currently not reactive or available for oxidation and release into the atmosphere. About 10-27% of the world's terrestrial carbon occurs in arctic and boreal regions, and carbon is accumulating in these regions at the rate of 0.19 GT y−1. Mean temperature increases of 11 C and summer temperature increases of 4 C have been suggested. Mean July temperatures on the arctic coastal plain and arctic foothills regions are 4-12 C, and mean annual temperatures are -7 to -13 C (Haugen, 1982). The projected temperature increases represent a substantial elevation above current temperatures which will have major impacts on physical processes such as permafrost development and development of the active layer, and on biological and ecosystem processes such as primary productivity, carbon storage, and species composition. Extreme nutrient and temperature limitation of this ecosystem raised questions of the responsiveness of arctic systems to elevated CO2. Complex ecosystem interactions with the effects of increasing temperature and CO2 and changes in the physical environment made a priori predictions impossible. The short stature of the vegetation, the large number of individuals and species encountered in a relatively small area, and the short growing season were advantages which were thought to increase the probability that manipulation of physical conditions would result in short- and moderate-term response. These factors were coupled with an appreciation of the important role of the arctic as a major carbon store, a carbon sink, and the unpredictability of the carbon balance under future global conditions. These factors all contributed to the selection of the arctic as the first ecosystem for in situ manipulation of CO2 and temperature to determine effects on ecosystem structure and function.
Author:
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Category :
Languages : en
Pages : 85
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Book Description
OAK B188 Response of Tundra Ecosystems to Elevated Atmospheric CO2. Atmospheric CO2 is expected to double by the end of the next century. Global mean increases in surface air temperature of 1.5-4.5 C are anticipated with larger increases towards the poles predicted. Changes in CO2 levels and temperature could have major impacts on ecosystem functioning, including primary productivity, species composition, plant-animal interactions, and carbon storage. Until recently, there has been little direct information on the impact of changes in CO2 and temperature on native ecosystems. The study described here was undertaken to evaluate the effects of a 50 and 100% increase in atmospheric CO2, and a 100% increase in atmospheric CO2 coupled with a 4 C summer air temperature rise on the structure and function of an arctic tussock tundra ecosystem. The arctic contains large stores of carbon as soil organic matter, much frozen in permafrost and currently not reactive or available for oxidation and release into the atmosphere. About 10-27% of the world's terrestrial carbon occurs in arctic and boreal regions, and carbon is accumulating in these regions at the rate of 0.19 GT y−1. Mean temperature increases of 11 C and summer temperature increases of 4 C have been suggested. Mean July temperatures on the arctic coastal plain and arctic foothills regions are 4-12 C, and mean annual temperatures are -7 to -13 C (Haugen, 1982). The projected temperature increases represent a substantial elevation above current temperatures which will have major impacts on physical processes such as permafrost development and development of the active layer, and on biological and ecosystem processes such as primary productivity, carbon storage, and species composition. Extreme nutrient and temperature limitation of this ecosystem raised questions of the responsiveness of arctic systems to elevated CO2. Complex ecosystem interactions with the effects of increasing temperature and CO2 and changes in the physical environment made a priori predictions impossible. The short stature of the vegetation, the large number of individuals and species encountered in a relatively small area, and the short growing season were advantages which were thought to increase the probability that manipulation of physical conditions would result in short- and moderate-term response. These factors were coupled with an appreciation of the important role of the arctic as a major carbon store, a carbon sink, and the unpredictability of the carbon balance under future global conditions. These factors all contributed to the selection of the arctic as the first ecosystem for in situ manipulation of CO2 and temperature to determine effects on ecosystem structure and function.
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Languages : en
Pages : 5
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OAK (B204) Response of Tundra Ecosystems to Elevated Atmospheric CO2 Part 3 of 3.
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Languages : en
Pages : 68
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Northern ecosystems contain up to 455 Gt of C in the soil active layer and upper permafrost. The soil carbon in these layers is equivalent to approximately 60% of the carbon currently in the atmosphere as CO2. Much of this carbon is stored in the soil as dead organic matter. Its fate is subject to the net effects of global change on the plant and soil systems of northern ecosystems. The arctic alone contains about 60 Gt C, 90% of which is present in the soil active layer and upper permafrost. The arctic is assumed to have been a sink for CO2 during the historic and recent geologic past. The arctic has the potential to be a very large, long-term source or sink of CO2 with respect to the atmosphere. In situ experimental manipulations of atmospheric CO2, indicated that there is little effect of elevated atmospheric CO2 on leaf level photosynthesis or whole-ecosystem CO2 flux over the course of weeks to years, respectively. However, there may be longer- term ecosystem responses to elevated CO2 that could ultimately affect ecosystem CO2 balance. In addition to atmospheric CO2, climate may affect net ecosystem carbon balance. Recent results indicate that the arctic has become a source of CO2 to the atmosphere. This change coincides with recent climatic variation in the arctic, and suggests a positive feedback of arctic ecosystems on atmospheric CO2 and global change. The research proposed in this application has four principal aspects: (A) Long-term response of arctic plants and ecosystems to elevated atmospheric CO2; (B) Circumpolar patterns of net ecosystem CO2 flux; (C) In situ controls by temperature and moisture on net ecosystem CO2 flux; (D) Scaling of CO2 flux from plot, to landscape, to regional scales (In conjunction with research proposed for NSF support).
![Response of a Tundra Ecosystem to Elevated Atmospheric Carbon Dioxide and CO2-induced Climate Change. [Annual Report]. PDF](https://books.google.com/books/content/images/frontcover/qk3XwQEACAAJ?fife=w80-h100)
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Languages : en
Pages : 84
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Predicting the response of northern ecosystems to increases in atmospheric CO2 and associated climatic change is important for several reasons, including the fact that northern ecosystems contain large stores of carbon, most of which is below ground and because northern ecosystems could conceivably be either sources or sinks for CO2 under future climatic and atmospheric CO2 concentrations. The carbon in northern ecosystems is equal to about 20% of the worlds̀ terrestrial carbon and about 70% of the carbon currently in the atmosphere. Eighty-three percent of this carbon is below ground in the seasonally-thawed upper soil layers and in the permanently frozen zone, the permafrost. Because of bogs and permafrost, northern ecosystems are unusual in that they can potentially store significant amounts of carbon over long time periods. Most other mature ecosystems have little capacity for long- term carbon storage. Given the right conditions, northern ecosystems can also release a significant amount of carbon. A substantial amount of the carbon stored in northern ecosystems, and much of the future storage potential, is in the tundra regions. These systems could conceivably act as sources or sinks depending on developing climatic and atmospheric conditions. Our recent work indicates that elevated CO2 alone will have little effect on carbon storage in the tundra. However, the combination of elevated atmospheric CO2 (+ 340 ppm) and air temperature (+4°C) in the absence of any change in soil water table or soil moisture content, should result in significant increases in carbon sequestering in the tundra. However, if changing climate results in a decrease in the water table and soil moisture levels, this may lead to sizeable losses of carbon from the tundra soils.
![Response of Tundra Ecosystems to Elevated Atmospheric Carbon Dioxide. [Annual Report]. PDF](https://books.google.com/books/content/images/frontcover/02KnwgEACAAJ?fife=w80-h100)
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Languages : en
Pages : 92
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Our past research shows that arctic tussock tundra responds to elevated atmospheric CO2 with marked increases in net ecosystem carbon flux and photosynthetic rates. However, at ambient temperatures and nutrient availabilities, homeostatic adjustments result in net ecosystem flux rates dropping to those found a contemporary CO2 levels within three years. Evidence for ecosystem-level acclimation in the first season of elevated CO2 exposure was found in 1987. Photosynthetic rates of Eriophorum vaginatum, the dominant species, adjusts to elevated CO2 within three weeks. Past research also indicates other changes potentially important to ecosystem structure and function. Elevated CO2 treatment apparently delays senescence and increases the period of positive photosynthetic activity. Recent results from the 1987 field season verify the results obtained in the 1983--1986 field seasons: Elevated CO2 resulted in increased ecosystem-level flux rates. Regressions fitted to the seasonal flux rates indicate an apparent 10 d extension of positive CO2 uptake reflecting a delay of the onset of plant dormancy. This delay in senescence could increase the frost sensitivity of the system. Major end points proposed for this research include the effects of elevated CO2 and the interaction of elevated atmospheric CO2 with elevated soil temperature and increased nutrient availability on: (1) Net ecosystem CO2 flux; (2) Net photosynthetic rates; (3) Patterns and resource controls on homeostatic adjustment in the above processes to elevated CO2; (4) Plant-nutrient status, litter quality, and forage quality; (5) Soil-nutrient status; (6) Plant-growth pattern and shoot demography.
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Pages : 35
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The overall objective of this research was to document current patterns of CO2 flux in selected locations of the circumpolar arctic, and to develop the information necessary to predict how these fluxes may be affected by climate change. In fulfillment of these objectives, net CO2 flux was measured at several sites on the North Slope of Alaska during the 1990--94 growing season (June--August) to determine the local and regional patterns of seasonal CO2 exchange. In addition, net CO2 flux was measured in the Russian and Icelandic Arctic to determine if the patterns of CO2 exchange observed in Arctic Alaska were representative of the circumpolar Arctic, while cold-season CO2 flux measurements were carried out during the 1993--94 winter season to determine the magnitude of CO2 efflux not accounted for by the growing season measurements. Manipulations of soil water table depth and surface temperature, which were identified from the extensive measurements as being the most important variables in determining the magnitude and direction of net CO2 exchange, were carried out during the 1993--94 growing seasons in tussock and wet sedge tundra ecosystems. Finally, measurements of CH4 flux were also measured at several of the North Slope study sites during the 1990--91 growing seasons.
![Response of a Tundra Ecosystem to Elevated Atmospheric Carbon Dioxide and CO[sub 2]-induced Climate Change.[Annual Report]. PDF](https://books.google.com/books/content/images/frontcover/vvz2jwEACAAJ?fife=w80-h100)
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Predicting the response of northern ecosystems to increases in atmospheric CO[sub 2] and associated climatic change is important for several reasons, including the fact that northern ecosystems contain large stores of carbon, most of which is below ground and because northern ecosystems could conceivably be either sources or sinks for CO[sub 2] under future climatic and atmospheric CO[sub 2] concentrations. The carbon in northern ecosystems is equal to about 20% of the world's terrestrial carbon and about 70% of the carbon currently in the atmosphere. Eighty-three percent of this carbon is below ground in the seasonally-thawed upper soil layers and in the permanently frozen zone, the permafrost. Because of bogs and permafrost, northern ecosystems are unusual in that they can potentially store significant amounts of carbon over long time periods. Most other mature ecosystems have little capacity for long- term carbon storage. Given the right conditions, northern ecosystems can also release a significant amount of carbon. A substantial amount of the carbon stored in northern ecosystems, and much of the future storage potential, is in the tundra regions. These systems could conceivably act as sources or sinks depending on developing climatic and atmospheric conditions. Our recent work indicates that elevated CO[sub 2] alone will have little effect on carbon storage in the tundra. However, the combination of elevated atmospheric CO[sub 2] (+ 340 ppm) and air temperature (+4[degrees]C) in the absence of any change in soil water table or soil moisture content, should result in significant increases in carbon sequestering in the tundra. However, if changing climate results in a decrease in the water table and soil moisture levels, this may lead to sizeable losses of carbon from the tundra soils.
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